10/20/01 - This FAQ is excerpted from a posting on The Cobra Forum. It gives details of our Bilstein shock and anti-roll bar installation.
For more information about the Bilstein spring and shock package, contact Doug Arnao at Vehicle Craft, 973-366-6577.
For information about an anti-roll bar package for the FFR Cobra, contact Mark Reynolds at Breeze Automotive, 508-612-0393.
The anti-roll bar installation we did isn't a bolt-in package. There was a fair amount of engineering involved, as well as considerable fabrication. You can't just bolt in some parts from Speedway Engineering and go.
That being said, here are Speedway's part numbers for the bars we are using:
Front:
608-125-350 - 35" x 1.25" x .125" hollow 48-spline bar
610-3 - aluminum straight 1.25 48-spline arm (2 needed)
Rear:
608-49-91 - NASCAR 37.5" x 0.91" hollow 49-spline bar
610-3-49 - aluminum straight 1.25 49-spline arm (2 needed)
Note that we tried a .188 wall bar on the front. The .125 bar calculates out to the rate Doug recommended for the front, but flex in the brackets, arms, and the car's chassis reduces its effectiveness somewhat.
However, the .188 bar turned out to be too stiff. Next we plan to go back to the .125 bar and upgrade to 1000 lb front springs. Ideally we should have 1100 lb front springs, but that would require new hardware because Doug can't get them in 2 1/2" diameter. We may try that next year.
You'll also need an assortment of rod ends, bolts, nuts, raw steel, and four each of the following Speedway parts:
605A-125 plastic bushing
605C-125 locating collar
We used 1/2" rod ends from Speedway at the front, which work out nicely because they fit right onto the lower shock mount bolt. We used 3/8" rod ends from McMaster-Carr at the rear to save space and because Doug said these are adequate.
The front bar is mounted in a bracket we fabricated from steel tubing and plate. The bar's centerline is about 3.5" from the front of the 4" round main frame tubes (this is a critical dimension). The rear bar is mounted in the corner of the frame just behind the rear cockpit bulkhead and below the trunk, also in a steel bracket we fabricated.
The front drop links are male and female rod ends threaded together, and attach to the lower shock mounting bolts on the front side of the shock.
The rear drop links were fabricated from 4130 tubing, with left hand and right hand nuts welded on the ends. The lower end attaches to a 4" x 3/8" bolt which runs through the rear of the lower control arm just inboard of the spindle attach bracket.
All rod ends have spacers next to them (which we fabricated from steel tubing) to allow them freedom of movement throughout the necessary range.
You'll need to bend the Speedway arms into some rather complicated shapes to make everything fit, especially at the rear. Nate did this with a torch, some clamps, and some big pliers (which is the way Speedway's tech support said to do it).
We also fabricated some brackets which allowed us to relocate the rear quad shocks down and inboard to clear the anti-roll bar arms and drop links.
If you don't want to go through all this fabricating, contact Mark Reynolds at Breeze Automotive, 508.612.0393.
Mark is working on a kit that will supply all the necessary components, including the weldments and possibly even the Speedway Engineering arms pre-bent to shape. You'll just need to bolt or weld the brackets in place, and then bolt everything together.
We considered revalving the Pro Shocks, and this might work ok on the rear shocks for the street.
However, for competition, we felt that small-body shocks have too little volume and would overheat, destroying their effectiveness after a few laps. Also Doug highly recommended the Bilsteins for their cost/performance ratio.
Due to the very low motion ratio of the front suspension, the FFR-supplied shocks are simply too small and too soft to get the job done in the front, in my opinion.
See the next question for a suggested low-cost upgrade for the street.
Based on our experience to date, I think keeping the rear 450 lb springs and going to 800 lb springs for the front would work ok for the street. This brings the front wheel rate up to about the same as the rear wheel rate. It actually improves the ride, because the car is more stable and balanced.
For street/competition, Doug Arnao recommends 1100 lb fronts and 550 lb rears.
Pro Shocks makes an 800 lb spring in 8" length. This will work fine, but you'll need helper springs (available from Doug) to keep the springs from falling against the shock when the suspension is at full droop. Or you could get 800 lb springs and helper springs from Doug.
Pro Shocks' small body shocks can't be made much stiffer than as supplied by FFR. You could go up one step on both bump and rebound to "5 7", but that's the stiffest valving Pro Shocks shows for the small body shocks. That would be ok for the rear on the street, but I think it's too soft for competition and it's certainly too soft for the front, even on the street.
For the front, Gary Cheney is trying Pro Shocks' 2" diameter large body shocks, at the stiffest available rebound setting and a couple notches down on bump. If they'll make it, the Pro Shock number would be AC579B. This is 370 lb bump, 600 lb rebound.
This should be ok for the street, but I think it's probably too soft for track use. If you're running on the track at all, call Doug Arnao and get Bilsteins.
Not at all. The spring and shock rates we're using for the front suspension seem high, but if you measure the motion ratio and do the numbers, this is what is correct. 800 pound front springs and 450 pound rear springs give equal wheel rates front and rear!
Our experience with our car confirms this. The car handles much, much better with higher spring and shock rates on the front, and still rides very nicely on the street. Really!
See my Motion Ratio page and my Cobra Suspension Spreadsheet for more information about why this is.
Yes, we started with stock FFR upper and Mustang lower control arms. We switched to FFR competition upper and FFR tubular lowers.
Yes, I agree that the Cobra should feel a lot more precise than it does when built to FFR specs. It's a little bigger than the Miata, and has that great lump of iron in the middle, plus much fatter tires, but still...
I think our car does feel much more precise, and much more forgiving than it did when we started. It's still perhaps not quite as nimble as a Miata, and it feels more brutal, maybe because of the exhaust note and lack of sound insulation. Also the large tires give the steering a heavier feel than a Miata.
But it does feel fantastic!
See my Suspension Results page for more details.
I originally wanted adjustable shocks, for the same reason, figuring we could click them down a couple notches for the street.
However, Doug has very strong credentials; he's a former SCCA National Champion. He recommended the Bilsteins as very good value for the money. He said he wouldn't bother with anything less than Penskes if we wanted adjustable shocks, and Penskes are quite expensive if you get both bump and rebound adjustment.
I found that the Bilsteins are fine for the street, even though they are much stiffer than the FFR-supplied Pro Shocks. I live in southestern New Hampshire, which has some fairly bumpy roads due to frost heaves. I find that I don't even notice the ride unless I stop to think about it.
The only place I've really noticed objectionable behavior was on a stretch of washboard road near Nate's house, where the road was so rough that the car felt like it was hopping around a bit.