I think I'm going to buy a Corvette

[yottabit]

GM and Chrysler have been able to match pretty much every DOHC engine with their pushrod equivalents and typically put out more torque. Just look at how simple the LS9 is and puts out 638hp without variable timing or direct injection.

Uh, I'm on your side but that's a pretty bad example since it's supercharged :/

 

[yottabit]

Really the only metric they suffer in would be HP/L, but.... What value exactly is that metric? It doesn't mean much of anything to me.

You're right, much more important honestly is HP compared to the size/weight of the motor

LSx motors are such a light compact package that it's pretty beautiful. Light enough to sub in for a turbo rotary, or turbo 4, etc without significantly throwing off weight distribution.

 

[Arkaign]

Really the only metric they suffer in would be HP/L, but.... What value exactly is that metric? It doesn't mean much of anything to me.

Yeah. I once was amazed at small motors and seemingly epic amounts of HP/L, but the more I looked into it, there are a lot of times this is kind of misleading. A great example is the Mazda Rotary in the RX-8. It's about the same size/weight as the LS2, even though it's measured internal displacement is very small. IIRC most of the DOHC V6 motors are just as big and heavy as well, if not heavier. A great example is the VG30DETT, which is close to 700lbs. A fully dressed LS1 is around 430, and the LS2 about the same.

All in all, I have an affinity for both types, they just produce vastly different sound and feel. It's good for us car guys that so many different types exist. I personally hated the rotary for a variety of reasons, but am still a little sad to see it go.

 

[Arkaign]

But it would seem that a DOHC engine is much better at moving air/fuel through itself, which is what an engine does

I think the air/fuel rate is determined more by the valves and fuel delivery system than location of the cams. Similarly, fewer but larger/more efficient valves may produce a similar effect to more/smaller valves in some applications. You can kind of eke this out by comparing the end results of things.

The S85 5.0 V10 in the E60 M5 was an incredibly complex motor, which ended up producing 500hp and 380tq, with a very high redline. Compare the fuel economy and powerband to the LS7 in the contemporary Z06, and you also got 505hp/470tq, with similar or slightly better fuel economy. It didn't rev as high, but that's just a question of gearing the car correctly was for, and top speed of a Z06 was in the same neighborhood as M5. Not an ideal comparison as the M5 is just a heavier vehicle, but it does show very different paths to similar end results.

I'm personally really glad that pushrods aren't the only option out there, but it's also really cool to see just how well even old tech can be extremely updated and tuned to produce an amazing amount of power and efficiency given the size and weight of the motor, while still having great durability and ease of working on them.

 

[exdeath]

All in all, I have an affinity for both types, they just produce vastly different sound and feel. It's good for us car guys that so many different types exist. I personally hated the rotary for a variety of reasons, but am still a little sad to see it go.

Well said. I'd rock a 20b RX7 FD no matter how much rotory sucks, just because. I'm a bit of a purist that way, and honestly I'm tired of going to car shows and seeing a stock TPI or LS1 in EVERYTHING. It's the same with all the TV shows: nobody builds motors, just throw a 350 crate motor in it in 5 minutes and spend the rest of the show installing custom fiberglass and LCD TVs and underglows and ugly 22" Foose wheels. Boring.

 

[nicolaskl]

Just look at how simple the LS9 is and puts out 638hp without variable timing or direct injection.

And look how it makes less power and gets significantly worse gas mileage than Fords 5.8, despite being in a car that's far lighter and more aerodynamic.

And I'll take the Boss 302 over the LS3 every single day and twice on Sundays.

 

[KentState]

And look how it makes less power and gets significantly worse gas mileage than Fords 5.8, despite being in a car that's far lighter and more aerodynamic.

And I'll take the Boss 302 over the LS3 every single day and twice on Sundays.

The power difference between the LS9/Ford 5.8 and LS3/Coyote 5.0 are close enough going about it two different ways. Both of the pushrods hit the market at least 5 years ago so it's not surprising that Ford makes 20-30 more HP albeit less torque in both applications.

As far as gas mileage, the difference is not that significant. 15/24mpg vs 14/21mpg which is heavily influenced by gearing. Though who really cares when you are dealing with over 600hp.

Personally, I'd take a LS7 in the Z06 over any of them.

 

[exdeath]

LS7 is too limiting with its thin cylinder walls. Better off with a LS3 or an aftermarket 427 block for big power.

 

[Elfear]

And look how it makes less power and gets significantly worse gas mileage than Fords 5.8, despite being in a car that's far lighter and more aerodynamic.

If you're talking about the supercharged 5.8L in the '13 GT500, it gets 15/24 mpg according to Edmunds and the ZR1 Vette gets 14/21 mpg. IMO, that's not significantly worse. Better highway mileage probably has a lot to do with gearing since the GT500 has a pretty high gear ratio (numerically low).

And I'll take the Boss 302 over the LS3 every single day and twice on Sundays.

The Boss 302 is a sweet engine but it's not the fairest comparison as one costs $11k and the other is $6.5k. For what they are the LS-series family are excellent engines with a huge aftermarket following. For that reason alone I'd rather have the LS3.

Edit: KentState beat me to it.

 

[AdamK47]

Personally, I'd get the LS3 vette, stroke it to 418 with dish pistons, and then add forced induction. That's just me though.

 

[KentState]

Personally, I'd get the LS3 vette, stroke it to 418 with dish pistons, and then add forced induction. That's just me though.

I'm hoping GM goes turbo for the next LSx engines. Improved power output and mileage with the same levels of boost. I would imagine that the LS9 loses at least 150hp to run the blower. Meaning the engine has to be strong enough for 800hp with only 640 getting to the flywheel. The same applies to the GT500 as well.

 

[nicolaskl]

The power difference between the LS9/Ford 5.8 and LS3/Coyote 5.0 are close enough going about it two different ways. Both of the pushrods hit the market at least 5 years ago so it's not surprising that Ford makes 20-30 more HP albeit less torque in both applications.

As far as gas mileage, the difference is not that significant. 15/24mpg vs 14/21mpg which is heavily influenced by gearing. Though who really cares when you are dealing with over 600hp.

Personally, I'd take a LS7 in the Z06 over any of them.

It's significant enough for the GT500 to avoid the GGT, and the fact that the GT500 gets better mileage in town despite being MUCH heavier and better highway despite having way worse aero can't all be attributed to gearing. The 12 GT500 beats the ZR1 also, and it has 3.73s.

 

[Throckmorton]

I think the air/fuel rate is determined more by the valves and fuel delivery system than location of the cams. Similarly, fewer but larger/more efficient valves may produce a similar effect to more/smaller valves in some applications. You can kind of eke this out by comparing the end results of things.

The S85 5.0 V10 in the E60 M5 was an incredibly complex motor, which ended up producing 500hp and 380tq, with a very high redline. Compare the fuel economy and powerband to the LS7 in the contemporary Z06, and you also got 505hp/470tq, with similar or slightly better fuel economy. It didn't rev as high, but that's just a question of gearing the car correctly was for, and top speed of a Z06 was in the same neighborhood as M5. Not an ideal comparison as the M5 is just a heavier vehicle, but it does show very different paths to similar end results.

I'm personally really glad that pushrods aren't the only option out there, but it's also really cool to see just how well even old tech can be extremely updated and tuned to produce an amazing amount of power and efficiency given the size and weight of the motor, while still having great durability and ease of working on them.

Well that's the point, with DOHC you can get more valve cross section onto the same diameter cylinders right?

HP/L does matter, because it measures how much power you're making per unit of air-fuel right? Or does an engine at full throttle not reach 1atm pressure on intake stroke? If an 5.7L OHV and a 5.0L DOHC engine are both sucking in the same amount of air to make the same amount of power, the higher displacement of the OHV one is moot isn't it?

BTW is it true that OHV engines with their smaller valve openings are more efficient at low RPM? If so, why?

 

[exdeath]

Charge momentum and port velocity. Large displacement + less valve area = high velocity intake charge at low RPMs = greater cylinder filling and volumetric efficiency at low to mid range. Charge momentum at any RPM is important for complete cylinder filling (and thus maximum boom), because the intake stream continues to "ram charge" under it's own momentum and fill the cylinder even at the start of the compression stroke. Momentum is M x V. We can't change the mass of the air, but we can affect the velocity with head/intake design and cylinder volume/piston speed to port area ratio. Smaller runner/valve/port per given swept piston volume = fluid has to move faster to get the same volume of fluid through the smaller opening = gathers more momentum and continues flowing even after the intake stroke has ended. This is why pushrod OHV engines have such great low RPM response, where less valve area promotes higher velocity at the lower and mid RPMs where peak airflow CFM isn't the limiting factor.

Higher RPM is less efficient in OHV in most cases, since the port/valve restriction on a OHV engine causes a "vacuum lock" situation where the piston is working hard in suction and canceling out it's power contribution past redline. But as you said, if a 5.7 OHV and 5.0 OHC are pulling in the same air mass and making the same power, it doesn't matter. That's why HP/L doesn't matter. The displacement of the engine isn't necessarily the volume of air being used. At high RPM the 5.7L OHV engine won't completely fill it's cylinders, so it's consuming similar air/fuel mass as the 5.0L OHC, while providing high intake velocity and more torque at low RPMs. At low RPM where the flow isn't a restriction, the 5.7 OHV will have .7L more air mass than the 5.0 OHC, possibly more due to the increased velocity (more than 100% VE), hence more torque.

Hence the characteristic pushrod engine torque curve with lots of instant low and mid range torque, which levels off and starts to dive bomb hard at a slightly lower redline than OHC where an OHC engine can rev higher before the "vacuum lock". What I mean by "vacuum lock" can be observed by pulling a plunger in a large syringe with a small inlet and observing the plunger. When you pull faster than the inlet can flow, it creates a vacuum that sucks the plunger back. This is a function of port/valve area (eg: the heads) and is why a dyno graph always shows power peak and then catastrophically plummets after redline/peak. Rev higher and you lose power because the heads can't flow anymore and you're using all your power to suck through a straw.

That said it doesn't really matter. Since the OHV engine will typically be higher displacement than a equivalent power OHC engine it will have larger bore diameter and have larger single valves compared to a small OHC engine with more smaller valves in a smaller bore.

Early OHC engines (eg Ford 4.6 circa 1996 and most others) had terrible low end due to TOO MUCH valve area. You could rev them to the moon and back, but intake velocity at low RPM was like hotdog in a hallway. No velocity at the low and mid range to promote charge momentum and cylinder filling. That's why many OHC engines in the 90s employed variable runner controls, etc. Now greater understanding of airflow and port and intake runner design has eliminated the need for that on modern OHC engines to give them low end comparable to a OHV. Likewise, advances in material physics and head design have allowed OHV engines to rev higher and have airflow comparable to OHC at the top end as well. You can find 2V OHV pushrod heads that have just as good CFM as any OHC head; OHV engine will just have to be higher displacement so the bigger bore allows for bigger valves.

So today, it really doesn't matter. There is nothing to be gained by bragging or arguing about making the same power as someone else with a bigger or smaller engine. Power is power. As long as you have moar, all is good. Let the final product and the dyno sheet do the talking.

 

[Ferzerp]

I really don't feel my engine is lessened by having one intake and one exhaust valve per cylinder....

They're really effing big valves


Let's argue about who has the most spark plugs though? That sounds fun.

 

[KentState]

snip...

Nice summary. The biggest differentiation right now is the car the engine is put in. A new Camaro would suck regardless of having an LS3 or Coyote because of the other issues.

 

[Arkaign]

exD does say it well, and with a greater understanding than I have. It goes without saying that I was once highly impressed with very large HP/L numbers, but when taken into consideration with actual motor size and weight, along with fuel economy and reliablity, it's kind of a meaningless metric in and of itself.

A great example is perhaps this :

2008 Honda S2000. F22C 2.2L (actually about 2.15L), 237HP, 162TQ, 18/25 Fuel Economy.

2008 Chevy Vette. LS3 6.2L, 438HP, 428TQ, 16/26 Fuel Economy.

It's worth noting that for both the S2000 and the Vette, the actual motor size and weight are very similar, the vehicle weight is similar, and both seem to do better than mfg ratings for actual highway fuel economy (EPA rules are insane about testing "highway" fuel economy, the tests include lots of deceleration/acceleration that more closely resemble driving on a highway through a partially congested metropolis than open interstate).

So, the S2000 beats the Vette on "HP/L", but most definitely loses in terms of how much HP/lb or HP/physical size of motor is achieved. And that's fair enough, the S2000 was never really a Vette rival, Honda probably could have put something out in the 400+Hp range for $50k+ if they had truly chased that goal, but the S2K was a mid $30s car.

 

[Arkaign]

Nice summary. The biggest differentiation right now is the car the engine is put in. A new Camaro would suck regardless of having an LS3 or Coyote because of the other issues.

Hahah yeah. The new Mustang would still kick ass with an LS3, the new Camaro would still be a fat pig either way.

 

[Throckmorton]

Charge momentum and port velocity. Large displacement + less valve area = high velocity intake charge at low RPMs = greater cylinder filling and volumetric efficiency at low to mid range. Charge momentum at any RPM is important for complete cylinder filling (and thus maximum boom), because the intake stream continues to "ram charge" under it's own momentum and fill the cylinder even at the start of the compression stroke. Momentum is M x V. We can't change the mass of the air, but we can affect the velocity with head/intake design and cylinder volume/piston speed to port area ratio. Smaller runner/valve/port per given swept piston volume = fluid has to move faster to get the same volume of fluid through the smaller opening = gathers more momentum and continues flowing even after the intake stroke has ended. This is why pushrod OHV engines have such great low RPM response, where less valve area promotes higher velocity at the lower and mid RPMs where peak airflow CFM isn't the limiting factor.

Higher RPM is less efficient in OHV in most cases, since the port/valve restriction on a OHV engine causes a "vacuum lock" situation where the piston is working hard in suction and canceling out it's power contribution past redline. But as you said, if a 5.7 OHV and 5.0 OHC are pulling in the same air mass and making the same power, it doesn't matter. That's why HP/L doesn't matter. The displacement of the engine isn't necessarily the volume of air being used. At high RPM the 5.7L OHV engine won't completely fill it's cylinders, so it's consuming similar air/fuel mass as the 5.0L OHC, while providing high intake velocity and more torque at low RPMs. At low RPM where the flow isn't a restriction, the 5.7 OHV will have .7L more air mass than the 5.0 OHC, possibly more due to the increased velocity (more than 100% VE), hence more torque.

Hence the characteristic pushrod engine torque curve with lots of instant low and mid range torque, which levels off and starts to dive bomb hard at a slightly lower redline than OHC where an OHC engine can rev higher before the "vacuum lock". What I mean by "vacuum lock" can be observed by pulling a plunger in a large syringe with a small inlet and observing the plunger. When you pull faster than the inlet can flow, it creates a vacuum that sucks the plunger back. This is a function of port/valve area (eg: the heads) and is why a dyno graph always shows power peak and then catastrophically plummets after redline/peak. Rev higher and you lose power because the heads can't flow anymore and you're using all your power to suck through a straw.

That said it doesn't really matter. Since the OHV engine will typically be higher displacement than a equivalent power OHC engine it will have larger bore diameter and have larger single valves compared to a small OHC engine with more smaller valves in a smaller bore.

Early OHC engines (eg Ford 4.6 circa 1996 and most others) had terrible low end due to TOO MUCH valve area. You could rev them to the moon and back, but intake velocity at low RPM was like hotdog in a hallway. No velocity at the low and mid range to promote charge momentum and cylinder filling. That's why many OHC engines in the 90s employed variable runner controls, etc. Now greater understanding of airflow and port and intake runner design has eliminated the need for that on modern OHC engines to give them low end comparable to a OHV. Likewise, advances in material physics and head design have allowed OHV engines to rev higher and have airflow comparable to OHC at the top end as well. You can find 2V OHV pushrod heads that have just as good CFM as any OHC head; OHV engine will just have to be higher displacement so the bigger bore allows for bigger valves.

So today, it really doesn't matter.

Interesting, never knew about charge momentum

 

[manimal]

Charge momentum and port velocity. Large displacement + less valve area = high velocity intake charge at low RPMs = greater cylinder filling and volumetric efficiency at low to mid range. Charge momentum at any RPM is important for complete cylinder filling (and thus maximum boom), because the intake stream continues to "ram charge" under it's own momentum and fill the cylinder even at the start of the compression stroke. Momentum is M x V. We can't change the mass of the air, but we can affect the velocity with head/intake design and cylinder volume/piston speed to port area ratio. Smaller runner/valve/port per given swept piston volume = fluid has to move faster to get the same volume of fluid through the smaller opening = gathers more momentum and continues flowing even after the intake stroke has ended. This is why pushrod OHV engines have such great low RPM response, where less valve area promotes higher velocity at the lower and mid RPMs where peak airflow CFM isn't the limiting factor.

Higher RPM is less efficient in OHV in most cases, since the port/valve restriction on a OHV engine causes a "vacuum lock" situation where the piston is working hard in suction and canceling out it's power contribution past redline. But as you said, if a 5.7 OHV and 5.0 OHC are pulling in the same air mass and making the same power, it doesn't matter. That's why HP/L doesn't matter. The displacement of the engine isn't necessarily the volume of air being used. At high RPM the 5.7L OHV engine won't completely fill it's cylinders, so it's consuming similar air/fuel mass as the 5.0L OHC, while providing high intake velocity and more torque at low RPMs. At low RPM where the flow isn't a restriction, the 5.7 OHV will have .7L more air mass than the 5.0 OHC, possibly more due to the increased velocity (more than 100% VE), hence more torque.

Hence the characteristic pushrod engine torque curve with lots of instant low and mid range torque, which levels off and starts to dive bomb hard at a slightly lower redline than OHC where an OHC engine can rev higher before the "vacuum lock". What I mean by "vacuum lock" can be observed by pulling a plunger in a large syringe with a small inlet and observing the plunger. When you pull faster than the inlet can flow, it creates a vacuum that sucks the plunger back. This is a function of port/valve area (eg: the heads) and is why a dyno graph always shows power peak and then catastrophically plummets after redline/peak. Rev higher and you lose power because the heads can't flow anymore and you're using all your power to suck through a straw.

That said it doesn't really matter. Since the OHV engine will typically be higher displacement than a equivalent power OHC engine it will have larger bore diameter and have larger single valves compared to a small OHC engine with more smaller valves in a smaller bore.

Early OHC engines (eg Ford 4.6 circa 1996 and most others) had terrible low end due to TOO MUCH valve area. You could rev them to the moon and back, but intake velocity at low RPM was like hotdog in a hallway. No velocity at the low and mid range to promote charge momentum and cylinder filling. That's why many OHC engines in the 90s employed variable runner controls, etc. Now greater understanding of airflow and port and intake runner design has eliminated the need for that on modern OHC engines to give them low end comparable to a OHV. Likewise, advances in material physics and head design have allowed OHV engines to rev higher and have airflow comparable to OHC at the top end as well. You can find 2V OHV pushrod heads that have just as good CFM as any OHC head; OHV engine will just have to be higher displacement so the bigger bore allows for bigger valves.

So today, it really doesn't matter. There is nothing to be gained by bragging or arguing about making the same power as someone else with a bigger or smaller engine. Power is power. As long as you have moar, all is good. Let the final product and the dyno sheet do the talking.

give this man a beer!

great post

 

[exdeath]

Interesting, never knew about charge momentum

If you've ever wondered about "variable intakes" or "intake resonance" or "manifold runner controls" or "short vs long runners" and things like that, manipulating and maximizing charge velocity, and thus inertia, at all RPMs is what it's all about. You want the air in the plenum to build up speed in the runners and continue flowing for as long as possible, even when the intake stroke has finished, but at the same time need to not have an airflow restriction at high RPM. Everything from intake manifold, to head ports, size and number of values, and cylinder volume and piston speed has a role in this.