DOHC V8s on GM's Mind?

[NOS2006]

I got word that GM was actually developing a small, very high-power and highly technological DOHC V8 for the C7 before the whole financial crisis fully developed. I don't want to say too much on it because I'm not sure how much is true, but I trust the sources I have on this. Just wondering your thoughts on this since we've always had pushrods in the Corvette and this would be an entirely new direction.

[Drew Dowdell]

Probably was part of the UV8 project.

But still, it was my understanding that the new 5.5 was designed to be able to use pushrods or (D)OHC as the application warranted.

[dado]

Probably was part of the UV8 project.

But still, it was my understanding that the new 5.5 was designed to be able to use pushrods or (D)OHC as the application warranted.

I was just reading something interesting. On this FORUM PAGEthere is some information on new SSC ultimate AERO 2 car.

There is a scan of the page where it says "the hole botton end of the engine is same, it's just that he is replacing pushrod heads with OHC cam"

Now i'm not sure if this is true or is this completely new engine .Something in the line of Nelson racing engine Revolution with 4 cams

[NOS2006]

Probably was part of the UV8 project.

But still, it was my understanding that the new 5.5 was designed to be able to use pushrods or (D)OHC as the application warranted.

It very well could've been. I've heard "at least 800 HP" in certain applications. Which would make sense if GM really was going to go with a wet dual clutch setup.

I didn't know that about the 5.5; I'll have to catch up on my knowledge on upcoming GM powertrains...

[Camino LS6]

DOHC conversions for Chevy V8s have existed for a very long time...

[Robert Hall]

DOHC conversions for Chevy V8s have existed for a very long time...

Never heard of any...do any exist in the wild other than a handful of prototypes?

[dwightlooi]

A few things...

(1) We don't know if the new small block (Gen V) will be 5.5. The reacing engine is 5.5 because the rules dictate the maximum displacement, the production engine is anyone's guess. If past practices hold true it'll probably be made a variety of displacements off odf the same basic block.

(2) My personal guess is that the C7 engine retain the Pushrods and 2-valves per cylinder, while adding Variable Timing, Direct Injection and Cylinder Deactivation. Power for such an engine ought to be about 450~470hp @ 6.2 liters, 400~420hp @ 5.5 liters or 350~370hp @ 4.8 liters. My guess is they'll go with the biggest internal displacement since engine size and weight doesn't change much between these.

(3) I seriously doubt that GM will build a DOHC engine off the 5th generation small block. It'll make more sense if they simply stretch the HF V6 by two cylinders. This will give an interesting 4.0 or 4.8 liter engine. The 60 deg angle also makes for very compact dimensions. A 360hp 4.0 60-deg V8 or 420hp 4.8 liter 60-deg V8 may be interesting for luxury car applications. Again, the chances of this is very small. Chances are the advanced pushrod will find its way into everything from trucks to vettes to Caddies.

[Drew Dowdell]

with regard to point 3: Adding 2 cylinders to the HF series was what the UV8 was supposed to be.

I'd imagine that casting a new block is more expensive than putting new heads (of a different valve train) on an existing block. Also that having two blocks (HF + SB) is less expensive than having three (HF + SB + UV8).

The 3.4DOHC (which will inevitably be brought up) suffered reliability problems not because it was converted from a pushrod block, but because GM cheaped out on some of the components (brittle plastic timing belt idler pulleys? really?) and very poor location of the alternator. Designing a block from the start to use either valve train configuration allows the engineers to consider the differences needed and account for them in the design.

[Camino LS6]

Never heard of any...do any exist in the wild other than a handful of prototypes?

Various aftermarket companies have made them over the years.

[Robert Hall]

Various aftermarket companies have made them over the years.

Not relevant...what counts are production engines.

[balthazar]

A lot of production pieces came from the aftermarket, but I am not up on the story RE OHC conversion heads for Chevy V-8s.

[CanadianBacon94]

i had heard that the UV8 was related to the DuraMin(half ton diesel)

[Camino LS6]

Not relevant...what counts are production engines.

Oh?

I guess I didn't read the rules.

I can't say that I know much about these conversions beyond the fact that they existed.

[Robert Hall]

Oh?

I guess I didn't read the rules.

I can't say that I know much about these conversions beyond the fact that they existed.

Yeah, what's the point otherwise? For example, I'm sure someone in the aftermarket could build a RWD V8 powered Cobalt, but it's still just as irrelevant, since the subject of the thread is GM production engines...

Edited September 9, 2010 by Cubical-aka-Moltar

[dwightlooi]

Actually, it shouldn't matter if GM is going to build a DOHC V8, SOHC V8 or Pushrod V8. What matters is whether GM will build a V8 that produces the amount of power the next generation of vehicles demand, and that this V8 does it while being smaller, lighter, more refined and more fuel economical than the competitions' offerings. The valve train configuration and other design choices should matter.

For any given horsepower we can say the following:-

Engine Size -- Advantage Pushrod

• Engine Weight -- Advantage Pushrod
  
• Fuel Economy -- Advantage Pushrod
  
• Refinement -- Advantage DOHC
  
• Displacement -- Advantage DOHC
  

[Robert Hall]

Actually, it shouldn't matter if GM is going to build a DOHC V8, SOHC V8 or Pushrod V8. What matters is whether GM will build a V8 that produces the amount of power the next generation of vehicles demand, and that this V8 does it while being smaller, lighter, more refined and more fuel economical than the competitions' offerings. The valve train configuration and other design choices should matter.

For any given horsepower we can say the following:-

Engine Size -- Advantage Pushrod

• Engine Weight -- Advantage Pushrod
  
• Fuel Economy -- Advantage Pushrod
  
• Refinement -- Advantage DOHC
  
• Displacement -- Advantage DOHC
  

Fuel economy will likely be the prime criteria in the next decade...power will be less of a concern as vehicles become lighter to meet the new CAFE standards.

[Camino LS6]

Yeah, what's the point otherwise? For example, I'm sure someone in the aftermarket could build a RWD V8 powered Cobalt, but it's still just as irrelevant, since the subject of the thread is GM production engines...

Well, all I was doing was adding some tangential information I happened to know.

Hell, I haven't even expressed an opinion in this thread!

[dwightlooi]

Fuel economy will likely be the prime criteria in the next decade...power will be less of a concern as vehicles become lighter to meet the new CAFE standards.

Well... if you really care about fuel economy more than anything else, you'll want to:-

• Reduce the number of cylinders to the minimum
  
• Increase the displacement to the maximum that the number of cylinders you have
  
• Increase the compression ratio to the maximum
  
• Reduce the number of cams
  
• Reduce the number of valves
  

[smk4565]

with regard to point 3: Adding 2 cylinders to the HF series was what the UV8 was supposed to be.

I'd imagine that casting a new block is more expensive than putting new heads (of a different valve train) on an existing block. Also that having two blocks (HF + SB) is less expensive than having three (HF + SB + UV8).

The 3.4DOHC (which will inevitably be brought up) suffered reliability problems not because it was converted from a pushrod block, but because GM cheaped out on some of the components (brittle plastic timing belt idler pulleys? really?) and very poor location of the alternator. Designing a block from the start to use either valve train configuration allows the engineers to consider the differences needed and account for them in the design.

Not to mention the 4.3 liter and 5.7 liter diesel engines of the 80s that were based on the gas pushrod block and those had terrible reliability. To do it, they have to do it right, and start from scratch, can't just retro-fit an existing engine block. That's like building a 3-series competitor out of a Cavalier. (had to get a Cimarron reference in there)

[Drew Dowdell]

I agree that taking an existing block and making it do things it wasn't designed to do is probably a bad idea..... but if it's designed from the start to use either configuration, I think it could work out well.

[regfootball]

A few things...

(1) We don't know if the new small block (Gen V) will be 5.5. The reacing engine is 5.5 because the rules dictate the maximum displacement, the production engine is anyone's guess. If past practices hold true it'll probably be made a variety of displacements off odf the same basic block.

(2) My personal guess is that the C7 engine retain the Pushrods and 2-valves per cylinder, while adding Variable Timing, Direct Injection and Cylinder Deactivation. Power for such an engine ought to be about 450~470hp @ 6.2 liters, 400~420hp @ 5.5 liters or 350~370hp @ 4.8 liters. My guess is they'll go with the biggest internal displacement since engine size and weight doesn't change much between these.

(3) I seriously doubt that GM will build a DOHC engine off the 5th generation small block. It'll make more sense if they simply stretch the HF V6 by two cylinders. This will give an interesting 4.0 or 4.8 liter engine. The 60 deg angle also makes for very compact dimensions. A 360hp 4.0 60-deg V8 or 420hp 4.8 liter 60-deg V8 may be interesting for luxury car applications. Again, the chances of this is very small. Chances are the advanced pushrod will find its way into everything from trucks to vettes to Caddies.

my SHO v8 had a 60 degree block. it had a balancer (ran smooth as glass BTW). would the 60 degree block require a balancer on a v8?

[balthazar]

Not to mention the 4.3 liter and 5.7 liter diesel engines of the 80s that were based on the gas pushrod block and those had terrible reliability. To do it, they have to do it right, and start from scratch, can't just retro-fit an existing engine block.

Diesel 350 was a completely different block. Blocks in the diesels were not a reliability/longevity issue. In fact, they are sought after today for performance rebuilds because they are so stout.

Cam location was likewise not an issue in the 350 diesel's reliability.

[regfootball]

my dad'd electra diesel popped the headbolts.

[regfootball]

Yeah, what's the point otherwise? For example, I'm sure someone in the aftermarket could build a RWD V8 powered Cobalt, but it's still just as irrelevant, since the subject of the thread is GM production engines...

if someone wants to use mine for that, i'll offer it as a donor....

[dwightlooi]

my SHO v8 had a 60 degree block. it had a balancer (ran smooth as glass BTW). would the 60 degree block require a balancer on a v8?

The reason the 90-deg bank angle is preferred on a V8 is that it allows the engine to use oversized crank counter weights. Naturally, a 90 deg V8 has about 1.4 times that of a 4-cylinder with a similar per cylinder displacement (eg. a 4.0 liter 90 deg V8 is about as bad as a 2.8 liter I4 in vibrations). However, it has a trick up its sleeve. In most engines (other than V8s) the crank weights are only heavy enough to balance the crankshaft itself and about 1/3 the mass of the rods. The counter weights do not balance most of the rod and the piston. This is because the pistons and rods go up and down, whereas the weights go around in circles. Geometrically it is impossible to cancel the moments of one with the other. If you try to use a heavier weight to counter the piston and the rod's, all you'll succeed in doing is trade up-down shakes for left-right shakes. In a 90 deg V8, a special circumstance is created because the piston and rod from the opposite bank happens to cancel out the side to side forces generated by oversized counter weights that balance out the rods and pistons. The balance is still not perfect -- the circular motions of weights can never perfectly match the reciprocating motions of the rods and pistons -- but it is very good. Good, enough to allow much larger cylinders before civility becomes objectionable. A 6.2 liter V8 has 775cc cylinders; a 4-cylinder with that size of cylinders will displace 3.1 liter and be quite rough. The down side is that the crank weights also make the engine significantly slow reving -- if you drive a V8 powered car and a V6 back to back, you'll notice that the engine rev significantly more slowly during downshifts than V6es.

A 60-deg bank angle on a V8 is not naturally balanced and it also does not allow balancing using heavy counter weights. However, it is narrower which makes a DOHC 60-deg V8 about the same dimensions as a pushrod 90 deg V8. In addition, the absence of heavy counter weights also make it capable of reving much more quickly which puts smiles on the faces of enthusiastic drivers. At 4.0 or 4.8 liters -- 500~600cc per cylinder -- vibrations are not horrible if you don't balance it. But, if you are after maximum civility, you can add a counter rotating balance shaft and achieve about 80% as good a level of balance as a 90 deg V8. Given the 4.0~4.8 liter displacement of a HF V6 derived V8, it means that the engines will be as smooth as a 90 deg 5.0~6.0 liter 90 deg engine. One word -- good enough.

At the end of the day, a direct injected 4.0 liter HF V6 derived 60-deg V8 will make about 360hp. A 4.8 liter version based on the 3.6 V6 will make about 400 hp. This is roughly equivalent to a direct injected pushrod of 4.8 to 5.4 liters. Civility and rev response will favor the DOHC V8. Costs, fuel economy, engine weight and compactness will favor a pushrod engine. One is not better than the other -- which is preferable really depends on what you are after.

Edited September 12, 2010 by dwightlooi

[dado]

I'm wondering. If block on Gen V is made to accomodate both DOHC and CIB design, and if DOHC heads are put on CIB block won't that leave empty space where cam used to sit in block. Will they put cam in block on Dohc engine (maybe it would drive some assesories) but then you get engine as large as noraml Dohc engine(external dimesnions)and extra weight from cam (5 cam). Im curios to see what size and weight will be Revolution engine from Nelson racing(i know it is machined from aluminium billet so i think wall can be thiner than in cast block)

Here is also one engine based on Small block (DOHC setup).Weight is 226 kg

SwissAuto

Edited September 12, 2010 by dado

[balthazar]

There's no need whatsoever to install a cam in a DOHC set-up of a dual-function Gen V block. It's not going to drive anything. A plug (maybe a simple idler) is likely all that would be needed to use DOHC heads- so we're only talking about 4 cams.

Yes- then the SB will be similar to other DOHC engines in external size, but that is not always an issue. The point is to utilize the most cost-effective way to address both sets of issues (the advantages of either set-up). I love the idea.

[dwightlooi]

There's no need whatsoever to install a cam in a DOHC set-up of a dual-function Gen V block. It's not going to drive anything. A plug (maybe a simple idler) is likely all that would be needed to use DOHC heads- so we're only talking about 4 cams.

Yes- then the SB will be similar to other DOHC engines in external size, but that is not always an issue. The point is to utilize the most cost-effective way to address both sets of issues (the advantages of either set-up). I love the idea.

Using an intermediate idler to drive the DOHC sprockets on the heads would not be an efficient or convenient way to do it. If not anything because the high placement of the IBC cam sprocket puts it at a very shallow angle to the OHC sprockets making it necessary to introduce two more idlers just to get the chain to wrap around the OHC sprockets enough. Chances are, you'll drive the overhead cams directly from the crank. At least one of the two cams that is, the other can be driven via helical gear or another chain from the first cam.

The IBC accommodations can be used to house a counter-rotating balance shaft if you want to go overboard. A 90 deg V8 is very well balanced with crank weights alone. But, it is not perfectly balanced. There is a bit of residual wobble in the Cg. You can add a counter rotating shaft to further cancel that out for a really serene engine. It'll cost you a bit of complexity and a bit of fuel economy from the extra friction, but the resulting engine may rival an I6 in smoothness.

[regfootball]

The reason the 90-deg bank angle is preferred on a V8 is that it allows the engine to use oversized crank counter weights. Naturally, a 90 deg V8 has about 1.4 times that of a 4-cylinder with a similar per cylinder displacement (eg. a 4.0 liter 90 deg V8 is about as bad as a 2.8 liter I4 in vibrations). However, it has a trick up its sleeve. In most engines (other than V8s) the crank weights are only heavy enough to balance the crankshaft itself and about 1/3 the mass of the rods. The counter weights do not balance most of the rod and the piston. This is because the pistons and rods go up and down, whereas the weights go around in circles. Geometrically it is impossible to cancel the moments of one with the other. If you try to use a heavier weight to counter the piston and the rod's, all you'll succeed in doing is trade up-down shakes for left-right shakes. In a 90 deg V8, a special circumstance is created because the piston and rod from the opposite bank happens to cancel out the side to side forces generated by oversized counter weights that balance out the rods and pistons. The balance is still not perfect -- the circular motions of weights can never perfectly match the reciprocating motions of the rods and pistons -- but it is very good. Good, enough to allow much larger cylinders before civility becomes objectionable. A 6.2 liter V8 has 775cc cylinders; a 4-cylinder with that size of cylinders will displace 3.1 liter and be quite rough. The down side is that the crank weights also make the engine significantly slow reving -- if you drive a V8 powered car and a V6 back to back, you'll notice that the engine rev significantly more slowly during downshifts than V6es.

A 60-deg bank angle on a V8 is not naturally balanced and it also does not allow balancing using heavy counter weights. However, it is narrower which makes a DOHC 60-deg V8 about the same dimensions as a pushrod 90 deg V8. In addition, the absence of heavy counter weights also make it capable of reving much more quickly which puts smiles on the faces of enthusiastic drivers. At 4.0 or 4.8 liters -- 500~600cc per cylinder -- vibrations are not horrible if you don't balance it. But, if you are after maximum civility, you can add a counter rotating balance shaft and achieve about 80% as good a level of balance as a 90 deg V8. Given the 4.0~4.8 liter displacement of a HF V6 derived V8, it means that the engines will be as smooth as a 90 deg 5.0~6.0 liter 90 deg engine. One word -- good enough.

At the end of the day, a direct injected 4.0 liter HF V6 derived 60-deg V8 will make about 360hp. A 4.8 liter version based on the 3.6 V6 will make about 400 hp. This is roughly equivalent to a direct injected pushrod of 4.8 to 5.4 liters. Civility and rev response will favor the DOHC V8. Costs, fuel economy, engine weight and compactness will favor a pushrod engine. One is not better than the other -- which is preferable really depends on what you are after.

My SHO v8 (3.4 litres) apparently was safe for production at up to about 325hp I guess. and it had a high redline (like over 7,000 rpm I think) and was smooth from idle to redline and loved revs. it was unlike any other v8 i had driven. unfortunately it was detuned to mate to the available crappy transmission so it limited the hp and torque greatly and the transmission was extremely unresponsive and slow overall. but the engine configuration and characteristics themselves I thought were fantastic and they crammed it under the hood of a typical fwd car. the packaging alone was worth beholding. that would make a great mid engine sports car motor configuration.

[dwightlooi]

My SHO v8 (3.4 litres) apparently was safe for production at up to about 325hp I guess. and it had a high redline (like over 7,000 rpm I think) and was smooth from idle to redline and loved revs. it was unlike any other v8 i had driven. unfortunately it was detuned to mate to the available crappy transmission so it limited the hp and torque greatly and the transmission was extremely unresponsive and slow overall. but the engine configuration and characteristics themselves I thought were fantastic and they crammed it under the hood of a typical fwd car. the packaging alone was worth beholding. that would make a great mid engine sports car motor configuration.

It is rev happy and low on vibrations for three reasons:-

• It is a 60 deg engine without the 90 deg engine's heavy crank counter weights (the same can be said of flat plane 90 deg engines)
  
• It is has a very short 79.5 mm stroke (vibrations are largerly a function of stroke length more than anything else)
  
• It is balance shafted
  

A 4.8 liter 60-deg eight wouldn't be quite as smooth and placid. But it won't be bad. FYI, the 4.0 will have a 80.3 mm stroke whereas the 4.8 would be 85.6 mm -- both are pretty short. I don't think you'll see a significant difference between the 4.0 and the SHO (Yamaha) 3.4 in terms of vibrations.

The SHO V8's basic architecture lives on today in Volvo's 4.4 liter V8 (also a 60 degree design). That engines is perfectly livable.

Transmission wise, the current GM lineup imposes the following limitations on "high reving" engines:-

RWD (longitudal)

• 6L45 - 7000 rpm / 258 lb-ft (max)
  
• 6L50 - 7000 rpm / 332 lb-ft (max)
  
• 6L80 - 6500 rpm / 439 lb-ft (max)
  
• 6L90 - 6200 rpm / 555 lb-ft (max)
  

FWD (transverse)

• 6T40 - 7000 rpm / 177 lb-ft (max)
  
• 6T70 - 7000 rpm / 280 lb-ft (max)
  

Basically you can't have high rpm engines that are too high on torque. And, you cannot have engines hitting over 7000 rpms period.

Edited September 13, 2010 by dwightlooi

[cavalier36]

they need to come up with a new DOHC V8 somehow. If they are going to build this ultra luxury Cadillac I think it would need something other than the 3.6L V6.

if you come up with a new DOHC V8 you would use it in alot of applications to justify it. Ultra Lux Cadillac, Tahoe,Escalade, Yukon, Camaro, Corvette, a RWD Chevy Sedan, A rwd Buick sedan. next gen full size pickups. as well as use it for Austrailian Holden models.

I think that would be enough volume to justify developing it.

[dwightlooi]

they need to come up with a new DOHC V8 somehow. If they are going to build this ultra luxury Cadillac I think it would need something other than the 3.6L V6.

if you come up with a new DOHC V8 you would use it in alot of applications to justify it. Ultra Lux Cadillac, Tahoe,Escalade, Yukon, Camaro, Corvette, a RWD Chevy Sedan, A rwd Buick sedan. next gen full size pickups. as well as use it for Austrailian Holden models.

I think that would be enough volume to justify developing it.

Personally, I don't think they absolutely need both a DOHC V8 and a Pushrod V8. I think they'll do equally fine with just the pushrod family, or both a pushrod and a DOHC, but not the other way around. One is not better than the other, even though they'll have somewhat different characters. If they want to do a DOHC, I am biased towards a 3.6HF V6 derived 60--deg V8 as opposed to a ground up 90 deg or 72 deg engine.

In all likelihood though, GM will probably put a pushrod V8 in all of the above. And, if it is a good one I am perfectly OK with it. The push rod configuration has many advantages such as smaller packaging, higher power density and low fuel consumptions (for a given output). There is nothing wrong with a 450~470hp 6.2 liter V8 pulling at a least ~17/25 mpg in a 4000 lb car. This is better than a DOHC V8 can muster with the same output level at the same vehicular weight. Heck, this is almost as good as a 3.6 HF V6. And, nobody ever complained about a Bentley pushrod 6.75L V8 being unrefined.

If they want to do a DOHC design, a 60 deg engine has sufficient advantageous to offset the need for a balance shaft and slightly inferior balance. It is narrower and it can be made on the same tooling as the V6. In fact, you can have it share the same rods and pistons too if you want. The combustion chamber design is mature and a pretty good -- a 4.8 liter unit will make about 400~416hp @ 6300~6500 rpm and about 360~371 lb-ft @ 3400~5000 rpm, all on 87 octane fuel. On 91 octane you can expect 2~3% better numbers on both counts. These are substantially better numbers than BMW's outgoing N62-B-48 4.8 V8 (367hp/369lb-ft). This also happens to marry well with the 6L80 transmission.

[regfootball]

they need to come up with a new DOHC V8 somehow. If they are going to build this ultra luxury Cadillac I think it would need something other than the 3.6L V6.

if you come up with a new DOHC V8 you would use it in alot of applications to justify it. Ultra Lux Cadillac, Tahoe,Escalade, Yukon, Camaro, Corvette, a RWD Chevy Sedan, A rwd Buick sedan. next gen full size pickups. as well as use it for Austrailian Holden models.

I think that would be enough volume to justify developing it.

i would be fine with a new family of motors, a 2.0 and 2.5 four. and a 4.0 v8 and maybe a 5.0 v8 if they can make them 60 degree to fit in transverse applications (i.e. lambda).

Edited September 13, 2010 by regfootball

[regfootball]

Personally, I don't think they absolutely need both a DOHC V8 and a Pushrod V8. I think they'll do equally fine with just the pushrod family, or both a pushrod and a DOHC, but not the other way around. One is not better than the other, even though they'll have somewhat different characters. If they want to do a DOHC, I am biased towards a 3.6HF V6 derived 60--deg V8 as opposed to a ground up 90 deg or 72 deg engine.

In all likelihood though, GM will probably put a pushrod V8 in all of the above. And, if it is a good one I am perfectly OK with it. The push rod configuration has many advantages such as smaller packaging, higher power density and low fuel consumptions (for a given output). There is nothing wrong with a 450~470hp 6.2 liter V8 pulling at a least ~17/25 mpg in a 4000 lb car. This is better than a DOHC V8 can muster with the same output level at the same vehicular weight. Heck, this is almost as good as a 3.6 HF V6. And, nobody ever complained about a Bentley pushrod 6.75L V8 being unrefined.

If they want to do a DOHC design, a 60 deg engine has sufficient advantageous to offset the need for a balance shaft and slightly inferior balance. It is narrower and it can be made on the same tooling as the V6. In fact, you can have it share the same rods and pistons too if you want. The combustion chamber design is mature and a pretty good -- a 4.8 liter unit will make about 400~416hp @ 6300~6500 rpm and about 360~371 lb-ft @ 3400~5000 rpm, all on 87 octane fuel. On 91 octane you can expect 2~3% better numbers on both counts. These are substantially better numbers than BMW's outgoing N62-B-48 4.8 V8 (367hp/369lb-ft). This also happens to marry well with the 6L80 transmission.

could they force induction the v8? any breathing difficulties with a 60 degree v8 beyond the same issues on a 60 degree v6? i.e. the intake design not having much room to work with.

[dwightlooi]

could they force induction the v8? any breathing difficulties with a 60 degree v8 beyond the same issues on a 60 degree v6? i.e. the intake design not having much room to work with.

Of course you can turbocharge a 60-deg engine, but if the primary application is to be turbocharged I'll prefer a 90 deg or 72 deg engine -- if only because you can use one turbo nestled in the Vee and reverse flow heads, instead of two turbos with one hanging off each side. The disadvantage of a 60 deg V8 vs a 60 deg V6 in turbo applications is that the V8 needs twin scroll turbos for optimal efficiency, the V6 doesn't. This is a slight cost adder, but it doesn't really take up any more or less space.

The intake design on the 3.0 and 3.6 HF V6 are already more than good enough. They flow enough air for 86~90hp/liter. A 4.0 or 4.8 V8 will be similarly performing. By any measure, that is good enough. Even if you can improve on the flow capacity of the intakes, you'll need to rev the engine above 7000 rpm to take advantage of it. Currently, GM automatic trannies don't support shift speeds above 7000 rpm so you can't go there unless you want to revamp the transmission lineup as well, or limit the deployment to manual cars.

Edited September 14, 2010 by dwightlooi

[aldw]

Using an intermediate idler to drive the DOHC sprockets on the heads would not be an efficient or convenient way to do it. If not anything because the high placement of the IBC cam sprocket puts it at a very shallow angle to the OHC sprockets making it necessary to introduce two more idlers just to get the chain to wrap around the OHC sprockets enough. Chances are, you'll drive the overhead cams directly from the crank. At least one of the two cams that is, the other can be driven via helical gear or another chain from the first cam.

The IBC accommodations can be used to house a counter-rotating balance shaft if you want to go overboard. A 90 deg V8 is very well balanced with crank weights alone. But, it is not perfectly balanced. There is a bit of residual wobble in the Cg. You can add a counter rotating shaft to further cancel that out for a really serene engine. It'll cost you a bit of complexity and a bit of fuel economy from the extra friction, but the resulting engine may rival an I6 in smoothness.

That's a very interesting concept, if GM were to do that it would be a really sweet engine for a luxury vehicle and be a technical one-up on the Germans.

[smk4565]

In all likelihood though, GM will probably put a pushrod V8 in all of the above. And, if it is a good one I am perfectly OK with it. The push rod configuration has many advantages such as smaller packaging, higher power density and low fuel consumptions (for a given output). There is nothing wrong with a 450~470hp 6.2 liter V8 pulling at a least ~17/25 mpg in a 4000 lb car. This is better than a DOHC V8 can muster with the same output level at the same vehicular weight. Heck, this is almost as good as a 3.6 HF V6. And, nobody ever complained about a Bentley pushrod 6.75L V8 being unrefined.

And where does this engine exist? Because when they put a 6.2 liter V8 into the G8 GXP, they got a 415 hp engine getting 13/20 mpg. Direct injection doesn't add 5 mpg. Bentley's engine is a dinosaur in a tank-like car with loads of sound insulation. Plus Bentley's old world customer base is used to it. What Bentley and Rolls do isn't really applicable to anyone else.

I think you have to build what the market demands, and the luxury car market looks for DOHC, whether it be V6 or V8, and they look for at least a 6-speed, now even a 7 or 8 speed. If Cadillac wants to go against the Germans,Jaguar and the Lexus LS460 and Infiniti M56, that is the price of admission.

[regfootball]

Of course you can turbocharge a 60-deg engine, but if the primary application is to be turbocharged I'll prefer a 90 deg or 72 deg engine -- if only because you can use one turbo nestled in the Vee and reverse flow heads, instead of two turbos with one hanging off each side. The disadvantage of a 60 deg V8 vs a 60 deg V6 in turbo applications is that the V8 needs twin scroll turbos for optimal efficiency, the V6 doesn't. This is a slight cost adder, but it doesn't really take up any more or less space.

The intake design on the 3.0 and 3.6 HF V6 are already more than good enough. They flow enough air for 86~90hp/liter. A 4.0 or 4.8 V8 will be similarly performing. By any measure, that is good enough. Even if you can improve on the flow capacity of the intakes, you'll need to rev the engine above 7000 rpm to take advantage of it. Currently, GM automatic trannies don't support shift speeds above 7000 rpm so you can't go there unless you want to revamp the transmission lineup as well, or limit the deployment to manual cars.

if the engine hasn't made anough go juice before 7000 rpm then there are other issues.

ultimate question. is a 4.8 litre 60 degree v8 or a 3.6 or 3.0 twin turbo a better uplevel option for cadillacs. fuel efficiency, packaging, power. at least if the v8 can be force fed then it perhaps can become a top level engine and the extra money spent by consumers on the force fed version can help amortize the base v8.

And where does this engine exist? Because when they put a 6.2 liter V8 into the G8 GXP, they got a 415 hp engine getting 13/20 mpg. Direct injection doesn't add 5 mpg. Bentley's engine is a dinosaur in a tank-like car with loads of sound insulation. Plus Bentley's old world customer base is used to it. What Bentley and Rolls do isn't really applicable to anyone else.

I think you have to build what the market demands, and the luxury car market looks for DOHC, whether it be V6 or V8, and they look for at least a 6-speed, now even a 7 or 8 speed. If Cadillac wants to go against the Germans,Jaguar and the Lexus LS460 and Infiniti M56, that is the price of admission.

i think chrysler having an 8 speed means GM will have to at least develop one.....

[NOS2006]

if the engine hasn't made anough go juice before 7000 rpm then there are other issues.

ultimate question. is a 4.8 litre 60 degree v8 or a 3.6 or 3.0 twin turbo a better uplevel option for cadillacs. fuel efficiency, packaging, power. at least if the v8 can be force fed then it perhaps can become a top level engine and the extra money spent by consumers on the force fed version can help amortize the base v8.

i think chrysler having an 8 speed means GM will have to at least develop one.....

Honestly, I expect the NG CTS or XTS to debut with an 8-speed. Lexus has one, Chrysler will have one next year. Both Hyundai and BMW are reportedly developing one. Mercedes has had a 7-speed for awhile.

[Robert Hall]

Honestly, I expect the NG CTS or XTS to debut with an 8-speed. Lexus has one, Chrysler will have one next year. Both Hyundai and BMW are reportedly developing one. Mercedes has had a 7-speed for awhile.

GM should trump them with a 10 speed.

[regfootball]

Nissan has a 7 speed also in the Infinitis.

[Z-06]

In 2006/7 GM had registered "8" and "eight" as trademarks, wonder what happened with it post-bankruptcy.

[dwightlooi]

And where does this engine exist? Because when they put a 6.2 liter V8 into the G8 GXP, they got a 415 hp engine getting 13/20 mpg. Direct injection doesn't add 5 mpg. Bentley's engine is a dinosaur in a tank-like car with loads of sound insulation. Plus Bentley's old world customer base is used to it. What Bentley and Rolls do isn't really applicable to anyone else.

I think you have to build what the market demands, and the luxury car market looks for DOHC, whether it be V6 or V8, and they look for at least a 6-speed, now even a 7 or 8 speed. If Cadillac wants to go against the Germans,Jaguar and the Lexus LS460 and Infiniti M56, that is the price of admission.

The GXP does not have the latest iteration of the small block and may have an unfavorable final drive. A 6.2 Pushrod without Direct Injection gets 16/25 in an Automatic Camaro SS. The manual version gets 16/24 in the same car. That's a relatively big, ~3900 lbs car. It is not unreasonable to expect that the next 6.2 does 0.5~1.0 MPG better with the expected 1 point bump in compression ratio that comes with DI. In fact, there isn't one DOHC V8 German or Japanese car of a similar weight with better mileage. This is despite most having more speeds in the tranny and smaller displacement with less power --e. Not one.

M3? 13/20 MPG ; BMW 550? 15/22 MPG ; Lexus IS-F? 16/23 ; Lexus LS460? 16/24 MPG ; M-B E550? 16/23 MPG ; Infiniti M56? 16/25

What makes you think that push rod engines make more noise than DOHC engines? For the most parts it doesn't. The main difference comes from the fact that you are using about 20~25% more displacement to get the same power. Bigger slugs, more reciprocating mass = a little more vibrations. However, this is not any worse than a DOHC engine of the same capacity, and it is actually more fuel efficient in most instances.

I don't think the average car buyer -- luxury or not -- knows what DOHC stands for or what a pushrod is. By average, I mean 80% of the car buying public. Enthusiasts and drivers do, but enthusiasts and drivers are also savvy enough to look at the horsepower, torque, MPG and other performance numbers. The average buyer will be satisfied if the engine "feels" strong, is smooth and runs quiet. The enthusiast and the gear head will look at 470hp, 17/25 MPG and 0-60 in 4.2 seconds and be satisfied.

In 2006/7 GM had registered "8" and "eight" as trademarks, wonder what happened with it post-bankruptcy.

8L55... well... it was put on hold like the 4.5 Duramax 72-deg DOHC Turbodiesel.

[smk4565]

Honestly, I expect the NG CTS or XTS to debut with an 8-speed. Lexus has one, Chrysler will have one next year. Both Hyundai and BMW are reportedly developing one. Mercedes has had a 7-speed for awhile.

BMW has an 8-speed now. The 7-series, 5-series, and 2011 X3 all have it. I believe the next 3-series will have it as well. And yes, Hyundai and Chrysler are expected to have one some time next year. 8-speed will probably be the norm in $35k and up in a couple years.

[smk4565]

The GXP does not have the latest iteration of the small block and may have an unfavorable final drive. A 6.2 Pushrod without Direct Injection gets 16/25 in an Automatic Camaro SS. The manual version gets 16/24 in the same car. That's a relatively big, ~3900 lbs car. It is not unreasonable to expect that the next 6.2 does 0.5~1.0 MPG better with the expected 1 point bump in compression ratio that comes with DI. In fact, there isn't one DOHC V8 German or Japanese car of a similar weight with better mileage. This is despite most having more speeds in the tranny and smaller displacement with less power --e. Not one.

M3? 13/20 MPG ; BMW 550? 15/22 MPG ; Lexus IS-F? 16/23 ; Lexus LS460? 16/24 MPG ; M-B E550? 16/23 MPG ; Infiniti M56? 16/25

What makes you think that push rod engines make more noise than DOHC engines? For the most parts it doesn't. The main difference comes from the fact that you are using about 20~25% more displacement to get the same power. Bigger slugs, more reciprocating mass = a little more vibrations. However, this is not any worse than a DOHC engine of the same capacity, and it is actually more fuel efficient in most instances.

I don't think the average car buyer -- luxury or not -- knows what DOHC stands for or what a pushrod is. By average, I mean 80% of the car buying public. Enthusiasts and drivers do, but enthusiasts and drivers are also savvy enough to look at the horsepower, torque, MPG and other performance numbers. The average buyer will be satisfied if the engine "feels" strong, is smooth and runs quiet. The enthusiast and the gear head will look at 470hp, 17/25 MPG and 0-60 in 4.2 seconds and be satisfied.

But you don't need a DOHC of equal displacement to get the power, so with the smaller engine, it is smoother and quieter. And look at the interior noise levels of GM's pushrod powered cars, none are all that quiet. Especially not when compared to a Hyundai Genesis or Lexus LS. The Ford 5.0 V8 gets better mileage than the GM 6.2 liter V8 and the Ford doesn't have DI either.

I think the car buying public does know the difference when they drive both. They may not know how to explain it, but I think they can tell the difference. Look at how many customers GM lost in the mid-size car segment with the 3800 V6 and 3.1 and 3.4 pushrod V6s they used in the late 90s and early 2000s. Compared to the Japanese DOHC engines, the GM engines weren't as smooth or refined, and customers noticed that. The Japanese had smaller, smoother, equally powerful, more fuel efficient engines, and that showed in the 1990s and 2000s as half of GM's customer base left.

[Drew Dowdell]

The only pushrod powered vehicle that GM makes that is intended to be quiet is the Lucerne, which meets or beats it's similarly priced Lexus competition in sound avoidance. Don't say "yes but the LS...." because at $70k instead of $35k you can afford another layer of sound insulation.

[dwightlooi]

But you don't need a DOHC of equal displacement to get the power, so with the smaller engine, it is smoother and quieter. And look at the interior noise levels of GM's pushrod powered cars, none are all that quiet. Especially not when compared to a Hyundai Genesis or Lexus LS. The Ford 5.0 V8 gets better mileage than the GM 6.2 liter V8 and the Ford doesn't have DI either.

I think the car buying public does know the difference when they drive both. They may not know how to explain it, but I think they can tell the difference. Look at how many customers GM lost in the mid-size car segment with the 3800 V6 and 3.1 and 3.4 pushrod V6s they used in the late 90s and early 2000s. Compared to the Japanese DOHC engines, the GM engines weren't as smooth or refined, and customers noticed that. The Japanese had smaller, smoother, equally powerful, more fuel efficient engines, and that showed in the 1990s and 2000s as half of GM's customer base left.

Actually, interior or exterior noise levels of cars have very little to do with the configuration of the valve train. The valve train for the most parts do not make the engine louder or softer in radiated noise. It does affect the displacement needed for a given power level and that affects felt vibrations more than noise. If the intent is to use engines with the smallest reciprocating elements such as to achieve minimum vibration levels, we'll be gravitating away from "big" fours like the 2.4 and 2.5s and we'll avoid big sixes like the 3.6 and 3.7s. Maximum refinement calls for 1.6~1.8 liter fours, 2.4~2.7 liter sixes and 3.6~4.2 liter eights. However, we are actually seeing wholesale migration to large fours and large sixes. Why? Because fewer cylinders for a given displacement equal lower frictional loses and better consumption performance. We have gone down that road before -- remember the Mazda K-series 1.8 V6? Very smooth, but not particularly efficient. Compare a 2.5 liter I4 from Nissan or Ford to a 2.5 liter Duratec V6 or Mazda K-series 2.5 V6. Same conclusions -- smoother, but less efficient. The same analogy can be applied to the Pushrod vs DOHC discussion. You are trading a little vibrational harshness for lower frictional loses.

Today, if you look at Pushrod V8s vs DOHC V8s of the same output (the pushrods will be of a larger displacement) you do not see a fuel economy advantage in DOHC V8s. In fact, the reverse is true. You see that DOHC V8s use more fuel.

The Ford 5.0 DOHC does not have a fuel economy advantage over the GM 6.2. The GM 6.2 turns in 16/25 on an automatic Camaro. The Ford 5.0 DOHC turns in 18/25 in the Mustang. However, the Mustang GT is 350 pounds lighter than the Camaro SS. Don't you think that having the equivalent of two additional adult passengers in the car hurts your mileage a little in the city? That there is no difference in highway mileage is actually impressive. Neither engine has Direct Injection.

I think we need to stop using the 3800 as an example. That is neither representative of today's Pushrod engines, nor particularly high on technological content. Technological content for the most parts have nothing to do with the valve train layout. For instance, you can have DI with or without DOHC. You can have cylinder deactivation with or without pushrods. You can have Variable timing either way too.

Edited September 16, 2010 by dwightlooi

[smk4565]

I think we need to stop using the 3800 as an example. That is neither representative of today's Pushrod engines, nor particularly high on technological content. Technological content for the most parts have nothing to do with the valve train layout. For instance, you can have DI with or without DOHC. You can have cylinder deactivation with or without pushrods. You can have Variable timing either way too.

A parallel can be drawn to the 3800. GM kept the 3800 around in the early to mid 2000s simply because it was cheaper to do so. Even though better technology existed out there, the way GM made money was by putting the bare minimum into cars and cashing in on Hummers and GMT900s. That worked for about 5 years, then it all came crashing down.

What they are doing with the small block V8 is similar. They keep milking along the existing LS-series engines even though there is better technology out there. They do this to save money. I am aware that while bankrupt money needs to be saved, but at some point they have to bring out something new. The rest of the market is not sitting still (well Chrysler is), pushing the LS series V8 along for another 10 years with minor updates is going to get GM left behind the curve, again.

[dwightlooi]

A parallel can be drawn to the 3800. GM kept the 3800 around in the early to mid 2000s simply because it was cheaper to do so. Even though better technology existed out there, the way GM made money was by putting the bare minimum into cars and cashing in on Hummers and GMT900s. That worked for about 5 years, then it all came crashing down.

What they are doing with the small block V8 is similar. They keep milking along the existing LS-series engines even though there is better technology out there. They do this to save money. I am aware that while bankrupt money needs to be saved, but at some point they have to bring out something new. The rest of the market is not sitting still (well Chrysler is), pushing the LS series V8 along for another 10 years with minor updates is going to get GM left behind the curve, again.

Over the past decade and a half, the small block gained an aluminum block, variable valve timing and cylinder deactivation. It now puts out a very respectable 70hp/liter and it beats competing DOHC power plants on fuel economy, engine weight and engine size. Today's small block makes more power and more torque, while weighing less, taking up less underhood volume and having better fuel economy than a superlative DOHC V8 like the 414hp BMW S65 4.0 liter V8 in the M3. I won't characterize this evolutionary record as one of "minor" updates.

It is slated to get direct injection next year and perhaps even dual independent VVT. The relocation of the in block cam to a higher location will reduce the valve train mass. Assuming that the Gen V engine gains a modest 6~7% in hp and 1 mpg it is to remain a perfectly competitive.

Perhaps you have a different take on this?

[smk4565]

Over the past decade and a half, the small block gained an aluminum block, variable valve timing and cylinder deactivation. It now puts out a very respectable 70hp/liter and it beats competing DOHC power plants on fuel economy, engine weight and engine size. Today's small block makes more power and more torque, while weighing less, taking up less underhood volume and having better fuel economy than a superlative DOHC V8 like the 414hp BMW S65 4.0 liter V8 in the M3. I won't characterize this evolutionary record as one of "minor" updates.

It is slated to get direct injection next year and perhaps even dual independent VVT. The relocation of the in block cam to a higher location will reduce the valve train mass. Assuming that the Gen V engine gains a modest 6~7% in hp and 1 mpg it is to remain a perfectly competitive.

Perhaps you have a different take on this?

Well Mercedes has a new 4.7 liter DOHC turbo V8 that makes 435 hp and 516 lb-ft of torque while offering a claimed 22% fuel economy gain over the outgoing 5.5 liter. The GM V8 may be competitive, but the ceiling is much higher on a DOHC engine. That is why pushrod 4 and 6 cylinders died off, there comes a point when pushrod can't compete anymore because DOHC advances faster.