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No slip on=Burning you exhaust valves.? How?

3K views 10 replies 6 participants last post by  fieldarcher 
#1 ·
Ok so i hear alot of things about removing the slip on will not generate enough back pressure, they say it will fxck up yur valves? but how what exactly does it do to mess up the valves? im running a carbed bike how bad will it effect my bike?

This is just a question i was curious about i am not running my bike with no slip on BTW.
 
#2 ·
It will mess up the fueling for your bike, running without a can effectively turns the exhaust into a straight through drag pipe, which works fine when flat out, however in the real world, we don't tend to be flat out all the time, and the midrange performance will suffer, because of the reduction in back pressure altering the timing of the reflected pulses within the exhaust which messes up the scavenging pulses. This can lead to the motor running hotter and leaner which is what can cause damage to the valves and pistons. If you have the jetting sorted out to run with an open drag pipe then it will be fine, however the midrange will suffer, large open pipes are not designed for midrange gains purely wide open throttle.
All aftermarket systems like Yoshimura, Akrapovic, etc are designed to improve the midrange, to do this they need a certain amount of back pressure and length, this is why under engine stubby systems don't work well, and also the underseat conversions also don't tend to work as well, and can be difficult to set the carbs up. Bikes that have an underseat system from new are designed to work with it, and will usually have slightly different cam timing etc in order to run with an extra 18 inches or so of pipe in the mix.
 
#5 ·


I have put a baffle/ db killer. its slightly longer than the can, with a K&N a/filter and a dynojet kit, set up on a dyno it runs clean, at 119.6 bhp at the crank, pulls clean on the road.
Mustapha is dead right, without the baffle only ran well above 9k. Also to loud even for me and I'm foocking deaf.:thumbsup::LolLolLolLol:
 
#7 ·
I'm running a stubby underneath the frame as well. I have the carbs jetted already and I can tell you first hand running it with no muffler for a mile or so that you can really feel the lack of power. I can't tell you for sure whether running my bike with a stubby under the frame has done any damage to the engine, but I've been riding it this way for 5,000+ miles with no detonation yet...yet.

Excellent question by the way.
 
#10 ·
I think Back Presure is a misnomer.
It's realy a presure wave like if you toss a peble into a pond.
The waves radiate out untill they hit something then come back.
The presure wave travels down the pipe and hits the collector or some other thing and comes back.
They try and make it so the returning wave comes back just about the same time the Exhaust valve is opening to help evacuate the cylinder of spent gasses.
Remember to modify the whole system, not just replace one or two parts.
 
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