DOHC V8s on GM's Mind?

[Z-06]

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.

And what are those advancements?

[z28luvr01]

And where does this engine exist?

Underneath the hood of a Camaro SS or Corvette

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.

I'm not sure if this is true on the GXP, but on the base G8 the V8 was based off the Vortec V8s in the trucks, not from the Corvette. Same architecture, I know, but there are differences. Every time there's an argument for the GM small block's efficiency, you bring up the G8 GXP. That's like assuming all BMW inline sixes are as efficient as the one in the X5.

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.

Really, are you sure that Bentley and Rolls aren't second tier luxury brands that compete with Lincoln and Acura because they didn't put enough technology into the engine?

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 wonder how many people left a Bentley showroom in disgust after finding out the car they wanted didn't have DOHC.

[z28luvr01]

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.

The '09 S550 gets 14/22. a 22% improvement would be 15/24. That's still less than a Camaro SS for similar performance. But Mercedes is Mercedes and Chevy is Chevy, so Mercedes wins.

[Camino LS6]

DOHC is not better,nor more advanced, than a pushrod engine.

It is however, larger, harder to package, more complex, and less efficient.

And that last point is the achilles heel.

GM is smarter than that I hope, in that they still decide on drivetrains based on RESULTS, rather than fashion.

Lauding DOHC and high transmission gear counts is simply absurd.

Show me the results, that's what matters.

[smk4565]

For every pushrod fan, why is there not a 3900 pushrod V6 in the Regal, instead of a 2.0 Turbo. If the pushrod is so light, easy to package, fuel efficient, powerful, etc, why is it gone from mainstream GM sedans except for the very dated Lucerne and Impala? The pushrod's days are numbered.

[dwightlooi]

Let's wait for the EPA numbers...

In theory, reducing displacement without reducing the number of cylinders and valves, while adding forced induction does not necessarily translate into better fuel economy.

Examples:-

• Cruze's 1.4T -- it is no more efficient than the Civic or Corolla's 140hp 1.8 liter fours
  
• VW/Audi 3.0T (supercharged) -- 18/27 mpg is good, but no better than a 3.6 or 3.8 NA V6.
  

Let's consider what happens when you go from 5.5 to 4.7 liters in a DOHC-32v setup.

• Your valve train drag remains about the same.
  
• Your piston to wall drag is insignificantly lower.
  
• Your intake pumping loses at cruise and light loads is the same (choked by the throttle body).
  
• Your exhaust pumping losses improves slightly.
  
• Your power and torque numbers drop more than the exhaust pumping losses reductions.
  

Net result, small gain in efficiency with slightly larger loss in output.

Now, to recover the lost power and gain some, you add forced induction. The following then happens:-

• The turbos introduce exhaust back pressure reducing cruise economy.
  
• The turbos and intercoolers add bulk and weight.
  
• You drop compression by about 1 point to accommodate the boost pressure lowering cruise economy.
  
• The turbo intake manifold usually doesn't have resonance tuned runners dropping cruise efficiency.
  
• Power increased more than the loss in efficiency, offsetting the losses from the reduction in displacement.
  

At power parity, fuel economy is similar, but engine is more expensive, more complex, bulkier and heavier. However, the torque band is broader which may improve the driving experience. If you strive to actually gain power, you end up dropping compression further and fuel economy goes down, although you gain more power than you lose in economy.

[Drew Dowdell]

For every pushrod fan, why is there not a 3900 pushrod V6 in the Regal, instead of a 2.0 Turbo. If the pushrod is so light, easy to package, fuel efficient, powerful, etc, why is it gone from mainstream GM sedans except for the very dated Lucerne and Impala? The pushrod's days are numbered.

A pushrod V6 is still larger than a turbo-4..... you're not *that* dumb.... or are you?

Here is a question: What is the maximum displacement DOHC engine that can fit in the CTS?

At most, you're looking at a 3.6 HF with it's cylinder sleeves removed to give it a total displacement of 4.0 liters.

What is the maximum displacement that can go in the CTS with pushrods? At least 7.0 litres.

Think about that.... you have a whole 3.0 liters of additional potential under the hood if you would just give up your love of the older DOHC valve train layout.

[smk4565]

A pushrod V6 is still larger than a turbo-4..... you're not *that* dumb.... or are you?

Here is a question: What is the maximum displacement DOHC engine that can fit in the CTS?

At most, you're looking at a 3.6 HF with it's cylinder sleeves removed to give it a total displacement of 4.0 liters.

What is the maximum displacement that can go in the CTS with pushrods? At least 7.0 litres.

Think about that.... you have a whole 3.0 liters of additional potential under the hood if you would just give up your love of the older DOHC valve train layout.

A Northstar fits in the STS, it would probably fit in a CTS. Heck, Mercedes gets a V12 into an SL roadster, I don't see why a small DOHC V8 wouldn't fit in the CTS. And max displacement doesn't have much to do with it, it is about refinement, noise and vibration. The pushrod 4 died, the pushrod V6 is hanging on by a thread in the Impala and soon to be deceased Lucerne, by 2012, the pushrod V6 should be dead too. DOHC is better in 4's, better in 6's, better in 8's.

If you took the 10 fastest pushrod powered cars and put them against the 10 fastest DOHC cars, I'll take the DOHC team any day of the week. Give me the Veyron, McLaren F1, Koenigsegg, Jag XJ220, Enzo, Murcielago, Zonda, 911 Turbo, etc compared to the Corvette ZR1, Viper, Camaro SS, CTS-V, Challenger and 300C.

[dwightlooi]

A Northstar fits in the STS, it would probably fit in a CTS. Heck, Mercedes gets a V12 into an SL roadster, I don't see why a small DOHC V8 wouldn't fit in the CTS. And max displacement doesn't have much to do with it, it is about refinement, noise and vibration. The pushrod 4 died, the pushrod V6 is hanging on by a thread in the Impala and soon to be deceased Lucerne, by 2012, the pushrod V6 should be dead too. DOHC is better in 4's, better in 6's, better in 8's.

If you took the 10 fastest pushrod powered cars and put them against the 10 fastest DOHC cars, I'll take the DOHC team any day of the week. Give me the Veyron, McLaren F1, Koenigsegg, Jag XJ220, Enzo, Murcielago, Zonda, 911 Turbo, etc compared to the Corvette ZR1, Viper, Camaro SS, CTS-V, Challenger and 300C.

Racing series in most cases are limited by class rules stipulating displacements. Race cars are hence forced to make power within the allowance of those rules. Road cars derived from companies involved in these types of racing activities are hence biased towards small displacements and high revolutions, or small displacements and significant boost pressures. Hence, many super cars are so biased as well given their progenitors' experiences.

The fact is that today, when you compare the best pushrod powerplants and DOHC powerplants from the leading mass produced vehicles, pushrod engines offer more power, lighter weights, smaller sizes and equal or better fuel economy, at a lower cost and possibly with better reliability.

A good example is the BMW S65 V8 in the M3. It displaces 4.0 liters and weighs 202 kg. The S65 spins to 8300 rpms, produces 414hp and 295 lb-ft. In the 3700 lbs M3 it gets 14/20 (city/hwy) mpg. You'll be hard pressed to find a DOHC V8 of a finer pedigree.

Don't like BMW? Look at the Lexus IS-F's 5.0 liter 2UR-GSE V8 then. 416 hp, 371 lb-ft, 222kg. The 2UR-GSE spins to a modest 6800 rpm. It gets 16/23 mpg with the help of an 8-speed automatic transmission.

Chronologically, their contemporary will be the LS3 V8. It displaces 6.2 liters and weighs 183 kg. It makes 426hp and 420 lb-ft installed in the Camaro. The LS3 spins to 6600 rpm and in the 3900 lbs Camaro gets 16/24 (city/hwy) mpg.

Less weight, smaller size, better fuel economy, a little more power, a lot more torque and a lot less money. What's not to like? Refinement? It's not bad. Not any worse than M113 5.5L V8 in the C55 AMG. Not surprising really given that -- despite the M113's lower displacement -- both engines have identical stroke lengths 92 mm, and stroke length more than anything else causes vibration harshness* The LS3 is actually less "raw" than the M156 in the C63 AMG at higher rpms, while not as "soft" on power or response below 4000 rpm.

* Vibration forces due to imbalances are in general a function mass x the square of piston speed, which in turn is a function of stroke x rpm.

[Drew Dowdell]

A Northstar fits in the STS, it would probably fit in a CTS. Heck, Mercedes gets a V12 into an SL roadster, I don't see why a small DOHC V8 wouldn't fit in the CTS. And max displacement doesn't have much to do with it, it is about refinement, noise and vibration. The pushrod 4 died, the pushrod V6 is hanging on by a thread in the Impala and soon to be deceased Lucerne, by 2012, the pushrod V6 should be dead too. DOHC is better in 4's, better in 6's, better in 8's.

As always.. you fail to see the point. Even if Cadillac managed to get the Northstar under the hood of the CTS, it'd still be maxed out at 4.6 litres. Even if GM could get 115 hp per litre out of the engine, you're looking at a max of 530hp. The CTS-V already has 556hp and there is still room for more displacement.

If you took the 10 fastest pushrod powered cars and put them against the 10 fastest DOHC cars, I'll take the DOHC team any day of the week. Give me the Veyron, McLaren F1, Koenigsegg, Jag XJ220, Enzo, Murcielago, Zonda, 911 Turbo, etc compared to the Corvette ZR1, Viper, Camaro SS, CTS-V, Challenger and 300C.

Give me a Veyron too... then I'll sell it and buy a Corvette ZR1, a Viper, a Camaro SS, a CTS-V, a Challenger, and a 300C, then I'll fly them all to the Nurburgring where me and 5 of my best C&G buds can play with them on the track for a week. Each of the vehicles you mentioned can run with anything in their price class. You may have valid issues with their interior trim, weight, or handling.... but the engine isn't the falling down point for those cars.

[z28luvr01]

The Northstar won't fit in a CTS. That's why the CTS-V got the LS6 in the first place.

[Camino LS6]

I want that Nurburgring trip!

Give us that Veyron, SMK!

[Z-06]

Make that two.

[dwightlooi]

As always.. you fail to see the point. Even if Cadillac managed to get the Northstar under the hood of the CTS, it'd still be maxed out at 4.6 litres. Even if GM could get 115 hp per litre out of the engine, you're looking at a max of 530hp. The CTS-V already has 556hp and there is still room for more displacement.

Just the facts...

The Northstar V8 has a bore spacing 102mm. It has 93mm pistons and 84mm strokes for a displacement of 4565cc. It uses VVT and makes 320hp @ 6400 rpm (70.0 hp/l) with 315 lb-ft, redlining at 6750 rpm. The Northstar weighs 195kg.

For comparison, an LS3 V8 has a bore spacing of 111.76mm. It has 103.25mm pistons and 92mm strokes for a displacement of 6162cc. It makes 436hp @ 5900 rpm (70.8 hp/l) with 424lb-ft, redlining at 6600 rpm. The LS3 weighs 183 kg.

[smk4565]

The Northstar is super old though, if they put money into it or came up with a new DOHC V8 it would be a different story. When the Northstar came out in 1992 it was making 300 hp. The LT1 5.7 liter of the day was making 250-260 hp, except for the Corvette that got a 300 hp version in the early 90s. The pushrod just doesn't fit Cadillac, and it won't sell in Europe. Cadillac will always be a North American brand unless they build a world car. Cadillac still builds cars with a 60s muscle car mentality.

And the new M5 has 570-600 hp out of a 4.4 liter DOHC, and the Ferrari 458 Italia makes 550 hp out of a naturally aspirated V8. CTS-V could fit a modern DOHC V8 I'm sure, GM just doesn't have one, so it gets the LS engine by default.

[balthazar]

LH2 Northstar was new for 2004.

[Robert Hall]

LH2 Northstar was new for 2004.

Have they upgraded it since then? 6 years is a long time...

[z28luvr01]

The Northstar is super old though, if they put money into it or came up with a new DOHC V8 it would be a different story. When the Northstar came out in 1992 it was making 300 hp. The LT1 5.7 liter of the day was making 250-260 hp, except for the Corvette that got a 300 hp version in the early 90s.

Ignoring facts will get you nowhere:

The LT1 in the B-bodies got 260hp.

The LT1 in the F-bodies got 275hp.

The LT1 in the Corvette got 300hp.

Lesser trim Cadillacs got a 275hp version of the Northstar.

If you want to exclude the 300hp LT1 from this argument, I'm fine with that, as long as you also exclude the 300hp Northstar. The fact is, it's basically a wash between the LT1 and Northstar. I'll add that the LT1 has a pretty high ceiling. The 330hp LT4 of 1996 was a LT1 with a different head design. And, using parts available from GM, my father is building one up that should be good for 465hp, not that that's entirely relevant.

I'm not necessarily dismissing DOHC engines, but you're dead wrong on the pushrod engine. And the fact is, not everyone who buys a European sports sedan agress with you. Consider:

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