How much manifold vacuum is needed to operate power brakes? I'm looking at a thumper cam and I need to know what are my limits. Nobody on the Brakes board answered this question.

 

I've heard, and read, that anything below 14in/Hg is gonna start to show. A long time ago, I had a 74 Camaro, 400cid/TH400 that had a solid cam (can't remember the specs) and it pulled about 12.5. It was fine when you first came up to a stop and just sat there. But if I got into stop and go traffic, I had no stop and all go. It was time to put it in Neutral.

If you have problems, buy a vacuum canister and hook it up soley to the brakes. It'll help, but it won't totally fix it. In a lot of stop and go traffic, it'll loose it's suction, just not as fast as the power brake booster.

Hope this helps.
AJ

 

I have been wondering this myself.
What kind of duration and lift will get you around 14in/hg?

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89 RS 350 TBI auto Hooker SC/LT headers Open element 3in K&N CVT protorque mini-starter

Daily driver 91 RS auto LO3 63k

New project- 89 Formula 350 WS6
383 or 400 to come!