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Discussion Starter #1
Here's what Kevin Cameron has said about restricting the outlet. "Exhaust pipes always create backpressure, but the more there is, the higher the amount of hot gases that won't be able to exit the cylinder while the exhaust port is open. Its heat, added to the fresh air/fuel mixture that enters the cylinder, may be enough to put the engine into detonation.

Sometimes a 1 or 2 mm reduction in tailpipe ID will result in a couple of extra HP,  
but the extra heat may make the engine detonate after a few seconds."
 

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who is Kevin Cameron?
 

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Discussion Starter #3
He writes a Tech column in the Canadian edition of Snow Goer. Usually a good read. This year his article about Ram-Air basically took a shot @ the Viper & its setup.

With the speeds a sled sees & the circuitous (long &twisty) route from the hood to the carbs, the benefits would be small. Not like a drag  car that has a  straight shot  from the scoop to the carb(s).

If ram-air was a big improvement, we'd have seen it on unlimited sleds. Most just run a open carb don't they?
 

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Revrnd, your friend would be right about the exhaust restrcition on a well tuned exhaust system, but none of the Ski Doo Twins have a well tuned exhaust system they are large volume to create less heat in the engine and therefore stave off their warranty issues until well out of warranty, if they were well tuned then you wouldn't be able to make more useable safer hp by restriction and believe you me that all of the S/D exhaust systems need more restriction, if I thought everyone could really grasp the mathamatical equations of exhaust systems I would post them here to show you how wrong the S/D exhaust systems really are.  --  Bill
 

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Bill, go ahead and post that stuff. I am a rocket scientist/auto tech.  LOL  
Many people do not understand how much an exhaust system can affect hp.
Bill, I did not know that the stock Doo exhaust was not up to snuff.What do you suggest for my 02 mxz 700 for trail riding? I have not done any other mods as of yet.

 Pete
 

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Discussion Starter #6
If the Ski-doo pipes are oversized & inefficient, what is to be said about FAST's "Fat Boy" pipes that they made?

I'd like to read some of your thoughts on pipe design too, Bill
 

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Fast Fat Boy Pipes were made for the rotary valve engine and if you compared the stock pipe with the Fat Boy you would see that in all instances the exit size of the exhaust pipe was smaller than the stock one. As for the Series III engines for example the muffler on an 02 800 has more volume than on an 01 and if you install an 02 muffler on an 01 exhaust pipe the HP falls as well the 02 exhaust pipe has more volume than that of an 01 and when you figure the pipe for the motor the over all volume is too large on any of the 01 and 02 800's, as well as the exit size of the exhaust is too large for the volume that the pipe holds.  --  Bill
 

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"if I thought everyone could really grasp the mathamatical equations of exhaust systems I would post them here to show you how wrong the S/D exhaust systems really are." --  Bill

Hey Bill, you ain't saying we is ignorant, is ya???  

Just kidding Bill, I am sure the volumes, dimensions, and pressures involved in exhaust systems are very complex.  I am very interested in an exhaust restrictor for my 01 800, since I haven't been able to get much else to work.  A couple of questions I have, are these really safe at flatlander elevations, and do I need to run higher octane fuel, especially if I am running 480 or 490 main jets?  I heard through the grapevine that another company that was selling restrictors quit due to too many meltdowns.  Also, for the 01 800's do I need to tack weld the restrictor in place, or will it stay put?

Thanks Bill, your always a big help.

Dave      
 

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We have restricters for all years of the 700 and 800 Twin Ski Doos, they don't weld in they have a flared end that wedges into the exhaust pipe and then you apply silicone around them and put the exhaust pipe back into the muffler and let it set up overnight and it is ready to go, the advantage of not welding them is that you can remove it if you want to. --  Bill
 

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Bill what about fuel requirements, and are they safe at Illinois and Wisconsin altitudes?
 

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You still use regular gasoline and we run 480 and 500 main jets with the restricter, if you install a head kit or cut your head then you need to run a minimum of 91 octane gasoline. We have hundreds of these exhaust restricters in the field and in the states that you mention as well as any others unless you are in the mountain states which is a different exhaust restricter along with other things, then the fuel requirements are regular gasoline only
 

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I used Bills restrictor on my 01 800 with no problems, I used EGT gauges and ran 480's with no problems. Screaming across lakes at wide open ,no problems. Hey Bill just to let ya know the V force reeds I bought off ya, I removed them the other day and the reed cages came loose on booth of them, and on one the reed tension adjusters, 2 of the 3 screws loosened off and the reed petal corner chipped off, about 1/4 inch missing. I can't believe it still ran, thats probobly why I seen 100 degrees difference in EGT.I thought the dpm was acting up.V force is coming good for the reeds. The two screws where out 3/4.,almost injested. Next time I'll loctite.Thank God for a short season, ha ha.
 
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