Turbo timing and vacuum help!

TurboRuf · 04-20-2002, 04:33 PM

I am converting my 930 from a twin Electromotive HPV-1 setup to a Twin-Plug distributor configuration (because I want on-boost timing control). I have a couple of questions and concerns.

When the car originally had Electromotive units installed in it, the highlighted parts where removed in the image I’ve attached. In fact, most of the vacuum items where capped off. Since these items are all vacuum related, how important are they for the engine to properly run with a distributor?

The distributor has a vacuum canister with vacuum line in and out ports. The out goes to the air box and the in connects to the throttle body. Is there anything that goes in between these two vacuum lines? Any type of vacuum limiter or anything else I might be missing?

Thanks

RarlyL8 · RarlyL8's Garage

I JUST came in from my garage - doing the very thing you have posted.
It would be helpful to know what year your engine is, what smog controls (if any) it has, and what distributor curve you have.

The line from the dizzy to the throttle body has a Thermo Valve on the USA/Japan/California engines. It is not present on the Euro engine. If you have the Euro dizzy curve all is well.

The line from the dizzy to Bypass Valve Housing and the Warm Up Regulator has a Cut Off Valve in it for full throttle retard control in the California motor only. Again, not needed.

On the Euro engine the dizzy Vac Pot connects directly to the Throttle Housing - nothing else is present.

EDIT - I went back and looked at your schematic. #28 is a Vacuum Control. I believe this will be needed to run a conventional distributor. The other items, Auxiliary Air Valve and Thermo Valve should not be required.

dean · 04-20-2002, 06:07 PM

#28 is the decel valve. The thing in the upper right is Aux air valve. I think.
Dean

RarlyL8 · RarlyL8's Garage

Dean - I believe they are the same thing. All the information I quoted is from Volume 1 of the Porsche Workshop Manual. They call this thing a "Vacuum Control". It is the only component listed that occurs in all four fonfigurations for the 930 - USA/Japan/California/and Euro.

RarlyL8 · RarlyL8's Garage

Here's a picture of mine:

TurboRuf · 04-20-2002, 07:57 PM

Thank you for the insightful information.

My car is an 85 Euro 930, so no smog controls exist.

The distributor curve is currently unknown. It’s a stock 930 distributor that was modified to fit the Bosch twin plug cap/rotor (similar to the Andial conversion). How can I determine the curve?

Since it is a Euro 930, do you believe #28 (Vacuum Control) is still required?

Thanks

RarlyL8 · RarlyL8's Garage

The "vacuum control" do-hicky is the only item in common with all versions of the 930. All I can tell you is that it is needed in the stock configuration of your engine. You must have something else that is taking its place sense it is missing.

I Don't know how to tell the curve of your distributor. Sounds like it was locked out for engine management to take over. If you run the part number and find that it is stock for your motor you might be in luck. I had to buy a Euro distributor to work with my setup.

It is really a pain when you mix California, Euro, and aftermarket components. Your situation is even more complicated.

rattlsnak · rattlsnak's Garage

Have you thought about getting different software from electromotive (like PAFB) that will allow on boost timing? Sure would be easier.

dean · 04-21-2002, 03:59 AM

I have run my 930 and my SC without #28 for years. They are not needed in my case. Plug the holes and try it.
Dean

1bar · 04-21-2002, 10:10 PM

I don't know what a "vacuum control" is, but I was told by my shop, and the workshop manual seems to agree, that #28 is the deceleration control valve. It happens to be vacuum controlled (maybe that's where the term comes in?) - the vacuum line opens the diaphragm and lets some air by the throttle body when you back off the gas, to reduce the emissions and to keep the engine RPMs from dipping as it tries to return to a stable idle.

Mine was malfunctioning, hanging the engine up at high RPMs - when on heavy boost, it would cause the RPMs to increase 500 - 1000 RPM whenever I tried to upshift.

I disabled it by inserting a ball bearing in the vacuum line. No more risk of overrevving on fast high speed upshifts. But I still have the problem at low speed, as the engine almost dies every time it tries to return to idle. It's likely that this thing should be replaced, not disabled, to get the car to run well. It's on my list...

Larry

TurboRuf · 04-22-2002, 02:57 AM

Thanks for the info 1bar, from what I’m reading I intend to leave #28 out.

Rattlsnak, it was my understanding the HPV-1's couldn't be "re-programed" for boost timing control. I talked quite extensively with ElectroMotive and they never mentioned such an option.

My only real concern is what RarlyL8 said about the timing curve, Euro vs. US, and how much this will affect drivability. Since I’m not sure of my distributors origin, this could toss a real Monkey Wrench in the program/conversion.

If anybody has any additional information on the timing curve difference between and Euro and US distributor, I would appreciate it. Also, what type of issues will I run into running a US distributor on a Euro modified engine?

Enjoy the drive!