Brake booster when going NA to Supercharged

[JohnJL]

My base car is an 83 SC, and has power brakes running off a vacuum line in the manifold to the booster.

I am in the midst of building a supercharged engine to replace the current motor and it occurs to me the booster will no longer have a source of vacuum as the manifold pressure will be around 1 bar just when I need brakes most.

Anyone offer any guidance about this?

thanks

[Bill Verburg]

Audi and late Porsche use an electro-hydraulic system. An electric pump pressurizes a hydrauic boost circuit.

Adaption to you car won't be easy.

Some hotrodders use a similar system, ATE used to have a stand alone system too.

Another option is also used by some hotrodders an electric vacum pump. I have no idea hoew effective any of these aftermarket systems might be.

Lastly depending on m/c and calipers you may be able to get away w/ no boost.

[Scott R]

I drove an electric 914 that had an electric vacuum booster pump, worked great, in fact there was no difference.

[burgermeister]

Probably a dumb suggestion for some reason, but is it possible to put the supercharger downstream of the throttle body? In which case, you'd have plenty of vacuum upstream of the supercharger. My Park Avenue appears to be set up that way.

[David]

Unless you're Hans Stuck, I can't see you being on boost and braking at the same time so it shouldn't be a problem. It's not on my car.

[jbrinkley]

me either, plenty of vac off boost

[dean]

There is a check valve in the system I think. You will not have a problem.

[JohnJL]

Thanks guys.

Heres the layout I am building from...where would vacuum be available here for the stock booster? My brakes are rebuilt SC units on stock rotors but I have no problems, they are predictable and never fade so I would like to keep them as-is. In a hot cabin I would prefer to keep the boosting there as it would be quite a workout on top of everything else going on. The car is very light so the brakes seem matched fine.








Oh and David, I drive more like Hans Schmuck. I was thinking of the activities at the end of the main straight...from WOT to a bit of trailbraking through the left, on the throttle again then down hard on the brakes. That's a lot of variation in the boost levels which I would think would in turn make the brake booster see varying vacuum signal, which would in turn make the brakes feel unpredictible?

[David]

What are you using for an intake manifold? Is there not a vacuum port on it for the brakes?

[Quicksilver]

Hook up a vacuum reservoir with a check valve and you will have an unlimited supply of vacuum even when the car is under boost.

[burgermeister]

Originally Posted by JohnJL

Thanks guys.

Heres the layout I am building from...where would vacuum be available here for the stock booster?

Between the throttle and the supercharger - vaccum just like any NA car.

I think there is a vacuum tank in the front of your car already (I wrote think, not know ), and it would have a check valve - under full throttle, even a NA engine has little vacuum.

[spuggy]

Originally Posted by burgermeister

Between the throttle and the supercharger - vaccum just like any NA car.

+1

Use the stock location between the throttle plate and the compressor, it gets vacuum. Note that if you plumb a boost gauge there that displays vacuum as well, you'll both see vacuum and be able to watch the boost building.

If you plumb the boost gauge after the compressor, you'll not see any vacuum at all (practical experience). Upside is a gauge plumbed here can "see" transient boost spikes - like a slow-reacting recirc valve or wastegate - not available in the stock location.

[greglepore]

My turbo 3.2 has no changes to the brake vac line at all, and no issues. There is a check valve.

[JohnJL]

Awesome, thanks everyone. Much appreciated.

For clarity, I am currently running a 3.0 with a 3.2 alu intake with the vacuum coming off the #3 intake near the firewall. That would obviously no longer work...

I dont have a vacuum tank now but have the old one around to reuse...

[David]

Why wouldn't the vacuum coming off the #3 intake work? That's where I get vacuum from my Carrera intake.

[RarlyL8]

The stock 930 vac/brake plumbing works under the conditions you have described (for a turbo anyway).
On occasion I have to apply the brakes and the throttle simultaneously when rounding a corner in order to keep on boost. No problems.

[spuggy]

Originally Posted by 125shifter

Why wouldn't the vacuum coming off the #3 intake work? That's where I get vacuum from my Carrera intake.

My mechanical VDO 30-0-25 gauge when plumbed on the throttle body reads ~16 PSI vacuum off-boost (e.g. idling, overrun), will show boost building over manifold vacuum.

When fitted to the intercooler (after the compressor): no vacuum, shows +-ve (above 0 PSI = atmospheric pressure) boost only.

[84_Carrera]

On my 'charged SHO, the setup was poorly designed - MAF & TB after the Vortech unit. I still had plenty of brakes, though the MC was undersized for the 4-piston Wilwoods I had on there & was a known issue (it was the original, slated-for-single-piston-calipers unit).

They make a vac reservoir IIRC somewhere online... I seem to remember seeing one of those as I had similar concerns.

[David]

Originally Posted by spuggy

My mechanical VDO 30-0-25 gauge when plumbed on the throttle body reads ~16 PSI vacuum off-boost (e.g. idling, overrun), will show boost building over manifold vacuum.

When fitted to the intercooler (after the compressor): no vacuum, shows +-ve (above 0 PSI = atmospheric pressure) boost only.

Which is why vacuum ports and MAP signal ports should be after the TB.

[JohnJL]

Sorry to ressurect such an old thread but I'd going the machine work now...

David or others, could you please verify that using the stock manifold ports on the intake (that is, downstream of everything except the actual heads' intake ports) will provide vacuum for a brake booster? Any a vacuum reservoir may or may not be present or necessary?

This is for a supercharger providing ~15lbs of boost.

Thanks again.