Quote:
Originally Posted by olddog
The peak Hp number only tells you how it will accelerate at full throttle, when the engine rpm is near where the peak Hp is reached. The torque curve over the usable rpm range tells you "the rest of the story."
A high strung small displacement SB that peaks 450 Hp at 7500 rpm is only making 315 lb-ft of torque. Its peak torque might be 375-400 down around 5000 rpm. Below 3000 rpm it might be below 200 and off idle could only be 75 torque. Such an engine would be no fun to try to drive normally on the street. The fact that the torque is all over the place, depending on rpm, you never know what to expect, when you mash it.
On the other hand, it is not hard to have a large displacement BB that also makes 450 HP but at 5500 rpm. It might have a peak torque of 550 at 4000 rpm. It could have about 450 off idle and climb to near 550 by 2000 rpm, with a flat line to 4000 rpm. Then slowly drop off until the peak Hp.
Even though both engines have 450 Hp, the difference between them is night and day. The BB with a flat torque range, will feel like it has twice the power, every where other than flat out. It will have so much more throttle response everywhere and pretty much the same response everywhere. It would be much more fun on the street. Yet when geared properly both engines pretty much run the same time in quarter mile.
So again, HP is not the question you should be asking.
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Exactly. Paraphrased, it's less about where and how high the HP and torque curves peak than it is about the 'area under the curve' - particularly for street use. A rich, fat torque curve will not only make it more fun on the street, but will often out-perform a higher HP engine that's 'peaky'.
That fat torque curve will also allow you to keep the revs down and, hopefully, keep from drawing unwanted attention from the local gendarmes - they really seem to come out of nowhere when the revs get much above 4,000 RPM.