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Different compression and power?

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Would sticking a standard bore 11:1 piston in my bike make much of a difference in power over the stock compression? It's an XR400 btw

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I think you'd definately see an increase, how much I'm not sure. Plus, I'd think you're getting real close to having to use race gas, depending on your elevation and what octane premium pump gas you can get.

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Ottawa is 374 ft / 114 m elevation. The lower in elevation you are, the higher octane you need to run. Visa versa when going up in elevation. I would try it on that 94 pump gas you have locally. If you get no pinging/predetonation under load, you are probably good to go.

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A higher compression mainly gives you a boost in low end torque and in top end power. If you are thinking of getting a high-compression piston you might as well get a 416/426 while your at it since a bore job is fairly cheap.

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I thought it was bigger piston= more low rpm torque and higher compression= more high rpm horsepower.

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Our local Honda service manager runs a 11:1 stock bore in his 400 and says it runs fine on pump gas.

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