Let’s play vacuum

I want to get my vacuum up a little to help my power brakes. I am going to install a canister first. Then will go to a electric vacuum pump if the previous doesn’t work. Will the pressure pump give too much vacuum if there is such a thing? How does the canister get installed? What hoses to where? A diagram would help. Thanks Frank

 

""too much vacuum" with regards to car's brakes. (not a problem)

The booster acts with both atmospheric pressure and engine/manifold vacuum.
The booster uses the vacuum on one side, (removing positive pressure on the vacuum side) and the positive pressure that is always present on the "atmosphere" side.

So, by having higher vacuum, the result is "atmospheric pressure" aiding the booster to require less pedal force to achieve higher brake power to the master cylinder.

Having a canister, hydro boost or other "vacuum/power assist" will not "overpower" the basically stable 14.x psi of atmosphere on the booster. So, do not worry about that. Just get what works to provide adequate vacuum to the booster over the entire range of your driving.

High lift/greater overlap result in low vacuum when "letting off the gas pedal/idling" and why vacuum assisted accessories do not respond as they should. A "stock" engine, typically had high vacuum at idle and "off throttle" (as in deceleration).

This is increased with downshifting manual with throttle closed, or with automatics that downshift at higher RPM vs those autos that tend to "coast" in the higher gears until near stopped.

But that "brake fade" from loss of vacuum in a power brake system, or from heat fade on a manual brake, is a butt pucker that you do not want.

I have never had a street car that had so low a vacuum, that it impacted brake effort, except the time I had the manifold to transmission modulator line leaking, and that was "pucker time"! (as well as way late upshifts at moderate throttle)

 

Thank you for the reply. Frank

 

What cid motor is this?
What cam is in it ?
Is this a fresh total rebuild, or a higher mileage motor that as a cam put on it?

The smaller the combustion chamber the more vacuum the motor will have.

On motors that have had a cam installed above a certain duration the motor will make more vacuum above / off idle then at idle.


In situations like this a storage can helps a good amount.

If you have a somewhat higher mileage motor I have seen them idle ok and run good ( relatively) yet the valves and valve seats showed what was the start of bad leakage and was reducing the level of vacuum by a good 3” Hg from what it could have been.

One thing to try to test out for a vacuum leak is this.

Get the motor fully warmed up so that the choke is open.

adjust the carbs mixture screws for the best stable idle, confirming that moving the idle screws either way changes that idle greatly.

Then at idle slowly close the choke .

If the motors idle speed goes up then there is a real good chance you have a vacuum leak taking place.

 

How much vacuum do you have at idle? Less than 10-11?

 

Another option is a larger power brake booster.
I have replaced a typical booster with a double diaphragm unit.

More assist with the same level of vacuum.

 

Lots of times, what's really needed is a proper tune-up including distributor advance calibration, and having the engine actually get the amount of fuel it needs, instead of what the carb/injection is providing.

Lack of fuel at idle often gets crutched by excess initial timing. But that has it's own set of problems.

 

First try raising your idle speed to 950 rpm that will likely fix it.