TOO MUCH PSI. Need dome cutting info please.

[BC250R]

Just rebuilt my 86 250R motor with all new bearings, seals and hotrods long rod crank. used spacer plate with 86 piston. The barrel was purchased already ported by Tony Carlson Racing with a matching honda head, i also have a cool head. I've measured both heads and they are 20cc. I have had the heads oringed therefore run no headgasket. The piston has 1mm of deck clearance and the bore is 66.5mm. After assembling the motor i fitted it to the frame and attached a compression gauge, kicked it a few times and got a reading of 197psi, way too high. I want to run high octane pump gas, about 98, therefore i need to relieve the compression by machining out the dome. i know i can buy a 22cc dome but from my calculations
(using this http://www.pontiacstreetperformance.com/psp/CRcalc2.html)
it probably wont be enough anyway.

I was hoping someone would have info on squishbands and maching domes to help get down to 165psi or slightly less.

Thanks in advance for any info you can help me with.
BC

[rustyhondas]

have you ever been to macdizzy.com it is a cool web site. you can look around a read allot for free.

the dude wants you to pay money to join though that sucks,but if you do you can have acces to everything.

this macdizzy guy is some sort of 2 stroke genious.

[deathman53]

you should be fine with 100 octane fuel, my friend uses 100 ll avaition fuel. The motor has a cut stock head and cr gasket. He has no problems with it. ~190 is the line for 93/94 pump gas, you should be fine using avaition fuel. I wonder if you know, but 165 is almost less than stock compression. If you are really bent on using pump gas, get a stock head and stock head gasket, they are cheap enough. I don't like cool-heads on atc's anyway, they put the spark plug straight out of the center, its hard to get at in that position.

[SWIGIN]

yeah you'll be fine....i ran my q-racer 250r with 220psi on 93 oct pump gas with out a problem

[BC250R]

Thanks guys, looks like i dont have a problem after all. Just had a bit of wrong info that led me to believe this was too high. i'll have it out on the dunes tomorrow!

[oscarmayer]

hellthat's onyl ike 8.75:1 compression. my drag car runs 9.35:1 comp and it's showing 240s across the board on each cyclinder. your fine. i'm more than certain you could even bump it more if you wanted, jsut make sure you use super unleaded fuel instead of the cheap stuff. if you get into the 250's range that's when you shoudl consider only racing fuel.

[jadleybray]

i wouldn't recommend anything higher than 240, max.....

[conig]

psi does not neccasarily get you an exact compression ratio, it also won;t carry from one two stroke to the next.

make sure your trying more then one gauge and two different brands its not uncommon for them to give you a different reading when testing static compression. its a safer way to get a true feel of what you want.

150psi going by the gauge is the limit for pump in a polaris motor so that should reiterate my point a quadracers compression has no bearing on what to do with a 250r. if you want to know exactly how to figure your compression I can assist but its alot of math and requires using cooking oil in the jug/head to get an exact fill amount.