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Torsion Bar sizes - thoughts and opinions

I am considering 2 paths WRT the rear suspension on my 930 - either going with a heavier torsion bar in the rear, or swapping to a Bilstein shock with the coilover provision and adding springs to stiffen thinks up a bit. My car is mainly street driven, with some light track time sprinkled in.

Any input?

Pat Kelley
87 930 505 code coupe
Old 03-09-2007, 12:04 PM
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rennsportsystems.com has good info about that and you can get parts from Steve, who runs that shop. He also answers questions.

A standard set up he and others recommend is 22mm in the front and 29mm in the back for mostly street, or 30mm for track and street. The website has a chart.

My car needs a little more, like 31mm, because I am running short gears and some extra horsepower, causing the car to squat. But my short gears have a lot to do with that. I am looking into that now.

You want to have your shocks match your torsion ratings, and this is done by valving the shocks to match your bars. You can order them that way from the start, at rennsport, and probably other places as well.

If 29 or 30mm torsion in the rear does not do it for you, you could always try the coils later for a little extra. But get the shocks to match your initial set up and you will go a long way to preventing common mismatch problems.

Use only high quality torsion bars if you are going with hollow bars, don't just get cheap ones.
Old 03-09-2007, 05:54 PM
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I am leaning toward keeping the stock torsion bars in place, and using a coil-over/adjustable shock setup to 'add' spring. Anyone else doing this??
Old 03-10-2007, 02:57 AM
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I've only heard of folks going coil springs only or helper springs with large torsion bars, but I don't see any reason you couldn't use stock bars with coil springs. This would take some load off the upper shock mounts since the bars would still carry some load.
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Old 03-10-2007, 08:53 AM
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The only downside I think of quickly is WEIGHT. Stock 26 solid with coil over adapters plus coils will weigh more than 31 hollow.

As I typed a few other issues: Corner balancing might be trickier since you'll have more locations for adjustment.

Note: If you wish to lower the car or keep it where its at, you'll STILL need to REINDEX the TB's down first. How far will you do this before preloading the coils? How do you determine how much load for the TB's before you load the coils? Do you get linear or multi rate coils? And who's going to tune the shocks?

Cost is another issue since you won't be able to sell off the 26's and you'll still have to buy more things. I was never completely convinced of this concept when JC Whitney sold them for a bandaid fix on old cars. JMHO, it may work out great.
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Old 03-10-2007, 03:37 PM
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What are you trying to achieve exactly in terms of handling results? If you are REALLY close already with your 26mm tosion bar, and feel that you need to fine tune it with a fancy shock than go ahead. Other than that, you are taking what seems to be a really complicated approach, in my opinion.

930's are meant to run torsion bars. To do a full coil over, you usually add a roll cage for support or weld and strengthen strut areas or somehow tie the whole suspension together so as not to strain your car by running a suspension on top of your car instead of underneath. It is an all or nothing approach.

If you want a street and light track set up, than get the torsion bar you need. And if it isn't quite enough you can always get a little more bounce with a shock with coils on top. But to use stiff coils and a light torsion bar is a mismatch as far as I can tell. You are essentially running two suspensions at that point, as alluded to earlier by Lukesportman. Yet you are compromising both systems by sort of going half way with each.

Strictly in my humble opinion, you need to talk to somebody like Steve at Rennsport or Stephen at Imagine Auto, or Pat at Pat Williams Racing, or just about anyone who is knowledgable at this stuff. They will get you the right parts, not some cheap tosion bar, or mismatched and overpriced shock set up. They will also custom valve your shocks if needed.
Old 03-10-2007, 05:51 PM
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Quote:
Originally posted by Lukesportsman
The only downside I think of quickly is WEIGHT. Stock 26 solid with coil over adapters plus coils will weigh more than 31 hollow.

As I typed a few other issues: Corner balancing might be trickier since you'll have more locations for adjustment.

Note: If you wish to lower the car or keep it where its at, you'll STILL need to REINDEX the TB's down first. How far will you do this before preloading the coils? How do you determine how much load for the TB's before you load the coils? Do you get linear or multi rate coils? And who's going to tune the shocks?

Cost is another issue since you won't be able to sell off the 26's and you'll still have to buy more things. I was never completely convinced of this concept when JC Whitney sold them for a bandaid fix on old cars. JMHO, it may work out great.
My thoughts too !
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1981 UK 930. G50/01 shortened, 964 3.8RS Fibreglass Body Kit, 18" Alloys 8.5" F & 10" R, 225's F & 285's R, Special Colour Metallic Blue Paint, FIA Sparco Evo's, A/C and Air Pump removed, Electronic Boost Controller, GHL Headers, Tial46 WG.
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Needs Fitting - Innovate XD-16 Kit, Kokeln IC. Stephen's K27 HFS, EVO Intake Assy & his Modded USA Fuel Head.

1983 UK 911 3.2 Carrera Sport Coupe. Black, Black Leather with Red Piping, Black Alloy Gear Knob, K&N Air Filter Element, Turbo Tie rods.
Needs Fitting - K&N CO Sensor, Round A/F Dial Gauge, Factory Short Shift Kit.

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Old 03-11-2007, 01:48 AM
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Stephen Kaspar of Imagine Auto says that going to coil overs is fine on a stock car. The car does not need to be reinforced unless you are going to fit coils of a very high rate (he did comment on the rates but I cannot recall). Obviously this also applies to the shocks. You wouldn't have stiff shocks on soft springs anyway. Basically he said for road use they are fine.
Racing spring rates would need the car reinforced.
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1981 UK 930. G50/01 shortened, 964 3.8RS Fibreglass Body Kit, 18" Alloys 8.5" F & 10" R, 225's F & 285's R, Special Colour Metallic Blue Paint, FIA Sparco Evo's, A/C and Air Pump removed, Electronic Boost Controller, GHL Headers, Tial46 WG.
Fitting - New service kit.
Needs Fitting - Innovate XD-16 Kit, Kokeln IC. Stephen's K27 HFS, EVO Intake Assy & his Modded USA Fuel Head.

1983 UK 911 3.2 Carrera Sport Coupe. Black, Black Leather with Red Piping, Black Alloy Gear Knob, K&N Air Filter Element, Turbo Tie rods.
Needs Fitting - K&N CO Sensor, Round A/F Dial Gauge, Factory Short Shift Kit.

http://www.danasoft.com/sig/Iamnotanumber.jpg
Old 03-11-2007, 01:52 AM
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I have this same dilema, squat on boost. Clint said I could use helper coils in addition to the stock bars. but it does seem like a backwards approach. I just don't want to mess with the rear arms. I don't want to lower my car at the moment, and i don't want to go get an alignment. For me it would serve as a bandaid and only be useful on boost. It looks sort of mickey mouse in theory. But ease of not ****ing around with the whole rear end makes me want to do it. A 6 or7 hundred dollar fix for the squat and an install time of maybe an hour and a half makes it feel like the easiest solution. except for the mismatch
Old 03-11-2007, 07:39 AM
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I would think it was dangerous to fit CO's to a car and then not corner balance it.
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1981 UK 930. G50/01 shortened, 964 3.8RS Fibreglass Body Kit, 18" Alloys 8.5" F & 10" R, 225's F & 285's R, Special Colour Metallic Blue Paint, FIA Sparco Evo's, A/C and Air Pump removed, Electronic Boost Controller, GHL Headers, Tial46 WG.
Fitting - New service kit.
Needs Fitting - Innovate XD-16 Kit, Kokeln IC. Stephen's K27 HFS, EVO Intake Assy & his Modded USA Fuel Head.

1983 UK 911 3.2 Carrera Sport Coupe. Black, Black Leather with Red Piping, Black Alloy Gear Knob, K&N Air Filter Element, Turbo Tie rods.
Needs Fitting - K&N CO Sensor, Round A/F Dial Gauge, Factory Short Shift Kit.

http://www.danasoft.com/sig/Iamnotanumber.jpg
Old 03-11-2007, 08:30 AM
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I think you have a point, but honestly, I have no flippin clue
Old 03-11-2007, 09:03 AM
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On the combo of torsion bar and coilover - this has been done many times by factory Porsche race cars. It IS a great way to get a higher spring rate on a 911 w/o killing the upper shock mount with a big spring in a coilover 'only' setup. Extra weight (vs a c/o only setup really - adding a coil is about 2-5 lbs more than the OE torsion bar) might be an issue and correct shocks are needed, but there is a lot of merit in using a coil to remove squat (with the stock bar) rather than going to a huge torsion bar. If you go to a big bar, you really need to upgrade or revalve shocks too, so it's actually cheaper to go to a correctly valved coilover shock with the added spring.

Just as any other suspension mod., I'd hope that the installer has some idea of what they're doing, and how to set up the system they're installing/modifying..... And, on that note, I had no idea that IA was doing race/high performance street suspension work.
Old 03-11-2007, 12:17 PM
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It wouldn't be a problem for me as I have a corner weight gauge. It wouldn't be a problem for Porsche either as they would have any equipment they wanted. But to add them without setting it up could be dangerous.
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1981 UK 930. G50/01 shortened, 964 3.8RS Fibreglass Body Kit, 18" Alloys 8.5" F & 10" R, 225's F & 285's R, Special Colour Metallic Blue Paint, FIA Sparco Evo's, A/C and Air Pump removed, Electronic Boost Controller, GHL Headers, Tial46 WG.
Fitting - New service kit.
Needs Fitting - Innovate XD-16 Kit, Kokeln IC. Stephen's K27 HFS, EVO Intake Assy & his Modded USA Fuel Head.

1983 UK 911 3.2 Carrera Sport Coupe. Black, Black Leather with Red Piping, Black Alloy Gear Knob, K&N Air Filter Element, Turbo Tie rods.
Needs Fitting - K&N CO Sensor, Round A/F Dial Gauge, Factory Short Shift Kit.

http://www.danasoft.com/sig/Iamnotanumber.jpg
Old 03-11-2007, 02:10 PM
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