924Board.org

[Rick MacLaren]

Yeah Peter is right, the one bar boost spring should bring you up to the peak of boost, and maybe over the peak.

Interestingly though, when I hooked up mine, bought used for like $50, it only brought the boost up to 10-11 PSI. Then the 0.2 bar spacer brought it up to 12-13 PSI. Finally, I used the manual boost controller to bring it up to 15 PSI.

And yeah, if your car has been serviced like every year for say $3000 CDN per year, you won't have to worry much about things blowing apart. But Peter is right that you could benefit from taking the thing apart and re-doing the rubber and gaskets all around that system. I wish I'd done it - I would have saved myself loads of $$$. Mine was really close to mint, had all kinds of weak gaskets and O rings that blew apart when I increased the pressure in the system.

Turbos are touchy.

So yes, you can go with the manual boost controller and make some wonderful performance out of your car, but ya really gotta put the bux out to all those ancilliary components that surround the turbo and gas intake systems.

I've been running mine a 15 PSI under the assumption, and I could be wrong, that I'm not running too lean. Time will tell. I know it's very close to being too lean, but I have another engine and head, so I'm not sweating it too much. I'm willing to blow up this one so I can bore out my other engine, sitting in my spare bedroom on an engine stand, to 2.2 litres.

OH! BY THE WAY! There is another speed mod for the 931 that is awesome. Jon has done it, and no doubt most of the guys here:

LOSE WEIGHT. It's the second-best bang, and the best bang for the buck with a 931. Ya remove your back seat and headrest, and the rear liner thingy. Dump your spare tire and other junk. And it's very quick.
_________________
1980 Porsche 931 C2H5OH/H2O injected 15 PSI
1979 Porsche 924

[ This Message was edited by: Rick MacLaren on 2001-11-01 01:47 ]

[NiceOldTurbo]

woah good idea about the weight thing. but i dont have removable head rests??? its all one part.

tyler

[John H]

Guys,

I have been running a modified 931 (924 Carrera GT Replica) for about 14 years now and a few observations on Rick’s and Peter posts of the 30 and 31 October

First
I agree that at about this stage in the waste gates life they are a bit worn. If you’re going to take the unit off to rebuild I would recommend rather than put the 1 bar spring in you remove the vent fitting at the top of the unit and install a vent line into the engine bay. This line can then be plumbed into the inlet manifold and used to adjust the boost.

If you have the waste gate off and then feed air into the unit you will see that it starts to open at around 5 lbs and fully open for American spec cars at about 7 lbs (for European it’s fully open at around 10 lbs). If you feed boosted air in to the spring chamber you then stop this premature opening and the the car has better throttle response. Also there is less wear on the waste gate and the waste gate valve.

When setting the whole operation up it pays to use a laboratory grade pressure gauge, Even the VDO units are not 100% accurate.

The advantage to adjustable boost is when you cannot ge the right grade of fuel you just turn the boost down. With a fixed spring if you can'’ get at least 96 octane you run the risk of detonation and a destroyed motor. Rick solves this by using alcohol injection.

Upping the boost doesn’t put any more wear on the waste gate than it already has – it’s only if you drive the car hard that the waste gate gets wear and you can do that on standard boost.

My car runs the GT intercoole and the Euro Spec pistons of 8.5 and when I set mine up system up years ago and at the time I marked the point of 1 bar and then how many clicks on the valve to take it up to 1.2 bar and how many to take it back to .7 (normal road pressure for me)The car has now done 260,000 miles and has had no failures to the engine ( in fact no failures at all) as a result of playing with the boost.

If you go to the following link http://communities.msn.co.nz/924CarreraGTInfoSite/photoalbums.msnw you can see my car and also at the same time an example of the intercoolers I have started to make based on the GT Intercooler. These are a straight bolt in – some work needed on brackets and a hood scoop required but are easier than fitting a 951 unit. Price to fabricate is around US$500 depending upon the availability of the second hand cores – if you want one send me an email

If you want an adjustable setup let me know and I will make a system for you – I don’t know what it’ll cost yet but the major cost is the valve and the fitting to the top of the waste gate.

Heat is a major enemy of the 931 and when you drive them hard – I have raced mine from 1986 to 1998 and found than to keep the temperature down to an acceptable level I have two oil coolers – one standard unit in the original mounting place and a smaller 9 row unit in front of the radiator. Once this was fitted the oil pressure remained pretty constant in a race and both oil and water temps didn’t get anywhere near what they used to be. The water temp used to be almost in the red on the standard gauge but once the second cooler was fitted it was normally at the ¾ mark when it was at it’s hotest

A further point to remember is if you go the wind up boost Don’t regulate the air to the original inlet point of the waste gate. Reason behind this is if you get any crap in the line and block the regulator then the waste gate don’t work and you have a dead motor. This is what probably happens to most blown motors.



[ This Message was edited by: John H on 2001-11-01 12:15 ]

[Peter]

Jon you have an interesting suggestion about removing the wastegate spring altogether (or at least I believe this is what you are saying). This is my understanding of your current system, please correct me where I am wrong and fill in what I may have missed.
I am looking at a simple diagram of the wastegate. To me the wastegate is basically a spring mounted on top of a piston, with a pressure vent line going to the bottom of the spring, which pressure vent line releases boosted air to counteract the downward force of the spring onto the piston, causing the piston to open releasing boosted air into the exhaust. In essence, the spring acts to keep the piston closed –creating boost: the pressured vent line acts to open the piston thereby bypassing boosted air to the exhaust and out the car.
On the 931 cars, there is only one pressure vent line (going to the bottom of the spring). Your suggestion is to remove the spring altogether. This will remove any downward force onto the piston. To create downward force onto the piston you attached another pressure vent line to the top of the wastegate. In essence you have two pressure vent lines: the first is attached to the bottom of the wastegate creating upward force and a second line attached to the top of the wastegate creating downward. If one stops here the engine would explode because of equilibrium of downward and upward force and a steady increase of boost.
However, on the second pressure line you install an air regulator valve so that after a certain PSI, the upward force is greater than the downward force and the piston opens.
However, what keeps the piston closed upon start up and idle when there is not sufficient downward boost pressure created?
Maybe I misunderstood you. Let me know if I got it right.
-Peter A. Holiat

[Peter]

John,
By the way, those are some great pics of your 931 and the intercooler you fabricated.
-Peter A. Holiat

[John H]

Sorry if I gave the wrong impression - the spring still stays and is set at what ever the factory setting is - (US or Euro Spec). It provides the force to keep the valve closed. Took me a few minutes to figure out how it all worked but it's real simple and easy to control the boost.

But as Rick's pointed out you nedd to have agood quality and accurate guage to set the pressure.

A tip is that you need to do it on a rolling road or have soem one you can trust set the valve when you're doing it on the road. Don't set it in 1sr gear as it gives a false reading.

Preferably use third gear get to about 3500rpm and then hold the boost by trying to keep the rev's up but also using the brakes to keep the load on the motor at these revs. Set the valve to what you want and you're away.

My car has been raced pulling 1.3 bar boost but when you change gear it would over boost shutting the fuel pumps down. So we backe dit off to 1.2 rather than disconnect the over boost switch.

[AppleBit]

I wouldn't doubt a cam grind like Web Cam Stage 1 camshaft would do wonders for a 931!

The cam in the 924/931 are the same. The cam grind is aweful! If you want some serious power without loosing _ANY_ low end power, the web cam stage 1 _WILL_ get you that....

Although with a DIS system and automatic vario cam timing, you will crap your pants at the power difference...

_________________
Classic British Sports Car Restoration v6 + v8 Engine Conversion Swaps

Porsche 924 Wide Body LS1 Corvette 500 Horsepower Engine

[Rick MacLaren]

Yeah I've got to try that Franco cam gear...

[Michael Kouridakis]

sometimes you guys really scare me

[numbers]

Peter, just thought I would respond per your request. I have an early '80 series one that I have owned since '85. I have been running a variable boost controller since about '87. I used the cheapest one I could find, about $5.00, and a boost guage that I bought from JC Whitney. The guage is still available for about $15.00 and it has the black background and green lettering of the '80 guages. I replaces the rally clock in the console bezel with no modifications to the bezel. It looks like it is a factory installation. Total cost $20.00. When I installed the guage, my stock boost was 7 PSI. At first I ran the car at one click on the regulator. This gave me 10 PSI. After a couple of years with no problems, I bumped it up to two clicks, or 12 PSI. Then a year later I tried three, and was getting 14 to 15 PSI. In 1991 I went for four clicks, which varies between 16 and 17 PSI depending on the gear, and have left it there every since. I still have my original engine, which I have never been into, and it runs fine. I do not use any kind of water injection, or extra fuel injection, or an intercooler. However, with each increase in boost, I did notice that the car ran hotter. I like in the Denver metro area, at 5200 feet of altitude. On summer days when the temperature gets above 90 degrees Farenheit, the guage will touch the red zone. However, it just keep on trucking. Also, with each increase in boost, you will see that your gas mileage gets worse. Both the temperature and the gas mileage make sense. It takes more gas to make more horsepower, and, of course, more horsepower equals more heat. But, the car goes just fine. If you find a good pressure relief valve that will work in line with the waste gate line, let me know, as I will try it. I have pic's of the boost controller and the guage if any one is interested. Also, I have designed an air-to-water intercooler that I just haven't had time to build. When I build it, I will post the design and the results.

[cs]

dave, what are you going to use for the water core in your design.

[larso]

How many miles have you put on the 931 Dave2

The number of years look significant but I guess it depends if you use it only on weekends or every day, interested if heat really does kill these 931 engines...

[numbers]

cs. Yes, I plan on the water core as it uses a lot less space and plumbing than an air-to-air for the same amount of heat reduction. My problem is the welding. I am a good mechanic, but have never did any welding. I need to be able to weld aluminum and brase the copper internals to the shell.

Larso, I have 78K on my 931, and had 48 K on it when I bought it. So, only 30 K under increased boost. About 10K at the 16-17 PSI level. That's in US miles.

[cs]

what type of core are you going to run the water through, some type oil cooler. i'm just wondering what would be good to use that wouldn't restrict flow. spearco sell the cores themselves, but even that alone is still around $200.

[Peter]

Hi Dave2,
Thanks for the reply. I guess you can up the boost without an intercooler and not have serious engine problems. I will however still install an intercooler as the engine is out and it is easier to do it now.
An air-to-water intercooler sounds good for a streetcar. However, as I plan on tracking the car and air-to-air intercooler is the better option. As for intercooling, I have given up on the idea of a 951 intercooler.
Installing the 951 IC into the front panel is straight forward, and veritable easy since the engine is out and I do not need to even cut the panel. However, plumbing the lines from turbo to IC then to intake requires custom fabrication and more modifications than I am able to do at home cheaply.
Presently I am looking for suitable, smaller IC for the area where the oil cooler is situated. Audi & Saab have promising units. I will post my results.
-Peter A. Holiat