coil overs vs. torsion bars

[paulgtr]

I have a slighty bent left front strut assembly that needs replacing. the unit is a boge assembly with a koni insert.
I have spoken to a shop that specializes in porsches and they have offered to replace both front struts with bilstiens at a price not much more than to replace only the left front boge/koni.
the shop owner also mentioned that it wouldn't be a big deal to put in the strut assembly that is set up for a coil over spring in place of the torsion bars.
I have a 1975 911s with the "s" brake option and turbo tie rods already in place. other options are to go to sport torsion bars.
any body do the coil over option instead of the torsion bars, what is the difference in ride and handling if any?

[Jeff Alton]

Most will tell you do not bother unless it is a track only car. That said, I have the parts on order and will be installing them shortly on my street/track car. I have different motivations than most though!! I can answer your questions better once I have them in.

Jeff

[paulgtr]

cool, keep me posted.

[Porschekid962]

what is the difference in the strut assembly for regular tbar setup versus coilovers? ive seen all of the erp 935 stuff but is it not possible to somply pull out the tbars and replace the boge's with coilover units?

[Jack Olsen]

The only reason to do it is if you need stiffer spring rates than are available with torsion bars. Coils reduce the space for wider wheels in front, and require pretty extensive reinforcements to the shock towers in back.

There won't be any difference in ride characteristics unless you increase spring rates. Whether you make that increase with torsion bars or coils makes no difference.

[paulgtr]

this is the whole thing. I am beginning to understand that I now own a car that has pretty much unlimited scope for modification. problem is that i need to figure out what is the best set up for what I want to do.
as it looks now, I will be using it 90 percent of the time as a road car and then once in a while taking a porsche club DE course and once I am more confident of my abilities going it alone to a regional track day. so it seems that if it is necessary, I can still go to a stiffer torsion bar.
the coil overs don't do anything better than the torsion bars do they? like they don't change some bad characteristic that torsion bars have or something?

[Yargk]

They are right about only getting springs for higher spring rates, but I don't think it needs to be just a track car. Obviously it should see track time and you shouldn't put that suspension to the test on the street. However, if the car will see a lot of street time it depends on the person as to whether they like the stiffness. I test drove an M3 with progressive 300-900 pound springs on some rural roads. It was absolutely planted, insanely stiff, and sent shivers up your spine if you didn't plan for a moderate bump. But I loved the way it felt connected and wouldn't mind driving it everyday.

31 mm torsion bars have a spring rate of around 350 pounds, right (vague memory)? And a 911 probably has at least the weight that an e30 m3 has on the rear so the thickest torsion bar is softer than that m3.

[Wil Ferch]

Notice that for 911's the coils are very small diameter ( bend radius) because of the small shock tower diameter we have. Most other cars designed form the outset with coils have much larger circular space to work-in. Things get crowded quickly in a 911 with coils....

The 911 shock tower also wasn't designed to take the spring load on the top of the tower. Best would be to reinforce this area and also tie this area into an expanded roll cage structure...something not usually done for a road car.

Coils allow easier ride height adjustment, but the front torsion bars are relatively easy compared to the back....