Race gas???

[blastin603]

so got a new top end for my RN bored 1 over with 35cc domes on blowsion girdled head. psi came out to be a hair shy of 200. i know you need to run atleast 100 octane with comp that high but wondering what the lowest octane i can get away with for freestyle riding. never really hold the ski wide open, if i do is very breif. i figured those octane reccomendations are for racing where you are constantly WOT. for now im mixing 2 gallons of c12 to 3 of 93 to get 100 octane

 

[stagesrt4]

i run 100 octane in my BB 781 with 210 psi

my X2 with 190 psi i ran at least 93 octane... if i have extra race fuel then i add a gallon or two as well

 

[blastin603]

ehh i may be getting different domes. rode today and retested.. 215 in both

 

[Lumpy]

Your gauge probably reads high. When I put my girdled ada on with 35cc domes it read a consistent 205-210 but I ran pump premium in it all day without any problems.

 

[RRicketts]

You will have detonation with that comp. race gas or new top end you decide.


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[fastgtfairlane]

my guess is your compression gauge is off.. stock thickness gasket, stock deck height and 35cc domes should be a pump gas setup.. dont go off your gauge, you need to know your squish clearance.. use your gauge for mechanical condition, not for determining what fuel to run..

 

[Vumad]

I wouldn't assume the compression gauge is off. That's risky.

I rebuilt my motor 1mm over with 35cc domes. Instead of 180, I got 200+ On 2 craftsman gauges. I'm at 170 now with 37cc domes.

 

[fastgtfairlane]

a friend with a 710 ported by art was running 33 cc domes with 93 octane fuel.. ran it 100+ hrs.. regardless of the gauge, you should never determine what fuel to run using only a compression gauge... gauges are quite inconsistant for the most part.. what psi it shows is only an indicator to show mechanical condition of the engine... use it to make sure both cylinders are equal and that the engine has good cranking compression only not octane ratings..

 

[blastin603]

i dont know whats going on. rode all day today with half 112 and half 93... ran awesome. let ski sit for 2 hours and checked again its at 225 psi! doesnt make sense to me... site says i should be at 185. would being bored 1 mil over make the much difference or is something wrong?? the base gasket i got also looked pretty thin..


also i compared my gauge to my buddies the other day and they both gave the exact same readings

 

[Quinc]

Are you leaving one plug in and holding the throttle open when you check? Try taking the plugs out and hold down the start button for 20 seconds, then check it again.