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Jetting Changes ?

"Dear Ralph" September 28, 1998 0
Dear Ralph: I have a 1997 Polaris Indy XC 700. I had the sled clutched before I picked it up. When I ran it...

Dear Ralph:
I have a 1997 Polaris Indy XC 700. I had the sled clutched before I picked it up. When I ran it against my friend’s Ultra I wasn’t very impressed. Next, I replaced the stock silencer with an aftermarket silencer, still using the stock pipe. Since the stock jets are typically a few sizes bigger than needed, I was wondering if I have to make any jetting changes? P.S. I now beat the Ultra by 4 sled lengths in an 1/8 mile on the grass!

Andy Vollert
Stevens Point, WI

In most cases when you replace the stock silencer with an aftermarket pipe you are reducing the outlet pressure which will make the engine breathe slightly better. If your engine is going to be pumping slightly more air, then it will need slightly more fuel to maintain the air/fuel ratio. Most silencer makers will tell you the net effect of installing a silencer is about 1/2 of a jet size, not enough to worry about. If you still have stock jetting in the sled, then you should be just fine. For an engine that is already jetted to the edge, then the addition of a different silencer could be just enough to make the difference.
Our experience has been that a different silencer, added to a stock machine with no other changes, is good for only one percent or two of a power increase (not much). The real benefit from a different silencer is to reduce the weight, many times approaching ten pounds. The problem is that many silencers are so much louder than stock they are illegal for use on public lands & trails. The leading silencer manufacturers have learned that you do not have to make your machine louder to make power, quite the contrary. Quiet silencers are now able to make as much, and more power than the loud pipes.

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