As far as I can tell, option 394 is 8/9x16 Phone Dial forged Magnesium wheels as used on the 944 Turbo Cup.
According to another source: In 1988-9 The 393 option is 7?/9x16 D90 (design 90) wheels.
951 362 115 30 - alloy wheel 7 J x 16 - ET 65 - FORGED silver
928 362 119 30 - alloy wheel 9 J x 16 - ET 60 - FORGED silver
For 1990 the S2 and Turbo wheels were different D90s
928 362 114 05 - alloy wheel 7,5 J x 16 - ET 65 - silver
928 362 118 05 - alloy wheel 9 J x 16 - ET 52,3 - silver

So maybe the book is wrong in saying that the 393 is 8/9x16. As long as you could have ordered the 394 option for a regular 944 then it would be legal.

D90 pic:

Thanks.

I think what you've found is sufficient proof to withstand any protest for 8/9 on a 1988 944. It really does look like it was a one year option. I guess they needed a few more orders of those magnesium phone-dials, maybe to fulfill a contract requirement. Who knows?

this photo isn't of D90 wheels, which are a cast wheel and made by Ronal ( I believe).

The photo is of Club Sport FUCHS wheels, which are forged aluminum and came on the '88.2 turbo S and '89 951

You need to look at the differences of these two wheels and feel their weight differential.

Design 90 wheels may look slightly like a Club Sport Forged FUCHS but they are no where near the same in structural strength. Absolute look. Or wheel width, structure, and fitment. They come from two different manufacturers and have entirely different costs; new cost as well as current values.

They have different part numbers

D90's are heavy! They came on my old S2

I knew there were forged Fuchs versions and cast Ronal versions but I thought they were lumped together as D90 type wheels as they look fairly similar. I did list the different part numbers for the forged and cast wheels. I'm sure mrgreenjeans is entirely correct. Was Frank Zappa your son?

Many do consider them as 2 D90 variants... they can be a little difficult to tell apart in non-close pictures. The "eyebrows" denote the forged clubsports.

I had those forged clubsports and ran them without protest, but I never did any tour events back then either. I can attest that they are a badass lightweight wheel.

After my first autocross with the car today, I don't think 7's & 9's is going to cut it. The car has issues.

It was a tough day. I was 3rd of 7 in ES, 1.3s out of 1st on a 65s course and only paxed 29th of 112.

As it stands, the car has M030 front and rear sway bars, but the springs & shocks are standard. I was running the new version of the Rivals S on 7's, which I really liked. This tire is easier to drive than the RE71R. I couldn't comment on total grip. I experimented a bit, but ended up starting each run with 31 psi in front and 34 in the back. Any less in the back and the tire was rolling over just too much.

The car was a handful. While the front end was quite responsive, it's the rear that was the problem. When the car really leans over, suddenly something weird happens to the trailing arm geometry/tire patch/camber or something and it wants to snap-oversteer. At present, the car cannot use all the grip even these little tires will provide.

Given the high-polar moment, making things happen relatively slowly, I was always able to catch it, but it was disconcerting. By the end of the day I was throwing it into a corner, letting the weird oversteer thing get started, then applying full power to settle the back end back down. That was working pretty good and is only possible because the LSD was doing it's job well.

I'm going to hope that the sport springs (plus a bunch more damping) is going to help this issue by limiting roll and pitch.

I'd sure like to know if this behavior rings a bell with those who've been down this path before?

What's your rear toe? That sounds like toe-out behavior. Do you need to crank in a ton of toe-in to prevent dynamic toe-out?

It's got 1/8" total toe-in in the rear. The back-end seems stable until this particular state is encountered. Toe-out may very well be occurring dynamically.

I think I remember an article by Jim Pasha(?) that the 928 would do this also, even with the 928 toe-control design, and he solved it with the spring & damper set he helped develop many years ago.

I suspect that this is probably just a typical, large-motion semi-trailing arm behavior. It may be what led to the old saying "slow-in, fast-out", in that by braking early (in a more or less straight line) for a corner and then powering thru it, this particular state of the rear suspension is not encountered. (I always thought that way of driving was more suited to the rear-engine 911's, but maybe it really had as much to do with the suspension design.) Being used to double a-arm I don't typically do this. I never raced the 944S2 I had previously, only a couple of track days which were driven sedately.

Also, the old saying "Any suspension design will work as long as you don't let it." may apply here. Just don't let it move so much (with higher spring/roll rates) and the problem will go away.

I don't recall experiencing anything similar with my 968, so I'd guess that a) there's something wonky with your car, or b) we had everything cranked down hard enough to mask any weird suspension behavior.

The biggest difference I see between my old setup and yours is that we were running a much bigger 1.25" custom front bar. We still had gargantuan body roll even with that bar, though, so I'm a bit skeptical that (b) is the explanation.

To sjfehr's toe point: I didn't save most of my notes from back then, but the last one I have on toe is that we were running 1/32" of toe-in in back (i.e. for all intents and purposes zero). That suggests that your problem isn't too little toe-in either.

Thanks for the info. Another good possibility I thought of later is a perished bushing or two in the rear. The front suspension bushings are all new, though not M030, but the rears may be 27 years old.

The rears don't get much love. Also look at the trans mount and shifter bushings when you are there.

Sounds familiar. Mine was more of an off-throttle oversteer disaster. As you described, being flat on the gas solved most all problems.

The m030 springs and torsion bars should help you out, but even those are still relatively soft.

I would definitely check out all the bushings.

Tire pressures seem a bit high for how light the 944 is, but tire rollover is tire rollover.