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I have a late 70s LT1 350 with 10 to 1 domes, a 3/4 Crowler cam and 194 fuelly heads, in a 1972 Nova with power assist brakes. I have no brake pedal unless I rev motor or has been idling a while. The plastic check valve in the vacuum canister is working.
I've been told that I need to plumb a canister into my brake system to store more vacuum to solve this. I will re bleed brakes this weekend. What do you think??
Thanks for your time
 

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I have a late 70s LT1 350 with 10 to 1 domes, a 3/4 Crowler cam and 194 fuelly heads, in a 1972 Nova with power assist brakes. I have no brake pedal unless I rev motor or has been idling a while. The plastic check valve in the vacuum canister is working.
I've been told that I need to plumb a canister into my brake system to store more vacuum to solve this. I will re bleed brakes this weekend. What do you think??
Thanks for your time
sounds like my problem......use a vacuum canister....should help....
 

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Had a 3/4 race cam, it was a Cam Dynamics (crane) 286H ([email protected]/.465/106) 3200-6200 all midrange power, sounded like a basket ball dribbling in my 70' LT-1 350, Had 8.5" of vac and brakes would work fine with the first push but was ok. My friend had low vac with a 396 (408) and the canister didnt work, so i recommended Rhodes lifters and they worked good. What intake are you running?
 

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Have you put a vacuum gauge on to find out how much you have?
 

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i'd love to see a cam card for a 3/4 cam,,, heard of 'em ,, never saw a cam card for one

I always wanted to know what happened to the other 1/4... :)

Seriously, bleeding the brakes will not cure your problem. You need to make sure your power brake system does not have any leaks. Make sure the booster is not leaking. Make sure the line from the manifold to the booster and the fittings are not leaking.

Probably a low vacuum situation due to the camshaft.
 

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get a hi rise dual plane intake unless you have one already, a single will kill all your vac.
Huh.?.?.?:eek:

How do you figure?

So I guess an open spacer on top of a dual plane intake will kill vacuum as well since it's just an open plenum. :rolleyes:

Or the slot or notch Edelbrock and everyone else cuts in the divider of the dual plane intake is done to kill vacuum?

Now, it's common knowledge that a dual plane will give a stronger vacuum "SIGNAL", but that's quite a bit different than a measured amount of vacuum.:yes:
 

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Huh.?.?.?:eek:

How do you figure?

So I guess an open spacer on top of a dual plane intake will kill vacuum as well since it's just an open plenum. :rolleyes:

Or the slot or notch Edelbrock and everyone else cuts in the divider of the dual plane intake is done to kill vacuum?

Now, it's common knowledge that a dual plane will give a stronger vacuum "SIGNAL", but that's quite a bit different than a measured amount of vacuum.:yes:
How come some are confused between the designs and benifits of a 180 and 360 manifold? :confused: Don't power brakes need a stronger vacuum signal?
 

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How come some are confused between the designs and benifits of a 180 and 360 manifold? :confused: Don't power brakes need a stronger vacuum signal?
Vacuum signal in reference to a carburetor is in terms of velocity.... Power brakes just need vacuum quantity above 12 generally, however a dual diaphragm 7" booster will work equally as well at a 11" booster and better because of surface area...but require less vacuum than the 11"...

Vacuum is the same whether it goes though 2" or 100' of tunnel if its 9" at 2 ft then it will be 9" at 100'.... however the strength of the draw of the vacuum is varied by the cams LS and Duration.. discounting reversion.
 

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How come some are confused between the designs and benifits of a 180 and 360 manifold? :confused: Don't power brakes need a stronger vacuum signal?
Not signal...:no: Just more vacuum period.:yes: We're not discussing booster signal strength here.:no:

Vacuum signal in reference to a carburetor is in terms of velocity.... Power brakes just need vacuum quantity above 12 generally, however a dual diaphragm 7" booster will work equally as well at a 11" booster and better because of surface area...but require less vacuum than the 11"...

Vacuum is the same whether it goes though 2" or 100' of tunnel if its 9" at 2 ft then it will be 9" at 100'.... however the strength of the draw of the vacuum is varied by the cams LS and Duration.. discounting reversion.
Well put.

The engine, because of it's mechanical design factors, is going to draw "X" amount of vacuum. It doesn't matter how much of a plenum the intake has. As long as the throttle blades are closed, it's only gonna "Suck" so hard.:rolleyes:

One thing the original poster can do to try and get a bit more vacuum is experiment with his timing curve and try to get a few more degrees of initial timing. This generally raises the idle allowing you to close the throttle blades a bit (to lower the idle back down)...thus making is run with a bit more IDLE vacuum.
It will also make the throttle response a bit snappier.:yes:
 

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And if you tune the idle mixture with a vacuum gauge, it will be easier.
You want the lowest steady idle with the highest vacuum. Turn both mixture screws equal number of turns. Properly tuned it may run and stop better.
 

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Discussion Starter #20
Thanks to all you guys

Thanks for your help

You people save me a lot of time and I appreciate your input. I'll re post up when I try your suggestions
 
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