924Board.org

[924RACR]

Just some notes about what I had to do to install my new Bilsteins into the racecar. Pics of some of the bits before installation at:
http://www.vaughanscott.com/construction.htm#SUSPENSION

Front struts:
I had a set of old 933 D-Prod struts rebuilt/revalved to my needs by Bilstein Motorsport. I installed coilover sleeves and spring perches over top of these (had to remove the dust caps to get them to fit on, but it's a nice tight fit) to locate the 2.5" racing springs. These struts bolt-in in place of the stock struts, a direct replacement. They appear to be set up for much more than stock camber; this would make sense, as they were built for cars running on slicks, which use a lot more static camber than a street car. As we (in IT) run on radials, we require much less static camber setting. This will need to be sorted out as we align the car (tomorrow night, hopefully).

That's really all there was to say about installing them; ride height, camber, caster and toe will all be adjusted on the alignment rack. No fabrication or modification required to make them fit (keeping in mind that I already had a set of the Paragon camber/caster plates in place of the stock upper strut mount, which are set up to provide an upper spring perch for the race springs).

For those wishing to duplicate this, however, you won't be able to buy these struts from Bilstein new. You will have to purchase their VW A1 36mm Rally struts. These are designed to take a stock sized spring, and will need to have adjustable spring perch collars fitted to use for racing. One other note, specific to the 933 struts, which will probably not affect the A1 rally struts, is that these DP struts are designed for a lowered car. This means that they have a shorter overall length; there is a reduction in droop travel (wheel extension relative to the body) as compared to a stock strut. This is OK for a race car, since we run them lowered (5" ride height), and will be expected to be different in the other struts. YMMV

Rear shocks:
These were expected to be a bit more involved, since they were an off-the shelf item from Bilstein, normally sold as a circle track shock. They were a 36mm shock, with 1/2" rod ends at each end (not the stock metric size), part number previously posted in another thread, revalved to match my suspension, smooth (not threaded) steel body, and set up to be user-serviceable if I need to change my valving mid-season. The struts, in comparison, need to be sent to Bilstein in case of a need for revalving. These off-the-shelf shocks are cheaper than a custom built shock, not to mention much quicker to get.

The first order of business was to address the mounting. With the 1/2" rod ends, if I used the stock shock bolts, the shocks would bang around loosely. The easy solution was to bore out the stock mounting holes to 1/2" (from 12mm, a very close size) using a big drill bit and a very sturdy, powerful drill. I borrowed a Bosch drill from work. This was very torturous, but straighforward.

This done, the shocks would bolt up, but the rod ends that come on the shocks are much narrower than the ends of the stock shocks, with their bushings and all. Therefore spacers needed to be made. The simple answer to this was a length of steel tube obtained, with a 1/2" ID, 5/8" OD, and so a wall thickness of 1/8". This needed only to be cut to length (12 and 16mm lengths, 4 each) to space the shock rod ends in the mounting point. We ended up with what looked like a collection of little short tubes, which the shock bolts were slipped through when mounting the shocks. For bolts, I bought new Grade 8 1/2" bolts and hardware from Lowe's (they have an excellent stock of hardware like this, much better than Home Depot), two bolts 5" long for the upper ends, two bolts 3" long for the bottoms. I would not go any lighter than Grade 5 for the suspension bolts.

One last problem had to be fixed before installing the shocks. The end of the shock where the nitrogen charge to pressurize the oil (these are monotube shocks, not twin-tube, but still use a gas charge to reduce foaming) is kept has a schrader valve (just like a tire stem) sticking out of it to add/remove the pressure, and is very wide. The width means that this end will not fit on bottom, into the trailing arm, like the stock shock. That's OK, though, since we'd rather mount these inverted, with the fat end up top, in order to reduce unsprung weight and improve performance. It also fits better inverted. However, the schrader valve will still hit the shock mount and interfere with suspension travel, possibly (worst case) causing the valve to be ripped off during compression of the suspension, sudden loss of N2 charge, and complete loss of handling control!

So, it was necessary for us to get out the die grinder and notch the shock mounts, making room for the valve to swing around. We'll have to keep an eye on that, make sure that there are no lasting negative effects of this mod.

The rear shocks are now bolted in, with spacers on either side of each rod end to keep them centered.

A final note, it is highly recommended that you keep your shocks and struts matched, just like your tires, as a mismatch could create some really evil handling characteristics. If you are running a twin-tube shock right now, like a Koni, you would be better off keeping them until you can afford a complete set of Bilsteins, rather than doing one end at a time, as they will (in particular) have very different durability characteristics over time. Therefore the car's behaviour could change substantially over the course of a race.

As for performance - can't say yet. I'll be out at Beaverun this weekend with the GTS Challenge, taking on my first competition in the GTS1 class, a Z3, and we'll see how they do. I'll be (as usual) seriously down on power, so if I can even hold my own, I'll be happy! I'll try and get an update in afterwards, let you know how I like them (previous set were Koni yellows).

Hope that helps, write back with any questions.
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[jjadczak]

I know this is going to be helpful if/when I decide to go to the next level in performance. Right now I'm still trying to figure out how to drive fast and consistently. I'd love to do this but we still have brand new hardware on the car and that includes shocks. The day they were out, watch out!!

Jeremy

[924RACR]

Of course, you could help finance the update by selling the used parts here...
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[jjadczak]

That is true my man, that is true. The next upgrade will be Racer's Edge Camber plates, and a header. But first I need a set of tires. I'll await your report from the Beav to see how your Pilots performed before I make my final decision. I don't need them until late June. Tire Rack should still have a set.

[924RACR]

Get the Paragon camber plates, they're cheaper, and allow you to run additional caster as well.
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[924RACR]

Just corner-balanced/aligned the car last night, finally, and took it for a spin around the parking lot. Wow, what a difference!

Actually, the difference was immediately evident when adjusting ride heights and alignment... with the car in the air, every time I adjusted, I had to make a small tweak and wait for the wheel to move. The damping is so effective that even at movement as small as 1/8" or less, you can see the effects. Holy Crap!!! The Koni's showed no influence over the wheel's movement.

Driving around the parking lot was also noticeably different, even for my crew chief, who rarely drives the car. Even the smallest motions are well damped, compared to not at all with the Koni's, with the result that the car has a really nice ride. That's with a full spherical bearing suspension, strut tower brace, and spring/bar rates about four times as stiff as stock. Crazy.

I have to admit, some of the drastic improvement may be due to the Koni's (one or more) possibly being blown, but even so, the car never ever rode this well.

Looking forward to hitting the track Saturday!
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype