Help needed for coilover setup....

[scca_ita]

Hi

Can anyone offer some guidence on putting coilovers on my long wheel base 66 tub.

It has 74 and later suspension components.

What should be done to re enforce mountings?

Spring rates - 3.6L - Timetrials AutoX street driving etc.

Use 935 Spring plates?

Expected Cost?

[TimT]

hmmmm


reinforce the rear upper shock mounts


and how did you get a long wheel base 66 tub?

[Jack Olsen]

It makes sense to put them in the back, I've been told, but in front they will encroach on possible tire/wheel width. If you do a search (on both this site and Rennlist), Roland Kunz once outlined the reinforcement needed to keep it from eventually hammering your shell apart.

[scca_ita]

and how did you get a long wheel base 66 tub?

The previous owner put updated torsion tubes on the rear. The only difference between the short and long wheel base is the trailing arms and the way the spring plates mount to the torsion tubes.

Put 69 or later torsion tubes in and then you can use updates suspension. In my case I am using alloy arms and have SC spring plates. I also have a steel turbo body.

Old picture - car looks like 74 IROC now

[82SC]

i thought the entire length of the car was changed...no?
wow...for racecar builders buying a 912 shell and doing those mods gets you a 911 chassis for cheap...

is that correct or are the SWB and LWB really different?

MJ

[jluetjen]

Hey ITA;
Are you going to be taking your 911 racing? I'm planning on going the same route with my 911, but that is still a couple of years down the road. I have learned a couple of things...

1) You will need to reinforce the shock mounting points (both front and rear) to handle the additional stresses which are currently being handled by the torque tube in the back and the frame rails in the front. At a minimum you will want to add the same reinforcements that the factory did with the RSR's. If you can getr a copy of Starkeys "R-RS-RSR" book (older editions will do, you don't need the latest $100+ edition), check out the RS Homologation papers in the appendix. I have a 3rd edition (dated 1998) and there are pictures on pages 186. To do it right you will need something like a full 8 point roll cage which is tied to the shock mounts.

2) Check the dimensions of the tubes that the rear shocks are located in. I believe that these tubes were given a larger diameter in the early 70's to allow more room for bigger shocks. This would suggest that they are a tight fit for coil-overs on our earlier cars. (I haven't taken the time to check mine yet).

3) Looking at published data, it seems like a fair place to start for coil-over units would be as follows:

Front Springs: 300 to 350 lb/in springs
Rear Springs: 500 to 600 lb/in springs

I haven't seen anything about what sway bars people use with this set-up, but there are some calculations that you can use that will most likely get you to a starting point. A good source for these would be Allan Staniforths's Competition Car Suspension.

[scca_ita]

is that correct or are the SWB and LWB really different?

This is correct. Putting new tubes in is not difficult. In fact if you are going to coilovers and adding longer trailing arms then only the trailing arm mounts need to be changed.

So thats why its good to pick up early 912 rollers.

[jluetjen]

For the sake of discussion, here is an example of an "8-point" cage design for a 911. I made this up using Grape Software's FEA software which is available as shareware. Note that for the sake of the model I added some cross braces in the floor area of the passenger compartment . These would most likely not be needed since the actual floor of the car's tub would serve the same function.

[Bobboloo]

In the Oct. 2000 issue of Excellence there is an article on a POC racer. The guy started with a 912 chassis and put in a 993 multi-link rear suspension and a 935 front suspension. For power he used a 3.6 993 motor.

The coolest thing is the 993 rear suspension because it's lighter than a trailing arm suspension, it adds rigidity with crossmembers and the best part is that the toe in adjusts under hard cornering to help keep the rear end behind the driver.

Of course this is the ultimate setup that won't be cheap. (labor)

Bobby

[TimT]

2) Check the dimensions of the tubes that the rear shocks are located in. I believe that these tubes were given a larger diameter in the early 70's to allow more room for bigger shocks. This would suggest that they are a tight fit for coil-overs on our earlier cars. (I haven't taken the time to check mine yet).

Yeap,

I tried to install coilovers w 2 1/4" spring in my car, the spring fit in the crossmember was almost an interference fit. Ended up having to mount the shocks and coils upside dawn. A quick calll to Kelly-Moss and i got the clevis adapters needed. Having the shock/coil inverted isnt such a bad thing

[cab83_750]

I should be getting my 'upside down coilovers' next week. I'll post how this task of my project would be going!!!!

[Elombard]

I had an engineer for a pretty large race team tell me one time that the shocks transmit the majority of the force to the chassis in quick transition - i.e. over a bump. That in that situation the springs did very little work. For this reason the shock mounting points needed to be very strong. He was telling me this because I was worrying about installing coilovers on the rear of a Datsun 510 (also has a trailing arm setup like a 911) race car without doing significant modifications to my roll cage. I ended up tieing the roll cage in any way but it makes me think that in a street application you might be able to get away with some upside down mounted coil overs without doing a bunch of reinforcement. Maybe some folks here have experience that would disprove that? I will not volunteer to be the guinea pig, however; for this project : - ))

[scca_ita]

My theory is this. By the time I spend money for torsion bars bushings shocks and bearings I will have

Rear

$350 - Torsion bars
$300 - Shocks
$60 - Bushings
$120 - Bearing kit
So $830 for the rear,

I have been quoted $2009 from racers group with 935 spring plates for coilovers.

I have the alignment tools but have found it very difficult and time consuming to align and setup the rear as is. The other option is to pay someone $200 - $400 each time I need to adjust things.

Point being I can adjust the rear with the new coilover setup because you now have separate height, toe and camber adjustments.

[Jack Olsen]

I would say ask the Racers Group guys what parts of the chassis they reinforce as part of the $2000 coil-over deal, and we can evaluate from there.

[A Quiet Boom]

Originally posted by scca_ita
and how did you get a long wheel base 66 tub?

The previous owner put updated torsion tubes on the rear. The only difference between the short and long wheel base is the trailing arms and the way the spring plates mount to the torsion tubes.

Put 69 or later torsion tubes in and then you can use updates suspension. In my case I am using alloy arms and have SC spring plates. I also have a steel turbo body.

Old picture - car looks like 74 IROC now

First I'd like to add that 1) your car is beautiful and probably even better with the IROC body and 2) you forgot to mention than the rear flares need to be mounted farther back when changing wheelbases. Next a small question, I've been considering redoing my rear flares in steel (just bought a brand new Tig ) and moving to the longer wheelbase, I thought I had all the parts I needed until you mentioned the torsion tubes. I assume these are the large tubes welded to the body? If so would it not make sense for me to get the newest ones possible to expand my transmission choices? And if the answer to that is yes then where can I get them? I figure a P-car salvage dealer could supply them but are they available new from Porsche? Lastly any helpful hints to make the torsion tube swap less painless than it looks? I'm and experienced welder and have done several racecar chassis including a "back-halved" Monte Carlo so I'm familar with getting things removed and new parts lined up etc.

As far as your question goes I don't have any answers for you but aside from the obvious safety and chassis stiffness a roll-cage adds to a car IMO it would add to the overall "look" of your car tremendously. Think of it, beautiful IROC body, wicked suspension, high powered motor and a rollcage to complete the "bad arse" image

[scca_ita]

I think the torsion tubes can be sourced. I have seen them from time to time on ebay - new. However I am not 100% sure.

If I were going to go to a longer wheel base with a fresh SWB tub, I would skip the torsion tubes and modify the existing trailing arm mounts, on the old torsion tubes, for the updated alloy arms and add coilovers. I think this will simplify the whole project and also get a killer rear suspension.

If you insist on replacing the tubes, the previous owner told me he made up a jig from a LWB car. Also the body acts as a jig too. If you look, the torsion tubes sit on raised surface that were use during initial manufacturing to hold tubes in place while they were welded to the body.

[A Quiet Boom]

Well, given that mine is a rust repair car (although the PO had an excellent job done) I'm not willing to trust the stock chassis to handle coilovers. With a young daughter who occasionaly rides in the back any cab intrusive rollbar is also out of the question. However I might consider making my own since I have the necessary equipment, removing the interior etc. is more work than I'd like to take on this winter. I'd sure like to hear other options for reinforcing the body for coilovers, since I tend to agree that they'd make the LWB transition easier as well as provide a better rear suspension. Anyway I've now got a lot to consider for "winter upgrades" hehe