Hey my friend is getting a 440 kit installed in his 400ex engine its a wiseco piston at 12.5-1 compression.....we were wondering if we could use 91 octane gas and boost it up with octane booster...what should the 12.5-1 piston run on and would adding octane booster be good enough.

 

I wouldn't run anything less than a 50/50 mix of race gas and 93 octane on a 12.5:1 piston. I had detonation problems on our crappy 91 octane with an 11:1 wiseco and an xr400 headgasket.

 

you will want to use race fuel, NOT octane booster. if you want to run off 91 octane, get 11:1 or lower.

 

I have a 02 400 ex just put a wiesco 440 12.5.1 kit in and iv blown two top end gaskets already i run 93 octane and i have a k&n filter and full big gun exhaust what should i do to stop this hd studs? higher octane?what should the jets be?

 

my friend runs 110 octane in his 440 12.5-1 EX he hasnt blown a gasket yet....93 octane is to low for that high of compression

 

NOOOO octane buster got to air port get 111 octane get 2 gallons of the 111 octane then go to store get 3 gallons 93 octane and when you mix them to make 5 gallons your octane will be about 100.2 and that about what they told me to run with my 12:1.

 

My friend has the 440 kit with 12.5:1, if he runs anything under a 50/50 mix of Premium pump gas and race/av gas he blows head gaskets. It'll also knock and tick like a bi*ch.

 

Thanks for the help i am going to put it hd studs and run a 50/50 mix gas and hopefully that will do it