VP ultimate 4 and jetting?

[aci clay]

i was just wondering how much or if at all using VP U4 race gas will effect jetting. taking the kid to mammoth this year and i know i'll have to rejet for elevation, (8500 ft.), but i don't know what the ultimate 4 fuel will do. He's on a crf250r. 1st big race and i want him to have every advantage we can do.:confused: :confused:

[bwamos]

Q1: What compression is he running? If hes not running greater than 13:1 then he isn't going to get any benefit from race fuel. In fact if he's 11:1 he's gonna loose "some" HP because of the detonation inhibitors (not gonna be noticible though only talking like 0.1hp).

The truth is you want to run the lowest octane possible you can without your enging getting any early detonation (pinging). As long as the engine doesn't ping you dont want it.

If your running 10.5:1 => 12:1 you want to use premium pump gas. If you're running lower compression (like 9:1 you want to use regular pump.

If he's running 13:1 or greater you will want race fuel, yes.

You'll get more benefit from proper tire pressure, suspension settings, and sproket gearing.

[bradley300]

it shouldnt affect your jetting unless it is an oxegenated feul. my 11:1 300ex ran fine on 93 octane, i think anything higher might be a good idea for some race gas. if its a fairly stock motor, your wasting your money on race gas