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Old August 18th 2019, 10:25
Simon Simon is offline
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Join Date: Feb 2007
Posts: 65
Originally Posted by H2OSB View Post
Your car is amazing similar to my '74 (though I'm insanely jealous of your R&P steering). My coil overs are VERY similar to yours. I have 944 housings with a Ground Control coil over kit(I'll try to add a pic from my phone in a bit), running 2.5 inch 120# springs. What are you doing for the rear? I have 26mm 924 upgrade torsion bars on the rear. I found them on the Auto Atlanta site on sale for $100 for the pair, brand new.
I've been thinking about the rear suspension quiet a bit the last 2 weeks, trying to determine what to do. I'll be using 944 aluminium trailing arms with probably the wider track flanges, maybe the smaller track flanges first since I already have a pair discs for those.
The torsion bars will be removed and replaced with coil-overs. Coil-overs are just so much easier to work with and I expect it'll take a bit of trial and error with the spring rates to get to a setup that I'm happy with, which is a lot easier with coil-overs.
Also that way I could run a slightly softer setup for the street and quickly switch to other springs if I want to do a track run. Not sure I'll do that since I'm lazy, but you never know :P

The brakes will probably be Boxster (986) rear calipers with stock 944 rear discs. These are almost the same as the rears on a Boxster (289x20 for 944 rears vs 292x20 for the Boxster rears). Again not the biggest fan of these discs because they are quiet heavy (6.4kg!) but I'm not sure it'll be easy to find or build something else since the offset is rather large (100mm) and the inside of the discs is used for the handbrake as well.

There are still a couple of things to figure out though:

Which coil-overs to use?
I've been involved with a bunch of motorsport stuff, mainly focussed on suspension and suspension development and I have to admit I've become a bit of a fan of Bilstein.
Their products aren't very expensive (apart from their MDS and 5-way EVO dampers) yet are very well designed and deliver very good performance. Apart from that parts are relatively easy to get and revalveing is easy if you want to do it yourself or not so expensive if you want them to do it.
So Bilstein it is

Then the question remains: Which exact coil-overs to use?
Since I'd like to keep using the car on the street I quiet like the Bilstein 944 Cup dampers because they use rubber mounts instead of spherical bearings. They also can be fitted directly to the top mounting point of the 1303 as well as of course the 944's trailing arm bolt.
Another reason to pick these is they use Bilstein's 46mm pistons which has more options available than their 36mm pistons, making it easier to customize them to how I'd like them to be.

Whilst the Bilstein cup dampers are a known quantity for 944s oddly enough I've been unable to find any information about people trying/using them on IRS beetles.
Since the angle of the damper compared to a 944 is slightly different I wasn't sure if the damper would fit, it could be the springs would rub against the trailing arm.
So I test fitted a pair and whilst it's definitely a tight fit, it seems like it's possible. There's about 1-2mm room between the spring an the trailing arm.
I'll need to massage the body right next to the top mount a bit to create enough clearance for the top hat, but I don't expect that'll be a problem.

I'm also considering using 2.25inch springs instead of 60mm springs. That's the way the Bilstein Cup dampers are delivered in the US (see for example the so called 944 escort cup front and rear set on the Lindsey Racing site and it would give a small amount of extra room/clearance which seems like a good idea.

The alternative would be to use a spacer like the racer's edge bolt to move the dampders away from the trailing arms, although that one only works with sperical bearings, or use smaller (36mm) dampers in combination with 2inch or 50mm springs. The selection of those is a lot smaller than 2.25inch and 60mm springs though.

I'm trying to figure this out this week, make a decision and order the relevant parts.

This is with KW 60mm springs btw, that's why they are yellow

What kind of system to use to guide the rear trailing arms?
Whilst I do quiet like the uniball setup in that it allows for very easy toe in/out adjustment, after reading up on it and talking to some people I think that for my current purposes it's slightly too direct and will pass through a bit too much noise/vibration/harshness.

There aren't that many alternatives but it seems like GWD's Performance torsion bar covers are the perfect fit.
The torsion bars can be removed because they are no longer required for guiding the spring plates, which saves about 6kg total, yet the guiding of the spring plates is nice an precise without such a direct connection as a uniball setup.
I also considered a similar product from Rebel Racing ( but I haven't been able to determine if these would fit on 944 parts.
I'll be ordering them this week, hope they'll be delivered soon

Apart from that I've been busy disassembling the whole rear suspension to get all the parts blasted and zinc plated. Takes a bit more time than expected, especially finding a company that can do this short-term, almost all of them are closed for the holidays :P

Last edited by Simon; August 22nd 2019 at 16:25.
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