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88 Turbo Coupe
11-30-2005, 08:00 PM
I can use before running race fuel on a 85 250r?
jason85atc250r
11-30-2005, 08:27 PM
i have a 20cc dome in my trx250r and they said thats the max with out race gas. it's the o ring type gasket.
TeamGeek6
11-30-2005, 09:53 PM
i have a 20cc dome in my trx250r .

Im confused (but thats normal) My original, unmodified 86 250R head measured 19.0 cc with a B8ES spark plug installed. Was the 85 dome different? Im using a extremely hot, long reach "5" racing spark plug which squishes it even more and it doesnt knock on 86 octane fuel.
jason85atc250r
11-30-2005, 09:56 PM
the stock head is a 22 or 23cc's.
deathman53
11-30-2005, 09:57 PM
I used a 18cc done with stock gasket on 94 octane, it ran fine.
Tri-ZNate
11-30-2005, 10:02 PM
smaller dome=Higher compression?
BigGreenMachine
11-30-2005, 11:22 PM
smaller dome=Higher compression?

Roger that.:beer
TeamGeek6
11-30-2005, 11:32 PM
Heres the formula, basically:

Stock compression ratio (8:1 for example) x (old head volume / new head volume)

8:1 with 20 cc head shaved to 18 cc:

8 x (20/18) = 8.9:1

Aint perfectly accurate, but easy to figure.

Supposedly, shaving the R head too much does bad things to the "squish band" around the outside of the head, it prevents the fuel from burning. Squish area is the part between the taper on the head dome and piston crown.