I've got a 400ex with a newly aquired (today), White Bros. R4, K&N air filter, and a 152 main jet from stock 148. I figure I'm gaining about 4-5 more H.P.. Will I gain more ponies using 113 octane? I've got a winter project planned, 11:1 stock bore kit, maybe a race cam, and titanium valve springs. I wanna keep it reliable and cheap. Any Ideas?

 

Higher octane doesn't mean more horsepower just more money.

 

when you go to compression over 10.25:1 INCREASE the Octane but it doesnt have to go to 113 if its a fourstroke, the YZ 426 has 12.5:1 but only requires premium gas. If you go to 11:1 USE 103 Octane or what ever is closest.