zodiacblueS

Does anyone out there have experience with the vac storage canisters available to help low vac power brake systems? I've replaced everything from the booster to combo valve, mc, lines, hoses, calipers, etc. and still have a hard pedal, I think due to the relatively low vacuum in my moderately built 455+. It will build up after a minute or so of running, but forget trying to pump them. Any vac storage canister users out there??
Thanks in advance.

jensenracing77

sounds like that is your problem. As long as the new booster is good I would add a reserve tank and see how it does.

joe_padavano

What size booster are you running? If the problem really is the vacuum level and not a booster that's too small, then other options are a hydroboost or manual brakes. I've got manual disks on my 70 W-30 and it stops fine with normal pedal effort due to the different M/C and pedal ratio from power brakes.

zodiacblueS

I was hoping you would chime in Joe. The booster was rebuilt and replated by Steve at Brakeboosters.com I spoke with him, did a couple of tests he recommended (pedal at start, and pulling valve after shutting down for hissing) and it seems to be functioning as designed/intended.

A vac guage shows ~11 to 12 in. at idle with a quivering needle. Cam is not very radical but Cutlass EFI ground it for the classic, loping idle and mid range power. Had it dialed in by a local Olds guy who races BBs down at Bandimere in Denver. I am at 5100 ft. above sea level here. But it's just a weekend cruiser. Performer intake, Qjet, PS,PB,AC etc.
Bored .030 over, FM Speedpros, decked to .05, big valve C-heads milled to about 78cc. volume, compression ~9.6. Runs and sounds fine, but can't get much assist without a minute to build up.

Thanks for your time. Just an old fart here.

joe_padavano

And THAT'S part of the problem. Sea level pressure is around 30" hg. At 5000 ft it's down to 25" hg. The power assist you get from a vacuum booster is a function of only two things, the area of the booster diaphragm and the difference in pressure between atmospheric and manifold vacuum. The vacuum gage reading is actually this pressure difference. On a stock engine at sea level, the vacuum reading would be around 20", so between the cam in your engine and the lower ambient air pressure, you're only getting 12" - that's only 60% of the normal power assist. Not sure a vac canister alone will do it. You may need an auxiliary vacuum pump and canister.