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Dirt Bike Discussions By Brand
Yamaha MX & Off-Road Dirt Bikes
High Compression piston for a YZ250F
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[QUOTE="Rich Rohrich, post: 157614, member: 16241"] The stock pipe with a 13.5:1 piston and proper deck height will meet your goals. An .080" plated overbore again with the stock pipe is an even better choice assuming it's legal for the class you are running in. Blueprinting the cylinder head holds some value, but no where near as much as the compression and deck increases. For your purposes porting is worth about $150 on these heads (simple blueprint and throat blend), and a proper blended valve job is worth about the same $$. Springs shouldn't prove to be an issue unless you have a TON of hours at high rpm. Given it's still a fairly new engine it appears thatt the best bang for the buck in terms of response coupled with top end power is oxygenated race fuel and sharp jetting on a totally stock engine. Best torque curve for the buck if you are taking the engine apart is a 13.5:1 compression .080" over piston, in a plated barrel with stock pipe and oxygenated race fuel. The chamber is open enough to to support even higher compression but the rpm ceiling makes it tricky to keep the valves out of the head when two-stroke MX ex-patriots ride them like 125s :) Guys who don't constantly bounce them off the rev limiter can safely run a LOT of compression. A properly setup high CR engine is no different to jet then a stocker. Heat has not proven to be an issue on these engines so far but if you spend a lot of time slugging along in mud at slow speeds then additional compression will require a commitment on your part to tune correctly for the situation. If you get the squish clearance right and tune correctly high compression won't matter. Pipes on these engines haven't shown themselves to have a particularly good price/performance ratio but I realize that won't stop folks from buying a trick looking pipe :) Eric and I will know lots more about the potential (and long term problems) of these engines as we test more and gather more rider feedback information. Good luck with your project. [/QUOTE]
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Dirt Bike Discussions By Brand
Yamaha MX & Off-Road Dirt Bikes
High Compression piston for a YZ250F
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