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Dirt Bike Brands - Other
426F cyl. head
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[QUOTE="DualSportr, post: 126904, member: 19592"] As far as the porting on a YZF goes, Powroll built the engines for the Four Stroke National winner last year. In testing on a flow bench it was found that: a: changing the size or design of the ports is not very helpful, plus there's not much room to work without breaking into a water jacket. b: a very tiny percentage of increase in flow can be obtained by just cleaning up the small imperfections and doing a good three angle valve grind. It will give slightly better throttle response and a bit more top end. c: riders who like more pull off the bottom and better midrange hit like the cams to be re-degreed. Powroll can do this for about $50 for anyone who's interested. This is a drop-in modification, and is recommended for owners who don't want to mess with a vernier sprocket. d: Like Rich said, the stock exhaust really does work. After exhaustive (pun intended) testing on the dyno, Powroll found no aftermarket system that worked as well overall as the stock system on the YZF. Some did give little peaks that weren't available with the stock pipe, but most also had valleys that didn't occur with the stock pipe. Testing was done using a hydro dyno, which allows the user to put a specified load on the engine to really find flaws in an engine's performance. Bang for your buck - For those riders who feel that too much is barely adequate, the best bang for your buck with a 426 is a stroker. They pull incredibly hard off the bottom, gain in midrange and are a little less revy than the stocker. Most riders, including the pros, find the 440 stroker engine too much hp for regular tracks, although Craig Decker used it to win a couple of 4Stroke National races at high elevations or on sandy tracks last year. Powroll also sells many strokers to quad racers who are utilizing the 426 engine in a quad chassis - the increased torque and smoother power delivery work well for the quad chassis. One warning - for those of you who are messing with your cams - Make Sure to follow Yamaha torque specs for the cam holder bolts -- It's very easy to over-tighten these and pinch the camshaft. We've even seen "race" mechanics do this. Hope this helps some of you save a few $$ :) [/QUOTE]
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Dirt Bike Discussions By Brand
Dirt Bike Brands - Other
426F cyl. head
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