autocross suspension

[SkiWaNow]

We recently aquired a 72 Opel GT and want to set it up for autocrossing. Can anyone give me suggesions on what springs to get, swaybar sizes etc? We have been looking at the sport spring set and sway bars from Opel GT source. They have a 1 inch front bar and a 3/4 inch rear bar. The front bar sounds about right to me, but any suggestions on the rear bar? I had a 7/8ths inch rear bar on my 240Z and when I took it off, the car was transformed. Of course, there are other variables involved. We are planning on running some 15x7 or 8 wheels with 225mm wide tires (probably Kumho Ecsta V700).

Pete Sprenger
skiwanow@comcast.net

[davegt27]

I would go with Gils sway bars Front and rear

warning the ride will get harsh once you start moving to an autocross setup

of course the car needs to be mechanically sound (that's my suggestion) first

but if you have a 240z you know that already

Davegt27

[Paul]

I'm not a GT owner, but RallyBob has listed a few recommendations before. Like: widening the front track by 1/2" per side (?), modifying the tie rod end to eliminate bump steer, solid mounting the steering rack and the use of a shackle. I think he has even listed shocks that work well. Also, there is relocting the rear trailing arm mount point on the spring bucket to improve anti-squat and making the panhard bar adjustable.

And don't forget a good auto-x alignment.... caster, negative camber and toe out.

HTH

[SkiWaNow]

I realized right after I posted my question that I forgot to mention that we are planning on running in the Street Prepared class. We are not too worried about a stiffer ride. Our theory is that it is a sports car and sports cars are supposed to ride rough

Does RallyBob have a web site. I am asking because you say he "listed" those modificaions.

What is the contact info for the Gil sway bars?

Pete

[namba209 (R.I.P.)]

Pete, I don't believe RallyBob has a website, most of the suggestions he makes are listed somewhere on this site and because this is a forum of questions and answers/suggestions, the site owner has set up a really great search engine on the site. Use the search button, type in a word or phrase and you'll get all the posts/threads with that word/phrase in it. Because this is a large forum and lots of inputs, it may take a while to read all the stuff, but it is worth it. As for contact with Gil, simple, go to www.opelgtsource.com and check out his on line catalog. HTH.

[Travis]

In my E Prepared GT I'm running the following, largely based on RallyBob's advice

OGTS Sport front spring
OGTS poly front bushings
Koni yellow front shocks
Modified Manta front bar, heimjoints between bar and control arm
custom delrin inner sway bar bushings


Rancho RS9136 rear shocks
custom longer and adjustable panhard bar
custom 180lb 2" lower rear springs
3/4" Addco Kadett sway bar (arms modified to be adjustable)
heimjoints between bar and axle
custom aluminum/bronze inner sway bar bushings
OGTS poly rear suspension bushings

I'm running a heim joint on one end of each rear control arm and panhard bar but you can't do that in your class.

While I wouldn't say it's perfectly dialed in, it is quite close and I'd expect an excellent starting point for you...

-Travis(I've been away from the list for a while...)

[davegt27]

oops you guys are quick you already posted the info

davegt27

[Paul]

We all wish RallyBob had a web site.... Actually he does... its this one. We all worship the pavement he drives on....

[SkiWaNow]

Let me just say thank you to all the help you giving me! I guess it is apparent that I am on a steep learning curve here with this car since I have only owned it for less than two weeks. I was just on the phone with Opel GT Source about getting some new rear brake pads (the rear brakes on this car are really the only thing that needs attention- the engine was just rebuilt 15,000 miles ago, the body is in great shape, and everything I have inspected so far looks great) and I realized his name is Gil and that is to whom you were refering.

Travis, you said that you have an OGTS front spring. Do you know if this is the same spring that Gil sells? If not where would I find one?

Has anyone tried cutting the rear spring? I heard from Opel GT Source (not Gil, but I have already forgotten his name) that the stock rear springs are rated at 160 lb. and the sport springs they sell are actually even less than that. I have 275 lb springs on my 240Z, which weights almost exactly the same, so these seem like really low numbers to me.

Pete

[Travis]

Travis, you said that you have an OGTS front spring. Do you know if this is the same spring that Gil sells? If not where would I find one?

Yes, it's their sport spring

Opel GT Source = OGTS = Gil

You'll need to have the rear springs made as no one stocks anything appropriate.

The 240z has an IRS right? If yes, you can't compare the spring rates directly. Most people like to compare wheel rates(combo of spring rate and motion ratio) for diffferent vehicles. To take this to the next level, you'll want to come up with a ratio of wheel rate to sprung mass for each corner. This will give an accurate comparison of 'stiffness' across differing vehicles. Spreadsheets work exceptionally well for playing with spring rates and noting their affect on 'stiffness' or the suspensions natural frequency, depending on how you like to look at it.

-Travis

[Paul]

Street prepared is all about handling and weight reduction. The rules for engine mods are almost as restrictive as stock except for ignition and carburation. Also, you'll need to shorten the gearing via smaller diameter tires or by changing the rear eand ratio, if thats even legal.

When I get home, I'll try to dig up some of Bob's recommendations for improving the GTs handling to add to the things mentioned by Travis and Dave.

Currently stuck in Atlanta

[Travis]

When I get home, I'll try to dig up some of Bob's recommendations for improving the GTs handling to add to the things mentioned by Travis and Dave.

With the exception of the Delrin AF bushings that Bob has custom made, I think you'll find most of his other suggestions to not be legal changes in SP. Bump steer, camber recovery curve, anti-squat, rear roll steer and so on....

-Travis

[Paul]

Travis,
Actually, I was thinking of wheel spacers for track width, springs, shocks, anti-sway bars, lightened flywheel, manifold porting, etc. But you are right Travis, in Street prepared the stock suspension points have to be maintained. The other stuff I mentioned was before I realized he was running in SP.

Okay, here is the condensed version... dated April 29, 2001.
* Widen front track by at least 1/2" ...
* Hard Poly or Delrin AF bushings with grease fittings
* Seam Weld the lower a-arms... ? legal?
* Correct for Bump Steer on a lowered car.... NOT LEGAL in SP
* on a lowered car cut the bump stops at least in half...
* Use the OGTS 1" Front bar (use 3/8" heim joints vs end link bushings
* Use OGTS rear bar
* Try to add 4* positive caster
* Adjust the camber
* solid mount the rack and pinion (Probably not legal, but who would know) Seam weld the brackets that are factory spot welded on the crossmember
*Use high-pressure gas shocks oin the front
*Use low pressure adjustable shocks on the rear
*180# rear spring for street and 200# for racing
*Rear trailing are attachment points... NOT SP Legal
* Polyureathane rear suspension bushings
* Adjustable panhard bar if lowered. NOT SP LEGAL

[Travis]

* Widen front track by at least 1/2" ...

Save this for last if you still have money in your pockets. While theoretically better, I'd bet it's hardly noticeable.

* Seam Weld the lower a-arms... ? legal?

Not legal

* Use the OGTS 1" Front bar (use 3/8" heim joints vs end link bushings
* Use OGTS rear bar

While not a bad place to start, it won't be long before you're modifying the arms to make them adjustable. No point in buying the expensive bars and cutting them up. I'd recommend using the cheaper Addco Kadett rear bar, as I did. I'm also happy with the 7/8" Manta bar in the front.

* Adjust the camber

Easier said than done...

* solid mount the rack and pinion (Probably not legal, but who would know) Seam weld the brackets that are factory spot welded on the crossmember

Only your conscious

*Use high-pressure gas shocks oin the front

Shouldn't matter either way

*180# rear spring for street and 200# for racing

Somewhere between 180 and 225 should be reasonable depending on driver, surface, roll bar size and so on. You'll find many differing religions relating to spring rate....

* Adjustable panhard bar if lowered. NOT SP LEGAL

This is actually open. I wasn't thinking straight before....

We must keep in mind that RallyBobs suggestions are just that, suggestions. Reasonable starting points. You'll find that the optimal setup will vary depending on driver preference, driving style, course style, course surface, tires and so on....

I'm somewhat surprised he hasn't popped his head up.

-Travis

[RallyBob]

We must keep in mind that RallyBobs suggestions are just that, suggestions. Reasonable starting points. You'll find that the optimal setup will vary depending on driver preference, driving style, course style, course surface, tires and so on....

I'm somewhat surprised he hasn't popped his head up.

-Travis

Huh?

There, I have now officially popped my head up....

How're things Travis? Long time, no hear. I'm just busy closing out my job this week (decided to move along), so I've been finishing up 'old' projects while taking all my tools home a carload at a time. It's kept me quite busy.

Anyway, what Travis says is absolutely true, I gave guidelines, not strict parameters to adhere to. Driver style and preferences mean a lot...my own preferences are not necessarily ideal for other people.

RE the solid rack mounts. If you replace the rubber bushings with metal bushings (no welding), then it's legal. You'll have to make them from scratch, yes, but IMO it's worth it.

RE the wider front track, again, I feel it's very worth it. The turn-in is dramatically better, and arguably 'feels' better too. But it may make the car oversteer more as well depending on your current setup.

HTH,
Bob

[Travis]

How're things Travis? Long time, no hear.

I had a big project at work that consumed my nights and weekends for the last few months. It was put on hold last Wednesday so I'm starting back up on the car again. The PEI event is coming up pretty quick...

RE the solid rack mounts. If you replace the rubber bushings with metal bushings (no welding), then it's legal.

I can't find any allowance in the rules for this, but I may have missed it...

RE the wider front track, again, I feel it's very worth it. The turn-in is dramatically better, and arguably 'feels' better too. But it may make the car oversteer more as well depending on your current setup.

This is difficult as more things are being changed than track width with this mod. The obvious is the scrubb radius, but the one that isn't quite as obvious is the wheel rate. If a given car tended towards understeer a bit much, this could obviously help, though not really due to having a wider front track width. A sway bar adjustment would have a similiar effect in this regard...

I expect I'll experiment with front track width at some point and will report back, though I am skeptical.

-Travis

[jeff denton]

Please tell me more about "solid rack mounts." What does that do?
Also, as I am preparing a custom right lower A arm (lengthened to increase camber) what would be the best bushing material? Our rules say "any bushing material may be used". Should they be solid, like bronze, maybe?
Thanks, guys!

[Travis]

Please tell me more about "solid rack mounts." What does that do?

The rack is what keeps the tires pointed in the right direction. As it is mounted in rubber mounts, the rack tends to move around a bit and the tires will follow. It's rumored that the rubber bushings can even be forced out of place, but it's never happened to me.

Also, as I am preparing a custom right lower A arm (lengthened to increase camber) what would be the best bushing material? Our rules say "any bushing material may be used". Should they be solid, like bronze, maybe?

It would be best to use chrome moly rod ends with teflon liners. I run the Endura 2000's from QA1

-Travis

[RallyBob]

I can't find any allowance in the rules for this, but I may have missed it...

You are right Travis, the rules now specifically prohibit metal bushings. It used to read that 'suspension bushing material is free', but it no longer reads that way. I stand corrected!

Bob

[GTJIM]

You are right Travis, the rules now specifically prohibit metal bushings. It used to read that 'suspension bushing material is free', but it no longer reads that way. I stand corrected!

Bob

..carve them out of ali and anodize them black .........