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Dirt Bike Discussions By Brand
Yamaha MX & Off-Road Dirt Bikes
YZF267 v. YZF290
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[QUOTE="EricGorr, post: 145825, member: 19611"] Regarding the discussion on the sleeve issue, some people use cast iron sleeves. Cast iron and nickel composite have their pros and cons. But in a high performance 4-stroke engine the cons of a sleeve are the reduction of heat transfer which results in a greater percentage of fuel used to cool the cylinder walls. Also the cast iron wears and contaminates the oil. The other obvious reason is that theres only one sized piston, so when the cast iron bore wears (faster than nickel composite because its softer) you'll have to replace the liner, which is expensive. My feelings are that the YZF series cylinder are too weak to handle the stress of being heated to 450F then having a cold cast iron sleeve dropped into them and wedged in a 10 ton press until it cools. The pundits may argue that cast iron contains graffite and produces a lower coefficent of frictiion than nickel and is softer so the rings seal better, but the thermal and wear issues are paramount on a dirt bike. I'm not going to blow smoke about this kit making another 5hp at any rpm over the stocker because I heard enough of that bovine fieces over in vendor's row at the recent Amateur Nationals, but the simple fact is the Wiseco 2mm oversize piston with a 13.2:1 compression ratio is a better bargain than any aftermarket exhaust system on the market. Steve Simpson and Pete Payne ran over 140 dyno runs on Pete's Dynojet rig and they said that the fuel made the biggest difference over bolt-on products like exhausts and air boxes. Pete if you're reading this please feel free to chime in, Eric [/QUOTE]
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Forums
Dirt Bike Discussions By Brand
Yamaha MX & Off-Road Dirt Bikes
YZF267 v. YZF290
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