Originally posted by: SandmanBlue
First, as a mechanical engineer, I would wonder what you are actually looking to do with these numbers. Peak hp or torque of an engine do not tell you very much other than one small piece of information. As an example – the peak hp and torque of a STOCK Banshee and a Raptor 660 are about the same (I won’t discuss the Raptor 350 because it’s not in the same league). Banshee’s peak hp is about 38 and the Raptor’s is about 37, peak torque is also similar – Banshee is about 30 lb-ft and the Raptor is about 31 lb-ft. If you go to Glamis and hill race, you will see that these two quads are pretty equal (I’ve owned both).

The biggest difference is that the Banshee only makes over 25 lb-ft of torque between 6000 and 7200 rpm, which is a very narrow range. The Raptor makes better than 25 lb-ft between 2500 and 7200 rpm. That’s the advantage of the big bore thumper – it can accelerate the atv over a wide rpm range, which means less shifting. You can feel this when you crack open the throttle at low rpm – the Raptor pulls really hard and keeps on pulling, while the Banshee bogs until you come on the pipe and then gives a quick rush of acceleration, then falls off quickly.

But that was stock – if you build either engine to about 50 hp, the differences are dramatic. A 50 hp Banshee will never make over 35 lb-ft of torque, and the rpm range is still very narrow. On the other hand, the 660 will make over 35 lb-ft torque from 2500 to 7000 rpm and will have a peak of about 43 lb-ft.

Remember, torque is acceleration. It is the measure of how much twist the engine puts on the rear axle. Horsepower is derived from torque. HP = Torque x 5252/RPM. HP is better explained as the top speed of your quad (especially noticeable when going up a hill), torque is just how fast you get to that speed.

Lastly, there is one major complication – gearing. The lower the gearing, the more torque you apply to the ground and the faster you accelerate. It won’t make you go any faster up the hill (your top speed won’t change), but you will get to that speed quicker.