Oldguard 7

As we all know big cams produce low that cause vacuum operated components such ad the brake booster and the headlights. My question is what is ysed to help the brake booster and the headlights to operate as they should.

Street Rat

An electric operated vacuum pump can be added to the car. Tend to be noisy.

Also vacuum reservoirs can be used. Vacuum is stored in a canister until needed.

gkull

I never had a problem with my big solid rollers. what is your present vacuum gauge reading. There are some things to try before going to a vacuum pump

fishslayer143

I installed a SSB Electric Vacuum pump with my Stroker 9 yrs ago.. It only has about 6 inches hg vacuum at idle so, no brakes at all. Pump works great,excellent brakes , maintains 18-20 inches hg constantly.. only runs when needed .. I hear it charge up about 15 seconds, when I turn on key, but after engine is running you cannot hear it ..

The Money Pit

Probably not the answer you are looking for, but my cam idles at 1000 with between 6 and 8 inches of vacuum. I converted my brakes to manual, and for the headlights converted to Miata electric actuators. Works great, and no worry about brakes or having the lights drop.

C6_Racer_X

Check valve plus vacuum reservoir can help for just about everything. You need a big reservoir for the brake booster to work, and a big hose from the reservoir to the booster.

If you want to change boosters, there are some hydraulic boosters that operate off the power steering pump. Those work if you have a power steering pump present. Tell the parts guy you have a 1994 GMC TopKick C6000 (or a Chevy Kodiak C60) with a 6.0L gas V8 and you need the power brake booster for that. I'm not sure how easily these swap into a C3, but they are an option that sometimes works for forced induction applications (where vacuum isn't always available).

TimAT

I had that discussion with the machine shop that I got my parts from. I ended up with an electric vacuum pump. Got it installed, built the motor, installed it and found out that I really don't need it. Running 11-12" at idle. Headlights are a bit slow, but the brakes seem fine. Now I can't get the electric pump out without a bunch of disassembly. It'll live there until I decide to pull the brake booster again.

Oldguard 7

5"hg

Neil B

I can't help you with the vacuum headlights, but I can tell you that my '69 Camaro has a 268/274@.050 solid roller in a 372 ci small block. It makes 7-8" vacuum at 1,200 rpm and the stock power brakes work perfect.

Neil B

How big is the cam and what is your idle speed?

Les

I bought and installed the pump in the link below at about this time last year. It made my brakes better than they had ever been. I can hear it when I first key the ignition before the engine fires. Once the engine lights, I don't even notice when it's running unless I happen to be standing outside the car. It's only on when needed, which isn't often.

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

zuendler

My engine makes 14"hg vacuum. If I want to get the wheels blocked I need more pressure than the bosster does support. This means I can feel a "dead stop" when pressing the pedal. This is when the valve in the booster is completly opened. With more force I can operate the brakes as it should, but I need to press the pedal far to get there (yes they are well bleeded). Has anyone expirienced this yet?
When I produce a lot of vacuum driving downhill, and then press the brake, it brakes noticeable better.
I have an electrical pump already here, will install and test it.

Booster has already replaced by new one, but did not make big difference.
I just need more power assist.

fishslayer143

14 in hg is typically enough , but if you use the electric, you will have 18-20 in hg constant.. your brakes will work well if everything else is OK

bence13_33

Oldguard:
I'm not sure if it helps or not but I ran a Comp Cams solid flat tappet (294S) and was able to idle between 800RPM-1000RPM with no problem.

I'm curious, does port/valve size and manifold type affect manifold vacuum?I feel like it does but I just wanted to hear from some more informed people with maybe an example or experience.

427Hotrod

Yes....intake impacts it to a good degree. On a single plane....a cylinder "sees" another valve open and essentially can draw through it too. A dual plane separates that.

Valve size impacts overlap impact.

Compression has a big impact also. Higher compression brings higher vacuum since there is a larger change in chamber/cylinder volume as piston drops.

JIM

dochorsepower

Blower !

69Vett

run baseline engine vacuum, without any vacuum lines connected. record that #.
anything over 11" is enough to operate vacuum correctly.
add components, anything that drops vacuum is a leak, and needs to be fixed.

v2racing

My engine runs about 9 inches in neutral and 7 in gear, but it pulls 20 inches at cruise and more on decel. My lights and power brakes worked great in my 80 when this engine was in it, but I made sure there were no leaks and the check valves were working. If any part of the vacuum operated items aren't 100%, you will have issues.

Mike

PainfullySlow

I went with a somewhat bigger cam and to be absolutely sure that I did not have vacuum issues, I bit the bullet and went with electric headlights.

red78vette

i have abuilt 400 sbc with a big solid roller cam and i put a vacuum reservoir where the charcoal canister was and it works fine for both brakes and lights