Will this cam have enough boost for power brakes? - Page 3 - Chevelle Tech
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post #31 of 39 (permalink) Old May 7th, 19, 3:52 PM
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Re: Will this cam have enough boost for power brakes?

.

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post #32 of 39 (permalink) Old May 7th, 19, 3:57 PM
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Re: Will this cam have enough boost for power brakes?

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Originally Posted by 70GS455 View Post
...But my guess is prob around 10" vac or less...
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Originally Posted by SFD View Post
Thanks, the best I could get out of it was 8- 9 vac.
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I don't think that anyone short of a very experienced cam designer, can tell you exactly how much manifold vacuum any cam will [email protected], ...

Hmm....just gonna leave this here...

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post #33 of 39 (permalink) Old May 14th, 19, 12:59 AM
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Re: Will this cam have enough boost for power brakes?

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Hmm....just gonna leave this here...
Scott, I see that you quoted only part of my statement. I didn't mean to imply that nobody can give the OP an idea of what level of manifold vacuum can be had with any given cam, (especially if they themselves have used that same camshaft in question, which BTW is what i previously stated, but you chose to leave out that part of my post when you quoted me).

I thought I knew a lot about camshafts until I communicated several times through email and through this board with the late great harold brookshire, (AKA "UDharold"). That guy enlighted me as well as other people here, and did so with the utmost patience, humility, and respect many many times. The guy was a plethora of camshaft knowledge. I guess it stands to reason since he designed both street and race cams for well over three if not four decades.

Anyway, as you may or may not know, lots of variables going on with camshaft operation. And ofcourse things like engine displacement alone can change how any one cam "acts" in one engine vs another. That's all I meant to say. Also, the valve overlap figure is just one variable in the amount of manifold vacuum it will cause. Because valve timing is more than just valve overlap. This really is a complex science.

The bottom line here is although some people might be able to give the OP a fair idea of what the cam in question might cause his engine to act like on the street, he should NOT be surprised if it turns out to be at least a little bit different than people told him it would be, once he fires up the engine. It was more of a heads up for him than an argument on my part. Peace.
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post #34 of 39 (permalink) Old May 14th, 19, 2:35 AM
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Re: Will this cam have enough boost for power brakes?

Scott, here's what you've quoted me as saying....
"I don't think that anyone short of a very experienced cam designer, can tell you exactly how much manifold vacuum any cam will [email protected],"
But as everyone can see here below, simply looking at the very next line in that same post I made that you've quoted, it sheds more light on what i was saying. So you've chosen to take my words out of context....
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I don't think that anyone short of a very experienced cam designer, can tell you exactly how much manifold vacuum any cam will [email protected], unless ofcourse they themself used that exact same grind/lobe profile that you have on the cam in question. There are so many variables that will effect vacuum.
Hmmmmm
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post #35 of 39 (permalink) Old May 14th, 19, 7:16 AM
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Re: Will this cam have enough boost for power brakes?

I said the same thing, AND, empirically, we were right Billy, as no one had the knowledge to be definitive. Its that complicated.
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post #36 of 39 (permalink) Old May 14th, 19, 9:24 AM
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Re: Will this cam have enough boost for power brakes?

I dont think even a cam grinder can tell you exactly how much vacuum you will get. Way too many variables. Idle speed alone makes a huge difference.
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post #37 of 39 (permalink) Old May 14th, 19, 10:53 AM
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Re: Will this cam have enough boost for power brakes?

vacuum reservoirs work remarkably well. mounted mine incognito under the horns in my 67 chevelle.
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post #38 of 39 (permalink) Old May 14th, 19, 1:23 PM
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Re: Will this cam have enough boost for power brakes?

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I said the same thing, AND, empirically, we were right Billy, as no one had the knowledge to be definitive. Its that complicated.
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I dont think even a cam grinder can tell you exactly how much vacuum you will get. Way too many variables. Idle speed alone makes a huge difference.
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vacuum reservoirs work remarkably well. mounted mine incognito under the horns in my 67 chevelle.
Thanks for that acknowledgement guys. Yes, cam dynamics really are a complicated thing. We can go by the numbers of the specs for general purposes, sure. But the published numbers in the cam listings and catologues usually only tell us part of the story.

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post #39 of 39 (permalink) Old May 14th, 19, 2:26 PM
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Re: Will this cam have enough boost for power brakes?

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Or would i be better off going to manual brakes? I am planning on using a twin diaphragm booster like the disk brake second gen trans am's came with. Thanks
I have NO issue with manual brakes, with a front disc setup installed. Even using the original 4 wheel drum MC. All good if you have functioning quads.


Of course, I went to a properly sized cam , given the 3.31 rear gear set , so no issue anyhow.

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