Low vacuume ?

[Rogie]

I am coming to the end of a long build and pull the car out of the garage today under its own power for the first time . It is a 72 cutlass 455 MSD fuel injection 4l80 e ( with stock tourq converter for now ) will wood 6 Pistons up front and LS1 brake swap in rear with will Wood duel tandem master and stock replace ment brake booster.
with car in park every thing feels ok but in gear brakes seem to fade while car is sitting still.
i don't won't to go to hydro boost if I don't have to.
is there any test I can do to see if my booster is getting proper vacuume?
is there a diffrent booster or vacuume canister I can use if booster is not getting proper vacuume.
I am pulling vacuume for the booster of the intake is this correct?

[67rally]

You can pick up a cheap vacuum gauge/tester for $15 or 20. Connect it to the intake port you have your booster attached to (with engine running) and it will tell you how much vacuum you have at idle.

[Rogie]

How much vacuume dose it take to operate a booster properly?

[MCB Matt]

You will want to see a minimum of 15" steady at idle. The canisters and pumps don't work well, we quite selling them for this type of application a while ago. Hydroboost if you don't want to deal with vacuum and want the most assist. They obviously take up much less space too.

Matt

[yellow1098Greg]

Looking for a good hydroboost installation explanation and info....don't know much about it myself

[MCB Matt]

Looking for a good hydroboost installation explanation and info....don't know much about it myself

There really isn't much to it. At the firewall, it's basically the same as a vacuum booster.

You will then need to run the lines, again, pretty basic if you are comfortable working with braided hoses/fittings.

There are many google images of house routing as well.

We sell Hydratech units ONLY!

Matt

[yellow1098Greg]

So if I want to run bigger rotors and calipers on the front and rear, it will really fix the vacuum issue? im assuming having a carb or efi doesn't matter much with hydroboost correct?

[MCB Matt]

So if I want to run bigger rotors and calipers on the front and rear, it will really fix the vacuum issue? im assuming having a carb or efi doesn't matter much with hydroboost correct?

Regardless of what disc kit you run, the Hydroboost will work and vacuum will no longer be an issue. Carb or EFI makes no difference either.

Matt

[rickpaw]

I am coming to the end of a long build and pull the car out of the garage today under its own power for the first time . It is a 72 cutlass 455 MSD fuel injection 4l80 e ( with stock tourq converter for now ) will wood 6 Pistons up front and LS1 brake swap in rear with will Wood duel tandem master and stock replace ment brake booster.
with car in park every thing feels ok but in gear brakes seem to fade while car is sitting still.
i don't won't to go to hydro boost if I don't have to.
is there any test I can do to see if my booster is getting proper vacuume?
is there a diffrent booster or vacuume canister I can use if booster is not getting proper vacuume.
I am pulling vacuume for the booster of the intake is this correct?

Also, since it sounded like the system is new, I'd check for air bubbles in the system before swapping out parts.

Just my $0.02

[andrewb70]

Also, since it sounded like the system is new, I'd check for air bubbles in the system before swapping out parts.

Just my $0.02

^^^This....of course also check how much vacuum is being pulled at idle.

Andrew

[battenheaded67cutlass]

Have you considered an electric vacuum pump to hook up to the Brake booster? I know it isn't as "perfect" as a hydroboost, but it is a lot simpler and much more affordable as well if you aren't going to be road racing it.

https://www.summitracing.com/parts/sum-760152





Can I ask what accessory bracket setup you are running to have a serpentine belt setup on a 455?


Very nice setup btw!

[oldstv]

I have a similar issue but i am LS, stock style master cylinder and duel type booster. My issue is only at start up, by the time I am at the first stop i have plenty of brakes.

[bd8134]

With the MSD Atomic EFI you can see what vacuum you are getting at idle and while you are running on the gauge. I have ~11 inHg at idle on a wide duration cam and my vacuum brakes are adequate, I don't like over boosted brakes anyway. A lot of cars use vacuum pumps for brakes, Audi, VW, Saab, etc, and electric cars or people converting to electric, if you feel you need to improve your brakes. The Bosch vacuum pumps I have used are quieter I believe than the SSBC style of vacuum pump. Summit sells a vacuum tank and companies like these http://www.evwest.com/catalog/produc...roducts_id=290 sell a vacuum switch to switch on the pump. They have a diagram on how it all connects up. You could also look to see if a dual diaphragm or bigger booster will work for you.

[TheBandit]

For reference, in gear at idle I have about 12" vacuum. Out of gear I have about 15". My 1970 factory single 11" vacuum booster (same as yours I imagine) seems to work fine; I don't feel "fade" like you're describing when holding the pedal down with my foot.

See what your vacuum level is in (R/D/1/2/3/4) and out of gear (P/N). If vacuum is bouncing around a lot, make sure the engine is in good tune and has an appropriate idle speed. If there is a big drop when changing from out of gear to in gear, you might also benefit from a looser/higher RPM stall converter. This will reduce the load on the engine during idle, which will also raise vacuum level, especially if you have a choppy cam.

On my old small block, the vacuum level and therefore the brake assist was pretty sensitive to the engine tune. Whenever I had a miss, it was clearly evident on the vacuum gauge because I'd get a periodic bounce in the needle and the vacuum / assist level was lower. When the carb tune was off, the overall vacuum would reduce along with the assist. When I had a stock stall converter and bigger cam with the vacuum level bouncing around, the assist was noticeably affected. When I went to a higher RPM stall, the idle speed was less affected by putting the transmission in gear and the vacuum was considerably more stable and higher than with the stock stall. I found that bumping the idle up from 600 to 800 or 800 to 1000 rpm could make a big difference and if I recall correctly I eventually decided to keep the idle around 1,000 rpm while out of gear and it would drop to around 800rpm in gear and have a reasonable steady vacuum level to supply the brakes. This also seemed to have good off-idle transition (which I also tuned via power valve and other BS carburetor stuff that I've long forgotten about)

I personally really like having a vacuum gauge inside the car. It's a good general indicator of the state of the engine.