Will this cam have enough boost for power brakes? - Page 2 - Chevelle Tech
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post #16 of 39 (permalink) Old May 3rd, 19, 9:31 PM
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Re: Will this cam have enough boost for power brakes?

Lobe duration at 0.050" is not the only predictor of idle quality. Something that everyone is ignoring and not considering is the lobe separation angle. This cam has a 109 LSA. It has 25 deg of overlap (at 0.050"). Unless it's a 525+ cubic inch motor, there will not be enough vacuum

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post #17 of 39 (permalink) Old May 3rd, 19, 11:34 PM
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Re: Will this cam have enough boost for power brakes?

why not just put a hydro boost on it best of both worlds still power brakes and no need to worry about vacuum.

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post #18 of 39 (permalink) Old May 4th, 19, 8:58 AM
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Re: Will this cam have enough boost for power brakes?

I guess I just dont u/s the thought process of needing a vac reservoir/dual booster/hydro boost for a STREET car. IMO that tells me is that the cam selection was one that was too large for the application. Could be trading away 30-50ftlbs of tq where its needed the most.

Remember, I used the word STREET.

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post #19 of 39 (permalink) Old May 4th, 19, 11:08 AM
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Re: Will this cam have enough boost for power brakes?

When Mark and I discussed my build, he first mentioned that cam. I decided on the next step down 228/238 and Mark had it cut on a 111 instead of a 112. I do not regret it at all. Cruise along in 3rd gear at 1200 rpm (3.42 gear, 27" tire, 10" tight with 2300 stall) and runs smooth as silk, but you can floor it and it kicks down to 1st, lights the tires and bang the limiter so quick you can't take your foot off the gas quick enough. With locked timing at 36 and 10:1 makes 11.5" vacuum at 775 rpm idle in gear, and 13" at 825 idle in park. 20" when driving at 1500-2500 rpm. This is at 2500ft elevation.
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post #20 of 39 (permalink) Old May 4th, 19, 5:56 PM
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Not to highjack but what should this cam be making for vacuum? 434, stroked 402 with a 454 crank 10:1.
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post #21 of 39 (permalink) Old May 4th, 19, 8:45 PM
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Re: Will this cam have enough boost for power brakes?

Ive got about 10" @ Idle and It works my stock power booster fine .
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post #22 of 39 (permalink) Old May 4th, 19, 11:55 PM Thread Starter
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Re: Will this cam have enough boost for power brakes?

Quote:
Originally Posted by pockets View Post
When Mark and I discussed my build, he first mentioned that cam. I decided on the next step down 228/238 and Mark had it cut on a 111 instead of a 112. I do not regret it at all. Cruise along in 3rd gear at 1200 rpm (3.42 gear, 27" tire, 10" tight with 2300 stall) and runs smooth as silk, but you can floor it and it kicks down to 1st, lights the tires and bang the limiter so quick you can't take your foot off the gas quick enough. With locked timing at 36 and 10:1 makes 11.5" vacuum at 775 rpm idle in gear, and 13" at 825 idle in park. 20" when driving at 1500-2500 rpm. This is at 2500ft elevation.

Mark is who spec'd that cam for me.

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post #23 of 39 (permalink) Old May 5th, 19, 4:51 AM
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Re: Will this cam have enough boost for power brakes?

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Originally Posted by 70GS455 View Post
Lobe duration at 0.050" is not the only predictor of idle quality. Something that everyone is ignoring and not considering is the lobe separation angle. This cam has a 109 LSA. It has 25 deg of overlap (at 0.050"). Unless it's a 525+ cubic inch motor, there will not be enough vacuum

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Valve timing is a big factor yes, but I don't agree with your conclusion regarding the cam being asked about. If it were specs for a cam going in a SBC engine, maybe. But not a BBC.

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post #24 of 39 (permalink) Old May 5th, 19, 9:50 AM
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Re: Will this cam have enough boost for power brakes?

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Valve timing is a big factor yes, but I don't agree with your conclusion regarding the cam being asked about. If it were specs for a cam going in a SBC engine, maybe. But not a BBC.
Lol. Ok

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post #25 of 39 (permalink) Old May 5th, 19, 9:58 AM
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Re: Will this cam have enough boost for power brakes?

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Not to highjack but what should this cam be making for vacuum? 434, stroked 402 with a 454 crank 10:1.
You have 83 deg of overlap (at adv.). Need to know the 0.050" lift duration numbers. I would guess they are around 240/250. But my guess is prob around 10" vac or less. You're on a 109 LSA also. I don't think this will be good for power brakes without a pump or booster

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post #26 of 39 (permalink) Old May 5th, 19, 2:12 PM
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Re: Will this cam have enough boost for power brakes?

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Not to highjack but what should this cam be making for vacuum? 434, stroked 402 with a 454 crank 10:1.
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.

It was mentioned that valve overlap being created by the cam is a big factor, and yes it is. But even the degree of valve overlap in and of itself is NOT a determining factor in manifold vacuum. Because it also depends on where in the stroke that overlap occurs. You can have two camshafts which create the same number of degrees of valve overlap, but if more of the overlap with one cam is taking place after top dead center, (ATDC) of the piston position, and the other causes more of the overlap to occur BEFORE top dead center, (BTDC) then that too can cause very different amounts of manifold [email protected] There are just too many variables going on.

This is just one of many reasons why I miss the late great can designer Harold Brookshire, (AKA "UDharold"). He would very often be able to look at all the cam specs of any one particular cam, (including the manufacture's listed valve timing specs for the cam grind in question) and provide a definitive answer.
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post #27 of 39 (permalink) Old May 6th, 19, 1:58 PM
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Quote:
Originally Posted by BillyGman View Post
Quote:
Originally Posted by SFD View Post
Not to highjack but what should this cam be making for vacuum? 434, stroked 402 with a 454 crank 10:1.
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.

It was mentioned that valve overlap being created by the cam is a big factor, and yes it is. But even the degree of valve overlap in and of itself is NOT a determining factor in manifold vacuum. Because it also depends on where in the stroke that overlap occurs. You can have two camshafts which create the same number of degrees of valve overlap, but if more of the overlap with one cam is taking place after top dead center, (ATDC) of the piston position, and the other causes more of the overlap to occur BEFORE top dead center, (BTDC) then that too can cause very different amounts of manifold [email protected] There are just too many variables going on.

This is just one of many reasons why I miss the late great can designer Harold Brookshire, (AKA "UDharold"). He would very often be able to look at all the cam specs of any one particular cam, (including the manufacture's listed valve timing specs for the cam grind in question) and provide a definitive answer.
Thanks for the reply Billy. Cam seems a bit to much for what I want in addition to the power brake dilemma.

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post #28 of 39 (permalink) Old May 6th, 19, 2:03 PM
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Re: Will this cam have enough boost for power brakes?

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Not to highjack but what should this cam be making for vacuum? 434, stroked 402 with a 454 crank 10:1.
Just looked it up. It is 243/251 at .050. It has 29 deg of overlap and will be too much for power brakes. 19-20 of overlap is the general rule of thumb as a limit for vac accessories in 450'ish ci motors.

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post #29 of 39 (permalink) Old May 6th, 19, 2:10 PM
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Quote:
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Quote:
Originally Posted by SFD View Post
Not to highjack but what should this cam be making for vacuum? 434, stroked 402 with a 454 crank 10:1.
Just looked it up. It is 243/251 at .050. It has 29 deg of overlap and will be too much for power brakes. 19-20 of overlap is the general rule of thumb as a limit for vac accessories in 450'ish ci motors.

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Thanks, the best I could get out of it was 8”- 9” vac.
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post #30 of 39 (permalink) Old May 7th, 19, 3:40 AM
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Re: Will this cam have enough boost for power brakes?

Power steering hydro boost, manual steering, electric vacuum pump, 8" dual diaphragm booster. Run whatever cam you want.

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