Anybody check manifold vacuum on your engines?

[fatbaldmoparguy]

I'm looking to build a 408 to put in a duster with power brakes. I was wondering what kind of vacuum readings people are running with various cubic inch and cam combinations and how well their brakes are cooperating.
Engine will likely have edelbrock RPM heads and manifold. I was hoping to be able to run a hydraulic roller in the mid 230's at .050 and still have enough vacuum to work brakes properly.

 

[bbrroowwnn]

Cam selection is key if you want to run power brakes....I believe you need at least 10 or 11 to run power brakes.....mid 230's at .050 duration is about as far as I would go with power brakes.....You can always run a vacuum reservoir and/or pump if you go larger and still want power brakes.....I run 228 @ .050 and at idle pull about 15

 

[Bad Sport]

13 to 14 inches is about minimum, mine is at 13 and the power brakes work, but stiffer than most.

Two options:

1) Go to manual
2) Install a vacuum pump to assist in operating the brake booster.

 

[MopaR&D]

Manual brakes FTW... these cars are light enough you don't really need power assist.

 

[SLOPAR72]

I personally like to see 14 inches for power brakes. I doubt you get anywhere near that number. However as said you can get by with manual or do something different for power assist....

As for a vacuum gauge, everyone needs one in their life lol....

JW

 

[BigBlockMopar]

I've found an electric vacuum-actuated vacuum pump out of some modern Volvo, hooks up in the vacuum lines to the booster.
It's supposed to turn on automaticly when vacuum gets too low for the brakebooster to operate properly.

Not sure why a modern car would need this but found it handy nonetheless.
Haven't installed it yet though, but will put it on my '60 NewYorker which has a rolled cammed 500" engine under the hood, and its early '60s brake system needs the vacuum badly.

 

[halifaxhops]

I have a vac pump and to tell you the truth if I was going to do it again it would be a hydra boost setup.

 

[olei]

I run a low vacuum camshaft, and I'm using Hella UP28 vacuum pump with success; https://www.summitracing.com/int/parts/hla-009428081

I run the pump in parallel with engine vacuum (using check valves). If you want to use the vacuum pump as a standalone you need the Hella UP30,
if I remember correctly.

For controlling the vacuum pump I use the Superior #K058 adjustable vacuum switch (don't use SSBC #28146SW vacuum switch, it's absolutely ****).

 

[halifaxhops]

I use the same switch for the same reasons!

 

[downsr]

I have a bullet roller camshaft in a 416.235@50 pulls 15 at idle

 

[moper]

The cam design is the key. Too much of the wrong thing will hurt vaccum. I don't think you'll be able to get a good compromise between performance, and braking ability, and a hydraulic roller. I agree on at least 14-15" if you want to run the factory booster. A custom cam grinder can help address some of the issues but best case to me is remove the power brakes, or upgrade to hydroboost.
I've installed hydroboost on a couple cars and it is much better than the vacuum booster in a performance car.

 

[SLOPAR72]

The motor that is currently in my car is around 12 inches. I was going to use the Booster I got with the Disk Brakes going on the car but will do without. I have done 2 Hydroboost retros and deal with them on our work trucks and are ultra simple and reliable...

JW

 

[Lustle]

I got power brakes and steering. 340, .040 over, 10:1 SCR, Comp XE274H, airgap with holley 670 street avenger. I make 12 inches around 850 RPM in gear. 14 around 1000 RPM in gear. If I leave it at 850 I gotta let it warm up good before I drive it. About 5 minutes. And even then it'll give me trouble at the first two stop signs (I make right turns at both, so it's doing double duty). At 1000 RPM it's never really a problem. The air gap makes it fairly cold blooded.

Bump the RPM up if you need to. My car actually runs great at 1000 idle in gear. It hits/pulls harder. It's just hard on it shifting into gear, I run about 12-1300 RPM out of gear to get the 1000 RPM in gear. Depending on cold/moisture on the day I'm driving it.

I'm looking at going solid roller this winter, along with headwork. And vacuum is going to be something I consider when I get a cam. But I won't let it hold me back from the right cam. I can put on a reservoir or take off power something if I have too.

 

[bbrroowwnn]

I got power brakes and steering. 340, .040 over, 10:1 SCR, Comp XE274H, airgap with holley 670 street avenger. I make 12 inches around 850 RPM in gear. 14 around 1000 RPM in gear. If I leave it at 850 I gotta let it warm up good before I drive it. About 5 minutes. And even then it'll give me trouble at the first two stop signs (I make right turns at both, so it's doing double duty). At 1000 RPM it's never really a problem. The air gap makes it fairly cold blooded.

Bump the RPM up if you need to. My car actually runs great at 1000 idle in gear. It hits/pulls harder. It's just hard on it shifting into gear, I run about 12-1300 RPM out of gear to get the 1000 RPM in gear. Depending on cold/moisture on the day I'm driving it.

I'm looking at going solid roller this winter, along with headwork. And vacuum is going to be something I consider when I get a cam. But I won't let it hold me back from the right cam. I can put on a reservoir or take off power something if I have too.

uh? vacuum goes down as RPM goes up.....ever have a vacuum gauge hooked up and snap the throttle? It goes to zero.....ever have a vehicle with those old vacuum wipers? The harder you push the gas pedal the slower the wipers move

 

[MOPAROFFICIAL]

Manifold choice helps, you will see manifold vacuum gains with a dual plane of around 2" over a single plane manifold.
Examples below mostly show what doesn't make enough vacuum. Fwiw
251@.050 solid roller 10.5"@850rpm w/dual plane, only 8" with single plane. cid 410
236@.050 hyd roller 14"@800 rpm w/dual plane. Cid 368
252@.050 solid 10.**" @800rpm dual plane. Cid 416
219@.050 hyd 19-20" @ 800rpm dual plane. Cid 340

 

[Lustle]

uh? vacuum goes down as RPM goes up.....ever have a vacuum gauge hooked up and snap the throttle? It goes to zero.....ever have a vehicle with those old vacuum wipers? The harder you push the gas pedal the slower the wipers move

So, idling in gear, I should have my RPM set as LOW as possible for best vacuum. Right?

I'm going to give you a minute before you respond to that. Oh and here's a tip. Load/throttle blade position has something to do with vacuum at RPM.