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DOHC V8s on GM's Mind?


#1

Posted 08 September 2010 - 09:36 AM

NOS2006

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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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#2

Posted 08 September 2010 - 09:42 AM

Drew Dowdell

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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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#3

Posted 08 September 2010 - 10:47 AM

dado

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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"
Posted Image

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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#4

Posted 08 September 2010 - 01:27 PM

NOS2006

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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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#5

Posted 08 September 2010 - 02:37 PM

Camino LS6

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DOHC conversions for Chevy V8s have existed for a very long time...
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#6

Posted 08 September 2010 - 03:12 PM

Cubical-aka-Moltar

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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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#7

Posted 08 September 2010 - 03:13 PM

dwightlooi

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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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#8

Posted 08 September 2010 - 03:46 PM

Drew Dowdell

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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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#9

Posted 08 September 2010 - 08:16 PM

Camino LS6

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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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#10

Posted 08 September 2010 - 09:09 PM

Cubical-aka-Moltar

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Various aftermarket companies have made them over the years.

Not relevant...what counts are production engines.
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#11

Posted 08 September 2010 - 09:18 PM

balthazar

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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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#12

Posted 08 September 2010 - 09:27 PM

CanadianBacon94

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i had heard that the UV8 was related to the DuraMin(half ton diesel)
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#13

Posted 09 September 2010 - 11:36 AM

Camino LS6

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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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#14

Posted 09 September 2010 - 11:59 AM

Cubical-aka-Moltar

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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, 09 September 2010 - 12:01 PM.

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#15

Posted 09 September 2010 - 01:26 PM

dwightlooi

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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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#16

Posted 09 September 2010 - 01:29 PM

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


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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#17

Posted 09 September 2010 - 03:13 PM

Camino LS6

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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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#18

Posted 09 September 2010 - 10:36 PM

dwightlooi

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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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#19

Posted 10 September 2010 - 08:38 PM

smk4565

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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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#20

Posted 11 September 2010 - 12:00 AM

Drew Dowdell

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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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