03 cobra question

[01L2Cobra]

HP per liter is very important on DOHC engines. None of those cars are intended to hit their power band at low RPMs where torque is most effective. In fact DOHC engines are not low end torque friendly at all instead they are intended to scream at high RPMs where HP is more effective. Even the non SC Cobras have bad low end Tq. Hell the 01 Cobras don’t hit their power band till 3K RPM. This is why hp per liter is so important on DOHC engines.

[BlackGT2000]

I don't see how that proves that HP per liter means anything. I do agree with what you said but it made no connection between displacement and horsepower. You made a better point about DOHC though.

[01L2Cobra]

The point of HP per liter on DOHC engines goes to show you just how well powered they are no matter what their displacement. As I stated above HP is the most important thing on DOHC as they typically do their best work in the upper RPMs. This is why the more Hp you have per liter the better the engine.

The rule of thumb I like to go by is anything 100hp or more per liter is over achieving, anything 90+hp per liter is great, and anything less is underpowered for its size. Just remember that typically the larger the displacement the larger and there for heavier the engine is. An example of this is shown between the BMW S54 (E46 M3) and the Ford 2001 Cobra 4.6 DOHC. The BMW S54 is over achieving with its 104.06hp per liter the Ford 4.6 DOHC is dramatically underpowered with its 69.27hp per liter.

[TheStang00]

^^ you still arent proving hp/liter is important. you do make a good point about dohc engines though. but torque still does matter a lot even in dohc applications, your powerband doesnt start till 3k right, well i know you max hp isnt at 3k, that tq is what lets you have high power in the lower rpms (3k to whatever your max is) so its definatly important. tq = ability to do work, so more tq = more power throughout rpm range because it has more ability to do the work at lower rpms, where things arent spinning as fast.

if a dohc engine is compact and light weight, but only makes 62hp/liter (i know the 4.6 isnt im not talking about it, just in general) then it is still a good engine. just like the ls series from gm except those arent dohc

[01L2Cobra]

Actually max torque in my 01 is reached at 4700RPM while max hp is achieved near redline at which point the tq is near what it was initially. Tq does affect the low end performance of the DOHC but this is no where near where they perform at their best. It is the areas above the max Tq where HP really matters and where the DOHC engines run at their best.

[BlackGT2000]

You are bringing up awesome points, all factual, but still hp/liter really means nothing, if you eliminate the weight factor than it has no bearing at all. Ls1 being a good example already used I am sure weighs around the weight of the ironblock E46 M3 motor, who knows maybe less you would likely know better than I do. It produces around what the M3 does in HP but still has much more displacement. I don't think that makes it a worse motor at all.

[01L2Cobra]

The LS1 is 400-425 lbs again much heavier than the 326lb BMW S54

Even if you were to over look the weight factor it still shows that a much smaller engine is producing the same or more power levels than a larger engine. And this is where when you look at Hp to L it shows you just how under powered it is.

[BlackGT2000]

So wouldn't it be more accurate to say that HP to weight is what counts not HP/liter?

[01L2Cobra]

No they both have their place.


Ok let me rephrase everything about HP to Liter what it does is show just how efficiently an engine works.

For the Ford 4.6DOHC to produce 104.06hp per liter same as the BMW S54 it would need to make 478.68 hp.

For the BMW S54 to produce 69.27hp per liter same as the Ford 4.6DOHC it would to make 221.66hp.

Again as I said before this just goes to show how underpowered the Ford 4.6DOHC really is.

[TheStang00]

i think your opinion of underpowered is just different really. and theres nothing wrong with that.

another point, how much more potential does that M3 engine really have still being N/A. now how much potential does say an ls1 have... tons. infact theres a member on here named mr. luos who just built one and its should be close if not past 100hp/liter.

about the torque, maybe i phrased it wrong idk, but i think we both know the importance it plays. i think we are on the same page there. what i was trying to say was that having a lot of torque means you can make more horsepower, in the rpms below your max horsepower. i still dont know if that makes sense

[BlackGT2000]

I am understanding the math of it totally and I can see how it would add up to efficiency, but what really matters is the end output of the motor. I mean an Ls7 is 7 liters and the Bmw M3 is 3.3 right....well the LS7 is putting out 530 about and the M3's motor is putting out 330...clearly the M3's is more Hp per liter but that really dosn't matter when it comes to reality. Sure the Ls7 weighs more I am sure, and that can matter, but I really fail to see how the efficiency matters when it comes to total output.

[01L2Cobra]

Well if you just want to see total out put from a smaller displacement engine eclipsing the power of the LS7 then I can do that but we are looking at the wrong BMW engine. The BMW S70/2 (McLaren F1 engine) is what we should be looking at.

BMW S70/2
Weight: 585lbs
Displacement: 6.1 liter
HP: 627

That’s 101.31hp per liter or 1.07hp per pound

LS7
Weight: ?
Displacement: 7.0 liter
HP: 500

That’s 71.43hp per liter

This LS7 and S70/2 comparison just goes to show that displacement is not the answer when the engine is not efficiently producing power.

[BlackGT2000]

Yeah I see that it does have more horsepower per liter... but I don't have any clue why that is significant. I mean the LS7 is producing more power per cam, but that dosn't mean crap either.

[TheStang00]

ls7 weighs 458 lbs, which is considerably less. if you calculate the hp per lb with the factory rating of 505hp, then it comes out to 1.10 hp per lb. so in the end, the ls7 is still more efficient in that sense. but it still makes sense to me that since the ls7 still isnt making as much hp/liter that it would still be easier to increase it through modding.

[01L2Cobra]

It is significant because it shows that the smaller engine is capable of producing power more efficiently. In fact it is producing an additional 29.88hp per liter. You have to ask why is the LS7 working less efficiently. What needs to be done to fix this problem? Why is the manufacturer unable or unwilling to spend the money to fix this problem?