just put a 425 i enginen my 65 cutlass . it has MT valve covers . has power drum brakes ftont and rear . my 11 inch vacuum booster is to big in diameter need help on what sizes fit and what brands . ive seen small ones on other a body cars but need some advice

 

The factory one for 65 Cutlass is 9 inch i believe.

 

^^^THIS. The 64-66 cars used a 9" booster. When disk brakes were factory offered in the 1967 model year, Olds changed to an 11" booster. If you plan to keep the drum/drum system, use a stock 9" booster. If you ever plan to go to disc brakes, either use the LH notched cover with an 11" booster the way the factory did it or go to a 9" dual diaphragm unit.

 

joe can i use a 8 inch dual diaphragm with drum brakes and will it work with front disc when decide to go that route

 

Yes, an 8" dual diaphragm booster provides the equivalent power boost as the OEM 11" single diaphragm booster.

 

thanks Joe i appreciate all your advice and knowledge in my 1965 Oldsmobile help
i

 

Or... Upgrade to discs now and eliminate the booster all together.
This is JMHO....
But I really didn’t notice much difference in feel and ANY difference in stopping power when I got rid of mine.
I can hustle my 3800lb car down from 124mph in time to make the short turn off at just about any track I go to.
-peter