Why GM should NOT build a DOHC V8

[dwightlooi]

To illustrate the competitiveness of the pushrod design, let’s compare three V8 engines. All are fielded in high performance production cars, all being of aluminum construction and none having direct injection.

* Chevy Camaro SS

** BMW M3

*** Mercedes-Benz C63 AMG

The pushrod engine offers the highest power and torque density, along with the best fuel economy. It is also the simplest, lightest, smallest and cheapest engine. Why wouldn’t you want a pushrod?

The most common reply to that is “civility”. Well, have you driven a small block lately? If you have, have you also driven the other two engines? I have done all that and here’s my opinion on the civility issue…

The engines have very different characters, but saying that the small block is less civil than the other two is a mischaracterization. The small block is burbly down low and throaty in a throbbing baritone sort of manner when wound out. The BMW V8 quiet and smooth, but also very soft, down low. Get it past 6000 rpm and it wails with a metallic rasp of an engine note. The AMG V8 is (surprising) also rather soft below 4000 rpm, softer in fact than the previous M113 5.5 liter it replaced or the current 5.5 they put in the E550. Wind it out and it responds with vigor and a brash metallic tone from about 4500 rpm to the rev limit of 7200 rpm. Overall, the C63 has the loudest exhaust (I mean this thing is loud enough to wake your neighbors), the M3 has the finest tremble and the Camaro SS is the least edgy and most mellow. I am sure that some of that is how the exhaust and sound insulation in the respective cars are set up, but I didn't get the impression that the pushrod engine is outdated or crude. So, there you go.

This is why I advocate that GM should double down on a good thing and stick to the pushrod V8. With direct injection, variable timing and cylinder deactivation, it’ll be more than up to snuff against anything projected for the next decade. If nobody else is doing it, that’s a good thing they get the monopoly on it!

And, it seems that they are. Currently, there are no plans for a DOHC replacement for the Northstar. There is however a Gen V small block in the works (rumored to be displacing 5.5 liters and sporting direct injection). So, I'll like to offer my congratulations to the General for not losing good judgment despite government ownership.

[Drew Dowdell]

I'll add that the pushrod, whether from GM or Chrysler, has a sound that is distinctly American. This is a characteristic that GM should be proud of an not massage to sound more like the German or Japanese counterparts.

[loki]

i agree, the only thing you have shown to not be very feasible, yet, on a CIB engine is HCCI and ....... is it cam profile changing? when physical cams are no longer needed then the discussion will change/simplify. until then, GM needs to focus on proven tech and keep working on HCCI for the 4 and 6 cylinder engines, move that tech into the smaller more economical 3 cyl that should be for volt 2.0.

although i will always be curious about "what if" all this tech was put into a v6, in the range of high 2L to ~the 3.9L CIB engine.

gm just needs a bigger v8 for HD trucks... and maybe for the corvette.

[smk4565]

If the pushrod was better, everyone else would be copying it. Automakers love to copy and jump on bandwagons. However, no one else, but bankrupt Chrysler has a pushrod. Mercedes has enough money to build any kind of engine they want, yet what do they make. The power similar power/efficiency argument of the LS3 and BMW 4.0 or 4.4Turbo is valid, but all your examples were performance applications. A Luxury car engine has to be refined and whisper quiet in everyday driving and on the highway, that is what the pushrod can't do.

About the cost argument, on a Cadillac, cost cutting should not be an issue. Plastic fake wood costs less than real wood, epsilon would be cheaper than sigma, solid rear axle costs less than independent suspension and magnetic shocks.

If GM had $30 billion sitting in the bank they would have a DOHC V8, the only reason they don't is because they are broke. So they have to justify why it is just as good as what the Germans and Japanese have. GM has lagged behind the imports in engineering for 30+ years, and it shows when they had 40% market share in the 1980s and about 17-18% market share now. They had cheap pushrods for all that time and half of their customers left, mostly going to DOHC imports. (and it goes beyond V8s, to all the 3100, 3400 and 3800 V6 cars that people traded in for Accords and Camrys)

[dwightlooi]

although i will always be curious about "what if" all this tech was put into a v6, in the range of high 2L to ~the 3.9L CIB engine.

gm just needs a bigger v8 for HD trucks... and maybe for the corvette.

Well, a simple way to gauge that will be to assume the same specific output as the LS3 ~69.8bhp/liter.

~272hp 3.9 liter Pushrod V6. And, that's before VVT, DI or AFM. Not bad really and quite competitive with the 3.5~3.6 liter HF V6es. Remember, the 3.9 pushrod is probably a smaller and lighter powerplant.

[Drew Dowdell]

If the pushrod was better, everyone else would be copying it. Automakers love to copy and jump on bandwagons. However, no one else, but bankrupt Chrysler has a pushrod. Mercedes has enough money to build any kind of engine they want, yet what do they make. The power similar power/efficiency argument of the LS3 and BMW 4.0 or 4.4Turbo is valid, but all your examples were performance applications. A Luxury car engine has to be refined and whisper quiet in everyday driving and on the highway, that is what the pushrod can't do.

About the cost argument, on a Cadillac, cost cutting should not be an issue. Plastic fake wood costs less than real wood, epsilon would be cheaper than sigma, solid rear axle costs less than independent suspension and magnetic shocks.

If GM had $30 billion sitting in the bank they would have a DOHC V8, the only reason they don't is because they are broke. So they have to justify why it is just as good as what the Germans and Japanese have. GM has lagged behind the imports in engineering for 30+ years, and it shows when they had 40% market share in the 1980s and about 17-18% market share now. They had cheap pushrods for all that time and half of their customers left, mostly going to DOHC imports. (and it goes beyond V8s, to all the 3100, 3400 and 3800 V6 cars that people traded in for Accords and Camrys)

Try to stay on topic SMK. We're talking pushrod V8s, not V6es, though I personally think the pushrod V6es would have been fully competitive in horsepower and torque given the proper development. The 3800 and the 3900 are very different engines. The 3800 was a 90 degree V6 while the 3900 was a 60 degree V6. Just switching the cylinder angle made a huge difference in "refinement".

Your argument that pushrods can't be whisper quiet and refined on the highway is laughable on it's face. The LT-1 in Buick and Cadillac applications had plenty of balls, was quiet enough for a library, and super smooth to boot. The 3.9 in the Lucerne I had was so smooth and refined that I didn't even realize I had mistakenly put it in 3 instead of drive until I noticed the instant MPG read out was unusually low.

66Stang and I took it for an experiment the next day where I took the Lucerne up to 80mph and dropped it into 3. There was no shudder, no increase in noise, no visceral difference in the feeling of the car.

The Germans like to make things complex. It's kinda what they do. Having DOHC doesn't guarantee refinement.

[dwightlooi]

If the pushrod was better, everyone else would be copying it. Automakers love to copy and jump on bandwagons. However, no one else, but bankrupt Chrysler has a pushrod. Mercedes has enough money to build any kind of engine they want, yet what do they make. The power similar power/efficiency argument of the LS3 and BMW 4.0 or 4.4Turbo is valid, but all your examples were performance applications. A Luxury car engine has to be refined and whisper quiet in everyday driving and on the highway, that is what the pushrod can't do.

Well, maybe it's because they just don't get it... yet.

As far as refinement of an engine is concerned, you can break it into three factors.

• Balance of the Engine
  
• Insulation and engine mounting
  
• Valvetrain slop
  

Of these, you are not going to see a difference between a DOHC V8 and a pushrod V8 when it comes to Balance and Insulation. That's has everything to do with bank angle, counter-weights and sound deadening. It has nothing to do with how the valves are operated.

With Valve train slop, it is really a matter of not allowing poor tolerances and valve float. It also has very little with whether the engine is a pushrod or overhead cam design. The higher valve train mass in a pushrod engine places a limit on how high of a rpm the engine can get to before the valve train becomes a limiting factor both in terms of durability and/or noise becomes an issue. But while this affects the redline of an engine can acheive without compromising durability, the racket the valvetrain makes at a given level of acceptable float or slop is similar. The only difference is that a given threshold for what's acceptable may arrive at 6000 rpm on a pushrod design, but 8000 rpm on a DOHC one.

There are many things when the biggest bandwagon is on the wrong track. People and companies are not immune from the tendency to jump on board with a broad trend even when the underlying facts are highly dubious. Global Warming is one example of what's basically junk science almost becoming a general consenses. The trend towards DOHC Vee type engines, IMHO, is another. The basic Achilles' Heel to the DOHC proposition is that it is a heavier, bulkier, more complicated engine with higher internal friction. It's only advantage is that it provides for better airflow and higher rpm capability. The problem is that a slower turning, bigger displacement engine can be more powerful, lighter, smaller and more fuel efficient. In addition, the airflow potential of a DOHC layout is not realized at the typical 6000~7000 rpm rev limits of a mainstream passenger car engine.

In certain racing applications where the rules limit displacement, and in various countries where the rules of the game or the law makes it highly advantageous to have a higher specific output, lower displacment engine. However, these do not apply to the market for V8 powered cars. This is not a displacement restricted competition event. The luxury/performance market for V8s is also not particularly sensitive to higher displacement taxes even when they do exist. The type of buyers who rank this highly will buy the I4 or V6 variant of the car; they'll buy an Audi 2.0T instead of a V8 S4, they'll buy a BMW 525 or 528 and not the 550. The decision to buy a V8 powered car is a deliberate one.

[smk4565]

The Germans like to make things complex. It's kinda what they do. Having DOHC doesn't guarantee refinement.

The Italians, Swedish, Japanese, South Koreans, and British use DOHC also. Ford, the best performing American auto maker only uses OHC, and is phasing out SOHC for DOHC. Chances are, that massive group is right, and GM and Chrysler (the only 2 to go bankrupt) are doing it wrong.

[Drew Dowdell]

The Italians, Swedish, Japanese, South Koreans, and British use DOHC also. Ford, the best performing American auto maker only uses OHC, and is phasing out SOHC for DOHC. Chances are, that massive group is right, and GM and Chrysler (the only 2 to go bankrupt) are doing it wrong.

OR, chances are, YOU are wrong and there is no single right answer to the valvetrain question.

[dwightlooi]

The Italians, Swedish, Japanese, South Koreans, and British use DOHC also. Ford, the best performing American auto maker only uses OHC, and is phasing out SOHC for DOHC. Chances are, that massive group is right, and GM and Chrysler (the only 2 to go bankrupt) are doing it wrong.

Well, on what technical or factual basis are you making that argument besides everybody is using it so it must be right?

Linking financial performance to engine type is like saying a computer manufacturer is in distress because the CEO wears a red tie instead of white suspenders that the other CEOs wore. Unless you can demonstrate the suspenders affected his performance running the company the connection is quite groundless.

As far as the failures of GM. IMHO, it is a failure of design, failure of quality, failure of product focus and a failure of labor. GM tried to be the value leader while doing most of its manufacturing in a high cost country. That in and of itself is a recipe for failure. To that end, it cut back on quality, technology and put out too many uninteresting vehicles -- which compounded the problem. The Pushrod engine has nothing to do with it.

I put forth an argument that a Pushrod engine is superior to a DOHC engine in cost, performance, packaging, weight and fuel economy. Perhaps you can educate us as to why that argument is flawed or inaccurate?

Edited February 16, 2010 by dwightlooi

[loki]

Well, a simple way to gauge that will be to assume the same specific output as the LS3 ~69.8bhp/liter.

~272hp 3.9 liter Pushrod V6. And, that's before VVT, DI or AFM. Not bad really and quite competitive with the 3.5~3.6 liter HF V6es. Remember, the 3.9 pushrod is probably a smaller and lighter powerplant.

yes, and before those improvements it is roughly 10% bigger than a 3.5L. just like how the new 5.5L will compete very well against ford's 5.0L. that would show how not dead CIB v6's can be. but that's prolly not the future.

Edited February 16, 2010 by loki

[smk4565]

I put forth an argument that a Pushrod engine is superior to a DOHC engine in cost, performance, packaging, weight and fuel economy. Perhaps you can educate us as to why that argument is flawed or inaccurate?

A pushrod is not superior on performance, given equal displacement, the DOHC engine will make more power. For example, 426 hp from an 6.2 liter LS3 and 518 hp from the AMG 6.2 liter. Or 315 hp from the 5.3 V8 and 412 hp from the Ford 5.0 V8. Then you have the 7.0 liter Z06 with 500 hp, but he 4.5 liter Ferrari 458 makes 562 hp. Even take the LS9, the most powerful pushrod with 638 hp and 604 lb-ft. The Koenigsegg 4.7 liter V8 makes 806 hp and 678 lb-ft (on E100 it makes 1,018 hp).

The Jag XFR gets getter mileage than the CTS-V.

[loki]

The Jag XFR gets getter mileage than the CTS-V.

why'd you even put this with out noting curb weight? or actual power too.... the cobalt ss beets the jag xf..... just throwin that out there, like you did. LOL

[Drew Dowdell]

A pushrod is not superior on performance, given equal displacement, the DOHC engine will make more power. For example, 426 hp from an 6.2 liter LS3 and 518 hp from the AMG 6.2 liter. Or 315 hp from the 5.3 V8 and 412 hp from the Ford 5.0 V8. Then you have the 7.0 liter Z06 with 500 hp, but he 4.5 liter Ferrari 458 makes 562 hp. Even take the LS9, the most powerful pushrod with 638 hp and 604 lb-ft. The Koenigsegg 4.7 liter V8 makes 806 hp and 678 lb-ft (on E100 it makes 1,018 hp).

The Jag XFR gets getter mileage than the CTS-V.

A DOHC 6 liter will NOT fit in the space that a Pushrod 6 liter can.

[Drew Dowdell]

SMK, why does this rather simple concept baffle you? Horsepower per litre displacement is stupid. Give me horsepower for overall package dimensions and get back to me.

[regfootball]

a car company needs to consider an engine application for all its global markets, and honestly the US and maybe saudi and AU are about the only places where big displacement motors are marketable now. Euros place tax on high displacement, Japan culture is to make high revving small displacement. Fuel economy pressures lead development money towards smaller displacement.

while the arguments for the pushrod v8 make sense to some degree you also need to consider that if a company is designing a series of modular engines, then they want to develop similar manufacturing processes and capabilities across a wide swath of the products. For example, the combustion chamber design of a cylinder on a DOHC motor can then be used for say, a 2.4 litre four, a 3.6 litre six, and a 4.8 litre v8. The investment in design, manufacturing and tooling can have application and be amotized over many more models and justify the continuous R&D that is needed to keep pace. If you can prove on a balance sheet that you can make enough aluminum block pushrod v8's that will meet epa needs and sell in adequate volume to justify the whole separate program for basically three areas of the world in mostly niche vehicles, then baby play on.

The fuel economy issue is real. We know the large v8 gets great mpg in the corvette, but look at the terrible mpg the G8 GXP got (epa and real world). and that was without the added drag of an AWD system which many buyers consider a requirement these days.

You know too, the rpm issue is a real thing to consider. For example, GM was never capable of making its pushrod v6's feel as eager or smooth as the best v6's from its competition. In v8's they can match better. But large displacement pushrod motors have had the rap deserved for not quite cutting the mustard, mostly in v6's. GM should have applied all it knew to make them better performers in all the facets needed.

Maybe one reason the huge displacement motors can't keep up is the long bore and high piston speeds. I'll also assume longer bore engines generate more rocking forces if their configuration is not inherently balanced. I'd like for you dwight to address this. Cuz if I am revving a small block to 7000 rpm i just want to know how that compared to a smaller motor. More specifically a good turbo four in a lighter vehicle.

If i were developing one vehicle from scratch myself I would probably do a small displacement inline 6 with turbo. v12, if it were a luxury car. a mid engine flat six would be interesting too. I have always been intrigued by a boxer four also.

Edited February 16, 2010 by regfootball

[dwightlooi]

A pushrod is not superior on performance, given equal displacement, the DOHC engine will make more power. For example, 426 hp from an 6.2 liter LS3 and 518 hp from the AMG 6.2 liter. Or 315 hp from the 5.3 V8 and 412 hp from the Ford 5.0 V8. Then you have the 7.0 liter Z06 with 500 hp, but he 4.5 liter Ferrari 458 makes 562 hp. Even take the LS9, the most powerful pushrod with 638 hp and 604 lb-ft. The Koenigsegg 4.7 liter V8 makes 806 hp and 678 lb-ft (on E100 it makes 1,018 hp).

The Jag XFR gets getter mileage than the CTS-V.

Well, let me ask you a question... why does having a greater output for a given displacement matter to you? In otherwords, why is specific output important?

Does it matter if the engine's displacement is larger, when that engine is lighter, smaller, more powerful, more fuel efficient and cheaper to build?

For example, is Ford 5.0 DOHC lighter than a Pushrod 6.2? Doubtful. Does a Ford 5.0 DOHC take up less room in an engine bay? Absolutely not. Does the Ford 5.0 DOHC produce more power? No, it doesn't. Does the Ford 5.0 DOHC cost less to build? No way. Is the Ford 5.0 DOHC more economical on fuel? Again, probably not. So... why is the Ford 5.0 DOHC a better motor?

[balthazar]

dwightlooi ~ >>'LS3 - chain-driven 16v pushrods'<<

Typo, no? Of course the camshaft is chain-driven.. but seems very odd to call a IBC valvetrain 'chain-driven'. Interesting.

DL- you make a strong argument I cannot disagree with on the surface of it. By engineering & business-case parameters, the LS3 in your chart is superior & your point is proven, IMO.

Where I must part ways with your POV is market perception. Cadillac can have a IBC V-8 AS LONG AS it is proprietory and never shared with another division. Too many will bash it for 'using a Chevy motor' (as if there were such a thing anymore).

[dwightlooi]

dwightlooi ~ >>'LS3 - chain-driven 16v pushrods'<<

Typo, no? Of course the camshaft is chain-driven.. but seems very odd to call a IBC valvetrain 'chain-driven'. Interesting.

DL- you make a strong argument I cannot disagree with on the surface of it. By engineering & business-case parameters, the LS3 in your chart is superior & your point is proven, IMO.

Where I must part ways with your POV is market perception. Cadillac can have a IBC V-8 AS LONG AS it is proprietory and never shared with another division. Too many will bash it for 'using a Chevy motor' (as if there were such a thing anymore).

Again, this is a matter of opinion. But, I do not feel that the sharing of the motor(s) between Cadillac and other "less prestigious" GM divisions will have a significant impact on the success of the Cadillac brand. Cadillac can distinguish itself from other GM brands through styling, quality and amenities. It doesn't have to focus on having a unique powertrain. Besides, the same argument for Cadillac possibly receiving a "bashing" for using Chevy motors can be made for Chevy getting an "image boost" for using Cadillac engines. Since Chevy has much greater volume, one can then argue that it works out to GM's overall advantage.

Nissan uses the same 3.5 liter VQ35 on both the Nissans and the Altimas. Toyota uses the 2GR-FE 3.5 liter in the ES350, RX350, Camry, Avalon, RAV4, Highlander and (jeez) Sienna. Audi shares the 2.0T FSI with the Volkswagens. None of the sharing has impeded the success of the respective luxury divisions. In anycase, Cadillac doesn't have powertrain exclusivity today to begin with -- the 3.0 and 3.6 liter V6es -- which account for the the majority of the volume -- are Chevy motors also used in the Equinox, Malibu, Camaro, you name it.

If, for instance, giving Cadillac a "unique" motor will add $1500 to the cost of the vehicle, I feel that this $1500 is better spent on upgrading the grade of leather used in the upholstery, using laminated glass on all side windows and perhaps making a rear view camera standard.

[Carguy]

I think the LS3 could become a premium engine and going further I could see a nice new V6 version of around 4.5L becoming a new base truck engine as well. Remember the V16 Cadillac concept engine was built around two small block V8's and everyone DREAMED about that being built. A premium,smooth and quiet DI AFM OHV Cadillac V8 and even V6 could be something unique and great for them.

[balthazar]

DL- the only difference in your Chevy/Cadillac EX is that for Chevy; that's a positive, for Cadillac, it's a negative.

Chevy has far greater volume, but Cadillac has far higher profit margins. What the exact present #s are, and what will play out down the road is unknown to me.

Again I see merit in your post, but understand I come from the 'first windo' WRT Cadillac- I am as familiar with the dawn of the marque as I am of the present (VERY likely moreso) and the journey from there to here. And for 70-some years, a Cadillac engine was only found in a Cadillac, and (at the risk of making an smk-esque leap of logic) Cadillac grew all during those 70-some years. The perception was buffed to a high luster and proprietory engineering was a major factor in that.

Who can make the stand AGAINST the fact that engineering became the first lynch pin to drop @ Cadillac ??

350 diesels ('78-up, Olds-built), 1.8L/ 2.0L 4-cyls in Cimarron ('81-up, Chevy built), 4.1L V6 in full-size ('82-up, Buick-built).

IMO ^^ the grease at the top of the slide.

Something to always keep in the back of one's mind.

Edited February 16, 2010 by balthazar

[dwightlooi]

I think the LS3 could become a premium engine and going further I could see a nice new V6 version of around 4.5L becoming a new base truck engine as well. Remember the V16 Cadillac concept engine was built around two small block V8's and everyone DREAMED about that being built. A premium,smooth and quiet DI AFM OHV Cadillac V8 and even V6 could be something unique and great for them.

Honestly, I don't see a Pushrod V6 stemming from the Small Block. The reason being:-

• A 60 degree Pushrod V6 will be a brand new design, not a derivative w/o shared tooling
  
• A 90 degree is not a smooth running configuration unless a balance shaft is used.
  
• With less cylinders and (possibly) a 60deg angle the packaging advantages of a Pushrod diminishes.
  
• The HF V6 already exists and there is no good reason for duplicity in the lineup
  

What I do see (and hope to see) is the continued evolution of the Pushrod Small Block. Probably fortification with VVT, Raised Cam, Cylinder Deactivation and Direct Injection in the Fifth generation due in this year or 2011. This will probably be accompanied by a reduction in displacement to 5.5 liters with little or no reduction in output from the 400~436hp of the current 6.2 (LS3).

By 2014~2015, we may see variable valve lift and dual co-axial VVT in the 6th Gen design.

[regfootball]

Well, let me ask you a question... why does having a greater output for a given displacement matter to you? In otherwords, why is specific output important?

Does it matter if the engine's displacement is larger, when that engine is lighter, smaller, more powerful, more fuel efficient and cheaper to build?

For example, is Ford 5.0 DOHC lighter than a Pushrod 6.2? Doubtful. Does a Ford 5.0 DOHC take up less room in an engine bay? Absolutely not. Does the Ford 5.0 DOHC produce more power? No, it doesn't. Does the Ford 5.0 DOHC cost less to build? No way. Is the Ford 5.0 DOHC more economical on fuel? Again, probably not. So... why is the Ford 5.0 DOHC a better motor?

the mustang gt that holds that 5.0 is way lighter, and most likely handles better. ford's pricing is fully in line or cheaper than the camaro. the motor may not cost less to build but the buzz ford will get from this is incredible and its likely that the new GT is quite a bit better than the Camaro.

the camaro has the mustang on exterior styling but its seriously looking like the Mustang GT has whipped Chevy's but on everything else for 2011......

[Drew Dowdell]

None of that answers the question of why go with a DOHC over a pushrod. Vehicle weight, styling, and price all being equal, which is the over all better engine?

[Carguy]

Honestly, I don't see a Pushrod V6 stemming from the Small Block. The reason being:-

• A 60 degree Pushrod V6 will be a brand new design, not a derivative w/o shared tooling
  
• A 90 degree is not a smooth running configuration unless a balance shaft is used.
  
• With less cylinders and (possibly) a 60deg angle the packaging advantages of a Pushrod diminishes.
  
• The HF V6 already exists and there is no good reason for duplicity in the lineup
  

What I do see (and hope to see) is the continued evolution of the Pushrod Small Block. Probably fortification with VVT, Raised Cam, Cylinder Deactivation and Direct Injection in the Fifth generation due in this year or 2011. This will probably be accompanied by a reduction in displacement to 5.5 liters with little or no reduction in output from the 400~436hp of the current 6.2 (LS3).

By 2014~2015, we may see variable valve lift and dual co-axial VVT in the 6th Gen design.

Well the 4.5L V6 based on the bore-stroke of the 6.0L V8 would obviously be 90 degree and would be FAR BETTER then the ancient 4.3L version used in the trucks today. I think properly refined and advanced it could be a wonderful torque advantaged and slower turning and efficent premium V6 over its DOHC high revving competitors. If your stated OHV advantages are true (and I believe they are) whats good for the OHV V8 could be good for a OHV V6 as well.

[smk4565]

SMK, why does this rather simple concept baffle you? Horsepower per litre displacement is stupid. Give me horsepower for overall package dimensions and get back to me.

Is the hood/engine bay in a Corvette or Silverado small? Packaging shouldn't really matter. They can fit a V12 in an SL roadster, they could fit a DOHC V8 in a Corvette, especially since they already did it back in 1991. E-class and 5-series fit DOHC V8s just fine, the CTS is the same size. The only reason GM sticks with the pushrods is because they don't have the money to make something new. All the arguments for the pushrod V8 were made for the pushrod V6 5-10 years ago, yet the high feature V6 replaced them because that is what the market demands. In time, the market will demand a switch of V8s as well.

[Z-06]

Is the hood/engine bay in a Corvette or Silverado small? Packaging shouldn't really matter. They can fit a V12 in an SL roadster, they could fit a DOHC V8 in a Corvette, especially since they already did it back in 1991. E-class and 5-series fit DOHC V8s just fine, the CTS is the same size. The only reason GM sticks with the pushrods is because they don't have the money to make something new. All the arguments for the pushrod V8 were made for the pushrod V6 5-10 years ago, yet the high feature V6 replaced them because that is what the market demands. In time, the market will demand a switch of V8s as well.

SMK, I am again going to explain you the reasons why the HF V-6 replaced the pushrod V-6.

1. HF engines are based on similar DOHC 4-cylinders which were developed for the Eco-tec engine family, not the V-8 push rods. It is easier and more economical to perform the economy of scales for V-6 based on the 4-cylinders, since those are engines shared in ALL GM brands and not only restricted to GM brands in America.

2. Because of displacement tax levied by many Asian and European countries, DOHC engines are used in light vehciles, as Dwight mentioned, NOT because they are more refined. So if I have to shell money for higher displacement, I will go for a lesser displacement engine producing similar performance, even if it means it is less refined than a higher displacement engine making similar power numbers and has a better feel to it. That is the main reason why Asian, European manufacturers have stuck with the DOHC's not because they are refined. The market demanded smaller displacement engines not refinement. Modern rules are now basing taxes on the emissions, but the old rules of taxing the displacement still persist in many countries.

As for the Pushrod V-8,

No other light auto manufacturer in the world other than American manufacturers sells enough volume of V8 engines to justify separate design and development cost for a V8 and be viable. Most of the V-8's sold by the luxury auto manufacturers are in America. In Europe and other countries they still sell majority of puny V-6 for their flagship cars. I will dare to say this the combined light vehicle V8's sold all over the world except America by all manufacturers will not exceed the V-8's sold by GM, Ford and Chrysler in their cars and pickup trucks. Barring luxury auto manufacturers and except for Hyundai and Toyota, which other manufacturers from Europe and Asia have a full fledged V8 serving in their light vehicles? Your highly acclaimed Tau engine is nothing but a big bored version with two extra cylinders of the 3.3L Lambda engine, so no Hyundai did not develop the engine from scratch.

As for the fitting of V8 in BMW and Merc sedans, let us fit a pushrod engine with higher displacement in the same engine bay and then compare which one will leave more space below those hoods. I have seen a 5.7L LS1 in a Honda S2000 without significant modifications. So yeah, pushrod packaging is comparable with a 4-cylinder OHC. :rollseyes:

[Nick]

Is the hood/engine bay in a Corvette or Silverado small? Packaging shouldn't really matter. They can fit a V12 in an SL roadster, they could fit a DOHC V8 in a Corvette, especially since they already did it back in 1991. E-class and 5-series fit DOHC V8s just fine, the CTS is the same size. The only reason GM sticks with the pushrods is because they don't have the money to make something new. All the arguments for the pushrod V8 were made for the pushrod V6 5-10 years ago, yet the high feature V6 replaced them because that is what the market demands. In time, the market will demand a switch of V8s as well.

Please share with us more delicious wine from your mind grapes.

[67impss]

Is the hood/engine bay in a Corvette or Silverado small? Packaging shouldn't really matter. They can fit a V12 in an SL roadster, they could fit a DOHC V8 in a Corvette, especially since they already did it back in 1991. E-class and 5-series fit DOHC V8s just fine, the CTS is the same size. The only reason GM sticks with the pushrods is because they don't have the money to make something new. All the arguments for the pushrod V8 were made for the pushrod V6 5-10 years ago, yet the high feature V6 replaced them because that is what the market demands. In time, the market will demand a switch of V8s as well.

Push rods still make for a Lighter engine better mpg and yes smaller package . The smaller package may mean that we get Alpha with a V8 with a cost savings or added structural rigidity due to the fact that they have to shoehorn a DOHC V8 in there, also the cost of maintenance would be higer. I rember the first V8 Monza's & Mustange II's you had to use a hole saw on the inner fender just to change spark plugs.

I say that Europe dose it their way because of tradition just as Detroit does,DOHC placement is the oldest technology anyway. When camless engines can be made cheap enough and are reliable then its a moot point and that day is coming very soon.

[Drew Dowdell]

Is the hood/engine bay in a Corvette or Silverado small? Packaging shouldn't really matter. They can fit a V12 in an SL roadster, they could fit a DOHC V8 in a Corvette, especially since they already did it back in 1991. E-class and 5-series fit DOHC V8s just fine, the CTS is the same size. The only reason GM sticks with the pushrods is because they don't have the money to make something new. All the arguments for the pushrod V8 were made for the pushrod V6 5-10 years ago, yet the high feature V6 replaced them because that is what the market demands. In time, the market will demand a switch of V8s as well.

Everywhere you see a DOHC engine that just barely fits, you could put a CIB engine of a over a liter displacement greater or more.

The pushrod 5.3 was able to fit, transversely in the engine bay of the W-body. The DOHC 3.6 was squeezed in there just barely.

[dwightlooi]

the mustang gt that holds that 5.0 is way lighter, and most likely handles better. ford's pricing is fully in line or cheaper than the camaro. the motor may not cost less to build but the buzz ford will get from this is incredible and its likely that the new GT is quite a bit better than the Camaro.

the camaro has the mustang on exterior styling but its seriously looking like the Mustang GT has whipped Chevy's but on everything else for 2011......

The Mustang is a lighter chassis to begin with. Part of the reason is that Ford decided to for go fully independent suspension for a live axle in the back. The chassis is also less rigid than the Zeta. It all adds up to an ~200 lbs difference in chassis weight.

None of this has anything to do with the DOHC 5.0 motor. As a matter of fact, the Mustang would have been even lighter and have more power and torque were it outfitted with a LS3 Pushrod V8.

The question I'll like to post to everyone is this:

"The 5.0 liter Coyote DOHC V-8 makes 412hp/390lb-ft with the help of four VVT actuators and 32-valves. It gets 16/24mpg in the 2011 Mustang 5.0. The 6.2 liter LS3 Pushrod V8 makes 426hp/420lb-ft with no VVT and just 16-valves. It gets 16/24mpg in the 2010 Camaro SS which is about 200 lbs heavier than the Mustang. The LS3 also weighs less, take up less room and cost less to manufacture. Why is the 5.0 DOHC a better engine?"

Anyway... let me summarize the discussion in the past dozen or so posts:-

• A Pushrod V8 lighter, smaller and less complex than a DOHC V8 of equivalent power.
  
• A Pushrod V8 has better fuel economy than a DOHC V8 of equivalent power.
  
• A Pushrod V8 is less costly to build than a DOHC V8.
  
• A DOHC V8 is advantageous in markets where taxes are levied on displacement.
  
• A DOHC V8 is advantageous in those racing series where rules limit maximum displacement.
  
• A DOHC V8 is perceived as more refined by some individuals.
  

Edited February 17, 2010 by dwightlooi

[regfootball]

well one thing is for sure. ford gave up on pushrod v8's for the mustang. i don't see them lamenting the decision at all. and in terms of investment, it made a lot more sense for them to invest in the 5.0. i havent checked but the 5.0 is probably a derivitive of the 3.7v6. which means they were able to have commonality in technology and actually have a new v8 under the hood.

considering the massively high hood on the camaro i dont exactly see how keeping the overall height of the engine so compact really matters. especially with the big freakin hood bulge on the v8. i have a hard time believing the packaging contraints under the mustang's hood are larger than the camaro's. it would be intersting to see if the chevy v8 can actually fit under the hood of the mustang, since the available space in the mustang to put the engine seems a lot smaller. how much valve area does that chevy small block have per cylinder vs the four valve overhead cam design on the ford, and what is the burning efficiency when the spark location is not central.

Edited February 17, 2010 by regfootball

[dwightlooi]

well one thing is for sure. ford gave up on pushrod v8's for the mustang. i don't see them lamenting the decision at all. and in terms of investment, it made a lot more sense for them to invest in the 5.0. i havent checked but the 5.0 is probably a derivitive of the 3.7v6. which means they were able to have commonality in technology and actually have a new v8 under the hood.

considering the massively high hood on the camaro i dont exactly see how keeping the overall height of the engine so compact really matters. especially with the big freakin hood bulge on the v8. i have a hard time believing the packaging contraints under the mustang's hood are larger than the camaro's. it would be intersting to see if the chevy v8 can actually fit under the hood of the mustang, since the available space in the mustang to put the engine seems a lot smaller. how much valve area does that chevy small block have per cylinder vs the four valve overhead cam design on the ford, and what is the burning efficiency when the spark location is not central.

The Camaro may not be particularly sensitive to the dimensions of the engine. But that doesn't make a bigger, heavier, more expensive, less fuel economical, less powerful and less torquey engine preferable!

The valve area of a pushrod design is smaller than in a DOHC design. This is why a DOHC design flows more air and has higher specific output. The problem is that, in order to operate the DOHC valvetrain, you end up with two much bigger cylinder heads, four times as many cam shafts and sprockets and twice as many valves. Complexity and costs aside, the DOHC design has much higher internal friction from all these added parts, a lot of extra bulk and a significant amount of extra weight. If you simply increase the displacement by about 20%, you end up with a smaller engine, a lighter engine, an engine with less internal friction and slightly better fuel economy.

Bigger displacement, better fuel economy? Sounds counter intuitive? Well, let me try to explain it...

1. It takes two otherwise identical cars the same amount of power to maintain a given speed.
   
2. To make the same amount of power you need to burn the same amount of fuel.
   
3. To burn the same amount of fuel, you need to flow the same amount of air.
   
4. At cruise, flow is being restricted such that just enough power is made for speed to be constant.
   
5. At cruise, the engine is not being choked by the airflow limits of the intake and valves.
   
6. At cruise, the engine is being choked by the throttle body.
   
7. The above holds true regardless of valvetrain design or displacement.
   
8. This means that none of the airflow advantages of a DOHC design matters.
   
9. The higher internal friction from the DOHC valvetrain however hurts (by increasing parasitic loss).
   
10. Hence, a reduction in displacement often do not increase efficiency but can sometimes decrease it.
    

Point to ponder: "When fuel economy is the paramount goal, Honda adopted a 1.3 liter SOHC 8-valve (LDA) Inline-4 for the Civic Hybrid and Insight. This is from the same company who also puts the F20C 125bhp/liter engine in the S2000. Why?"

When a DOHC-16v 1.8 liter engine is more efficient than a DOHC-16v 2.4 liter, it is not because it is 1.8 liters per say. It is because the 1.8 liter engine has smaller bore circumferences and/or stroke length which reduces bore friction. Since they are both DOHC-16v designs, the level valvetrain friction may be quite similar. Therefore, the 1.8 liter engine nets an increase in efficiency. However, a SOHC 8v 2.4 liter of a similar output to the 1.8 liter DOHC 16v may have similar or better fuel economy.

Similarly, when you compare a 4 liter DOHC V8 and a 6.2 liter Pushrod V8, the amount of reduction in bore friction may be more than offset by the increase in valvetrain drag. This is often excerbated by the lower torque output of the smaller engine necessitating a top gear which keeps the engine at higher rpms. The net result is that the 4.0 liter DOHC V8 in an M3 is less economical on fuel than a 6.2 liter Pushrod V8 in a Camaro SS.

Edited February 17, 2010 by dwightlooi

[smk4565]

SMK, I am again going to explain you the reasons why the HF V-6 replaced the pushrod V-6.

1. HF engines are based on similar DOHC 4-cylinders which were developed for the Eco-tec engine family, not the V-8 push rods. It is easier and more economical to perform the economy of scales for V-6 based on the 4-cylinders, since those are engines shared in ALL GM brands and not only restricted to GM brands in America.

Your highly acclaimed Tau engine is nothing but a big bored version with two extra cylinders of the 3.3L Lambda engine, so no Hyundai did not develop the engine from scratch.

You are right on economies of scale. So it makes sense that the 4, 6, and 8 cylinder engines are all of the same design and architecture. Hyundai obviously gets it, they have 4, 6, and 8 cylinders all sharing technology. The Tau V8 still cost over $200 million to develop, it isn't something they just threw together. It probably isn't an accident that BMW makes a 3.0 straight six and a 6.0 V12 either, or that they use the same double vanos, direct injection and turbo technology across the board. Economies of scale are used by others better than GM, the LS3 doesn't have the same features that the 3.0 or 3.6 V6 have.

[smk4565]

The Ford 5.0 V8 gets 17/25 mpg in the Mustang.

[regfootball]

part of the reason so many went to smaller OHC engines was the ability to keep the valve mass low corresponding with smaller displacements which were enabled by the equation.... more air in + more air out + more efficient combustion chamber layout + less rotational mass + lower piston speeds = more power and fuel economy. quicker revving and response. i hear about less valve float but i do not know what that is.

an OHC motor may not have one singular camshaft, but it ain't got all those pushrods rocking back and forth either. If the valvetrain on an alum OHC motor is lighter and more responsive it may not necessarily be as deficient as you suggest.

if you apply all the tech you suggest to the small block, i see where you are headed. but a- they haven't done it yet which begs the question (why) and 2- your solutionb advocates a 5.5l block which is reducing displacement but at the same time you are advocating for as much displacement as possible.

a nice balanced inline 6 has only 2 camshafts. Its a little taller, but its not a wide V either.

A lot of Hondas have only one cam per bank also.

I'm not opposed to the small block v8, I just think if the solutions to making its advantages were as clear as you say, it'd been done by now. And with FE being the big thing these days, cars like the G8 GXP and its crappy fuel economy most certainly do not make a good case for proliferating v8's.

Edited February 17, 2010 by regfootball

[balthazar]

>>"when you compare a 4 liter DOHC V8 and a 6.2 liter Pushrod V8, the amount of reduction in bore friction may be more than offset by the increase in valvetrain drag."<<

This would be very interesting to examine scientifically. I don't think bore differences, and the accompanying smaller piston rings (the friction source there) is going to be detectable without specific instrumented testing. Do not forget side loading --> increased friction of larger pistons, too. Stroke differences should be more demostratable, but it looks like most modern motors are over-square designs anyway; minimizing things there as much as performance goals allow.

Whats far more likely a source IMO is lifters (IBC: 8, DOHC: 0) and cam bearings (IBC: 5, DOHC: 20). What this net friction tests out as, IDK. Let's leave the rockers in both as rollers, tho again (IBC: 16, DOHC: 32 (or more)).

I would like to see the common sense test of this: taking the same car and replacing the engine from one type to another & running careful MPG tests on both combos. The honda EX above could also involve preferences of performance capability & engine costs, that together may trump putting the s2000 4 in the civic.

Edited February 17, 2010 by balthazar

[dwightlooi]

The Ford 5.0 V8 gets 17/25 mpg in the Mustang.

I was trying to compare apples to apples there.

The 5.0 Coyote V8 is 16/24 with the manual transmission. The 6.2 LS3 in the Camaro is also 16/24 with a manual transmission.

The Coyote V8 gets a 1 mpg boost with the automatic (which has a wider ratio spread than the manual). The automatic Camaro SS does not use the LS3, but the 6.2 liter L99 engine. The L99 also gets 25mpg on the freeway. However, we were comparing the LS3 and the Coyote previously, so I didn't want to bring the L99 into the discussion.

[Drew Dowdell]

Yeah, so... Dwightlooi is someone not even I would mess with on numbers....

[dwightlooi]

part of the reason so many went to smaller OHC engines was the ability to keep the valve mass low corresponding with smaller displacements which were enabled by the equation.... more air in + more air out + more efficient combustion chamber layout + less rotational mass + lower piston speeds = more power and fuel economy. quicker revving and response. i hear about less valve float but i do not know what that is.

an OHC motor may not have one singular camshaft, but it ain't got all those pushrods rocking back and forth either. If the valvetrain on an alum OHC motor is lighter and more responsive it may not necessarily be as deficient as you suggest.

if you apply all the tech you suggest to the small block, i see where you are headed. but a- they haven't done it yet which begs the question (why) and 2- your solutionb advocates a 5.5l block which is reducing displacement but at the same time you are advocating for as much displacement as possible.

a nice balanced inline 6 has only 2 camshafts. Its a little taller, but its not a wide V either.

A lot of Hondas have only one cam per bank also.

I'm not opposed to the small block v8, I just think if the solutions to making its advantages were as clear as you say, it'd been done by now. And with FE being the big thing these days, cars like the G8 GXP and its crappy fuel economy most certainly do not make a good case for proliferating v8's.

There is two catches in all of this...

(1) The heavier actuated mass in an SIBC design limits maximum rpm and the smaller relative valve area limits airflow potential. However, the pushrod design is adequate for handling the rev limits of most production car engines (6600~7000 rpm). And, there airflow advantages of a DOHC design is typically not realized below about 6000 rpm or so. Hence, when you compare a pushrod design a DOHC design redlined at 6000~7000 rpm with power peaks coming in the 5500~6500 rpm range, the advantages of a DOHC valve train is minimal.

(2) None of the above matters at cruise, because no matter how well or poorly the engine flows air, the restriction is the throttle body. So no matter how well the engine flows air, the pumping losses governed really by trying to move a given volume of air against the restriction of the throttle body. This in fact is one of the major reasons why diesels are so much more efficient. Diesels don't have a throttle body, the flow the maximum amount of air the engine can suck in at a given rpm all the time. Diesels control power simply by metering fuel -- running very lean at cruise to slightly rich when you floor it.

[Z-06]

You are right on economies of scale. So it makes sense that the 4, 6, and 8 cylinder engines are all of the same design and architecture. Hyundai obviously gets it, they have 4, 6, and 8 cylinders all sharing technology. The Tau V8 still cost over $200 million to develop, it isn't something they just threw together. It probably isn't an accident that BMW makes a 3.0 straight six and a 6.0 V12 either, or that they use the same double vanos, direct injection and turbo technology across the board. Economies of scale are used by others better than GM, the LS3 doesn't have the same features that the 3.0 or 3.6 V6 have.

You conveniently forgot the following from my argument to make up your argument.

No other light auto manufacturer in the world other than American manufacturers sells enough volume of V8 engines to justify separate design and development cost for a V8 and be viable.

GM can justify spending $$ to build a V8 which is superior and not restricted by economies of scale because of over 1M sales of V8 vehicles. And your last statement about LS3 not having same features as the HF family again proves the point that you did not read what dwight had to say about LS engine family and its potential.

As for the $200 M from Hyundai - there is something called testing and complying to standards. That money had to be allocated in a separate funding from the small engine development. Oh just to let you know it takes close to $1B to research and develop an engine.

[regfootball]

You are right on economies of scale. So it makes sense that the 4, 6, and 8 cylinder engines are all of the same design and architecture. Hyundai obviously gets it, they have 4, 6, and 8 cylinders all sharing technology. The Tau V8 still cost over $200 million to develop, it isn't something they just threw together. It probably isn't an accident that BMW makes a 3.0 straight six and a 6.0 V12 either, or that they use the same double vanos, direct injection and turbo technology across the board. Economies of scale are used by others better than GM, the LS3 doesn't have the same features that the 3.0 or 3.6 V6 have.

are nissan's v8's versions of their 4's and 6's?

[dwightlooi]

OK... since there seems to be a lot of people calling for a DOHC V8 from the General. Let's set all the cost issues aside and compare what a DOHC V8 and a Pushrod V8 may look like from the general. Please consider the specifications and tell us why you think one is better than the other. Or, if you disagree with my estimates and numbers feel free to challenge them with your reasoning's.

[regfootball]

There is two catches in all of this...

(1) The heavier actuated mass in an SIBC design limits maximum rpm and the smaller relative valve area limits airflow potential. However, the pushrod design is adequate for handling the rev limits of most production car engines (6600~7000 rpm). And, there airflow advantages of a DOHC design is typically not realized below about 6000 rpm or so. Hence, when you compare a pushrod design a DOHC design redlined at 6000~7000 rpm with power peaks coming in the 5500~6500 rpm range, the advantages of a DOHC valve train is minimal.

(2) None of the above matters at cruise, because no matter how well or poorly the engine flows air, the restriction is the throttle body. So no matter how well the engine flows air, the pumping losses governed really by trying to move a given volume of air against the restriction of the throttle body. This in fact is one of the major reasons why diesels are so much more efficient. Diesels don't have a throttle body, the flow the maximum amount of air the engine can suck in at a given rpm all the time. Diesels control power simply by metering fuel -- running very lean at cruise to slightly rich when you floor it.

typically in years past even if GM's pushrod engines could in theory make 6500 rpm, their NVH and revving characteristics in the higher rpm ranges were not as desirable, and I would tend to think that has everything to do with the valvetrain having a tough time remaining smooth at the higher rpm whereas many of the production OHC motors out there can safely spin like nothing to way higher rpms than their redline limits (despite purported additional friction), its often that their redlines were set because that was all the accessories off the engine could handle. And a lot of times the transmissions too set the max power the factory was willing to warranty.

Kind of a 'would you rather have a pushrod motor that seems strained with a 6000-6500 rpm redline, or would you rather have an OHC motor with 7000-7500 rpm redline that really feels like it could go up to 8000-8500 and still not feel strained.' If pushrod mills can do an 8000 redline with no fuss and be just as smooth (primarily referring to the v6 ones here) then ahem, someone should maybe build it.......but there are no takers.

Edited February 18, 2010 by regfootball

[loki]

typically in years past even if GM's pushrod engines could in theory make 6500 rpm, their NVH and revving characteristics in the higher rpm ranges were not as desirable, and I would tend to think that has everything to do with the valvetrain having a tough time remaining smooth at the higher rpm whereas many of the production OHC motors out there can safely spin like nothing to way higher rpms than their redline limits (despite purported additional friction), its often that their redlines were set because that was all the accessories off the engine could handle. And a lot of times the transmissions too set the max power the factory was willing to warranty.

Kind of a 'would you rather have a pushrod motor that seems strained with a 6000-6500 rpm redline, or would you rather have an OHC motor with 7000-7500 rpm redline that really feels like it could go up to 8000-8500 and still not feel strained.' If pushrod mills can do an 8000 redline with no fuss and be just as smooth (primarily referring to the v6 ones here) then ahem, someone should maybe build it.......but there are no takers.

just for a solid example

sounds like what you're referring to is the RX cars. the autos have a lower redline, mid 7000s?... lower HP #s.... the manuals go up to almost 9k and have a higher output.

[dwightlooi]

typically in years past even if GM's pushrod engines could in theory make 6500 rpm, their NVH and revving characteristics in the higher rpm ranges were not as desirable, and I would tend to think that has everything to do with the valvetrain having a tough time remaining smooth at the higher rpm whereas many of the production OHC motors out there can safely spin like nothing to way higher rpms than their redline limits (despite purported additional friction), its often that their redlines were set because that was all the accessories off the engine could handle. And a lot of times the transmissions too set the max power the factory was willing to warranty.

Kind of a 'would you rather have a pushrod motor that seems strained with a 6000-6500 rpm redline, or would you rather have an OHC motor with 7000-7500 rpm redline that really feels like it could go up to 8000-8500 and still not feel strained.' If pushrod mills can do an 8000 redline with no fuss and be just as smooth (primarily referring to the v6 ones here) then ahem, someone should maybe build it.......but there are no takers.

I tend to disagree on that. I think we need to break the causes of "strained" down to two separate factors which really have nothing to do with each other.

(1) The first being the onset valve float. This happens at an engine speed beyond which the valve springs can no longer move the valves fast enough to close them at the same rate as the intake cam lobe's trailing edge. What happens then is that the lifters become separated from the cam lobes as the lobes pass under them and then shortly thereafter slaps onto the base circle. This is not only an acoustic issue it also a durability issue as the impacts wears out the valvetrain in relatively short order.

In general engines are designed not to have valve float or only extremely minute amounts of it right at with very limits of rev limits. This applies to all engines, OHC or Pushrod. The only difference being that for a given amount of spring tension, it occurs soon on pushrods than on DOHC designs. You can always increase spring tensions and the problem will go away, but this increases startup wear (which accounts for the majority of engine wear) and decreases fuel economy due to increased valve train friction. In otherwords, regardless of valvetrain layout you are not going to see a lot of float related noise. The redline rpm of the engine may be higher or lower due to the limitations imposed by the onset valve float on a particular valvetrain layout, but the amount of float related noise at that rpm is unlikely to be very different. In fact, if the designers are conservative, there won't be any and the redline will simply fall another 200~300 rpms to make sure of that.

(2) The second factor for strained is engine vibrations. I4s have 2nd order up-down vibrations. V6es have end to end shake (worse on 90 deg sixes than on 60s). I6es and H engines are naturally balanced. V8s have end to end shake, but less than V6es due to the ability to use heavier counterweights. Vibrations get worse not with rpms per say, but with piston speed. So, it really is more a function of stroke length than displacement. Again, this affects engines univerally irrespective of valvetrain design.

IMHO, GM engines of yore were redlined at rather low rpms because the cylinder heads and intakes of the time didn't flow enough air to benefit from higher rpm limits. An L98 makes its maximum 200~240hp at 4000 rpms. Even if you let the engine rev to 6000 rpm, you are not going to get anything out of it. The engines also had rather crude acoustics mainly due to poor tolerances and lack of component stiffness. This is not the case today. At 6000~6400 rpms, the LS3 in the Camaro SS did not rattle or sound more sloppy than a Mercedes M113 5.5 liter in the C55 AMG at the same revolutions. Not that either sounds as silky as a Lexus 4.6 at the redline, but they are both bigger engines with possibly less sound insulation and/or mount damping.

[smk4565]

Personally, I like to see GM double up on the 2.0 turbo and turn that into a 4.0 liter twin turbo V8. That could produce 400-450 hp and lb-ft and produce peak torque around 2,000 rpm where it is most usable. A larger 4.6-4.8 liter turbo V8 could be used for high performance cars. GM already acknowledged they are worried about Hyundai (Honda has as well), Hyundai has a DOHC V8 that is one of the world's 10 best engines. Really Honda is the one that should worry the most, at least GM has a V8, Honda has nothing to give Acura. Hyundai was a joke 10 years ago, now they are the brand everyone fears, where will they be in 10 years? What is Hyundai attacks the luxury segment with full force, what if they make a full size pickup? Hyundai is making profit on small cars and family sedans/crossovers, they aren't even in the luxury and truck business that most automakers rely on for profit. In time, Hyundai is going to move into the high profit margin segments. GM better be prepared.

[regfootball]

if i recall the premise of the thread was why not put this v8 in the ATS, but if this in principle is so watertight, then it should be an acceptable engine in the base XTS. Why then would GM NOT put this in the XTS? apparently since size of the small block is no issue.....

[Drew Dowdell]

if i recall the premise of the thread was why not put this v8 in the ATS, but if this in principle is so watertight, then it should be an acceptable engine in the base XTS. Why then would GM NOT put this in the XTS? apparently since size of the small block is no issue.....

Because the XTS is a showcase for the GM's next Gen Hybrid technology.

[regfootball]

so do the hybrid with the v8 then......