torsion or coilovers?

[kinein]

Dear Abby, lol

i have a 86 911, its my daily driver i drive it like i stole it everyday, now i need help deciding between upgrading my stock torsion setup 23 28 .

the car

3.2
ultra widebody

335 30 r18 rear tires
275 35 r18 front tires so i have grip

strut brace

currently have new boge sports shocks

i was goin to go with rear coil overs with 400 pound spring and front torsion 24mm...

talk to a couple buddies some sayin can go with 24mm 30mm torsion setup

i plan on taking it out on the track just for a good drive but not to race, but i like to take high speed turns and what not thats why i got wide tires....

or just stick with stock

future plan is to put a big hp engine in it either 3.6 or V8 not sure yet..

[Flieger]

Personally, I would just stick with torsion bars, bigger if you think you want stiffer ride.

Coil-over springs will cost more to convert the car, then you will need to reinforce the chassis for the new load path. That is at the very least.

Coil-overs have their greatest benefit in the rear, where you get easier ride height adjustment and you can run the 935 style spring plate and raise the trailing arm mounts for better kinematics- roll center and such.

In the front, the coils can limit tire width depending on backspacing and fender clearance. The front torsion bars are easy to index and only serious race cars need stiffer springs than a torsion bar can provide.

If you want coil-overs, go all-out in the rear with 935 style suspension, raised pivots, and reinforced damper (now spring) mounts and leave the front torsion bars.

[boba]

The main advantage to coil overs is the ability to change setup from track to track. This makes sense for a race car, not so much for a street car or occasional track car. As Flieger mentioned chassis upgrades would be required, which is not a issue for a race car with a cage and reinforced pickup points. Many have done this conversion because they want to, but it is not needed to have a great handling track car. Cost wise you can get equivalent spring rate for much less with the torsion bars.

[175K911]

First, with Boge struts you really shouldn't change the torsion bars from stock. They're not up to the task.

I ran 23/33 torsion bars on my '86, had tried 23/31 and it still had way too much understeer. So leave your front torsion bars alone and go way bigger in the back. With 23/28 it must push like crazy. But any change in torsion bars pretty much dictates that you'll need some custom valved Bilsteins, or Vons from Elephant. Even the off the shelf Bilstein Sports aren't valved for much more that what you've got now.

[kinein]

Originally Posted by Flieger

Personally, I would just stick with torsion bars, bigger if you think you want stiffer ride.

Coil-over springs will cost more to convert the car, then you will need to reinforce the chassis for the new load path. That is at the very least.

Coil-overs have their greatest benefit in the rear, where you get easier ride height adjustment and you can run the 935 style spring plate and raise the trailing arm mounts for better kinematics- roll center and such.

In the front, the coils can limit tire width depending on backspacing and fender clearance. The front torsion bars are easy to index and only serious race cars need stiffer springs than a torsion bar can provide.

If you want coil-overs, go all-out in the rear with 935 style suspension, raised pivots, and reinforced damper (now spring) mounts and leave the front torsion bars.

so putting coil overs in the rear with my current stock spring plate will basically bring no benefit only being able to adjust the ride height easier?

i was goin to go with torsion upgrade all around until i came across a set of used rears for a gd price, soooooooo

thanks for the advice

[Flieger]

Originally Posted by kinein

so putting coil overs in the rear with my current stock spring plate will basically bring no benefit only being able to adjust the ride height easier?

Yep, and once the car is corner-balanced you never change it. Racers might to tweak setup for a particular track, but only if they are very experienced.

[kinein]

Originally Posted by 175K911

First, with Boge struts you really shouldn't change the torsion bars from stock. They're not up to the task.

I ran 23/33 torsion bars on my '86, had tried 23/31 and it still had way too much understeer. So leave your front torsion bars alone and go way bigger in the back. With 23/28 it must push like crazy. But any change in torsion bars pretty much dictates that you'll need some custom valved Bilsteins, or Vons from Elephant. Even the off the shelf Bilstein Sports aren't valved for much more that what you've got now.

so leave the fronts alone leave stock setup for front.....deal i agree
now with the rear so if i had a 400 lb spring on the rear can i leave stock spring plate and still enjoy full benefit of the setup? do remember i have wide tires in the rear 335

[kinein]

i mean a 400lb spring on a coilover

[175K911]

If you have 23mm front torsion bars, you don't have stock. The stock bars were 18.8mm. But to answer your question if I understand it, yes, stay with the 23mm front torsion bars you currently have.

In the back, you can't install coilovers without strengthening the chassis. The engine and trans have to come out so you can weld strengthening plates in back, gusseting the tops of the shock towers, and weld in a roll cage with the rear legs attaching to the chassis in back right next to the shock towers. There are people who've gotten away with not doing the cage part but the new springs will cause chassis flex in the back. There's no way to do it right without at least welding in the reinforcements and gussets.

[petevb]

Originally Posted by kinein

so putting coil overs in the rear with my current stock spring plate will basically bring no benefit only being able to adjust the ride height easier?

Only a small benefit, reduced stiction in the rear suspension.

If you are going to have a roll bar or cage I would suggest you connect it to the rear shock towers and go coilover. Raise the outboard pickup with 935 style spring plates, ideally raise the inboard trailing arm pickup also. The amount you move these is critical so don't guess or just use what's off the self without some guidance.

If you do not have a cage or bar I would suggest going torsion bar, and I'd suggest not going more than 23mm front torsion bars as I don't think your chassis will be stiff enough to properly use the stiffer springs. Assuming you will lower the car I would probably suggest lowering the inboard trailing arm pickup slightly in this case depending on ride height.

Either way the Boges shocks are not up to the task. You will either need to replace them or back off on the T-bar rates. If you do replace them make sure you raise the spindles on the struts up front (again assuming you lower the car).

[a_bayuga]

Any faux pas with leaving the current torsion bar in the rear and instead use a lighter lb. coilover main spring to offset the need to reinforce the chassis?

[kinein]

ok well then it is what it is then, next car maybe go that route.......stick with torsion bars then

[petevb]

Originally Posted by a_bayuga

Any faux pas with leaving the current torsion bar in the rear and instead use a lighter lb. coilover main spring to offset the need to reinforce the chassis?

I believe the SC/RS and some other cars had that option, though I suspect strongly they were run reinforced as well.

We can run some quick numbers for an idea of the effect:

In a stock car the shocks probably transfer in the ballpark of 50 lbs of force peak over a bump to those pickup points by themselves, so that's probably close to what the unreinforced pickups were designed to see without reinforcement.

If you run stiff springs, you should really also run stiff shocks to control them; with anything like 31mm T bars or 400 lb springs, properly matched shocks will probably transfer more like 100 lbs of force over bump to those pickup points, so we're already over 2x the initial design.

Now add coil springs to that. Even if the coil springs themselves are only 200 lbs each to support half the car's weight, remember that you're taking half the corner weight of the car (which is 800+ lbs on a rear corner). So you're adding 400 lbs to that corner, or more like 700+ lbs when the suspension goes over a bump and compresses 1.5". Suddenly we're at 700 + 100 from the shocks = 800 lbs, or 16x design load.

Now I'm sure there is some margin in the original design, especially if the considered the shock bottoming out, but there probably isn't anything like a 16x factor of safety. Short answer- I'd personally really want to reinforce those points even if the coil-overs are only "helper" springs.

[kinein]

Originally Posted by petevb

I believe the SC/RS and some other cars had that option, though I suspect strongly they were run reinforced as well.

We can run some quick numbers for an idea of the effect:

In a stock car the shocks probably transfer in the ballpark of 50 lbs of force peak over a bump to those pickup points by themselves, so that's probably close to what the unreinforced pickups were designed to see without reinforcement.

If you run stiff springs, you should really also run stiff shocks to control them; with anything like 31mm T bars or 400 lb springs, properly matched shocks will probably transfer more like 100 lbs of force over bump to those pickup points, so we're already over 2x the initial design.

Now add coil springs to that. Even if the coil springs themselves are only 200 lbs each to support half the car's weight, remember that you're taking half the corner weight of the car (which is 800+ lbs on a rear corner). So you're adding 400 lbs to that corner, or more like 700+ lbs when the suspension goes over a bump and compresses 1.5". Suddenly we're at 700 + 100 from the shocks = 800 lbs, or 16x design load.

Now I'm sure there is some margin in the original design, especially if the considered the shock bottoming out, but there probably isn't anything like a 16x factor of safety. Short answer- I'd personally really want to reinforce those points even if the coil-overs are only "helper" springs.

i shouldve done that before they just painted the car.....ill save them for the next project car, i am just goin to stick to the torsion bars not really goin to track it, but i wouldnt mind a good handling street car......next on the list soundproofing then interior pics to follow

[kinein]

thank you all for the insight, some was chinese and some was not.......

[boba]

I just saw this car, it is a '74 Carrera RS. It is one of 109 built by the factory for homoligation. Approx half were sold to race teams and the rest to street use. This one was for street use but has all the '73 RSR mods and evidence of special bits stamped with the chassis # so the FIA inspectors knew Porsche was not fudging the number of cars produced.

Anyway the reason this is interesting for this thread is that the car has the larger Dia rear shock mounts for coil overs and the mounts are solid welded. Also seen is one of the reinforcing plates on the cross bar.

[MJHanna]

Frt coilover on one of my cars.

Rear (not the best photo)

Shot of top shock mount and tied to rest of car

[Flieger]

Interesting, how about some shots of the whole machine?

[slow&rusty]

Wow..a timely thread. I just debated this a few months ago and went back and forth in my head and after talking with Clint at RSR for quite some, kicking around ideas and such, I decided to coilover my entire car. The twist is I am going to leave the rear torsions in place and install rear coilovers to address the squat my car has under acceleration.

The whole "reinforce the chassis" argument will depend on the spring rating you choose and your intended use for the car (street only, race, mix of both etc).

My car will never see the track and will only be a pleasure vehicle that gets used on the occasional weekend, so making a decision to coilover the car was simpler.

To coilover the entire car cost about $1000 more than if I was going to upgrade the torsion bars and re-valve my Bilsteins to match.

I will have a full build \ intensive picture thread coming in the next week.
Yasin

[kinein]

Originally Posted by slow&rusty

Wow..a timely thread. I just debated this a few months ago and went back and forth in my head and after talking with Clint at RSR for quite some, kicking around ideas and such, I decided to coilover my entire car. The twist is I am going to leave the rear torsions in place and install rear coilovers to address the squat my car has under acceleration.

The whole "reinforce the chassis" argument will depend on the spring rating you choose and your intended use for the car (street only, race, mix of both etc).

My car will never see the track and will only be a pleasure vehicle that gets used on the occasional weekend, so making a decision to coilover the car was simpler.

To coilover the entire car cost about $1000 more than if I was going to upgrade the torsion bars and re-valve my Bilsteins to match.

I will have a full build \ intensive picture thread coming in the next week.
Yasin

looking forward to it