When looking at gained power on a dyno chart, the peak power is only relevant if that is the only RPM you run at. In general, the total 'gained' power is the difference in _area_ under the power curves, not the difference at any given point. Of course, this isn't the number that the aftermarket manufacturers quote, because it has different units (it would be HP*RPM, not just HP). But my point is, a 1hp gain doesn't sound like much, but if it's a 1hp over the entire power curve, it is a noticeable gain.

Also, think of it this way. If there was a 1 hp gain over the entire rpm range, that only increases the peak power from 27 to 28hp, or roughly 3.8% gain, not very significant. But, in the midrange, say around 5000rpm, your power increased from 16 to 17hp, or a 6.25% gain, which is more significant. Plus, if you add 1hp with a pipe, 2hp with a 416 kit, 2hp with a cam, etc, it starts to add up. If you never bought any of those 1-2hp mods, you'd still have a stock bike, but if you buy them all, you've got a good 6-7hp gain over stock.

cstark

your confusing rear-wheel horspower with primary clutch horspower. the sp500ho does have 38hp but only 24hp at the rear wheels. the regular sp500 had 32hp and 18hp at the rear wheels. kinda makes the honda look like they have there engines turned down it terms of horspower. polaris gets lots more horsepower from there 500 than honda.

later
jon

I've seen the Dynojet graphs. They don't tell you the parameters of determination that result in the graph. They also come up with "SAE Corrected HP" vs Speed (MPH-not rpm)--what is that? They don't determine torque. I would like to see a graph of torque/HP vs engine speed (rpm).

I agree with you, TxDoc2; torque and horsepower, vs. rpm curves give a better picture of engine performance than quoting the peak values alone, or, plotted against "mph" (which gear?).

Knowing the torque at a given rpm, the horsepower developed at that point can be calculated by formula; however, the peak horsepower occurs at a higher rpm than the torque peak. With a torque vs. rpm curve, a corresponding horsepower vs. rpm curve can be constructed, and vice versa.

I still wonder: where does the horsepower figure printed on your Certificate of Origin come from?

Tree Farmer

HEY tree farmer. good explanation of Horspower. i never knew exaclty what HP was being a just turning 15

I beleive we are missing one factor here and that is the torque figures. You can have two identical displacement engines with different mods, but totally different output specs. One may be built for torque, one for higher RPM eg. truck/tractor pulls and deisel engines opposed to drag racers. I would like to see what the actual torque specs are for these ATV engines. To me it would be a better comparison for a Utlity user then HP. HP and TORQUE only increase together to a point. An engine built for high torque will show lower HP ratings, but will have more working power to climb, pull, and turn big tires then an engine built for HP.

For instance, I have been working on an old 440 magnum (car engine) to put in a old Power Wagon 4X4. Now, all the mods for a car are different then for a 4x4 truck. First, the advance curve, then the exhaust, cam, carburetion, etc. Adding big tube headers to this engine decreases the HP, but will increase the torque by over 100 ftlb, changing to a truck distributor with a different advance curve will also add to higher torque at lower RPM. At some point during the building of an engine to increase HP, the torque actually starts to decrease and visa versa. What I mean to say is, there is a balance point, as you increase the HP of an engine you will get to a point where you will actually see the torque start to drop off. TORQUE is the power to do work, that is what interests me.
Deisel engines for example show lower horsepower ratings ,but high torque figures ie. the earlier Cummings Deisel...160 HP... 425 ftlb. TORQUE, opposed to gas engines such as the Chrysler 426 Hemi...425 HP .... 425 ftlbs TORQUE.

Here's an interesting bit of motor head trivia; below 5252 rpm any engine's torque will be higher than its horsepower, above 5252 rpm any engine's horsepower will be higher than its torque.

Horsepower = torque x rpm / 5252


You decide....what's more important to you!

Anyone else have any input here, HP vs Torque.

Only arctic cat tells its customers how many hp their engines produce.irritating.
Little thing "funny", Voxan (a french motorbike company) gives you the dyno chart of the bike you buy.
I'd like to find a dyno near me.

Just found this little tid bit from Saleen Performance Techtalk:
It is said that; "Horsepower sells cars, but torque wins races." Could it be that torque is really the only 'motivational' factor here?

Torque accelerates.
Horsepower sustains speed against energy losses.

If your really interested you can check out this link.
Torque vs Horsepower

I think you got that backwards.. Horsepower accelerates, torque does work.

Motorhead
If you read the article in the link I provided you will see that torque accelerates and HP maintains. This is physics. Torque is a rotational "force" measured in ftlbs that starts a mass (automobile)moving. Something moving at a constant speed has no acceleration, hence needs no force.
Trying to accelerate after an engines RPM has past its peak torque or torque band will show little gain.