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Hi,

This is my first Trx400. That was oversized to the 440 kit 12.5:1 with a Hot Cam's Stage 2.

I have read some things like stay away, not reliable. It goes forever. Then there are people that say they are reliable, get new heavy duty head studs and get a new bigger oil cooler for the over heating problem. Run race octane.

Here is my question. What octane would you use or what octane do you use?
 

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Run the lowest octane that does not "detonate" due to the compression or heat - 95 to 97 is about as high as you can go without losing power - 93 to 95 GOOD GRADE pump gas will probably be sufficient (good grade means brand name - I like British Petroleum, but I use VP racing 94 octane without alcohol in my race engine
 

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True, the lead won't hurt (other than a lead oxide build-up on the valves) and lead raises octane. I use VP Racing T4 100 octane - no lead, no alcohol, but I am racing and not just recreational riding.
 

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try this

change to a lower compression piston,the savings on gas price will pay for the price of the piston before you know it, then run some 93 non ethanol gas and your all good...if you want to go with a better oil cooler set up try four stroke tech.com for the correct setup for a 400ex.throws the cooled oil right on the cam where it tends to be the hottest.
 
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