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  1. #1
    Join Date
    Dec 2001
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    CR500 expansion chamber mods

    my 500 has a CT RACING drag port job with the head rechamberd to suit alcohol,45cc compaird to 65cc stock.The head and modifyed piston have been replaced with stock parts.Although the exhaust port hase been raised,the compresion is close to stock due to the 1.75mm overbore.It runs stock pipe/muffler/carb/ignition.My question though is there a mod i can do to the pipe to better match to port job without taking to much away from the little bottom end power i have already.I thought maybe shortening the header pipe would do the trick,but how much?I dont want to shorten the muffler,it's to loud as it is.I trail ride this thing.PS a 39.5mm PWK carb is on it's way to help out the top end power. CHEERS for the help.

  2. #2
    Join Date
    Aug 2000
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    I shortened the headpipe on my Husky for top end tuning. I run an FMF Fatty. The pipe in stock form it was tuned for mid range, however my engine was tuned for mid/top. By removing 2 ea 1/2 inch headpipe sections I raised the tuning point of the pipe by quite a bit. I used some free software from the Macdizzy site to determine port and pipe tuning, but in the end It really was done by feel. I knew that the engine never really came on the pipe. It had tons of overrev and was very fast, however it never really pulled hard at any one point. Sure the flat torque curve was nice, however I felt there was more to be had by a properly tuned pipe (for the engine).

    The shortening of the headpipe moved the torque peak up, and slightly softened the mid range. As I have a powervalved engine, the low end remained unchanged. Interestingly enough, the power valve needs to open sooner with the shortened pipe. HMMMMM.


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