Brake Vacuum Line Hook Up At Engine

[goldgunner]

1980 911SC with CIS removed

I need some advice please:

Should the power brake booster vacuum line be attached directly to the large nipple at the engine throttle body?

If not - where? Any interim hook-ups necessary?

Thanks!
Jim

[mb911]

There should be a Y connector one end goes to the large nipple at the back of the TB and the other side foes to a fittinf on the air box Below the throttle plate.. It should be a venturi looking y with a vw part number on it

[goldgunner]

Thanks Ben - but since my CIS is removed, I don't / won't have an 'air box'. Hence the direct shot to the throttle body?

[Grady Clay]

Jim,

With the CIS removed, what do you plan to install?

With carburetors or MFI the solution is to install the Sportomatic vacuum check valves in the intake manifolds/throttle bodies (six are best). You can use a Sportomatic vacuum reservoir. If you intend much track or auto-X, an additional electric vacuum pump will keep the power brakes properly functioning.

Best,
Grady

[goldgunner]

Thanks Grady

Here's the plan - parts in hand, slow rebuild slowly getting there -
Clewett / Electromotive TEC3r EFI thru 3.2 Carrera manifolds and fuel injector rails.

[Grady Clay]

Jim,

What does that EFI use for a throttle body? Does it have vacuum ports? If you use the Carrera 3.2 throttle body, I suppose you could plumb a check valve into the Aux Air Regulating Valve port (in the L manifold, just below the throttle), to a vacuum reservoir and then to the brake servo. With the OE Fuel Pressure Regulator and the Pressure Damper still in the fuel circuit, they are controlled by the vacuum from the throttle body via a Y-part. You could make that a 4-way “Y” (an “X”) with the additional line to a check valve, reservoir and brake servo.

Do you have a good schematic air/fuel/electrics diagram for the EFI? You are going to want to combine that with the Porsche diagrams for the Carrera 3.2 so you can troubleshoot your system both now and in the next 20+ years.

Best,
Grady

[goldgunner]

ouch...I'm afraid you're making my head hurt...

Throttle body is the 3.2 carrera, along with the manifolds and fuel rails.

It has a number of nipple 'ports'.

The OE Fuel Pressure Regulator and Damper are still in the circuit...

So far, this 'plug and play' system hasn't been quite as advertised.

I understand, I think, what you're describing as to 'bleeding' (?) off of the fuel pressure regulator and damper connector.

You're thinking that a seperate vacuum draw for the brakes would 'distort' the regulator and damper functions?

Are you describing the check valve, reservoir and servo already exisiting at the front end of this system? Or suggesting additional components?

[Grady Clay]

Jim,

Sorry, no pain intended. This is supposed to be fun.

Post the instructions (or links) for the EFI. These days “plug ‘n play” seems to mean “plug this in and then play around with it until somehow you get it to work – or not.” I can’t install even the simplest software any longer for all the warnings and “protection.” If it weren’t for great Pelicans like KobaltBlau, I wouldn’t be on-line now. Carburetors and MFI are sort of the DOS 1.x for Porsche.

Part of having this be fun is understanding all the subtle little things. Mystery (proprietary) black boxes frustrate me. I like to know the “why” and “how.” That way I can confirm it is working as intended and, if not, how to diagnose and repair it.

I don’t think there is any issue with the vacuum for the brakes. There should be already a hose attached to the intake manifold that remains undisturbed.

I understand, I think, what you're describing as to 'bleeding' (?) off of the fuel pressure regulator and damper connector.

You're thinking that a separate vacuum draw for the brakes would 'distort' the regulator and damper functions?

While I don’t know for sure, I don’t think having an extra vacuum port here would have any effect on the function of the fuel regulator/damper. It was simply an easy place to find vacuum.

Are you describing the check valve, reservoir and servo already existing at the front end of this system? Or suggesting additional components?

The system doesn’t have a check valve (other than in the servo) or reservoir. Usually these conversions are accompanied with cams with more overlap. This results in less vacuum available for the brake servo. One way around this is to install a check valve(s) near the intake valve to allow a “pulse” of vacuum when the intake valve opens and the throttle is still closed. The vacuum reservoir simply serves to “accumulate” that vacuum.


The reason I want to see the EFI instructions is because I think they ignore the vacuum to the brake because it is in place and doesn’t need to be disturbed.

Best,
Grady

[goldgunner]

Grady - Other than the Electromotive TEC3r installation manual, there are no other instructions or roadmap...sadly.

Working with Richard Clewett and his plan, and the TEC3r system, and the rest of my 'plan', I've either accomplished or will have:
1. 3.0 to 3.2 Mahle P & C's
2. 964 Cam
3. Dual Plugs
4. Crank firing trigger / sensor and pulley
5. MAP sensor (Manifold Air Pressure)
6. MAT sensor (Manifold Air Temperature) [Tube housing between manifold halves]
7. IAC Motor (Idle Air Control)
8. TPS (Throttle Position Sensor)
9. EGO Sensor (Exhaust Gas Oxygen)
10 CLT Sensor (Coolant Temperature Sensor)
11. Cam Sync Adapter
12. DFU's (Direct Fire Units - Coils)
13. ECU (Electromotive TEC3r Engine Control 'Black Box' Unit)
14. Injectors and plugs to 'match' the above
15. Carrera 3.2 intake manifolds modified:
A. Add nipple for MAP Sensor
B. 'Add' metal & machine - match with heads intake ports

The Carrera 3.2 throttle body does have a large nipple for the vacuum brake line. Hence my original query as to whether this would now be a 'direct' hose hook-up.

However, you've got me thinking I'll need to have some interim pieces:
a check valve and vacuum accumulator. I need help identifying and specifying those components: Porsche OEM? Aftermarket generic? Whut?

Please keep the questions coming and the help flowing...

Regards - Jim

[Gunter]

Quote: The Carrera 3.2 throttle body does have a large nipple for the vacuum brake line. Hence my original query as to whether this would now be a 'direct' hose hook-up.

Just hook it up there and try it; the diaphragm in the Servo can will absorb some vacuum-fluctuation.
On the original SC-CIS, the vacuum line to the Servo brake booster comes from both above/below the throttle plate with the "Y" connection, if I remember correctly. That way, it is meant to be functional for vacuum with closed, and open, throttle.

[goldgunner]

OK Gunter - thanks for the advice.
But I do have a question, in regards to what you noted:
"On the original SC-CIS, the vacuum line to the Servo brake booster comes from both above/below the throttle plate with the "Y" connection, if I remember correctly. That way, it is meant to be functional for vacuum with closed, and open, throttle."

I'm missing something here...If the throttle is Closed, and no air is 'rushing' thru the throttle body, how is/would a vacuum be 'pulled'? Whether above or below the throttle plate?

[mb911]

with vacum from the engine intake!

[Gunter]

When the butterfly is closed, there is still vacuum created under the plate because, in idle, the pistons are still sucking air. I think that's why Porsche made a dual-connection for above and below the throttle plate.
I think that's right; I'll have another look on my SC.

[alphie]

Gunter or anyone....

Has this been confirmed regarding the stock CIS brake boost vacuum location? I removed most of my CIS with the installation of bitz efi. I attached the brake boost to the hacked-up air box nipple (which is below the throttle plate.

I imagine the vacuum is strongest under closed throttle - which is where most braking will occur. How can vacuum be achieved under WOT whether the booster line is attached above or below the throttle plate?

[alphie]

Gunter or anyone....

Has this been confirmed regarding the stock CIS brake boost vacuum location? I removed most of my CIS with the installation of bitz efi. I attached the brake boost to the hacked-up air box nipple (which is below the throttle plate.

I imagine the vacuum is strongest under closed throttle - which is where most braking will occur. How can vacuum be achieved under WOT whether the booster line is attached above or below the throttle plate?

[mb911]

I found that hooking up underneath the throttle plate and still using the venturi tube there was plenty of vacum.

[greglepore]

Isn't there a fitting on the left manifold for vaccum as well? I seem to recall that that is where its tapped for the booster on my 3.2

[bose213]

Originally Posted by mb911

There should be a Y connector one end goes to the large nipple at the back of the TB and the other side foes to a fittinf on the air box Below the throttle plate.. It should be a venturi looking y with a vw part number on it

Hi. I just read your comment about the Y connector. When I connect the vacuum booster hose to that Y connector, the engine starts to stall. Same when I block this Y connector with my finger. The vacuum booster itself is working properly. No vacuum leaks. Do you know what is wrong? Thanks.

[pmax]

Originally Posted by goldgunner

1980 911SC with CIS removed

I need some advice please:

Should the power brake booster vacuum line be attached directly to the large nipple at the engine throttle body?

If not - where? Any interim hook-ups necessary?

Thanks!
Jim

I would plug it up and live without the booster.

The booster works off a venturi setup in the CIS system drawing vacuum from the port at the airbox which you don't have the equivalent of anymore.