| Author | Message | ||
     Midknyte |
IL4's have a reputation for non-liner power delivery - a spike in power in the upper revs. Why do they do that? | ||
| Firemanjim |
Not really,the big bore bikes--GSXR 1000 and Hayabusa,CBR 954,etc--deliver power all over the place.Just that a IL4 feels different than a v-twin.The little bikes--600's might be a bit peaky,though. | ||
| Lovematt |
It has to do with the Cams used, the timing of those cams, and air intake characteristics (small or large diameter inlets), and the bore/stroke of the motor. This combination (along with a few other things) give the motor its characteristics. Usually IL4s are short stroke motors which means they like to rev...air flow can be optimized at higher revs along with the Cam profiles and timing. All of this can add up to a motor that takes off on its own. Add a turbo and it can be even more non-linear. Cars are the same way...I have driven the same car where one time there was a "revving" cam and the power was a bit low off idle but it would launch by itself around 3000-4000 RPMs without changing the throttle input. The way the cams and air inlets worked best was at higher air flows (big inlets and cams with large lift short duration) . It was kind of wierd...giving the car the same amount of gas and it was accelerating harder and harder by itself. Then I drove the same car with a "torque" cam in it and there was good power down low but it topped out at about 5000 RPM (this time the car had small inlets and cams with lower lift and longer duration). | ||
| Chasespeed |
Actually, as far as cam profiles go...thelonger the duration, the higher up in the rev-range teh power is gonna want to be made. All this actually has to do with, intake manifold runner length, intake port cross section, length, etc... BUT, nice long runners, and a high lift, long duration cam...up high power.. those are teh cams that create the lopy, rumpety idle you hear..., teh duration is so long, that is a little valve overlap, and at low speeds, it all but kills vaccuum. Lobe seperation Angle is a factor too... Chase | ||
| Josh_ |
Hmmm, mine seems to be pretty linear with 80+ft/lbs from 3500-8000RPM ...  (note image is from Dale Walker/Holeshot showing the benefits of his mufflers vs a stock bike) | ||
| Lovematt |
I keep mixing that up! That is correct about the longer duration...allows more air through since the valves are open longer....and open farther. I stand corrected. | ||
| Chasespeed |
No worries bro...I wasnt trying to correct YOU, just to make sure the correct info is out there... The truth is, I could have gotten ALOT more in-depth, but, decided that was enogh for people to chew on.. Chase |
