Boost Pressure?

[81Turbo]

First of all let me say thanks to all of you on this board who contribute your time & wisdom so generously. Although I am not an active contributor to this board, I read it regularly.

I bought a 1981 930 a little over a year ago and at that time maximum boost would be about 0.7 bar. Since then it appears to have dropped slightly to about 0.6 bar. Can anyone tell me what the correct maximum boost pressure is and if this slight decrease in boost is indicative of a waste gate problem.

One other problem that I'd like to find an answer to before I take the car in is relaterd to starting. My car is quite difficult to start when cold often taking judicious application of throttle at the exact moment of firing. This has been the case since I bought the car so I've gotten used to it. The car fires immediately when hot and idles perfect. The problem I am having is with "warm" starts, i.e., after sitting for 2 - 4 hours. During this period the only way to gat it started is to keep turning over the starter while applying gas continuously. Sometimes this takes 4 or more attempts to get it going after which it idles like a Model T for about 30 seconds.

Any information on either of these subjects would be greatly appreciated.

Thanks,
Todd Gillespie

[beepbeep]

Todd:

Nice car-choice, i have black on black 81' 930 too

About warm start: there is a so called "cold start valve" that helps starting the car when engine is cold. It bypasses throttle and there is a electrical contact going to it.

First of all, check it for the leaks. Second, connect power to it and check if it opens. Third, check and possibly replace temperature switch.

One of those three things is busted.

About boost, check if:

1. Wastegate is opening too early (weak spring in it)
2. Gases are leaking trough wastegate -unbolt exhaust pipe from WG and run the engine, if you hear loud sound wastegate is leaking.
3. Turbo-impeller is worn down -unlikely (detach hose from turbo and take a look at the vanes)

Problem nr. 1: my guess is that termo-sensor is disconnected

Problem nr. 2: my guess is that wastegate is worn and leaking internally.

Cheers!

[cstreit]

I concur, either the wastegate spring has lost strength, or you had leaks... You may also have blown o-rings to and from your intercooler.... That's a cheap and easy fix...

If it's getting worse, I would bet o-rings... THe wastegate spring doesn't go bad that fast...

I believe (but i'm not 100%) that proper boost was 0.8 bar for the euro turbo.

[81Turbo]

Thanks guys, I'll check into these things.

Todd Gillespie

[Greg-slant/cab]

I am not sure if your vehicle is equipped with a fuel accumulator or not. My car was very difficult to start cold. I had to time it like you said...and crank and crank the engine over. After it started it would start fine all day unless it sat for 3 or 4 hours. I was told the accumulator holds pressure in the system. A faulty one does not hold pressure making the car build back up before it will start. Some one else might be able to explain it better but I replaced mine and it worked great.

------------------
Greg-slant/cab
http://www.geocities.com/gregslantcab/

[Jerry S]

Hello all,

Last I read, stock boost ranges from 0.7 to 0.85 bar based on the factory spec book. I have also heard that typically a normal turbo runs about 0.8 bar. What would be the difference between 0.8 and 0.7 in terms of power, and could you feel the difference ??

thanks

[81Turbo]

Thanks for your input Greg. My car does have a fuel accumulator and I also suspected this to be the problem. I really wanted to get some more input on this before I took it in to be repaired as the only authorized Porsche service where I live is the dealer and the price of parts is scary to say the least. I've heard of a few people who have had the replace parts until problem solved nightmare which I want to avoid. At least now I have some consensus on possible problems.

Jerry; as for whether or not I could feel the difference with the drop in boost pressure, the answer is YES!

Thanks again,
Todd

[Natchamp]

The difference would be 2.2lbs of boost and you definately should be able to feel it if everything else it right but its not going to be earth shattering.

.7 bar = 10.3lbs
.85 bar = 12.5 lbs

------------------
Mark
The Beast
mark@hargett.com