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Old 10-09-2004, 08:04 AM
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power brake vacuum low

Hello everyone: My problem is I need about 18" of vacuum to my master brake booster cannister. Right now I only have 13" at the booster and off the intake. I'm running 350cu in. ZZ4 motor. I've seen wilder cars with sounds of a bigger cam than mine, and they are running power brakes with enough vacuum. There are two companies for street rod brakes that offer these pumps. One costs$269.00, the other is $389.00. There's got to be a cheaper way and just as good as the expensive pumps. I know someone has had to do this, I can't be the only one. Ant information would be appreciated. Thank you, Dave
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Old 10-09-2004, 04:27 PM
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I wonder how much vacuum a emmissions air pump (smog pump) would pull on it's intake side? The size controls the ammount of air it pumps, probably the ammount of vacuum at the intake. The things go for next to nothing at the junk yards. We'll see if we can get some input from other board members. Anybody???
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Old 10-09-2004, 11:21 PM
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Search the knowledge base, a few months ago this topic came up and there was talk about some Cadillac vacuum pumps that were easily adaptable along with some links to some tech info

Better yet, just gop to "Search" and look at posts in here, just put in "Cadillac vacuum pump" and have it search the body of posts, there's a few in here.

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Old 10-10-2004, 05:29 PM
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A vacuum reservoir is the cheapest way. One would hold enough vacuum for one mad slam of the brakes. However, my 442 pulls only 8" of vacuum at idle and the stock booster and master cylinder have no problem operating the two 4 piston Wilwood front calipers and 11" drums in the rear. What makes you say that you need 18"?

Also, I will be using a vacuum reservoir snatched from my Ram next year after I put a bigger solid lifter Lunati cam in my 406 this winter. I'm expecting around 6" of vacuum at idle and I don't think I'll need anything more than one reservoir.
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Old 10-10-2004, 07:12 PM
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yES, A VACUUM CANNISTER WORKS, i USED ONE ON A PRETTY WILD '65 gto I BUILT A WHILE BACK.

Yep, the cannister is worth looking into, I used one with a wild '65 GTO I built a while back and it worked well but had drums all the way around. I actually got more than one brake slam with it too!

Like GB, I'm building my new blown 383 SBC motor using a Lunati 50139 solid roller and have 4 wheel discs, so I'll be dealing with the vacuum concern as well when the time comes.

GB - How do you estimate your vacuum with a particular cam and intake system? If you have a formula, can you share?

Thanks, Larry

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Old 10-11-2004, 05:55 AM
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To tell you the truth I'd like to see a formula for vacuum too. I'm basing my estimate on what I know about my engine as it is right know. I've got a high duration circle track cam in it now and the Lunati cam has much more lift and a bit more duration. I'm also changing the intake and modifying the heads, so I think planning for 6 inches is about right.

Generally for me, if I can look at the specs and the manufacturer's intended purpose of the cam grind and have doubts about streetable vacuum, I'd count on it. Lunati should be able to give you an estimate of what to expect, but your blower may throw things for a loop.
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