I upgrade the brakes on my 54 chev to a dual master power assist unit. It calls for 18lbs of vacuum. I checked at the booster and I had 12. So I found a vacuum resevior for a 79 chev truck and it bumped the boost to 15 lbs. Do I dare put another one on there or is there a better way to go. Pretty sure I have no leaks anywhere....thanks for any advice you can give me.
A perfect vacuum is 30 INCHES. Not pounds. Vacuum is pulled from the engine via the intake manifold or carb/f.i. port. Unless you are using a vacuum pump Adding vacuum reservoirs/canisters of any size does not increase vacuum. It only increases volume. To increase vacuum without engine internal modifications, you would need a pump.
Also, even if the engine only pulls 12 or 15 inches at idle, during closed throttle decelleration the vacuum will probably jump up to 18 or 20 inches. The vacuun tank should hold some of this in reserve for things like brake boosters or vacuum actuators in the HVAC system. You may be OK with what you've got, but test it out in an empty parking lot somewhere first. Then install a vacuum gauge in your car and watch how the readings change under different driving conditions. Then you'll start to see how and when different carburetor vacuun circuits and your distributor vacuum advance work.
You might want to play with the carb some... Adjust the idle mixture screws to ge the highest reading with the vacuum gauge.. I got something like 26" of vacuum from a freshly rebuilt 302 Ferd with a "stock" HO roller cam.. Once tuned, I was able to dial down the rpm's (just for the hell of it) too 300-350 and it was still running..
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