I am about to order power brake conversion from SSBC and seen that they have a 9 and 11 inch boosters. I plan on running a roller valvetrain with tall valve covers will the 11 inch interfere with that or should I stick with the 9 inch?
There was recently an article about this in one of the Pontiac mags, the bottom line was that there was no advantage as far as vacuum. The only adv. to the smaller one was more clearence for valve cover, wiper motor etc. Personally, being the purist that I am LOL I think the smaller one looks a bit goofy. But then again, that solely my opinion...
The bottom line to the article was that although the larger unit has more diaphram area, the smaller unit used an advanced interal system and thus offered equal vacuum. I also think the smaller diameter unit is also a deeper unit. That may be how it is able to "hold" the equal amount of vacuum...
I think the 9" is a dual diaphragm (please confirm 1st), in which case it should work as well or maybe better than the 11" which is a single diaphragm. Looks a lot better than your valve covers self-clearancing on the booster too.
Another option, that is expensive, but provides a huge improvement in brake pedal response, is the hydroboost brakes. Packages much easier, cleans up the firewall, provides great pedal feel, and works no matter what engine vacuum you have.
