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blottermachine

cr125 exhaust port idea

6 posts in this topic

Hey all! I noticed if I look in from my exhaust flange that it doesnt match the shape of the head at all. Has anyone took the head and matched it up to the exhaust flange dimensions? BTW it's an 06 cr 125

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Hey all! I noticed if I look in from my exhaust flange that it doesnt match the shape of the head at all. Has anyone took the head and matched it up to the exhaust flange dimensions? BTW it's an 06 cr 125

I've always been intrigued with Boyesen 's products so went right to the source to get the facts on this subject. Check it out:

When the new ’02 CR250 engine was introduced, the initial feedback was “what happened to the throttle response and bottom end power”. On the dyno the servo operated exhaust valve, case reed engine was impressive, but on the track it was…dare I say disappointing. We spent lots of time looking at ways to improve the low end performance issues with a RAD Valve solution and while testing found the stock exhaust flange cracked and failed at the o-ring groove. Initially our thought was to offer a replacement solution for the failing stock flange. Of course Eyvind wouldn’t settle on that, and looked at some ideas to improve the design to help the stumbling bottom end performance.

On the 02-03 CR250’s, the exhaust flange was circular and did not match up smoothly to the “D” shaped exhaust port. Additionally the inside shape has been optimized to increase pressure pulse energy to improve the throttle response and bottom end power. The ’04 CR250 stock exhaust port and flange was changed for the better, but still had room for improvement. A similar design change was made on the ‘04 Boyesen flange to help pump up the bottom end.

To summarize, the Boyesen Exhaust flange’s billet design eliminates failures of the stocker while adding much wanted bottom end power and throttle response.

Available for: 02-03 Honda CR250 :: BEF-02, 2004 Honda CR250 :: BEF-02A, 2002 CR125 :: BEF-01, 98-08 KTM65SX :: BEF-40A.

MSRP :: $58.95 - $84.95

so i guess the case reed 250's werent the only ones with this mismatch. boysene offered a flange that was stronger as well as fixed the port shape mismatch.

Edited by mynewcr250

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I really don't think any gain would be worth the effort. On a 1000 horse engine, sure.

btw, with that said, 2strokes4me's post seems to match up with what some people have said. more reliable, yes, power increase, no. maybe on a dyno.

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