924Board.org

[Kaos]

Hi All,

I just found some decent photos taken of my car at a local Detroit region SCCA autocross on 5/28/07. Just thought I would share.

I ended up performing fairly well in the event, winning the indexed class (calculated with a handicap based on your car class).

The car is a 1988 Porsche 924S Special Edition running in "Stock" Class. This means completely stock except: a custom catback exhaust, race alignment, race brake pads, double adjustable Koni shocks (with stock M030 springs), custom hollow front sway bar, and Kumho V710 race tires.

Results: http://detroit-scca.org/e107/e107_files/public/1180394061_7_FT0_2007_05_28_solo_memorial_day_final_results_by_class.pdf


Pics:

[macBdog]

Beautiful car and great result congrats. BTW what is the rationale behind a hollow sway bar? I thought you would go for the meatiest sway bar possible. maybe you can hide some NAWZ in the hollow cavity
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1979 931 with a 350 chev
1973 911E with EFI

[John Brown]

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

[!tom]

A hollow sway bar of a certain spring rate will be lighter weight than a solid sway bar of the same spring rate.
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78 924 NA
5-lug

[924RACR]

Car looks great!!
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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[Kaos]

The reason I use a hollow sway bar is to be both stiffer and lighter. The torsional stiffness of a bar is directly proportion to Diameter^4, so that a large diameter thin walled bar will be much stiffer (and significantly lighter) than a smaller diameter solid bar. Think about it this way - when you are turning a solid bar, the outside of the bar will turn alot, whereas the inside won't turn at all. So, the inside of the bar does not offer much resistance.

The hollow bar that I used is simply an off the shelf race part. Essentially the same setup is used in NASCAR - a hollow bar with splines on either end (basically the same as a torsion bar). They sell the bars in different lengths, and different wall thicknesses.

See here:
http://www.1speedway.com/standard_swaybars.htm

I attached some standard off the shelf splined arms. I had to cut and welf the arms a little for fitment (changed from a straight arm to a hockey stick shape). I drilled 5 holes in the end of the bar for stiffness adjustment.
See here:
http://www.1speedway.com/Swaybar_Arms.htm

I used to run a 27mm front sway bar from a 944 turbo. My custom setup is 1-1/4" (31.8mm)x 0.095" wall thickness, and weighs about the same as the 27mm bar including all the brackets.

The main reasoning behind going to a custom setup was to allow a large range of adjustment, and be no heavier than my existing setup. I have two different wall thickness bars that I have tested. The good thing about the inside diameter being different (and not the OD) is that the bar just bolts on with the same brackets and bushings. I have 1-1/4"x0.095" and 1-1/4"x0.125" bars. The thicker bar is a little too stiff for my setup, as "stock" class requires stock springs and rear sway bars. The multiple holes on the sway bar arms allow enough adjustment between courses.

These guys make a similar sway bar setup:
http://www.tarett.com/items/944-series-products/front-swaybar-assy-85-95-944-968-944fsb-detail.htm
However, they do not make a fitment for the 924 steel front control arms. I was able to make my custom setup for a fraction of the $650 asking price.

Jon A.

[morghen]

great pictures. looks like you had fun.
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Supercharger and EFI kits
https://www.the924.com

[genikz88]

Do you have any pictures of your front sway bar installed? I'm not looking forward to spending $450+ for the Weltmeister unit, especially if I can copy your setup for much less than that. I've got a 924S too
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Chris
'88 924S

[ronjeds]

Kaos - Congrats on your results. I also have an '88 Special Edition (with 030) which I'm planning to autocross for the first time later this month. Are you running the stock 15x6 front, 15x7 rear rims? What size tires are you using? I'll be using standard street tires for this first race - Any recommendations regarding initial tire pressures for the first run? Thanks!
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Ron

1988 924S Special Edition

[Kaos]

Genikz88 - I will take some pictures and post them. I ordered a new camera, and am waiting for it to arrive.

ronjeds - I use Kumho V710 in 225/50-15 size on the stock 15x6 and 15x7 wheels. The front tires look a little pinched on the skinny 6" rims, but seem to work well. In order to prevent the front tire from rubbing on the spring on the inside, I use a 1/4" spacer between the wheel and the hub. I also had to clock the spring in a certain orientation to further prevent spring rub. For balance, I also use a 1/4" wheel spacer in rear, but it is not necessary for tire clearance. I run 36psi front and rear pressure.

For several years prior, I ran Hoosier A3S05 in 225/45-15. The shorter gearing helps acceleration everywhere, but requires more shifts to third gear on some courses. Rev limiter in second gear is somewhere around 55mph, which is quite low compared to most cars. The Hoosier's are more expensive, and do not last as long as the Kumho's, and produce very similar lap times.

My rain tire setup is the Hankook Z212 street tire in 205/50-15 for the front and 225/45-15 in the rear. I run these at 37psi front and rear.

Good luck with your first Autocross. These cars are very well balanced, and I'm sure you will have a blast.

[924RACR]

I too run the Hoosiers, but R6's in my case (for road-racing)... also running the 225/45/15's, on 15x6" rims... yes, they look funny, but boy do they stick!!

I have coilovers up front, so no issues with spring rub.
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[ronjeds]

Kaos - One more question. Do you have a limited slip differential? My car does not and I'm concerned that may hamper my progress out of tight corners. Thanks for your input on the tires!
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Ron

1988 924S Special Edition

[Kaos]

Yes, I have a stock LSD, and I have had to rebuild the clutches in it.

I used to have an 1985/2 944 that I autocrossed. I raced it a few times on crappy street tires with no LSD, and wheelspin really wasn't an issue. I think the wheelspin becomes really bad when you have race tires - causing alot of weight transfer off of that inside wheel. This is where a stiffer front swaybar can help reduce the wheelspin.

My advice for now is: just try it and see. If you are the occaisional autocrosser type, then don't worry about it. Just drive the car and have fun.

If you are a maniacal hardcore autocross junkie like myself, then you can spend the money on a diff (and get your hands dirty rebuilding it every couple of years).

[Matt Norton]

What do you inflate your tires to?
Do you just Do SSCA or Porsche club too. I am doing Zone 1 Porsche club in two weeks not allot of time
to install anything special.
I running stuck with cast iorn headers, K & N replacement air filter, Bosh platinum +4 plugs, KB gas
shocks, Goodrich on steel rims(hoping to replace these in a year or so) I plan to replace fenders with DP
ones in a year or two as well.

I will be re-packing the CV joints before the event just got a kit.
any good advice for a first timer?


87" NA 924 S
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Red 1987 924S with plans for D Productions Kit
From American International Racing.

[Kaos]

I do SCCA events only, as the local PCA only does DE events (no autocrosses).

Tires are the second largest contributor to autocross performance (after the driver). Good tires make a crappy car fast, and crappy tires make a good car slow.

The tires quality and construction really dictates how much tire pressure is required. A set of touring tires will have terrible soft sidewalls, and will require very high pressures to prevent tire sidewall rollover (like 45-50 psi). A good high performance summer tire will have much stiffer sidwalls, and require much less pressure. Like I said in the post above - I run Hankook Z212 at 37psi all the way around. So, pressure is really tire dependant, but in general crappy tires will require higher pressures than recommended by the manufacturer.

Advice for the first timer -

1)Walk the course as many times as time will allow. I typically walk a course 6-10 times if enough time is allotted. At the solo National championships, I walked the course 20+ times prior to driving it.

2) Don't worry so much about your car. It's a Porsche. It won't break. Just concentrate on getting through the course. More than likely, your car will have more speed available than you are able to harness your first time out. So, a stock engine and suspension will be just fine.

3)Don't worry about winning your class the first time out. Just drive to the best of your abilities and have fun!