Why GM should NOT build a DOHC V8

[G. David Felt]

This company rocks, the new KV4-RR is a freakin amazing engine and only 162lbs of weight. I see no reason why GM could not use this style of design for a V8.

There is a difference between crate engines or race engines and production engines covered by a 5yr/100,000 mile warranty expected to endure the drudgery and neglect of mundane automobiles. Production also has to have a wide and tractable power band whereas motorsport engines only have to perform within a relatively 2000~3000 rpm range and it is the job of the racer to not allow rpms to fall out of the prescribed range.

The problem with reving any engine that high is that you end up using a lot of valve lift, duration and overlap to get the engine to breath with good volumetric efficiency high up. Cams like that generally don't idle well at 600 rpm, most do not idle at all that low. VVT mitigates that somewhat by allowing you to dial out the overlap but it still results in a rather soft lower rpm response. Besides, the high valve spring rates needed to prevent valve float at such rpms causes increased wear and reduced fuel economy.

With Pushrod engines in the 45~50 cu-in per cylinder bracket, we know that we can get to about 6600 rpm without using exotic materials. Throw in titanium valves and the like and you can push it to about 7000 with no reliability or durability issues. With DOHC 4-valve designs, you can get to about 8200 rpm using the "normal" stuff, about 9000 if you really try. For most production cars though, these are all more than adequate rpm capability.

I have to think that if Katech can build engines that people use in the abusive world of racing that this V4 can handle the drudgery and neglect of mundane auto drivers.

[dwightlooi]

It doesn't really work that way...

It is perfectly acceptable that a race engine be rebuilt every 3~4 races. It is not acceptable that you rebuilt your mundane engine every 3 to 4 years. It is perfectly acceptable for a race engine to idle at 3000 rpm, any production engine that does that will see the car make a U-turn straight for the service department the moment it is driven of the dealer's lot. It is generally a non-issue for a race engine to make good power between 6000 and 8000 rpm and suck everywhere else, an everyday engine that does that won't be acceptable to the diehard S2000 fan and won't ever pass SMOG. Generally speaking, race engines to not have to be long lived, clean or civil. Fuel economy isn't even a factor. The same thing goes for drive train, brakes, tires and other parts. They just have to deliver maximum performance and not grenade itself for the relatively short duration of a race.

By the time you take a race engine, tone it down to the point where it pulls smoothly from 600 rpm, passes emissions, lasts 200,000 miles even when the driver changes the oil every 20,000 miles it is no longer the spectacular performer. In fact, a lot of race grade stuff actually sucks in daily use even when you won't think they would. A good example is forged pistons. Yes, it is stronger, yes it can put up with more abuse and detonation before failing, and yes it is more expensive. But, because it also has a higher thermal expansion it needs to be fitted lose when cold in order to have the right clearances when warmed up. This leaders to a noisy cold engine, high oil burn rates and most importantly greatly increased wear over time. A race car has no problems with that but you do.

[G. David Felt]

It doesn't really work that way...

It is perfectly acceptable that a race engine be rebuilt every 3~4 races. It is not acceptable that you rebuilt your mundane engine every 3 to 4 years. It is perfectly acceptable for a race engine to idle at 3000 rpm, any production engine that does that will see the car make a U-turn straight for the service department the moment it is driven of the dealer's lot. It is generally a non-issue for a race engine to make good power between 6000 and 8000 rpm and suck everywhere else, an everyday engine that does that won't be acceptable to the diehard S2000 fan and won't ever pass SMOG. Generally speaking, race engines to not have to be long lived, clean or civil. Fuel economy isn't even a factor. The same thing goes for drive train, brakes, tires and other parts. They just have to deliver maximum performance and not grenade itself for the relatively short duration of a race.

By the time you take a race engine, tone it down to the point where it pulls smoothly from 600 rpm, passes emissions, lasts 200,000 miles even when the driver changes the oil every 20,000 miles it is no longer the spectacular performer. In fact, a lot of race grade stuff actually sucks in daily use even when you won't think they would. A good example is forged pistons. Yes, it is stronger, yes it can put up with more abuse and detonation before failing, and yes it is more expensive. But, because it also has a higher thermal expansion it needs to be fitted lose when cold in order to have the right clearances when warmed up. This leaders to a noisy cold engine, high oil burn rates and most importantly greatly increased wear over time. A race car has no problems with that but you do.

As I said, the Katech V4 can last and was engineered to handle both the common mans world and race day. Their clear testing process covers the dole drum daily driving and the abuse of racing. Check out their testing: http://www.katechengines.com/engineering/testing/

[Guest [email protected]]

due to lots of the facts of the great abc engine that i have read here , i have nothing to say except that you all have a mising point , which is the really main reazon why GM dont want to move a way fom the push rod engine to dohc , i m a bussiness man and i think i have the answer: GM has found that this tipe of engine has came to stay due to the fact thAT IT HAS BECOME A GREAT BUSSINES TO GM IN THE AFTERMARKET WORLD , ENGINE SWAP. AND ON AND ON ETC gm CARES LESS ABOUT THE PEOPLE THINCK which say that GM atayed inthe stone age with this engines , but this is simply because GM have found a very very lucrative bussiness in the racing world, and if you are making insane $$$$$$$ selling oranges would you ever move to apples,????? even if you will be moving to a better or newer tech????????????? , with out kowing the repercution in the bussiness??? i didint think so so eat this GM probably never will move to dohc if money will not be greater , gm can make a few dohc like it has done but will not get into it deep, and for your info NO OTHER COMPANY IN THE WORLD HAS MADE AN ENGINE THAT HAS EVER GOTTEN SO IMPORTANT AND POPULAR LIKE THE GREAT SBC, AND THE REAZONS ARE OVIOUS COZ ALOT OF PEOPLE HAVE POSTED THE FACTS ABOUT IT I DONT NEED TO EXPLANE IT AND SADLY FOR MANY BUT ITS COMPLITLY REAL , THE BUSINESS FOR GM WITH THIS ENGINES ARE SO BIG THAT EVERY CONTRY IN EUROPE HAS BUILT A SUPER CAR WITH THe LS3 LS7 LS2 ETC ETC ETC ENGINE CHECK ISSABENDECK1 MY YOU TUBE CHANEL AND YOU WILL BE IMPRESSED OF HOW MANY PUSH ROD ENGINES FROM GM ARE POWERING A HOLE BUNCH OF EUROPEAN SUPERCARS EVEN LAMBORGINI HAS A CHEVY ENGINE IT IS THE 2015 LAMBORGINI INDOMABLE A TWEN TURBO 572CI BBC , GM THE MECA of the best engines ever made

[dwightlooi]

due to lots of the facts of the great abc engine that i have read here , i have nothing to say except that you all have a mising point , which is the really main reazon why GM dont want to move a way fom the push rod engine to dohc , i m a bussiness man and i think i have the answer: GM has found that this tipe of engine has came to stay due to the fact thAT IT HAS BECOME A GREAT BUSSINES TO GM IN THE AFTERMARKET WORLD , ENGINE SWAP. AND ON AND ON ETC

Well... if it does not have the merits discussed -- frictional minimalization, power density, mass efficiency and cost effectiveness -- why does it have the aftermarket clout to begin with?

[G. David Felt]

due to lots of the facts of the great abc engine that i have read here , i have nothing to say except that you all have a mising point , which is the really main reazon why GM dont want to move a way fom the push rod engine to dohc , i m a bussiness man and i think i have the answer: GM has found that this tipe of engine has came to stay due to the fact thAT IT HAS BECOME A GREAT BUSSINES TO GM IN THE AFTERMARKET WORLD , ENGINE SWAP. AND ON AND ON ETC

Well... if it does not have the merits discussed -- frictional minimalization, power density, mass efficiency and cost effectiveness -- why does it have the aftermarket clout to begin with?

LOL, Those are all the great Marketing Lies of why people push the crappy DOHC v8's. They have high horsepower with sucky Torque and are average at best.

Also I have yet to see DOHC engines last 500,000 miles or a million miles or more. Sorry still not sold on DOHC garbage.

[Lamar]

LOL, Those are all the great Marketing Lies of why people push the crappy DOHC v8's. They have high horsepower with sucky Torque and are average at best.

Several foreign automakers, primarily in Europe and Japan, switched to DOHC in order to get around displacement taxes, and they decided to move all their engines to that configuration instead of building both DOHC and OHV.

To your other point, about DOHC V8s not making any torque, I'd request that you look at the numbers from some current V8s. Ford, Nissan, Toyota, take your pick.

Also I have yet to see DOHC engines last 500,000 miles or a million miles or more. Sorry still not sold on DOHC garbage.

They may not be V8s, but half-million and million-mile Hondas, VWs, and BMWs exist. Again, look around.

[G. David Felt]

LOL, Those are all the great Marketing Lies of why people push the crappy DOHC v8's. They have high horsepower with sucky Torque and are average at best.

Several foreign automakers, primarily in Europe and Japan, switched to DOHC in order to get around displacement taxes, and they decided to move all their engines to that configuration instead of building both DOHC and OHV.

To your other point, about DOHC V8s not making any torque, I'd request that you look at the numbers from some current V8s. Ford, Nissan, Toyota, take your pick.

Also I have yet to see DOHC engines last 500,000 miles or a million miles or more. Sorry still not sold on DOHC garbage.

They may not be V8s, but half-million and million-mile Hondas, VWs, and BMWs exist. Again, look around.

Ford Nissan and Toyota all have engines that have to rev to 6000rpm or higher to create the HP and the torque is tapped out by the time you hit 4000+ or in toyota's case 4400. The torque to HP ratio and curve suck. I do not see a consistent pull with the HP and Torque together.

Yes you find a bunch of DOHC 4 bangers and some V6 with half a million to a million miles but passenger cars do not haul the loads that work trucks, SUV's do and so far I have not seen even in passenger cars that have DOHC v8 engines them lasting as long as pushrod engines do.

[Lamar]

Ford Nissan and Toyota all have engines that have to rev to 6000rpm or higher to create the HP and the torque is tapped out by the time you hit 4000+ or in toyota's case 4400. The torque to HP ratio and curve suck. I do not see a consistent pull with the HP and Torque together.

Now, see, if you had said "torque CURVE" we'd have been all right.

Yes you find a bunch of DOHC 4 bangers and some V6 with half a million to a million miles but passenger cars do not haul the loads that work trucks, SUV's do and so far I have not seen even in passenger cars that have DOHC v8 engines them lasting as long as pushrod engines do.

OK, here you're introducing different issues.

Besides, most DOHC V8 passenger cars today aren't even kept long enough by anyone that long, much less driven that far. Reason: the majority of such engines are in luxury cars, bought by people who these days fly transcontinentally instead of driving.

[G. David Felt]

Ford Nissan and Toyota all have engines that have to rev to 6000rpm or higher to create the HP and the torque is tapped out by the time you hit 4000+ or in toyota's case 4400. The torque to HP ratio and curve suck. I do not see a consistent pull with the HP and Torque together.

Now, see, if you had said "torque CURVE" we'd have been all right.

Yes you find a bunch of DOHC 4 bangers and some V6 with half a million to a million miles but passenger cars do not haul the loads that work trucks, SUV's do and so far I have not seen even in passenger cars that have DOHC v8 engines them lasting as long as pushrod engines do.

OK, here you're introducing different issues.

Besides, most DOHC V8 passenger cars today aren't even kept long enough by anyone that long, much less driven that far. Reason: the majority of such engines are in luxury cars, bought by people who these days fly transcontinentally instead of driving.

Darn Symantec of the English language!

[Lamar]

Mind you, I'm not leaning one way or the other as to which valvetrain GM should use on a V8. They can build what they want, and I'll be fine with it...

provided it's better than just "good enough."

[Guest mac11wildcat]

the whole debate here is flawed; mostly in SMK's points.

Ford's engines make so much more power at 5.0L because their compression ratio is much much higher. You cant compare horsepower output as a result of valve-train design on two completely different engines. So really, theres no way to prove either side right. the chart shown at the top of this page however is a pretty compeling objective look.

However, you simply CANNOT beat LS's on the power/$ side. Plain and simple.

No one is doing 5.0 swaps into their Camaro's, and if they are theyre getting nothing from it.

DOHC engines have their place and excel in high performance, limited displacement, high RPM applications; its what they were designed for. IE less displacement for the same power. further allowing foreign auto companies to make tiny little 4 cylinders with enough power to sell.

[dwightlooi]

Well, a lot of time has gone by since this thread was started. We now know what kind of animal the Gen V small block is:-

General Motors Gen V Small-block V8 (RPO Code: LT1)

• Displacement: 6.2 Liters (6.162 cc)
• Bore x Stroke: 103.25 mm x 92 mm
• Compression Ratio: 11.5-to-1
• Construction: Aluminum block & heads w/ Iron cylinder liners
• Fully Dressed Weight: 211 kg
• Valve Train: In-Block-Cam, Pushrods, 2-valves per cylinder, variable valve timing, cylinder deactivation
• Fuel Supply: Direct Gasoline Injection
• Fuel Requirement: 91 Octane Premium Gasoline (Recommended; not required)
• Power Output: >= 450 hp (SAE Certification pending)
• Torque Output: >= 450 lb-ft (SAE Certification pending)
• Redline: 6600 rpm
• Fuel Economy: >= 17 mpg City / >= 27 mpg Highway (EPA certification pending)
• Performance Claims: 0-60 <= 3.9 secs (3,250 lbs Base Corvette C7)
• Confirmed Applications: Corvette C7
• Expected Applications: Cadillac V-series products, Holden Commodore HSV products

[Guest dohc guy for ever]

its simple really, liter per liter the pushrod can't compete for example: how much hp/trq do you really think a 4.0 pushrod v8 will make compare to a 4.0 dohc v8, if you really want to be fair, use the 7.0 ls7 and build a 7.0 dohc and see what happen, i bet the 7.0 dohc will have more hp/trq than the ls7 and rev higher, still don't believe me well compare the 5.7 ls1 to most 5.7 dohc and look at the results, hell compare the 5.7 ls1 to the 5.0 dohc and it still won't be a match, cough cough, 2012 5.0 mustang, lexus isf. pushrod need 10000000+ liter just to make the power and trq of a equal dohc period, end of story.

[riviera74]

It sounds like the new Gen V V8 is going into the Sierra/Silverado too, given that I just saw that new Sierra commercial bragging about AFM and VVT and all those (newer) engine technologies. The better question is whether the Gen V will find its way into a Cadillac flagship, not just Corvettes and Camaros and trucks.

[G. David Felt]

its simple really, liter per liter the pushrod can't compete for example: how much hp/trq do you really think a 4.0 pushrod v8 will make compare to a 4.0 dohc v8, if you really want to be fair, use the 7.0 ls7 and build a 7.0 dohc and see what happen, i bet the 7.0 dohc will have more hp/trq than the ls7 and rev higher, still don't believe me well compare the 5.7 ls1 to most 5.7 dohc and look at the results, hell compare the 5.7 ls1 to the 5.0 dohc and it still won't be a match, cough cough, 2012 5.0 mustang, lexus isf. pushrod need 10000000+ liter just to make the power and trq of a equal dohc period, end of story.

Not sure what glue this guy is sniffing as DOHC has never outperformed a traditional pushrod. They have lots of HP and very little Torque and as such require masses of fuel and other gadgetry to make them fly.

Yes I know many will point to all the exotic cars and even Porsche with their DOHC motors, but when you get it down to a basic motor, they all fail when you compare raw basic output compared to a pushrod.

[loki]

i kinda wish gm would make a small to mid 3L v6 with the gen 5 tech. could make it a retrofit for the high value engines. max ~250 hp and decent boost in economy.... but i'm sure the hp overlap and small market would kill this idea. boo hoo.. haha

[G. David Felt]

Loki, are you saying that like what GM is doing with their new Ecotec Engines, build a crate motor for replacements that includes VVT, cylinder deactivation from 6 to 3 during cruzing and direct injection? All 3 of these items are on the new Ecotec3 v8 engine lineup.

[Drew Dowdell]

its simple really, liter per liter the pushrod can't compete for example: how much hp/trq do you really think a 4.0 pushrod v8 will make compare to a 4.0 dohc v8, if you really want to be fair, use the 7.0 ls7 and build a 7.0 dohc and see what happen, i bet the 7.0 dohc will have more hp/trq than the ls7 and rev higher, still don't believe me well compare the 5.7 ls1 to most 5.7 dohc and look at the results, hell compare the 5.7 ls1 to the 5.0 dohc and it still won't be a match, cough cough, 2012 5.0 mustang, lexus isf. pushrod need 10000000+ liter just to make the power and trq of a equal dohc period, end of story.

You can't fit a 7.0L DOHC engine where you can fit a 7.0 Pushrod. Any place you can fit a 7.0 liter DOHC, you can fit a 9, 10, or 11 liter pushrod. Power per liter is a red herring.

[Lamar]

its simple really, liter per liter the pushrod can't compete for example: how much hp/trq do you really think a 4.0 pushrod v8 will make compare to a 4.0 dohc v8, if you really want to be fair, use the 7.0 ls7 and build a 7.0 dohc and see what happen, i bet the 7.0 dohc will have more hp/trq than the ls7 and rev higher, still don't believe me well compare the 5.7 ls1 to most 5.7 dohc and look at the results, hell compare the 5.7 ls1 to the 5.0 dohc and it still won't be a match, cough cough, 2012 5.0 mustang, lexus isf. pushrod need 10000000+ liter just to make the power and trq of a equal dohc period, end of story.

You can't fit a 7.0L DOHC engine where you can fit a 7.0 Pushrod. Any place you can fit a 7.0 liter DOHC, you can fit a 9, 10, or 11 liter pushrod. Power per liter is a red herring.

It's a Honda fanboi argument, that's what it is...

[loki]

Loki, are you saying that like what GM is doing with their new Ecotec Engines, build a crate motor for replacements that includes VVT, cylinder deactivation from 6 to 3 during cruzing and direct injection? All 3 of these items are on the new Ecotec3 v8 engine lineup.

basically. aren't there millions of 3.8's, 2.8, 3.1, 3.4, 3.5 and 3.9's out there? sadly fwd, but if these can get nearly a 50% increase in hp (based on the 4.3L increase). but it's just a dream. why get a 4cylinder if a 3.0L v6 with 210+ hp and 200+lb feet.. and w/o advancing VVL for 4 cylinder's like dwight showed, ... i still think v6's are in demand, but are just being marginalized to 'sport models'.

[riviera74]

Loki, I agree with you that there SHOULD be a successor to the 3800/3900 V6 pushrods, based on Gen V V8 engines. The original 3800 was derived from a Buick V8 from 1962, and GM used it from 1975-2008 with relatively few alterations to the fundamental engine design. It will probably have to be at least a 3.6L V6 or smaller to accommodate today's smaller engine bays.

I really have no issues with the Ecotec 4cyl, except it is all DOHC, which tend to be expensive. Going HCCI aside, GM should probably consider ditching DOHC and go back to OHV stat.

[G. David Felt]

Loki, I agree with you that there SHOULD be a successor to the 3800/3900 V6 pushrods, based on Gen V V8 engines. The original 3800 was derived from a Buick V8 from 1962, and GM used it from 1975-2008 with relatively few alterations to the fundamental engine design. It will probably have to be at least a 3.6L V6 or smaller to accommodate today's smaller engine bays.

I really have no issues with the Ecotec 4cyl, except it is all DOHC, which tend to be expensive. Going HCCI aside, GM should probably consider ditching DOHC and go back to OHV stat.

I totally agree with the ditching the DOHC and staying with OHV. I think they can still make great strides on a reliable engine with this technology.

[Drew Dowdell]

The new 4.3 Ecotec isn't physically bigger on the outside than the 3.6... there's no reason it couldn't fit in anything that already has the 3.6

[dwightlooi]

Honestly, I am not a big fan of GM doing the 4.3 V6 and 5.3 V8s. To keep logistics, tooling and development costs to the minimum, all pushrod engines should use the same bore x stroke dimensions and share internals. By standardizing on 103.25 x 92 mm cylinders, they will still have a sufficient spread of power power levels for relevant applications:-

• (C1) Super Cars -- V8 Supercharged, 91 Octane, VVT, DI, VVL, 6162 cc -- 700 bhp @ 6800 rpm / 650 lb-ft @ 3800 rpm
• (C2) Maximum Performance Cars -- V8, 91 Octane, VVT, DI, 8/4 AFM, 6162 cc -- 460 bhp @ 6000 rpm / 465 lb-ft @ 4600 rpm
• (C3) Performance Cars -- V6, 91 Octane, VVT, DI, 6/3 AFM, 4622 cc -- 345 bhp @ 6000 rpm / 350 lb-ft @ 4600 rpm
• (C4) Sport Compact (RWD) -- V4 Supercharged, 91 Octane, VVT, DI, VVL, 3081 cc -- 300 bhp @ 6000 / 300 lb-ft @ 2600 rpm

• (T1) Heavy Duty Trucks / Vans / SUVs -- V8, 87 Octane, VVT, DI, 8/4 AFM, 6162 cc -- 420 bhp @ 5200 / 440 lb-ft @ 2800 rpm
• (T2) Medium Duty Trucks / Vans / SUVs -- V6, 87 Octane, VVT, DI, 6/3 AFM, 4622 cc -- 315 bhp @ 5200 / 330 lb-ft @ 2800 rpm
• (T3) Light Duty Trucks / Van / SUVs -- V4, 87 Octane, VVT, DI, 3081 cc -- 210 bhp @ 5200 / 220 lb-ft @ 2800 rpm

This covers everything you don't want a DOHC I4 or DOHC V6 in the engine bay. There can be some cross population of course... for instance, the base engine for a RWD Sport Compact may use the (T3) 210 hp normally aspirated V4, similarly a Police Caprice may be given the (T1) truck V8 instead of the (C2) Performance Car V8 in view that even pursuit law enforcement vehicles probably don't care for 40 more hp and will like to drink a steady diet of 87 Octane.

Any purported advantageous to a 4.3 or 5.3 liter displacement can largely be equaled with AFM engagement and/or sacrificing some power and torque in favor of a late closing intake cam (a mild Atkinson cam) instead of actually varying the static displacement.

You'll still keep the a pair of DOHC engine lines for displacement tax stricken markets. Not because they are more efficient, or higher performance, but because they are cheaper for owners in those markets to buy and operate. Besides the Super 2.0 V6 will be extremely refined from a vibrational and noise standpoints

• (S1) High Performance Cars (Displacement Restricted) -- V6 Supercharged / Turbocharged, 91 Octane, VVT, DI, VVL, 1998 cc -- 420 bhp @ 6200 rpm / 360 lb-ft @ 2000~6000 rpm
• (S2) Performance Cars (Displacement Restricted) -- I4 Turbocharged, 91 Octane, VVT, DI, VVL, 1998 cc -- 270 bhp @ 6500 rpm / 260 lb-ft @ 1800~5500 rpm
• (S2) Economy Cars (Displacement Restricted) -- I4 Turbocharged / Miller, 87 Octane, VVT, DI, VVL, 1998 cc -- 200 bhp @ 6000 rpm / 180 lb-ft @ 1600~5600 rpm

Edited July 16, 2013 by dwightlooi

[riviera74]

^QFT, Dwightlooi. That is easily the best idea (from an engine standpoint) I have heard of in years. Dear GM, why not do this?

[G. David Felt]

Awesome Post Dwight, thanks for sharing this standardization of engines. This totally makes sense for a Global platform with minimal cost to meet the the needs of the market place.

My question for you, if you had to do this same list for CNG and Diesel, what would it look like?

[dwightlooi]

Awesome Post Dwight, thanks for sharing this standardization of engines. This totally makes sense for a Global platform with minimal cost to meet the the needs of the market place.

My question for you, if you had to do this same list for CNG and Diesel, what would it look like?

CNG engines are basically the same as the gasoline engines, except that you need bulky tanks and you can use a lot more compression. Or you can run them at the gasoline compression levels and not reap the full benefits. So, basically, you'll swap pistons for pent roof pistons to bring compression to about 14~15:1.

Diesels can be simply six engines. Four low displacement, high specific output diesels for the European market which is largely displacement tax hampered. Two heavy Pushrod 4-valve / cylinder Duramax engines heavy duty vehicles. The four CDTi diesels, share pistons, rods, valves and most internals. In fact, the 6 and 8 cylinder engines are basically two banks of the 3 and 4 cylinder powerplants, sharing the same turbo and aftercoolers amongst other things. Likewise the Duramax engines are internally identical except for the number of cylinders, with the V6 having a single balance shaft for harmonics reductions and the V8 having none.

• (D1) Heavy Duty Trucks / Vans / SUVs / Buses / Limousines -- V8 Duramax Turbo, #2 Diesel, DI, 6599 cc -- 400 bhp @ 3000 rpm / 770 lb-ft @ 1600 rpm*
• (D2) Heavy Duty Trucks / Vans / SUVs / Buses / Limousines -- V6 Duramax Turbo, #2 Diesel, DI, 4949 cc -- 300 bhp @ 3000 rpm / 575 lb-ft @ 1600 rpm

• (E1) High Performance European Cars -- V8 CDTi Bi-Turbo, #2 Diesel, VVT, DI, 3196 cc -- 272 bhp @ 4200 rpm / 472 lb-ft @ 2100 rpm
• (E2) Performance European Cars -- V6 CDTi Bi-Turbo, #2 Diesel, VVT, DI, 2497 cc -- 200 bhp @ 4000 rpm / 350 lb-ft @ 2000 rpm
• (E3) Economy European Cars -- I4 CDTi Turbo, #2 Diesel, VVT, DI, 1598 cc -- 136 bhp @ 4200 rpm / 236 lb-ft @ 2000 rpm*
• (E4) Ultra Economy European Cars / Diesel-Electric Hybrids -- I3 CDTi Turbo, #2 Diesel, VVT, DI, 1199 cc -- 100 bhp @ 4000 rpm / 175 lb-ft @ 2000 rpm

* Existing Engines

The E-series is intended to maximize tax benefits in the EU by using the highest specific output configuration as well as diesel fuel. The E-series also offer more cylinders and greater refinement compared to the competition. Whereas the typical BMW or MB diesel in the 250~300 hp class is a V6, the E-series uses 8 cylinders. Whereas the typical 140 hp four cylinder diesel in Europe is a 2.0L, the CDTi is a 1.6. The Duramax 6.6 is already a very successful product. Instead of the stillborn 310hp 4.5L DOHC 72 degree V8 for lighter duty commercial vehicles and trucks, the Duramax 5.0 V6 picks up that role using a cut down Duramax 6.6 reverse flow block offering essentially the same output using 0.5 liters more displacement but 2 fewer cylinders.

[G. David Felt]

That Rocks Dwight

Thank you!

[dwightlooi]

The three facts which many people fail to recognize is that...

High Specific Output does not translate to Better Fuel Economy. In fact, many of the design choices made to achieve high specific outputs reduce fuel economy. Let me give you a few examples. A 4-valve or 5-valve cylinder head with two cams per cylinder bank allows greater valve area and lower actuated valve-train mass. This gives you better breathing potential at high RPM, wide open throttle, conditions. But, what you think has more friction? One camshaft or four? One sprocket or four? 12 valves, 24 valves or 30 valves? The answer is obvious, more stuff rubbing together creates more friction -- friction which must be overcome by energy produced by burning fuel, hence it hurts fuel economy. Some people mistakenly reason that better breathing potential reduces pumping losses which offsets the greater friction. This is absolutely untrue except when the throttle is fully open -- which is not how EPA mpg tests are conducted or how most people drive their cars 99% of the time. Anytime the pedal is not all the way to the metal, the breathing of the engine is constricted by the throttle butterfly not the intake valves. Another way to achieve high specific output is through supercharging or turbocharging. Superchargers force feeds the engine with more air by driving an air pump with power produced by the engine consuming additional fuel. Turbochargers do it with relatively "free" energy otherwise wasted through the exhaust -- although they do hurt aspirational efficiencies somewhat by imposing a requisite increase in exhaust back pressure. However, both systems, in order to allow the engine to operate on compressed air without pinging or knocking, also reduces the compression ratio. This hurts fuel efficiency at cruise and anything but wide open throttle scenarios by reducing effective charge density when the engine is not in boost or not in full boost -- which is most of the time. DOHC multi-valve design, superchargers and/or turbochargers also add mass and bulk to the powerplant. All of which increase the dead weight the vehicle lugs around hurting fuel economy. It's very simple really, at any given displacement a DOHC multivalve engine, supercharged engine or turbocharged engine is less fuel efficient than an SOHC 2-valve or pushrod engine that is normally aspirated. The latter will make less power, but it will be more fuel efficient.

While High Specific Output allows lower displacement engines to be used to satisfy a given performance requirement, that smaller displacement engine is not necessarily lighter or more compact. Dual cam heads are taller, wider and heavier. In many instances, a dual cam engine is about the same weight and exterior dimensions as a SOHC or pushrod engine roughly 25~50% greater in displacement. This is especially so with Vee type engines. A 436hp LS3 pushrod 6.2 liter V8 from the last generation Corvette weighs 183 kg vs 202 kg for a 414hp DOHC 4.0 liter S65 V8 in a BMW M3 (both engines having port injection and aluminum blocks). Turbochargers add weight, and their required accessories like intercoolers, bypass valves, pipings and the like add even more. A twin turbocharged V6 like the VR38DETT in the Nissan GT-R -- arguably one of the best of its breed -- makes an impressive 520 hp from 3.8 liters and six cylinders. But it weighs 276 kg. A similarly powerful (505 hp) pushrod V8 like the 7.0 liter LS7 from the 6th Gen Corvette Z06 or the new Camaro Z28 weighs 206 kg. Let's forget high power engines for a second and look at run of the mill four cylinder powerplants from the same manufacturer. A Saturn 1.9L SOHC 8-valve engine weighs 89 kg whereas the DOHC version of the same displacement (same block actually) weighs 100 kg. If you are wondering, Honda -- the company that makes 125 bhp/liter 9,000 rpm S2000s -- chooses a SOHC 2-valve per cylinder design for the current Insight Hybrid for better efficiency than a comparable DOHC engine of similar output.

Some of the design choices you can make that has the most benefit to fuel economy specifically trades Specific Output for reduced Specific Fuel Consumption. The best example of this is the use of the pseudo Atkinson cam grind. Such a cam grind intentionally extends the opening duration of the intake valves well into the compression stroke. This allows air to be kicked back out the cylinders as the piston goes up and negated compression for the first 20~30% of the intake stroke. Because the power stroke is the not reduced the expansion ratio of the engine is effectively lengthened and the energy recovery is significantly enhanced. The engine is 20~33% less powerful, but about 10~15% more fuel efficient. The Prius and Fusion Hybrid (most hybrids for that matter) use a Pseudo Atkinson engine. Another classic trick to improve fuel economy at the expense of specific output is the deliberate use of narrow intake tracts and/or small or asymmetric intake valve openings. The smaller the office and the narrower the tract, the higher the air velocity at any given mass air flow rate. This translates to greater swill and/or tumbling action inside the cylinders which leads to better fuel-air mixing and more even and complete combustion. This dates back to the 1976 Honda Civic CVCC and though supplanted to some degree with the reliance on high injection pressures and direct atomization in today's newest DI engines, this technique is still beneficial enough that some manufacturers (Honda and Jaguar comes to mind) which uses a cam switching system to enable a very low lift valve at lower engine speeds to improve economy.

So... when somebody says this engine is more efficient because it makes more horsepower per liter, think again! And, if moronic legislators push displacement taxes as a means to reduce fuel consumption, carbon foot print and/or energy dependence, maybe you shouldn't vote for them!

Edited July 18, 2013 by dwightlooi

[G. David Felt]

Very enlightening. Thanks for the overview.

[Drew Dowdell]

But doesn't DOHC allow for more options with VVT and VVL?

[dwightlooi]

But doesn't DOHC allow for more options with VVT and VVL?

The easy way to put it is that DOHC allows for more "convenient" implementations of VVT and VVL.

When it comes to VVT, because a Pushrod or SOHC engine uses a single cam to operate both the intake and exhaust valves, varying the phasing of that cam advances or retards both in unison. This is called "synchronous" VVT-- the L99 and LT1 engines use this scheme. This is the common and most "straight forward" design, but benefits are not as great as systems able to vary the intake and exhaust timings independently. However, SOHC and pushrod designs can implement cam-in-cam independent VVT (ala Dodge Viper's 8.4 V10) and achieve the same benefits.

When it comes to VVL, there is really no advantage or disadvantage either way. Systems that use locking/unlocking lifters or followers can be implemented on SOHC or DOHC or Pushrod designs with similar ease. The simplest will be the design used on Jaguars and Porsches, which basically have concentric lifters which locks an unlocks (see below). Systems using an eccentric shaft (eg. BMW's valvetronic or Nissan's EOVVL) can also be implemented either way. In fact, the systems become less complex and less costly if you have less valves (ie. 2-valves vs 4-valves).

As you can see, you can use a concentric lifter to operate the valve stem or a pushrod. It really doesn't matter.

Edited July 18, 2013 by dwightlooi

[G. David Felt]

Thanks Dwight, that is great info as I never really understood it myself till know. Appreciate the time to teach us this.

[Drew Dowdell]

may seem like a silly question.... how do they get the cam inside the other cam?

[dwightlooi]

may seem like a silly question.... how do they get the cam inside the other cam?

The outside cam is driven directly by the sprocket and operates the exhaust valves directly with lobes just like a regular camshaft. It is also hollow so a "rod" can go inside it.

The inner cam is basically a rod that goes inside the outside cam. It operates individual cam lobes which are slipped over the outside cam and pinned to the inner cam through slots cut in the outer cam. In fact the cam lobes of the outside cam were also slipped over it and pinned in place except it is fixed in place to the outside cam instead of being movable.

The drive chain operates the outside cam via a cam phaser. The inner cam is connected to the outside cam via a second cam phaser which varies it in relation to the outside cam.

[Drew Dowdell]

Only a very modest increase in mass over a single standard cam then?

[dwightlooi]

Only a very modest increase in mass over a single standard cam then?

Mostly, just the extra phaser and the fact that the cam itself will weigh as much as a regular camshaft which is NOT gun drilled or hollow cast for weight reduction. Many are not anyway.

[Drew Dowdell]

Thanks for your lessons.. I couldn't quite wrap my head around the cam-in-cam construction.

[carguy10101010]

@ Dwight

Given the excellent argument for OHV engines you have made here, is there any technical reason that GM chose to put the 3.6L LFX into the 2015 Colorado instead of the 4.3L ecotec? There was an offhand comment made somewhere that "they tested both and the LFX returned better fuel economy". I can't even seem to find where I read that, but given the argument that you are making here that is almost definitely not true. EPA numbers would seem to further validate your thesis considering that a heavier and less aerodynamic silverado with the 4.3L ecotec is rated 17/22 while the lighter and more aerodynamic traverse with the 3.6L LFX is only rated 16/23.

Given what you have written and your obvious knowledge of both powerplants and their advantages, is there any good reason to put the LFX in the upcoming colorado instead of the ecotec? Or could this just be a case of GM refusing to use the 4.3L ecotec to ensure differentiation from the Silverado?

[Drew Dowdell]

Given what you have written and your obvious knowledge of both powerplants and their advantages, is there any good reason to put the LFX in the upcoming colorado instead of the ecotec? Or could this just be a case of GM refusing to use the 4.3L ecotec to ensure differentiation from the Silverado?

Which would just smack of "Old GM" thinking if true.

[carguy10101010]

Given what you have written and your obvious knowledge of both powerplants and their advantages, is there any good reason to put the LFX in the upcoming colorado instead of the ecotec? Or could this just be a case of GM refusing to use the 4.3L ecotec to ensure differentiation from the Silverado?

Which would just smack of "Old GM" thinking if true.

It really would be disappointing. The 3.6L LFX seems to be a great engine, but the 4.3L ecotec just really seems to fit the bill better, particularly for a truck application. Based upon Dwight's arguments here it would actually seem that in most V6 vehicles across the lineup the 4.3L ecotec would provide similar or super performance to the LFX while offering better fuel economy as well. I could certainly understand why another automaker -say Hyundai - would choose to not begin developing a line of pushrod engines alongside the DOHC engines they already have, but since GM has already spent the investment it would seem to be common sense to put that investment to use.

But maybe there is some other advantage to the LFX over the ecotec that makes it the better choice where it is implemented?

[Drew Dowdell]

My guess is that it has more to do with production capacity rather than anything else. GM thought they would be pushing a lot of existing buyers to the 285 hp 4.3 liter instead of them all opting for V8s like they have been... and they're betting that soon... any day now... customers will wake up and see the light and buy the V6. .... any day now...

edit - It probably also lets them claim that they have a mid-size truck with over 300 horsepower.

[dwightlooi]

Well, it wouldn't be the first time GM (or any manufacturer) has made a decision which -- from a technical merits standpoint -- isn't the best one. It may be that the 4.3 is a "new" engine whereas the LFX line is up and running with capacity to spare. That said, the LFX while decent on Fuel Economy isn't particularly spectacular in this regard. The 3.6 Lacrosses and CTSes have worse MPG numbers than Nissan 3.7s or the like.

Honestly, though, I really didn't support the idea of the 5.3 V8s and 4.3 V6es. There is no real good reason for all these added complexity to small block supply chain and manufacturing. All the Pushrod engines should have the same bore x stroke, the same rods, the same pistons, the same wrist pins, the same valves, the same valve springs, the same injectors, main bearings, etc. Namely, they should all be based on the 103.25 mm bore and 92 mm stroke the 6.2L V8s use. This will produce a 4.6 V6 and a 3.1 V4. The trucks and SUVs get either the V4, the V6 or the V8 -- at 210, 315 and 420 hp. That is enough to cover the entire truck and SUV spectrum in non-displacement tax limited markets. For those markets with heavy displacement based levies, the 5.3 and 4.3 won't cut it either! For those markets, A 2.0T serves the budget conscious customers in trucks and passenger cars alike.

[regfootball]

in the new colorado, i think the engine choices are perfect. Although I could see the 4.3 being added as a top level option later.

The 3.6 is a car engine and really for most people a midsize truck is intended to be a car anyways. Think Ridgeline. If you really need a truck for utility you'll get a full sizer.

Really looking forward to seeing the real world FE of the 2.5 in it. The combined in the Malibu is 29 mpg. The old S10 iron duke had a rep of fabulous mpg yet enough power to do some light duty hauling. I think the new 2.5 is perfect as the volume motor. It'll be like having an economy car with a truck bed for the occasional Ikea haul etc.

That's the type of engine that would kickstart popularity in that class again.

Edited December 14, 2013 by regfootball

[dwightlooi]

in the new colorado, i think the engine choices are perfect. Although I could see the 4.3 being added as a top level option later.

The 3.6 is a car engine and really for most people a midsize truck is intended to be a car anyways. Think Ridgeline. If you really need a truck for utility you'll get a full sizer.

Really looking forward to seeing the real world FE of the 2.5 in it. The combined in the Malibu is 29 mpg. The old S10 iron duke had a rep of fabulous mpg yet enough power to do some light duty hauling. I think the new 2.5 is perfect as the volume motor. It'll be like having an economy car with a truck bed for the occasional Ikea haul etc.

That's the type of engine that would kickstart popularity in that class again.

I doubt it... the two engines are very close to each other in output. The 3.6 actually having more horsepower, although the 4.3 has more torque. Having both is redundant. The problem with the 2.5 is similar to that with the 3.6. Yes, it's usable as a truck engine, but not ideal as one. Not ideal because it is a relatively high revving engine with a modest bottom end. Yes, it revs to 7000 rpm, but that's not where most truck engines need to do their daily work. A best engine, albiet one which does not exist, will be a 3.1L Pushrod Inline-4 or V-4. That's be in the 210 hp class with about 230 lb-ft of twist. It'll be stout, simple and cheap to build and maintain. In fact, even if you are sticking to the DOHC configuration the Atlas 2.9L Inline-4 currently being used is better than the 2.5L.The one thing about very big fours is the below average refinement from the 2nd order vibrations which gets worse with engine size. But even here the 2.5 is not the shining city on the hill. While it is true that I4s tend to be less refined as they get bigger in displacement, what really drives vibrations up more than anything else is NOT displacement per say, but stroke length. The only reason big fours then to be bad in this regard is that they tend to have long strokes amongst other things. The 2.5 has a 101mm stroke which is about the longest around. The 6.2 V8 actually only has a 92mm stroke. Long strokes are slightly more fuel efficient and makes an engine more compact (any stroke increase grows deck height once instead of engine length four times as is the case with bore increases). The 2.5 is refined only because of its dual balancer shafts, but even with these some vibrations leak through and you can put balancers on any engine of any displacement or valvetrain setup.

[regfootball]

well, the last colorado was no sales champ or mpg champ with the atlas, and it's simpler to cast an in line 4 block than a v block. the 2.5 engine is developed and each vehicle additional they sell with the engine writes the cost of it down even further. as far as the torque curve, i am sure they can retune the engine for truck duty just fine. most colorado buyers are looking for an economy car with a truck bed. the old S-10 4 banger was just fine as a car engine too.

The big thing with the Chevy and the Colorado is just to get the truck back in the market again. Over time once people get used to it in the market again, and there is demand, it's extremely likely they will add the 4.3 as a top level option.

http://www.fueleconomy.gov/feg/bymodel/2007_Chevrolet_Colorado.shtml

the old Atlas 4 had pathetic fuel economy. Perhaps one reason why sales of that truck were in the crapper. 16 and 22? LMAO

Edited December 14, 2013 by regfootball

[dwightlooi]

You know, I think a good entry level truck engine might actually be... a 3-cylinder Inline based on the 6.2L (L86) DI-VVT-AFM Small block.

• 103.25 x 92 mm x 3-cyliners = 2,310 cc
• 3/8ths of 420hp = 158 bhp @ 5600 rpm
• 3/8ths of 460 lb-ft = 173 ft-lbs @ 4100 rpm
• One CAM, 6-valves, 3-pots = fewest and lowest parasitic losses in the industry

[carguy10101010]

well, the last colorado was no sales champ or mpg champ with the atlas, and it's simpler to cast an in line 4 block than a v block. the 2.5 engine is developed and each vehicle additional they sell with the engine writes the cost of it down even further. as far as the torque curve, i am sure they can retune the engine for truck duty just fine. most colorado buyers are looking for an economy car with a truck bed. the old S-10 4 banger was just fine as a car engine too.

The big thing with the Chevy and the Colorado is just to get the truck back in the market again. Over time once people get used to it in the market again, and there is demand, it's extremely likely they will add the 4.3 as a top level option.

http://www.fueleconomy.gov/feg/bymodel/2007_Chevrolet_Colorado.shtml

the old Atlas 4 had pathetic fuel economy. Perhaps one reason why sales of that truck were in the crapper. 16 and 22?

No it wasn't a sales champ, primarily because it was anemic in performance, lacked any significant fuel economy advantage over the half tons, and had a price that was within a stones throw of the half tons. The reveal last month appears as if they are taking some of those mistakes to heart and are really working to keep the new truck from having the same failings as the previous one. There is plenty of interest in a smaller truck, for active types and do it yourselfers, who also commute to the office during the week - and that is exactly who this truck looks to be pitched to. Those that have a lifestyle which is well complimented by a truck - hence the lifestyle truck terminology.

But the genesis of the question is why would anyone (from a technical standpoint anyway) choose to put the 3.6L LFX into a new truck (or most vehicles really) over the 4.3L ecotec, when the ecotec has a torque curve shifted to the left producing its peak torque and hp at lower RPMS which is nicer for NVH, and is more fuel efficient to boot. Its not that the LFX is bad - not at all - but if that little bit of additional peak power is not worth additional NVH and lost fuel economy it seems to be a worse choice in the new Colorado, the Traverse, and most places where the LFX is used.

I am not convinced that the 2.5L will sell well in the Colorado. The revving that motor will have to do to produce the desired power will neither be pleasant nor fuel efficient. The prospect of the 2.8L duramax is the real interesting engine choice for this truck. The potential fuel economy from said engine along with its ultra low rpm torque curve could turn out to be a real winner if its not too expensively priced.

[carguy10101010]

You know, I think a good entry level truck engine might actually be... a 3-cylinder Inline based on the 6.2L (L86) DI-VVT-AFM Small block.

• 103.25 x 92 mm x 3-cyliners = 2,310 cc
• 3/8ths of 420hp = 158 bhp @ 5600 rpm
• 3/8ths of 460 lb-ft = 173 ft-lbs @ 4100 rpm
• One CAM, 6-valves, 3-pots = fewest and lowest parasitic losses in the industry

I don't think that this would give many customers the performance they are looking for. An engine like that would have to go into something like the S10's or rangers of old, that started at ~$12,000. I guess that price point might be $16,000 - $18,000 now, but any more than that price point I think that people will want. How does the NVH of an I3 compare to an I4? Is it noticeably worse?

Could they not just make an I4 out of "half" of the 6.2L small block? Would you think it would be easier to produce a "half" 6.2 as a V4 as you mentioned above than as an I4? I think that you're dead on. It certainly makes a lot of sense to base all of the pushrod engines off of the same bore/stroke in order to create the largest carryover of shared parts.

Edited December 14, 2013 by carguy10101010