DualSportr

Member
Aug 22, 2000
527
0
After spending a few hours perusing the forums (hey, I've been gone for awhile, I had to get my dirtrider.net fix!), I noticed one thing in common on many threads in the Thumper section.

So many people are falling for the pipe advertisers horsepower claims! These numbers just make me furious when I see them in print. " 5 horsepower increase on your XR400 with our system!" What a load of hoey!

One thing to keep in mind when looking at horsepower claims on pipes. Many companies use the "___ increase in peak horsepower" number as their claim to fame. This means they look at the peak number with a stock bike, then the peak number with their modification installed.

This completely takes 99% of the power you're actually using out of the equation!!

The most honest way of showing increases is this:

Take horsepower readings at every 400-1,000 rpm. Then compare each number, and come up with a total percentage.

Here's an example:
RPM - Bike A HP - Bike B HP
4,000 - 17.82 - 14.62
4,400 - 20.52 - 0
5,060 - 26.20 - 28.64
5,700 - 33.93 - 33.24
3,620 - 40.74 - 39.22
6,900 - 43.56 - 43.56
7,580 - 45.70 - 46.15
8,200 - 45.54 - 47.52
8,800 - 44.25 - 47.44
9,400 - 41.13 - 45.69
10,100 - 0 - 41.43
10,750 - 0 - 0

(zeros show where that particular engine would not hold a load on a hydro-style dyno).

So, if we were comparing these bikes by peak numbers, we'd say that bike B has almost 2 hp more than bike A.

But if we add the numbers up, then figure an average: Bike A average = 29.94 hp. Bike B average = 28.79. In this case, Bike A has 1.15 hp MORE than bike B!

Anyway, my point is, you don't ride a bike at peak rpm all the time, in fact, you don't ride it there very much at all (unless you're flat tracking or running Paris to Dakkar). In the real world, the average gives you a much better idea of what that modification will do for you.

So, when you see pipe ads with claims of a 'five horsepower gain over stock!', it may be true at ONE rpm point. What about the rest of the time you're riding?

Oh, in case you're wondering, the bikes shown above are a YZF 426 with a 440 stroker (and other mods), and a stock CRF 450. I'm not telling you which is which. You can guess!
 
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BigBore

Member
Jun 16, 1999
693
0
Yup. Its ridiculous what some companies claim. I spoke to Big Gun when I was interested in purchasing a system for my XR600. They claimed an 8hp increase. Riiiiight. :silly:
 

DualSportr

Member
Aug 22, 2000
527
0
Cal, I won't hold it against you - especially since I've got a stable full of FMF, White Brothers, Pro Circuit, Supertrapp, Thumper, Powroll, PSI and assorted others :)
 
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