2009 Corvette ZR1 LS9 Engine

[hightower99]

Here’s some more fuel for the fire. DOHC is almost always used because we want at least a 4 valve cylinder head. We can argue that a pushrod engine is almost always 2 valve because of the packaging limitations that are common in that type. I will note that these issues can be worked around.

What I thought was interesting is why did Bombardier’s new V220 V6 aircraft engine use a two valve head? This is an all new 3.1L 220 hp (aero engine rated) engine which was a ground up new design from the makers of Rotax and other engine brands. These guys really have a lot of engine expertise and they elected to use a SOHC driving only two valves.

Food for thought.

Possible reason for using 2VPC heads is cost and ease of maintenance. Aero engines need constant maintenance and resetting/checking 12 valves takes alot less time then checking 24 valves. Also Bombardier states that the engine was designed with low-maintenance in mind. Also because this engine is a 120deg V6 they needed to keep the overall width down and if they had chosen DOHC 4vpc or even SOHC 4 vpc the heads would certainly contribute to greater overall width. Another thing to consider is the fact that aero engines are much more static when it comes to changing loads, they normally stay within a relatively small RPM range and are not asked to change loads quickly (other than from idle to full-power at take-off and even then the actual transistion isn't important). 2vpc designs are well suited to this kind of work.

[Matra et Alpine]

So its not covered in gold, and not in one of the most expencive cars ever?

Just a minor correction, Slicks ..... the engine is NOT covered in gold.
THe engine BAY is to allow for a larger passenger compartment and small body and to keep the weight down avoiding large bulky heat sheild/wrap.

[Slicks]

Yes.

If you honestly think the only(or main) reason Ultima chose a Chevy OHV V8 is price then I feel very sorry for you.

So you would agree that in high performance applications, such as racing, the best engines are all DOHC? Even if there was no displacement limit, I highly doubt that they would be using pushrod engines due to their lack of ability to rev that high.

No, I believe that when displacement is limited to small cubes, then OHC would be superior(or better yet cam-less engines) because of how high its capable of revving.

[Slicks]

BMW believes 500cc/cylinder is the most efficient, with the M3 getting bigger and heavier the I 6 had reached its limits.

Ah, yes I forgot about BMW's little theory.
Why not just turbo the I6 like in the 335i though?

Thats why in a recent British survey BMW drivers had more sexual encounters/week than drivers of other brands...

LMFAO... I don't know whats more funny. The fact that you believe a survey like that, or the fact that you believe that BMW owners were truthful on the survey.

[Kitdy]

If you honestly think the only(or main) reason Ultima chose a Chevy OHV V8 is price then I feel very sorry for you.

I would like to know where you drew that extraneous conclusion.

In no way did I indicate that price was the only or main reason that Ultima decided on an LSx.

EDIT:

No, I believe that when displacement is limited to small cubes, then OHC would be superior(or better yet cam-less engines) because of how high its capable of revving.

Would you then agree that if you are limited to a certain weight that the best performance engine would be an OHC engine?

[Slicks]

Again you misunderstand the question. The majority of cars made today have DOHC engines. Even when only talking about V engines or even V8s DOHC is still king as more DOHC engines are made then OHV. Why is that?

And again I will ask you, does that trully mean they are "better", or is it that more manufacturers know how to make OHC engines(combine their 4 cylinder OHC engines).

To answer your question about the Ultima. They wanted an engine that is cheap and that has a large, publicly available R&D program. If they where based in Europe then they would have used a DOHC engine probably with some sort of turbo system.

lol...

BS you are constantly saying that the LSx series of engines have inherent performance advantages over DOHC engines. Also I explained why people would rather swap in an LSx engine over a 4.6L DOHC ford engine... Displacement.

The inherent performance advantages are weight and size, we both know this. People would rather swap an LSx because the Ford engine WONT FIT. You cannot consider an engine that wont fit into your car, therefore it is not a displacement argument.

I Am Canadian... But I live in Denmark and have been here for almost 6 years. LSx engines are pretty much non-existent here as is any form of tuning support for them.

May I ask how you were able to get a ride in 2 C6 Z06's over there, seeing there are probably only a handful of people with them, and one hell of a "right place right time" kind of moment to ride in one.

And yes. You can fit much larger DOHC engines into a BMW chassis.
I am currently helping do some fabrication (Roll-cage and dashboard) on an E34 chassis that will house a 7.1L BMW N73 engine modified by Noelle motors that will pump out 660HP NA (with no lumpy idle).

Pics of engine/chassis?
Are you pretty much just removing the firewall or what?

[Slicks]

I would like to know where you drew that extraneous conclusion.

In no way did I indicate that price was the only or main reason that Ultima decided on an LSx.

Sorry but it sounded like it:
me :"Do you seriously think that Ultima is trying to save that much money?"
you :"Yes."

Would you then agree that if you are limited to a certain weight that the best performance engine would be an OHC engine?

Most likely.
But my argument has always been for real world (not restricted class racing) performance.

[Slicks]

Just a minor correction, Slicks ..... the engine is NOT covered in gold.
THe engine BAY is to allow for a larger passenger compartment and small body and to keep the weight down avoiding large bulky heat sheild/wrap.

My mistake. I knew the engine bay was lined with gold, but I also read the "engine cover" was gold. Must of meant the engine bay, or "hood".

[Kitdy]

Most likely.
But my argument has always been for real world (not restricted class racing) performance.

Ah. A distinction that was not apparently apparent to me. So in a scenario of what is the absolute fastest, a OHC setup is superior to OHV, probably due to power being (roughly) proportional to rpm.

In road engines however, I am not sure what is necessarily better.

Are OHV engines necessarily better for torque?

[hightower99]

And again I will ask you, does that trully mean they are "better", or is it that more manufacturers know how to make OHC engines(combine their 4 cylinder OHC engines).

You are joking right? I can't understand the logic behind that question. You say that OHV design has some good advantages in size and weight when used in conjunction with V8 configuration right? So if that was such a great advantage the only reason you can think of as to why other manufacturers don't make OHV V8's is because they base their V8s on their I4s? Are you trying to imply that other manufacturers don't know how to make an OHV V8? It is plainly obvious why DOHC designs are dominant... Because they allow a better overall engine. Please I want to know why you think that the majority of V8s and every other engine configuration is dominated by DOHC designs?

The inherent performance advantages are weight and size, we both know this. People would rather swap an LSx because the Ford engine WONT FIT. You cannot consider an engine that wont fit into your car, therefore it is not a displacement argument.

Umm who says that a 4.6L ford V8 won't fit? Won't fit in what? They are a little wider at the heads and alittle taller... do you think that posses the biggest concern?

May I ask how you were able to get a ride in 2 C6 Z06's over there, seeing there are probably only a handful of people with them, and one hell of a "right place right time" kind of moment to ride in one.

Well one of them is owned by a friend of a friend and the other I saw at a small car gathering for american cars in sweden, that and generally the scandinavians are very friendly
Unfortunately I couldn't persuade either owner to let me drive them

Pics of engine/chassis?
Are you pretty much just removing the firewall or what?

I haven't seen the engine and I don't have nor would I post any pics if I did have them. I have been told that it won't take much to fit the engine, although the said they needed to modify the section of the transmission tunnel at the firewall, hence the custom dashboard that I am helping with.

[jediali]

Are OHV engines necessarily better for torque?

not necesarily - either can prove effective. An engine that is optimised for lower speed gas movement will provide better torque, so longer slimer intake geometry, earlier overlap in valve timing etc. 2 vpc would be fine but OHC would reduce friction.

If you consider torque as a direct result of MEP (mean effective pressure) in the cylinder then best torque would logically come from an engine that maintains a good volumetric efficiency over the revband. To do this the engine would benefit from variable intake and valvetiming and accurate combustion control at different revs.... I think

[culver]

Ah. A distinction that was not apparently apparent to me. So in a scenario of what is the absolute fastest, a OHC setup is superior to OHV, probably due to power being (roughly) proportional to rpm.

In road engines however, I am not sure what is necessarily better.

Are OHV engines necessarily better for torque?

No, they are not inherently better. Traditionally in US cars a pushrod motor and OHC motor of equal hp will have different displacement. The larger displacement pushrod motor would oddly enough have more torque.

However, given equal displacement and design intent, there is no reason a DOHC motor can't have just as much torque.

However, it is likely the designers of OHV motors are more likely to tune the motor for low end torque as a 2 valve head is actually well suited for low end work but not as well suited for high RPM work. A 4 valve head can be tuned for low end work but oddly enough many 4 valve motors actually cut air flow to one of the valves (or in Honda's case don't open the valve) at low RPM. I'll spare you the details. In any case, it is likely the designer of a 2 valve head will tune for lower RPM work because the 2 valve head isn't a disadvantage at low RPM. A 4 valve head is more likely to be tuned for higher RPM work because that gives you the bigger HP numbers for marketing and, at speed it gives you passing power. Also I am only talking about low RPM torque. I can take two otherwise identical engines and tune one to have both higher HP and torque but both may be higher in the rev range. Nissan did this with the G35. The earlier cars had ~365hp. The later cars had ~290. However, Nissan simply retuned the motor for higher RPM operation. The motor lost torque in the lower revs where you would commonly use it. While the numbers looked better, the actual acceleration numbers were basically unchanged. Sorry, that was probably a bit to off topic.

[culver]

Ah. A distinction that was not apparently apparent to me. So in a scenario of what is the absolute fastest, a OHC setup is superior to OHV, probably due to power being (roughly) proportional to rpm.

In road engines however, I am not sure what is necessarily better.

Are OHV engines necessarily better for torque?

No, they are not inherently better. Traditionally in US cars a pushrod motor and OHC motor of equal hp will have different displacement. The larger displacement pushrod motor would oddly enough have more torque.

However, given equal displacement and design intent, there is no reason a DOHC motor can't have just as much torque.

However, it is likely the designers of OHV motors are more likely to tune the motor for low end torque as a 2 valve head is actually well suited for low end work but not as well suited for high RPM work. A 4 valve head can be tuned for low end work but oddly enough many 4 valve motors actually cut air flow to one of the valves (or in Honda's case don't open the valve) at low RPM. I'll spare you the details. In any case, it is likely the designer of a 2 valve head will tune for lower RPM work because the 2 valve head isn't a disadvantage at low RPM. A 4 valve head is more likely to be tuned for higher RPM work because that gives you the bigger HP numbers for marketing and, at speed it gives you passing power. Also I am only talking about low RPM torque. I can take two otherwise identical engines and tune one to have both higher HP and torque but both may be higher in the rev range. Nissan did this with the G35. The earlier cars had ~365hp. The later cars had ~290. However, Nissan simply retuned the motor for higher RPM operation. The motor lost torque in the lower revs where you would commonly use it. While the numbers looked better, the actual acceleration numbers were basically unchanged. Sorry, that was probably a bit to off topic.

[Cyco]

Ah, yes I forgot about BMW's little theory.
Why not just turbo the I6 like in the 335i though?

Because they already had the 335i, and Motorsport's preference for naturally aspirated engines...

LMFAO... I don't know whats more funny. The fact that you believe a survey like that, or the fact that you believe that BMW owners were truthful on the survey.

The survey did, not set out to draw that conclusion, the car ownership was incidental to the rest of the survey. There where other breakdowns against postcode, age and income etc.

Why would you believe BMW driver to be less truthful than drivers of other cars, or people making more or less income, or in different postcodes?

[hightower99]

Are OHV engines necessarily better for torque?

No they are not in fact if you look at the numbers, OHV engines produce less specific torque then DOHC engines.

At low RPM 2VPC designs have enough valve circumference to allow enough mass flow while maintaining velocity enough to keep VE up. However because OHV engines like the LS7 are designed to run up to a relatively high redline the intake ports, cam design, and manifold design are optimised to help achieve the massflow necessary to keep VE up at high RPM, which means that the velocity advantage of having restricted intake circumference does not exist.

DOHC 4VPC designs can (and are) optimised over the majority of the rev range. Having a large intake circumference is not a disadvantage at low RPM because the cam characteristics are easily changed (like with BMW's Valvetronic system) to allow the system to maintain proper velocity to keep VE up at low RPM. At high RPM 4VPC allows greater massflow, which allows higher RPM which means more power.

Just look at the LS7, it is a torque monster only because of its huge displacement. It only scrapes up 67.75lbs-ft. per L displacement. Compare that to what almost everyone thinks is a torque weakling the E90 M3's S65 that makes 73.77lbs-ft. per L displacement. If it was like the LS7 it would only put out 271lbs-ft. of peak torque.... On top of that the S65 has a much better torque curve. All of that goes to show that DOHC has significant performance advantages.