Originally Posted by williamluke
I always wondered about shortening the slipon. But I wanted to know if it has any adverse effects on performance?
Adverse affects on performance can very with how you actually mod the can. I just did this mod and without PCIII I lost power on my low and mid range. Top end seems to be, maybe, slightly better. Remember, this is not an engineered can, and if you start reading into back pressure and air/fuel mixtures, apart from a cheap decent sounding mod, this is very primitive to a two bros, yosh or leo slip-on.
With PCIII you can correct the changes in back pressure by altering the air/fuel mixtures. PCIII offers preloaded maps for different slip-ons so you will have to find one that gets close. A custom tune on the dyno will do this properly and is the best recommended option to properly adjust for any mods you do.
I have found with PCIII thus far - since I haven't been able to get dyno time, the Yoshi Slip-on with aftermarket or stock air filter pre-loaded PCIII map has been the best.
Bottom line, if you do cut the stock can down there are two things to consider performance wise. You don't want to run too lean of a fuel mixture because you could burn the exhaust valves and you most likely will lose some power on the low and mid range until you can get a custom tune.