Spring rate for rear coilovers

[Obiwan]

Hello guys,

I would like to install coilovers on the Front and the Rear of my SB. On the rear I've got 944 S2 aluminium trailling arms and want to remove the torsion bars to install uniball links. Knowing that the SB will be powered by a 2.4 T4 engine what will be the right spring rate for the rear coilovers ? (mainly street usage but want to go also on the track)

I'm interesed into Bilstein 944 escort cup rear coilover or the Koni cup ones

Thx,

Peter

[F4P]

hello obiwan and what about QA1?

less expensive than bilstein and koni..

[Wally]

The 944 cup racers use 300-400 lbs for rear set-ups...
That would be a start I guess (emphasis on 'guess')

[Obiwan]

Originally Posted by F4P

hello obiwan and what about QA1?

less expensive than bilstein and koni..

Hi F4P, I think we "know" each other from an other germanlook forum
I'm looking closely your progress on SB high quality parts production. (I'll buy from you the uniball link for my 944 aluminium arms but I'm also very interested in your camber plates, front coilover studies. I think I'll also contact to discuss about callipers brackets to adapt my 996 callipers onto the beetle)


QA1 is also an alternative coilover solution. I' haven’t any feedback on QA1 quality. In addition I expect an issue between coilover body and the 944 arms. QA1 coilover are "generic" and the lower mount hole is cantered and not misaligned as the Bilstein is.

I've also contacted Intrax in Netherlands to have some information on their RAS & 1K2 coilovers.

Bilstein Escort cup rear coilover
with helper spring: $875
w/o helper spring: $745

Koni cup coilovers (w/o helper spring) : $735

[Wally]

Lee Arnold (LAperformance) is said to make very nice rear coil overs specific for 944 alu arms in bugs with adjustable shocks for 300 pounds or s/th?
I would probably use those if I'd go additionally coil-over on the rear.

[evilC]

With the Uniball set up you will be loading the top bolt fixing on the dampers to >700lbs that puts a considerable bending moment on the 12mm bolt and a substantial twist on the forged arm so it is vital that the forces are redistributed back into the chassis. A full 5 bar Kafer Cup brace is the solution for this.

As regards to the spring rate you can compare the current wisdom on torsion bar selection - 23.5mm dia for mainly street and 25.5mm dia for mainly track with the equivalent wheel rate and then convert that back to the coil spring rate. It all revolves around lever arm lengths. The torsion bar conversions are available on the web - just Google. Coil springs in especially 2 1/4" dia are readily and cheaply available so it is feasible to try some different poundages around the starting point even to the extent of taking corner weights into account.

When you have decided on the spring rate talk to the damper suppliers about appropriate dampers.

Clive

[ricola]

I ordered my coil-overs today, if using with steel arms make sure you get the smaller diameter springs (1.9") or they may foul on the trailing arm. I bought pro-techs and have in the past, much better than previous AVO and GAZ from my personal experience in quality and value for money (they are all ally bodied and retail at £80+VAT each but easy to get money off). They also build them to your exact spec for the standard price, today I was offered options on length, bushing type and size (rubber/spherical) as well as rod diameter 10/16mm

http://www.protechshocks.co.uk

I'll receive them on tuesday

[F4P]

you can use search QA1 in this forum you have feed back on it

it's 50% less than escort cup .

[Obiwan]

Thanks guys for your feedback. It's really appreciated.

Regarding rear axle reinforcement, I've got the Eyeball engineering torque bar.
http://eyeball-engineering.net/TorqueBar.html

Intrax answered to my questions. They can build specific coilovers based on 944 ones on my desires. Nevertheless the price is too HUGE for me (2350€). A bilstein cup set is about $2000.

UK Pro-Tech coilovers can also be a good alternative regarding the price of an equivalent set. Especially if it possible to select coil overs with off-set lower eye mounts.

[evilC]

Originally Posted by ricola

I ordered my coil-overs today, if using with steel arms make sure you get the smaller diameter springs (1.9") or they may foul on the trailing arm. I bought pro-techs and have in the past, much better than previous AVO and GAZ from my personal experience in quality and value for money (they are all ally bodied and retail at £80+VAT each but easy to get money off). They also build them to your exact spec for the standard price, today I was offered options on length, bushing type and size (rubber/spherical) as well as rod diameter 10/16mm

http://www.protechshocks.co.uk

I'll receive them on tuesday

Great link Rich, I will lock it away in the brain cell for future reference!

Originally Posted by Obiwan

Thanks guys for your feedback. It's really appreciated.

Regarding rear axle reinforcement, I've got the Eyeball engineering torque bar.
http://eyeball-engineering.net/TorqueBar.html

Intrax answered to my questions. They can build specific coilovers based on 944 ones on my desires. Nevertheless the price is too HUGE for me (2350€). A bilstein cup set is about $2000.

UK Pro-Tech coilovers can also be a good alternative regarding the price of an equivalent set. Especially if it possible to select coil overs with off-set lower eye mounts.

The Eyeball Eng. torque bar is not suitable IMO for a full coil over conversion. The unit should be no less than a 5-bar Kafer Cup brace set that fully triagulates the the top fixing position for the coilover unit. The EE torque bar won't prevent the top fixing from moving upwards or sideways. The EE torque bar may resist the frame horns from moving downwards under torque but the bar is under a point load bending moment that also has a bolted joint at its maximum bending moment position. It all goes against the very basic principles of structural engineering although you can make anything strong enough if you add enough weight.

Offset eye mounts on dampers should be avoided at all costs since they will impart a side load to the internal seals that will fail all too quickly.

Clive

[Obiwan]

Thanks Clive for your explanations on the EE torque bar limitations. I'll sell it & look for a 5-bar Kafer Cup brace set.

Regarding your "general" comment on the offset eye mounts, I understand your point of view but I'm also confident in Bilstein engineers that designed the escort cup set with the an offset eye mounts for the rear coiloovers. Until now I've not seen such complaints or issue on this bilstein set on sevrals Porsche 944 dedicated forums.

[Wally]

Originally Posted by ricola

I ordered my coil-overs today, if using with steel arms make sure you get the smaller diameter springs (1.9") or they may foul on the trailing arm. I bought pro-techs and have in the past, much better than previous AVO and GAZ from my personal experience in quality and value for money (they are all ally bodied and retail at £80+VAT each but easy to get money off). They also build them to your exact spec for the standard price, today I was offered options on length, bushing type and size (rubber/spherical) as well as rod diameter 10/16mm

http://www.protechshocks.co.uk

I'll receive them on tuesday

wow! How can they make them that cheap?
Can you expect a quality shock for this amount of money plus an all alu body and spring??
Do you have any long term experience with them Rich?

[ricola]

I used pro-tech dampers on my Phantom GTR, they were good and held up to the elements well. I can't remember the exact history but I think the Pro-tech owner was with one of the other companies and then left and set up on his own. The fact that they are relatively small and build to order to your exact specs cheaper than any competitors in ally rather than steel means they win hands down for me...

I used Gaz on my GTM Libra, they corroded quickly and the damping rate was poorly matched, owners often had to do a DIY calibration side to side to get them close to matching, not able to rely on just doing same number of clicks on each side! The bushes tended to destroy themselves after a year or so too...

I had AVO on my speedster, these also suffered from corrosion.

Hopefully they will arrive today and I'll get some pics up tonight... If you can't wait, look in my friend's sti speedster replica build blog, link is on my site...

[Wally]

Originally Posted by ricola

I used pro-tech dampers on my Phantom GTR, they were good and held up to the elements well. I can't remember the exact history but I think the Pro-tech owner was with one of the other companies and then left and set up on his own. The fact that they are relatively small and build to order to your exact specs cheaper than any competitors in ally rather than steel means they win hands down for me...

Can't argue with that! Good find!

[evilC]

Originally Posted by Obiwan

.......................
Regarding your "general" comment on the offset eye mounts, I understand your point of view but I'm also confident in Bilstein engineers that designed the escort cup set with the an offset eye mounts for the rear coiloovers. Until now I've not seen such complaints or issue on this bilstein set on sevrals Porsche 944 dedicated forums.

I don't doubt Bilstein's expertise on this one its just that it kinda goes against the grain. The dampers that Bilstein supply are presumably set for 2.5" coils? with the threaded section that goes low down on the damper body so the potential for the coil to foul the arm is pretty high. If you use Rich's 1.9" coils and carefully select the spring length then there is a better chance of acheiving the clearence.

It occurs to me that offsetting the eyelet to get better clearance is just the same as putting a spacer on the bolt and using the standard eyelet. Assuming that the bolt is long enough, the load position and hence the BM will be the same for both the offset eyelet and the standard eyelet with spacer, although the angle at which the damper operates will be less vertical than normal but should be still within the ability of the bushes/bearings.

Clive