RPM in relationship to Horsepower - Other Cars Forum

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RPM in relationship to Horsepower
Monday, February 11, 2008 5:29 AM
I was idly thinking the other day about the fact that most engines top out around 6000rpm, however if you screw around with the head design and make the whole thing rock solid you could probably rev it a lot higher. The 2.4 Ecotec, for example, makes 173hp at 6,200rpm. Well, what if you doubled the rpms and instead of 6,200 you made 13,000? Wouldn't it theoretically be able to make at least 346hp without turbocharging?

I realize that the calculation isn't that simple. Horsepower climbs in a curve, it's not a number you can just double if you double the rpms, but at the same time if you had enough flow and could feed it enough gas and air, it most certainly would pull a heck of a lot more than 173hp.

It's probably just air bubbles in my brain and I'm probably out to lunch. But I thought we could talk a little shop and amuse ourselves at trying to figure if it could be done, and if so, how.

Re: RPM in relationship to Horsepower
Monday, February 11, 2008 6:22 AM
I don't agree with you, some people might.

I think it comes down to a lot more then if I built it good enough and ran 13,000 rpms it'd make double power lol



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Re: RPM in relationship to Horsepower
Monday, February 11, 2008 6:34 AM
its not about makin the engine capable of 13000 its making the engine efficient at 13000. if you are doubling everything in the system it might not be the right mixt fo that high if a speed



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Re: RPM in relationship to Horsepower
Monday, February 11, 2008 6:52 AM
no, it depends of the tq its making at xxxxx rpm.



05 M6 YJ GTO 1 of 447 12.523@111.30
Re: RPM in relationship to Horsepower
Monday, February 11, 2008 6:57 AM
HP doesnt continusely build. It will drop off, you will start losing hp with the higher rpms. If you increased the airflow and actually built the engine to run higher rpms, it will work. But it wont be a double in hp, in a 4-cylinder atleast. Also remember that higher RPMs will decrease engine life.


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Re: RPM in relationship to Horsepower
Monday, February 11, 2008 8:07 AM
13000 RPM, You won't get you 2.4 eco to go that high. The stroke is too long. If you want high reving then you should go with the 2L 86 bore 86 stroke. Plus forged pisons and rods, a stanalone ecu, and some rediculous cam profiles and something to make let it breath. With about $15,000 into the engine you might get a 2.0L eco to 9500 rpms without throwing a rod every 200kms, but it won't run on gasoline, it will idle like a bucket of bolts and be gutless below 5000 RPM.

Conclusion: This is why god made turbos for street cars. Fo under 5K you can get you 300+ hp 4 banger, that you can still drive daily. So stop being a NA pansy and get on the FI train.




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Re: RPM in relationship to Horsepower
Monday, February 11, 2008 3:36 PM
HP is a mathematical calculation involving torque and units of time. If the torque curve was perfectly flat all the way up to 13000rpm, than the HP would climb in a straight line.

I think most engines top out around 6000rpm because in order to have an engine that has decent low end torque, they would have to sacrafice top end power.
Re: RPM in relationship to Horsepower
Monday, February 11, 2008 3:38 PM
HP is determined by how much torque an engine makes and how high an rpm peak torque is made at. The problem with your theory is that an engine that makes however many hp at 13000 rpm NA is that the amount of cam overlap and compression required to make the torque necessary at high enough of an RPM makes it undriveable at lower RPMs. Which is why the OEMs don't do it that way. But you've got the basic idea right, which is that moving the torque and its peak higher in the rpms will make more horspower at a higher rpm. But the hard part of that is building an engine capable of that.




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Re: RPM in relationship to Horsepower
Monday, February 11, 2008 8:21 PM
Actually, HP= (TQ x RPM)/(5252)

Building an engine capable of that isn't that hard, just making a larger displacement one is. If you look at motorcycles. Liter bikes tend to rev to about 10k while their 600cc brothers tend to rev to the 14k+range.



05 M6 YJ GTO 1 of 447 12.523@111.30
Re: RPM in relationship to Horsepower
Tuesday, February 12, 2008 5:28 AM
Early S2000's did what, 10k RPM? They made a TON of HP, but what is the one problem everybody has with them? No torque.
High-revving works great for sport bikes because there isn't any weight to accelerate, but in a passenger car, it's just no fun.




fortune cookie say: better a delay than a disaster
Re: RPM in relationship to Horsepower
Tuesday, February 12, 2008 8:41 AM
I agree that any engine that revs like a mother will have little torque. However it's the too small displacement size that's really the problem. Torque is more or less the result of engine size, that's why the 8.1 Vortec engine in big trucks makes more torque than the 2.2 Ecotec The trick is to get an engine that's around 3 liters but, at the same time, make sure that the cylinder size is very small. Like a 3 liter V12 or the Hartley H1 2.8 liter V8. The smaller the individual pistols, the harder you can rev that sucker and if you can supply it with enough air and fuel you can make power wayyyyyyyy high, while still making some decent torque.

Obviously this sort of engine wouldn't work very well in a small car, but if you had it in a 2500lbs or less vehicule; you could make it go like a bull that go twapped in the nuts.

A 1966 Ferrari 275 GTB weighed 2500lbs and had a 3.3 liter V12. I think that with modern technology we should be able to improve on that.

Re: RPM in relationship to Horsepower
Tuesday, February 12, 2008 9:18 PM
Quote:

It's probably just air bubbles in my brain and I'm probably out to lunch.

I'm gonna go with this theory...















and what everyone else said.
Re: RPM in relationship to Horsepower
Tuesday, February 12, 2008 9:39 PM
Ya you need to be able to get enough air into the cylinder when you're going at 13,000 RPMs, in which case you'd get wicked valve overlap with nasty reversion/scavenging and possibly not getting all the exhaust gases out resulting in crap charge for your next cycle. As your RPM climbs, your volumetric efficiency (mass of fresh mixture taken into the
cylinder during a normal intake process) tanks, and then so does your HP and Torque. It's all about finding the sweet spot of the engine.
Then again if you did a bunch of head work, turboed it, aggressive cams (that would murder low rpm operation) and all the stuff all these guys on this site do. you could get close to the rpm (13000 is a bit high), but the power and torque wouldn't double...I don't think.

Please correct me if I'm misinforming anyone, I think I've got it right.
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