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421 serval mx/hare scramble bike


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hey guys, I do some MX'ing and also a few hare scrambles a year with an occasional grass drag.when I trail ride, I ride like im in a race at all times. I'm trying to decide to upgrade my pipes or not. I'm currently running pro circuits and I absolutely love them but my fear is that they may be limiting my 421 serval a bit. they hit nice and hard down low and have solid pull all the way through. I rode my buddies ported stock cylinder 4 mil with CPI pipes and they were absolutely gutless down low- I had to keep the r's up pretty high just to ride, while the power band may have hit harder (im not really sure I wasn't hooking well)  the pro circuits seem to pull for A longer period of time because they hit so much earlier. what does everyone think?


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Your comparing pipes on 2 different motors..

There are a few dyno comparisons on your setup In the dyno room. Have you checked them out?

The cc difference and port layout would likely make the cpi feel entirely different than that of your friends stock cyl.

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I am the motor builder lol. I did order my parts from Nate with KaN - very respectable and knowledgable guy. And Ya I've been looking at dyno sheets as well- I put my motor low 70's with my setup looks like cpi's can hit 80hp

So are running as cast then, no porting?


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  • 5 weeks later...

Ported servals on "drag" pipes is currently the best all around setup.  I've ridden my 421 with Shearers on the track and handling is it's only down fall.  Motor is amazing if geared right.  As cast servals are kind of dog turds.  If your not going to port, you might as well save the cash and have Redline port your stock jugs like he did for JD and run the SLP's.

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