924Board.org

[R.J.]

Hi guys, I've been lurking for a while now, but it's time I seek some professional advice. I'm more active on Rennlist but the guys over there aren't big on 931's. So the question is which of the above cars to build for a dedicated Driver's Ed car and eventually a track car. I have both sitting in my garage. Any thoughts on tranny, ignition, mod-abilty, engine differences and the availabilty of spare parts would be appreciated. I am aware of the differences between model years like lower production number, digital ignition, increased compression and 944 tranny swaps on the later cars, but I would like to know how these differences would apply to a track only car, as in which would be better to build up. I live in Vancouver, BC and most of the track events would be at Mission. Thanks for any input, R.J.

[Lizard]

R.J.

Glad to see the 931/924 starting to take off in the lower mainland, I would love to see a track car get going up here, and if you need assistance on a track day I may be able to arrange coming down and giving you a hand in the pits

anyway I would have to say that for the price of the tranny and that you arent probably going to be pushing SUPER high hp #s I would go with the 1981, with the audi tranny a they are cheaper to fix, although if you have a good snail shell tranny w/ good 1/2 dogteeth, then go with the 1980 as it will withstand more torque/hp.

I would recommend going with the 1981 pistons however for slightly more lowend power, I strongly recommend though that you get either a digital ign system w/ a knock sensor (msd?) and or convert to a system such as megaultrasquirt EFI, there are 2 benifits to that, the megaultra squirt would control IGN and fuel, and also free up alot of room in the engine bay for routing of IC lines, for either a air air or air water IC, I strongly recommend an IC for the track, and also installing a slightly larger oil cooler in the front or running another one tandom.

you may also cosider if the resources are close enough to you, building a custom exhaust manifold and using a newer turbo, and one with oil and water cooling.

anyway good choice of cars.
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3 928s,

[R.J.]

Thanks for the info Lizard. I think I've heard about you before from guys on Rennlist like Rich Sandor and company, does that sound right? Anyways, I'm handy with a wrench (used to be a tech at Weissach) but I am really looking to do the most with what the car has stock other than add an intercooler which from everything I've read does not sound easy. Other than adding an IC I am willing to rebuild non-critical components as they break. For example when the motor goes I'd add the '81 pistons during the rebuild assuming I started with the '80. When (if?) the turbo goes I'd send it out for a modern rebuild. I'd rebuild the brakes and suspension before hitting the track. And keeping in mind that both cars have good trannys and the fact that I don't want to add aftermarket fuel and ignition controls which model year would you go with?

[Lizard]

Yah I know Rich Sandor, he has a nice 951, well on the outside anyway

I would personally go with the 1980 if you wish to retain all the stock systems K.I.S.S. the 1981 gets too complicated when it comes to the ign setup imo for track use, and if the syncros are good in the 1980 go with it. although if the 1980 has 4 bolt suspension take the 5 bolt out of the 1981, and I am glad to hear you are going to rebuilt the suspension, what route are you planning on going, coil over, or factory spring, or 250lb autocross springs?

I would also recommend taking the intake manifold, throttle body and charge tube out of the 1981 and put them on the 931, the single butterfly would be better.

if you have looked under the hood on the 931, then you obviously know there really isnt any room for adding an air air IC up front due to the placement of the fuel dizzy, you could use an RX7 gen 2 IC and adapt that for a top mount, but wont be very efficent, or you could move the battery to the back and install a air water unit in the battery tray, however doing that, unless you have a good heat exhanger and a fan on a switch for the heat exhanger then you will get heat soak and could run into detonation issues.
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3 928s,

[R.J.]

Hey Lizard, I'm all about keeping it simple... What about the '81 ignition system makes it a no-go for track duty? Or, what about the '80 makes it better? What do you think about a front mount IC? I have no problem replacing the front bumper if necessary. Whats the absolute easiest way to get an IC in there? Regarding suspension and brakes, I'm not to concerned about fitting in to any particular race classes, I just want to learn to drive better and have fun. I'll be using Koni yellow M030 struts and hubs from a 951 Turbo S along with the brakes. At the rear just 951 Turbo S torsion bars with 951 brakes and aluminum trailing arms. I have been stock piling all this harware just waiting to put it to good use.

[Lizard]

well good luck with the installation of that hardware on the 1980 due to the fact you have to keep the torsion bar carrier for the snailshell tranny,

and the reason I wouldnt use the 1981 ign system is that is is DITC, it has more vacuum lines, and also alot more sensors to go wrong, the 1980 unit is a very simple design and you could always use the 1980 distibutor to install an MSD 6A ign modual very easily,

also the 1981 DITC system can get abit or corrosion on the connectors which cause it not to run right and then you are chasing ghosts, and trying to track down intermitant issues. where on the 1980 system it is just 1 box in front of the drivers wheel
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3 928s,

[Paul]

Have you considered a 924S? Much more fun on the track, IMO.

[R.J.]

I had considered that as well as an '83 944. Why would you say that a 924S would be more fun? I kind of like the idea of turning up the boost a bit and hopefuly ending up with a faster car than a naturally aspirated 924S or 944 car. [/list]

[Lizard]

the 931 will definatly be more fun on the track imo,

you will be able to get WAY more power than a 944/924S NA,
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3 928s,

[R.J.]

Hey Lizard, got your PM, I'm gonna get set up on messenger. Any thoughts on an IC installation? I have no problem removing headlights and linkage, changing front bumper and obviously removing all AC components. The only thing I wont do is add a hood scoop.

[Paul]

Depends on the rules of the class of the car that you are racing. I'm guessing that a legal 924S will be more fun on the track than a legal 931. I'm also guessing a 924S will be less expensive to prepare and to run in the long term. We need input from the racing side of the board....
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White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.

[Lizard]

well for the IC install, if you want air air the a front mount is the only way, however then you come to the issue of the location of the fuel dizzy, and moving that wouldnt be easy if even possible, so if you want to stick with CIS I would recommend that you go with an air water unit, and install it in the battery tray area, you could use the ac rad for the heat exchanger and get a large electric fan to mount in front and run on a switch to keep it cool and help prevent heat soak.
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3 928s,

[John Brown]

RJ:

I think I understand your viewpoint as it seems to match my own regarding the 931 vs 24S or 44.

I don't think there is a clear winner 80 vs 81. Our car is actually an 80 which at this time has had the snailshell traded for the 'Audi' and an 81 motor installed but we have retrofitted the 80 ignition. Don't ask, it all just happened.

I'm not much into worrying about whether the snailshell will handle more power than the Audi unit. Neither one seems to have any problem. If the snailshell breaks and parts to fix are scarce (they are) the Audi is an easy install as all the hardpoints are there. The Audi is much harder to change gears or final drive and there are fewer of each available. In fact, our snailshell was traded to a fellow who wanted it for serious use in 924DP type cars and they had the parts, time, and dollars to fiddle with it. Now that we are into racing we could wish we had it back; but I don't think it's the end of the world for us to be using the Audi trans. I think Vaughan Scott (924Racer) went to the Audi largely for lack of affordable repair parts for the snailshell.

The alloy rear suspension arms are a worthwhile upgrade! Mine are off a 924S. I thought my front was off a 24S also; but the other day I noticed there is no speedo drive provision so at this point I'm not sure WHERE I got those spindles. Oh well.

I don't know this myself. It's from people whose knowledge I trust. The digital ignition of course allowed Porsche to get some more out of the car. However, it may be conservative retarding at temp to save the street car and warranty repairs, hey?! There is also no way to control it at all. Should you wish to. It is what it is. The 80 distributor based ignition is straight forward and adjustable the old fashioned way. I have wired our car so that I can pretty easily swap the two systems. Presently the 80 is installed because we were having some intermittant running problems at speed and wanted to diagnose and adjust. Once I'm done with that we may put the digital back in. (As it seems the problem is fuel system based anyway).

Out of the box, of course, your 81 is making more power. But the difference is probably very small once you tweak each with only 'track car' stuff.

I'd pick the best chassis, either year, as the basis and use the other car as rolling spares!!!

BTW, I don't know if anyone goes there anymore; but ther used to be a project car section. We're 'LJs Project'.

Cheers
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John
80 931 - #931 44Cup
99 Escalade - tows track cars
gone but not forgotten: original 924.org car - 82

[Lizard]

John a couple of points on your comments which are very good, however the 1980 has a larger turbo compressor wheel and does push a few more CFM of air flow, and also does have the lower compression pistons which will allow for a larger detonation safe zone with more boost, so technically the 1980 is the one which can be tweeked more. although the 81 has the higher compression which would limit the amount of boost being able to be run it would give more low end.

also in regards to the Snailshell trannies. we actually have a guy by the name of George, dont know his contact # but if you call MCL they can supply you with the # as they send ALL of there tranny work to him to have it done, also I would like to note that he aparently has alot of parts just sitting around in stock, although he does charge a pretty penny for labour the G31 is a very easy tranny to work on, so you could just buy the parts from him and install them yourself.
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3 928s,