Compression going up

[clutch22]

well when i bought my 250r back in december it had like 168psi, then 175, then 180, now its at 190psi. Pretty sure this is just cause the last owner hadent rode it in 6 months, but anyway.. i'm at 190psi, should i be using avgas?

[RichM1983]

Once an R goes over 180 you need to up the octane.

[number5]

This would be the first time I heard this. Without mods. I used to test aircraft engines and if a engine increased in performance it just ran out of oil or gauges needed to be recalibrated. So Im thinking your compresion tester if giving you false readings.

[clutch22]

Sorry but i'm pretty sure that i'm getting true comp. readings. Thats about the hardes thing to do is let an engine sit for that long...
right now i'm runnin 89 octane, so i should probly up it.

[TheFontMaster]

180 PSI is the highest you should go on 93/94 pump gas. It's right at the limit of running pump gas. Unless you want to put in a different gasket, or dome (if you have an aftermarket head) then you should step up to race gas.

[sandspanker]

I have a 350 power valve and a 330 power valve both at 200psi. the least i go on fuel is 50/50.

[clutch22]

ok thanks... my dad is a pilot and buys barrels of avgas at a time ... so i'll just use that.

[clutch22]

Originally posted by TheFontMaster
180 PSI is the highest you should go on 93/94 pump gas. It's right at the limit of running pump gas. Unless you want to put in a different gasket, or dome (if you have an aftermarket head) then you should step up to race gas.

Soo... i have about 3-4 gallons left that i have mixed up of 89octane... would it be allright for me to use the rest of that stuff up?

[86 Quad R]

was the engine a fresh build when ya purchased it? i've experienced atleast a 10% increase in compression after builds.

as stated. 180-190 is the cut off for pump gas. if your over that i would think abour running a higher octane fuel but i DO NOT recommend you mix fuel and gas. run either one or the other. if the quad sits for any period of time the two have potential to separate as well as the mix oil.

[TheFontMaster]

Originally posted by clutch22
Soo... i have about 3-4 gallons left that i have mixed up of 89octane... would it be allright for me to use the rest of that stuff up?

You could probaly get away with it, but I wouldn't run it just to be sure.

[MathR601]

First it's not only the PSI static compression that tells you what octane you must run... You should be good with 93 octane... I would run it if it was me.
For your compression raise, it could be the carbon that built up on the piston and on the head which make reduce the volume and makes more compression. If you are running a cheap oil with a high ratio i.e 32:1 or 20:1, that could be the cause.

[clutch22]

Originally posted by MathR601
First it's not only the PSI static compression that tells you what octane you must run... You should be good with 93 octane... I would run it if it was me.
For your compression raise, it could be the carbon that built up on the piston and on the head which make reduce the volume and makes more compression. If you are running a cheap oil with a high ratio i.e 32:1 or 20:1, that could be the cause.

hmmm... i've never really thought bout carbon buildup... i mix 32:1... but i dont think my oil is cheap.. Maxima Castor 927 ... but idk.. maybe that is cheap stuff.