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Join Date: Apr 1999
Location: Hoboken, NJ USA
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What upgraded springs to use for Auto X

Can someone advise me as to what springs I should upgrade to, to replace weak original stock springs. My car is a 1973 2.0 Liter with a 911 SC suspension with Khonis all around. I have 6 x 16 fuchs wheels/tires. My problem is that after autocrosing for my first time last year My front tires came off the ground about a foot in hard turns. I gather this is not an expensive upgrade after talking with others. Any help would be appreciated guys/girls.

Regards,
John Pfeufer
Old 10-18-1999, 07:05 PM
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Gosh, for autocrossing, it's almost a given you're going to wind up with lower and stiffer (21-22mm front, 140 lb+ rear) torsion/coil springs all around, and DEFINITELY going to have to run larger sway bars (19-22mm front, 16-19mm rear). I would consider the sway bar swap first, and some sticky tires (Yokohama A008, for instance) before upping the spring rates. It's a tune a little here, tune a little there situation, which can wear a hole in your wallet if you're not careful.

If this is a daily driver/weekend boy racer, you might want to give conservative thought to the spring issue, unless your fillings are fairly new! When pushed hard, 914's are inherently going to lift the inside wheel on turns. Just make sure that fat-ass tail doesn't break loose; otherwise, "She'll be comin' round the mountain "

Good luck.
Old 10-19-1999, 04:52 AM
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I think the first thing to do is read the rules for whatever series you wish to drive in. Under some rules, spring changes are "free". Under some, they move you to a pretty hairy class where you'll never be competitive.

If you have an SC front end, do you have the SC torsion bars? I don't know what size those are or how they measure up to the stock 914 bars...

If you only have the stock swaybar up front (and rear, for that matter), and the same size torsion bars as the stock 914 stuff, you don't want to go more than about 100# rate in the rear or the car will get rather tail-happy. Which can be fun, but isn't the fast way around the course.

I think that torsion spring stiffness increases with the fourth power of the diameter (could be the cube) which means small torsion bar changes have large effects on the spring rate. With stiffer front springs (or sway bars), you want to stiffen up the rear of the car to keep it balanced. You can use the fourth-power rule and the 100# number as guides, but that probably will still require a fair amount of fine-tuning, possibly even changing the springs again.

Josh "Josh2" Hadler has 22 gun-drilled bars up front (equivalent to 21 or 20 non-drilled, I hear) and 200# springs in the back, with a 19mm sway bar (may now be a 22) up front. He likes that setup a lot.

If you want to be able to fine-tune the balance of the car, then get one of the adjustable sway-bars. They're pretty easy to install (see the tech article on this site). They'll stiffen up the front somewhat more, so even stiffer (slightly) springs would be in order. But they will allow you to do some adjustments.

I recommend ditching the rear sway bar if you upgrade the springs at all. In some cases, the rear bar lifts the inside rear wheel. All of a sudden, you can't put power down (unless you have a limited slip diff). Or, with the stock setup, the bar can "bottom" on the trunk floor. Your spring rate on the one wheel goes near-infinite, and you lose all traction on that wheel. Oops! Most people control the rear roll resistance with springs.

Good luck!

--DD
Old 10-19-1999, 06:21 AM
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I agree with DD in that you should ditch the rear sway bar. I don't lift with it out and I plan on upgrading the rear springs as they are stock and sagging but damn it sure goes around those corners for being a stock setup.

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Old 10-19-1999, 08:48 AM
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Thank Dave Darling for this one...

In a past post on suspension stuff, Dave recommended the book, "How to Make Your Car Handle," by Fred Puhn. Available in Paperback at Amazon.com for $14.36...

I just picked up a copy last week and it should be required reading for anyone thinking about upgrading their suspension or tuning it for performance. Excellent material throughout. I have finished skimming through it once and will have to read it through a couple of times to absorb it all... but I am sure it is going to give me a lot more savvy when I get around to fixing up my suspension. I don't have it in front of me, but I recall a picture of a Porsche with tires lifting as it rounds a corner and of course discussion of the suspension details that cause it...

I recall, as Dave does, the torsion stiffness goes as the 4th power of the rod diameter, so for example a 22mm sway bar has 1.8 times the stiffness of a 19mm sway bar!

....have fun.

- Dave Bell
Old 10-19-1999, 11:25 AM
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