NOS2006

DOHC V8s on GM's Mind?

68 posts in this topic

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.

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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.

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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"

3360210d.jpg

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

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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...

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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?

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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.

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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.

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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.

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Various aftermarket companies have made them over the years.

Not relevant...what counts are production engines.

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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.

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Not relevant...what counts are production engines.

Oh?

I guess I didn't read the rules. :neenerneener:

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

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Oh?

I guess I didn't read the rules. :neenerneener:

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 by Cubical-aka-Moltar

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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

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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.

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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!

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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

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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)

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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.

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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?

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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.

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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....

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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.

smooth_v8_balance2.jpg

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 by dwightlooi

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