Piston compression..........

[B450r]

wht is the highest compression u can use while using pump gas.......... like 12:1 or 12.5:1

let me know..
THANX

[stocktires]

on a 450r, 13.5:1 is the highest one should go with pump fuel.

[krt400ex]

Originally posted by stocktires
on a 450r, 13.5:1 is the highest one should go with pump fuel.

DO NOT GO THAT HIGH!!!!! THAT IS REDICULOUS!!!!

12:1 is right about ur the highest u want to go. 12.5:1 is border line. i know a guy who is a professional engine builder and he races a 450R. he had no race gas one day so he ran pump gas on a 12.5:1 comp piston, his jetting was correct, and he burnt up his piston and rings. he has learned from experiance and i am passing it on to u. 12:1 is it.

[stocktires]

Originally posted by krt400ex
DO NOT GO THAT HIGH!!!!! THAT IS REDICULOUS!!!!

12:1 is right about ur the highest u want to go. 12.5:1 is border line. i know a guy who is a professional engine builder and he races a 450R. he had no race gas one day so he ran pump gas on a 12.5:1 comp piston, his jetting was correct, and he burnt up his piston and rings. he has learned from experiance and i am passing it on to u. 12:1 is it.

I disagree on this topic again, but I will say that for an everyday weekend warrior type of rider, a 12.5:1 should be the perfect set-up. 12:5:1 in a 450r motor is not NEARLY pushing the limits. Its not a 400ex krt, these CRF style motors can take MUCH more than a XR based motor.
You engine builder buddy is an idiot.

[stocktires]

http://www.thumpertalk.com/forum/sho...light=race+gas

Very good thread, please check it out!

[stocktires]

Originally posted by krt400ex
DO NOT GO THAT HIGH!!!!! THAT IS REDICULOUS!!!!

12:1 is right about ur the highest u want to go. 12.5:1 is border line. i know a guy who is a professional engine builder and he races a 450R. he had no race gas one day so he ran pump gas on a 12.5:1 comp piston, his jetting was correct, and he burnt up his piston and rings. he has learned from experiance and i am passing it on to u. 12:1 is it.

His jetting was NOT correct, you can't just change fuels like underwear.

[krt400ex]

Originally posted by stocktires
His jetting was NOT correct, you can't just change fuels like underwear.

#1, with race fuel u will need to lean out ur jetting a little, so his jetting was a little rich. that would not hurt a motor if anything it will help.

#2, i am finished argueing, i answered u in the other post we were arguing over. the guy i know is not an idiot. in fact he is one of the very few sponsored privateers racing. i would say that it would take some experience on and off the track to achieve something like that.

[400eXr1d3rZ]

krt400ex, he burnt up his piston and rings? How were the conditions outside? If it's extremly hot, your bike will run hot, hotter<overheat<detonation. Higher octane gas is a good idea whens it's 98+ degrees outside. But not mandatory.

[dork]

there are many variables that control how much compression you can get away with on pump gas: cam duration, chamber turbulence, rpm, elevation, engine load, jetting, etc. so if someone's gonna make a blanket statement about it, then it should be on the conservative side. in the case of a 450r, 12 to 12.5:1 is reasonable. 13-13.5 is race gas territory for, at least 50/50 mix. also you don't always jet leaner on race gas, it depends on the specific gravity of the fuel and whether or not its oxygenated.

[krt400ex]

Originally posted by dork
also you don't always jet leaner on race gas, it depends on the specific gravity of the fuel and whether or not its oxygenated.

u r right, ogenated fuels go richer, but he doesn't run that.


he was running a sparks full race motor. basically the same one that john natalie ran, but his compression was lower. he is now running a 14:1 comp, u know stocktires, he should be just fine on pump gas...right?