GM Building New DOHC V8

[Zenmervolt]

Originally posted by: Demon-Xanth
For reference:
Summit Racing P/N NAL-19156261 $6,426.39
GM LS2 (6.0L) crate engine, 400HP, weighs about 450LBs

Summit Racing P/N FMS-M-6007-M146 $6,229.95
Ford 4.6L DOHC crate engine, 305HP, weighs about 550LBs.
(2003 Mustang Mach 1)

Both V8s, both put in similar vehicles, both cost pretty close to the same price and come with the same equipment. Which would you rather have?

Which is what I said earlier. And what you repeated after I said it. And what hasn't been disputed by anyone so far in this thread. Why say it again?

ZV

 

[MercenaryForHire]

Originally posted by: Zenmervolt

Originally posted by: Demon-Xanth
For reference:
Summit Racing P/N NAL-19156261 $6,426.39
GM LS2 (6.0L) crate engine, 400HP, weighs about 450LBs

Summit Racing P/N FMS-M-6007-M146 $6,229.95
Ford 4.6L DOHC crate engine, 305HP, weighs about 550LBs.
(2003 Mustang Mach 1)

Both V8s, both put in similar vehicles, both cost pretty close to the same price and come with the same equipment. Which would you rather have?

Which is what I said earlier. And what you repeated after I said it. And what hasn't been disputed by anyone so far in this thread. Why say it again?

ZV

My guess is for reference.

- M4H

 

[Colt45]

What does this have to do with torque? OHC just means you'll be able to spin it faster.

 

[Howard]

Originally posted by: Zenmervolt

Originally posted by: fbrdphreak

Originally posted by: Howard
Maybe so, but why is that?

That's a great question, but one I can't personally explain.

Calling ZV?

In terms of HP/Litre, OHC wins. In terms of HP/lb, OHV wins pretty handily since OHV allows greater displacement per pound.
ZV

I think it would be more accurate to say that non-OHC OHV wins at power/mass/cost, but not necessarily at power/mass.

 

[Zenmervolt]

Originally posted by: MercenaryForHire
My guess is for reference.

- M4H

Why not just edit the previous posting? Would be more efficient. Besides, why bother with reference when there's no dispute?

ZV

 

[Zenmervolt]

Originally posted by: Howard

Originally posted by: Zenmervolt

Originally posted by: fbrdphreak

Originally posted by: Howard
Maybe so, but why is that?

That's a great question, but one I can't personally explain.

Calling ZV?

In terms of HP/Litre, OHC wins. In terms of HP/lb, OHV wins pretty handily since OHV allows greater displacement per pound.
ZV

I think it would be more accurate to say that non-OHC OHV wins at power/mass/cost, but not necessarily at power/mass.

"OHV" is universally recognized as referring to pushrod designs, so specifying "non-OHC OHV" is redundant (and slightly pedantic). Regardless of how it is referred to, OHV engines are indeed lighter and smaller (physically) than OHC engines barring the use of some very exotic materials in the OHC engine. Given identical materials, the OHV engine will be lighter.

Like everything, I am sure that there are a few exceptions, but it's nearly universal that OHV is lighter than OHC.

ZV

 

[Howard]

Originally posted by: Zenmervolt

Originally posted by: Howard

Originally posted by: Zenmervolt

Originally posted by: fbrdphreak

Originally posted by: Howard
Maybe so, but why is that?

That's a great question, but one I can't personally explain.

Calling ZV?

In terms of HP/Litre, OHC wins. In terms of HP/lb, OHV wins pretty handily since OHV allows greater displacement per pound.
ZV

I think it would be more accurate to say that non-OHC OHV wins at power/mass/cost, but not necessarily at power/mass.

"OHV" is universally recognized as referring to pushrod designs, so specifying "non-OHC OHV" is redundant (and slightly pedantic). Regardless of how it is referred to, OHV engines are indeed lighter and smaller (physically) than OHC engines barring the use of some very exotic materials in the OHC engine. Given identical materials, the OHV engine will be lighter.

Like everything, I am sure that there are a few exceptions, but it's nearly universal that OHV is lighter than OHC.

ZV

It's the exceptions I'm talking about. If you cap the max RPM of the two types, OHV is likely to have a higher HP/lb ratio, but if you maximize displacement while keeping mass constant (for the purpose of this comparison), as you increase the redline, OHC will eventually surpass OHV in HP/lb because OHV will crap out before OHC does.

That's why I said OHV is not necessarily superior at power/mass. Also, I wasn't sure that everybody knew that OHV meant pushrods, since OHC is OHV but OHV isn't always OHC, so I threw in the non-OHC part.

EDIT: I don't disagree that OHV is lighter than OHC for a given displacement.

 

[Zenmervolt]

Originally posted by: Howard
It's the exceptions I'm talking about. If you cap the max RPM of the two types, OHV is likely to have a higher HP/lb ratio, but if you maximize displacement while keeping mass constant (for the purpose of this comparison), as you increase the redline, OHC will eventually surpass OHV in HP/lb because OHV will crap out before OHC does.

That's why I said OHV is not necessarily superior at power/mass. Also, I wasn't sure that everybody knew that OHV meant pushrods, since OHC is OHV but OHV isn't always OHC, so I threw in the non-OHC part.

EDIT: I don't disagree that OHV is lighter than OHC for a given displacement.

FWIW, the Mercedes Ilmor 500I CART engines were pushrod designs and they ran 12,000+ RPM. Given a determined engineer, it's possible to design an OHV engine without flow issues at high RPM, and also to overcome the normal limitations of valvetrain mass.

By the time that redline was increased enough to raise the hp/lb of an OHC design sufficiently, the engine would be incredibly peaky and probably close to impossible to drive on the street.

For all practical purposes, the RPM limitations of a modern OHV design aren't going to come into play. However, the marketing benefits of OHC and the way that OHC allows engineers to more easily design the intake and exhaust ports tends to make OHC more popular. Also, in-line engines don't have a convenient location for an in-block camshaft like a vee engine does, so OHC is a natural choice for an inline engine.

ZV

 

[MercenaryForHire]

Originally posted by: Zenmervolt

Originally posted by: MercenaryForHire
My guess is for reference.

- M4H

Why not just edit the previous posting? Would be more efficient. Besides, why bother with reference when there's no dispute?

ZV

"Postcount++" perhaps?

Oh, and postcount++ for each of us for debating the worthiness of it.

- M4H

 

[fbrdphreak]

Originally posted by: MercenaryForHire

Originally posted by: Zenmervolt

Originally posted by: MercenaryForHire
My guess is for reference.

- M4H

Why not just edit the previous posting? Would be more efficient. Besides, why bother with reference when there's no dispute?

ZV

"Postcount++" perhaps?

Oh, and postcount++ for each of us for debating the worthiness of it.

- M4H

:thumbsup:




++

 

[Howard]

Originally posted by: fbrdphreak

Originally posted by: MercenaryForHire

Originally posted by: Zenmervolt

Originally posted by: MercenaryForHire
My guess is for reference.

- M4H

Why not just edit the previous posting? Would be more efficient. Besides, why bother with reference when there's no dispute?

ZV

"Postcount++" perhaps?

Oh, and postcount++ for each of us for debating the worthiness of it.

- M4H

:thumbsup:




++

What? I refuse to believe that we are all just neffing.

 

[fbrdphreak]

Originally posted by: Howard

Originally posted by: fbrdphreak

Originally posted by: MercenaryForHire

Originally posted by: Zenmervolt

Originally posted by: MercenaryForHire
My guess is for reference.

- M4H

Why not just edit the previous posting? Would be more efficient. Besides, why bother with reference when there's no dispute?

ZV

"Postcount++" perhaps?

Oh, and postcount++ for each of us for debating the worthiness of it.

- M4H

:thumbsup:




++

What? I refuse to believe that we are all just neffing.

I refuse your refusal








++

 

[Howard]

Originally posted by: fbrdphreak

Originally posted by: Howard

Originally posted by: fbrdphreak

Originally posted by: MercenaryForHire

Originally posted by: Zenmervolt

Originally posted by: MercenaryForHire
My guess is for reference.

- M4H

Why not just edit the previous posting? Would be more efficient. Besides, why bother with reference when there's no dispute?

ZV

"Postcount++" perhaps?

Oh, and postcount++ for each of us for debating the worthiness of it.

- M4H

:thumbsup:




++

What? I refuse to believe that we are all just neffing.

I refuse your refusal








++

touché

 

[Zenmervolt]

Originally posted by: MercenaryForHire

Originally posted by: Zenmervolt

Originally posted by: MercenaryForHire
My guess is for reference.

- M4H

Why not just edit the previous posting? Would be more efficient. Besides, why bother with reference when there's no dispute?

ZV

"Postcount++" perhaps?

Oh, and postcount++ for each of us for debating the worthiness of it.

- M4H

You figured it out! Damnit.

ZV

 

[RU482]

Originally posted by: sonoma1993
I could be wrong on this, but wasn't GM thinking about putting the northstar v8 into the Chevy corvette awhile back?

Actually, I think they were playing with the idea of a Caddy clone of the vette, and I think that had a northstar

 

[Ktulu]

Originally posted by: redly1

Originally posted by: sonoma1993
I could be wrong on this, but wasn't GM thinking about putting the northstar v8 into the Chevy corvette awhile back?

Actually, I think they were playing with the idea of a Caddy clone of the vette, and I think that had a northstar

Well isn't the XLR build on the Corvette platform minus the northstar V8.

 

[imported_Baloo]

Originally posted by: Toastedlightly

Originally posted by: Howard

Originally posted by: fbrdphreak
No more uber-low end torque

Why can you get lots of low-end torque with pushrods but not with OHC?

I'd assume you could muster more by having far better paths for your intake and exaust ports due to not having push rods in the way.

You clearly have never actually seen the internal setup of a push rod engine - overhead cams are a much bigger obstacle to get around than push rods. Push rods are not in any position where they are in the way of an intake or exhaust manifold - they are down inside the cylinder bank. But then, you just assumed. Bad assumption

 

[fbrdphreak]

Originally posted by: Ktulu

Originally posted by: redly1

Originally posted by: sonoma1993
I could be wrong on this, but wasn't GM thinking about putting the northstar v8 into the Chevy corvette awhile back?

Actually, I think they were playing with the idea of a Caddy clone of the vette, and I think that had a northstar

Well isn't the XLR build on the Corvette platform minus the northstar V8.

I dunno but the CTS-V is touted as Cadillac's Corvette. Same drivetrain, four doors.

 

[YBS1]

Originally posted by: fbrdphreak

Why? Their OHV offerings are already quite good, where else does it have left to go? Great power, great reliability, low cost, good mileage? Maybe for an all out performance engine to get more out of the displacement?

No more uber-low end torque [/quote]

The most direct answer is to better suit the luxury and/or near luxury segment of the market. As excellent as the LSx motors are, OHC engines are inherently "smoother" running and a better fit for that target market.

 

[YBS1]

Originally posted by: Ktulu
Well isn't the XLR build on the Corvette platform minus the northstar V8.

And yes, the XLR is built on the Corvette platform in Bowling Green.

 

[fbrdphreak]

bump for an interesting article!

 

[Apex]

Originally posted by: Zenmervolt

Originally posted by: fbrdphreak

Originally posted by: Howard
Maybe so, but why is that?

That's a great question, but one I can't personally explain.

Calling ZV?

OHC allows for easier optimization of high-RPM flow characteristics for intake and exhaust ports. along with less valvetrain mass and lower valvetrain inertia. These advantages combine to make OHC engines easier to optimize for high RPM performance.

OHV, with its higher valvetrain mass and inertia and more restrictive port design lends itself to lower RPM optimization.

Of course, these are generalizations and a determined engineer can make an OHC engine that has massive low-end torque, or an OHV engine that can scream at high RPM.

The big advantage of OHV is physical size. For example, Ford's DOHC 4.6 litre (281 CI) is physically larger than the old 5.0 litre (302 CI) OHV engine. The DOHC 4.6 is physically a very wide and tall engine, I believe that even an older OHV Ford 351/428 would not be physically larger than the DOHC 4.6. Of course, with size, assuming equal materials used, comes weight. So an OHV engine can be ligher overall (even though valvetrain mass is increased).

A 3.5 litre Nissan VQ engine is not significantly smaller than Chevrolet's small block, and the Chevy engine, in some trims, is actually lighter.

In terms of HP/Litre, OHC wins. In terms of HP/lb, OHV wins pretty handily since OHV allows greater displacement per pound.

This is another reason why OHV typically means more low-end. A larger engine will have more low-end torque. Since OHV allows larger displacement for a given physical size, it typically yields more low-end torque.

Assuming that everything except valve activation is the same, there should be negligible difference between an OHV and an OHC engine. It's just that the two lend themselves to different optimizations.

ZV

4.6L DOHC V8 vs 5.0L OHV V8

That's not as funny as this picture though:

Miata engine + tranny in front vs 5.7L Small Block Chevy engine + tranny in back

 

[exdeath]

Originally posted by: Howard

Originally posted by: fbrdphreak
No more uber-low end torque

Why can you get lots of low-end torque with pushrods but not with OHC?

It?s all about port velocity and cylinder filling.

OHC designs have a larger cross sectional valve area thus allowing more air flow at higher speeds which allows for more power on the top end. This isn't possible on OHV engines because it would be too complicated, if not impossible, to route 4 pushrods and rockers, etc, through the small space next to and above each cylinder. OHC engines are pointless without going more than 2v per cylinder, as you gain nothing but the disadvantages (weight, complexity, package size, etc). You also have a limit to how big you can make 2 valves and still be able to fit them in the cylinder without colliding and making them light enough to reciprocate fast enough. Thus OHC allows for higher quantity of smaller valves to increase the total valve area and allow for more horsepower at high RPMs.

On the low end, the large cross sectional area reduces gas flow velocity. Because the displacement of the cylinder is constant, the pressure/vaccum drawing air into the cylinder is constant. With constant pressure, you can vary the flow area to vary the velocity. When you put your finger in front of a garden hose you are increase the velocity by reducing the area; the mass flow rate and pressure remains the same.

High mixture velocity is necessary to efficiently fill the cylinder on the intake stroke by relying on mixture momentum and scavenging to pack as much mixture into the cylinder as possible when the engines pistons are not doing a good job of that on their own (i.e.: at the low end of the RPMs). With a OHV pushrod engine you have higher port velocity at low RPM, due to the smaller cross sectional area of less valves. What happens is there is momentum in the intake stream caused by the higher velocity, such that cylinder filling continues even as the piston has already stopped moving down. In fact the intake valve remains open and the cylinder continues to fill as the piston has already started to move up. This allows more mixture = more power. Port velocity is crucial to low end torque. However OHV engines typically cannot rev as high or make as much power on the top end as OHC engines due to the more restricted flow rate.

OHC engines with more than 2 valves per cylinder trade off this low RPM port velocity for high RPM breathing at the cost of low end torque to gain high end horsepower. Most OHC engines use variable intake runner systems that block half the intake ports below a certain RPM and open them at higher RPM to get both good low end torque and top end horsepower. The best of both worlds. Ideally, a OHC engine should produce more power on a smoother power band than a OHV engine, all other factors held constant. But engines like the LS7 prove that you can make *any* engine do whatever you want if you throw enough money, exotic materials, and engineering into it.

Better yet is forced induction (specifically a belt driven supercharger) on a 4v OHC design. You get the high flow rates at the top end, with the blower to take full advantage of the increase flow rate. But also at the low end of the scale, you have the blower pressurizing the intake, so that even with the larger cross section, as soon as those valves crack open the tiniest bit, the mixture rushes in at high velocity due to the supercharger forcing it.

Thats how my '03 Cobra is set up and it works wonders 4v OHC engines love superchargers.

 

[exdeath]

By the way, the only reason GM even makes the 32V DOHC Northstar is because people who buy Cadillacs demand 'more advanced' and 'exotic' technology. They don't need it, it's completely a psychological comfort for the consumers of that market segment.

Due to people being completely clueless about engines, some people think overhead cam multi valve engines are deemed as somehow automatically better and more advanced than pushrod engines in every way just because its 'newer' as far as they know.

If you ask me, a pushrod OHV 2V engine with torque on the bottom end is more suited to move these heavy luxary cars where the owners just want to push the gas and go and don't care about revving it to next Sunday. They aren't supposed to be sporty and high revving noisy air breathing monsters. It would also be in a smaller package and allow for more passenger or cargo space.

There are applications for both types of engines. For example, multi valve high revving free breathing DOHC 4v engines respond to forced induction much better than 2V pushrod engines, where the smaller ports that give high velocity in the low RPMs becomes a severe air flow restriction at high RPMs. Technically, that is true, but then again look at the top fuel dragsters running 40 psi boost with 14-71 blowers on 2V pushrod V8s making 8,000 HP... so who knows.

 

[freebee]

THe OHV vs OHC debate (as pointed out in several posts) is a marketing issue, not an engineering one. There are good applications for both designs, it is simply a matter of what the consumers demand in a particular model.

That said, GM engineers are stupid. Forget the extra torque, GM needs to learn how to make music from its engines. How many more people would buy a corvette if it sounded like an F430?