any dirt late model guys? help road race car.

[MadBill]

I'm no major chassis expert, but I think some of the preceding advisers have missed the fact that you are now building a car for (essentially) road courses.

Here's my take for a road race set up:
o The Z bar (Watts link) determines roll center height; it does not affect rear steer. The angle of the lower trailing links does.
o Minimize it via zero angle lower links.
o 3 links are more common and easier to work with than 4 links.
o Keep the anti squat low, <20%.

Keep researching any particular aspect until you find at least three credible sources that agree with each other. "The man with a watch knows the time. The man with two is newer quite sure."

[ZIGGY]

MadBill - I think the OP intends to use a Z-link configuration for his rear control arms, not a lateral Watts link.

[englertracing]

MadBill - I think the OP intends to use a Z-link configuration for his rear control arms, not a lateral Watts link.

Yes z link for the controll arms and probably a mumford for the lateral location.

And mad bill why <20? I'll have no brake hop induced by a short SVSA (my torque arms length) because ill be using brake floaters to isolate them.

I'm sure I won't stumble upon a bunch of people who have done this...
But I'm doing it to do something different. It's not really a competiton car just for fun/learning so I want to build a dirt late model type car for the street. The body is opel gt







Picture that with wide 5 hubs front and rear and an winters aluminum rear.
Fabricated front arms and basically a full tube chassis.

A 2.7l aluminum head pinto with 2 48 dcoe webbers or itb. set back most of the way throuh the firewall.

[MadBill]

MadBill - I think the OP intends to use a Z-link configuration for his rear control arms, not a lateral Watts link.

Yes z link for the controll arms and probably a mumford for the lateral location.

And mad bill why <20? I'll have no brake hop induced by a short SVSA (my torque arms length) because ill be using brake floaters to isolate them...

Just that in my experience, a little A-S goes a long way, especially when one doesn't have big V-8 torque to contend with. Our 2200# Vintage/GT1 Mercury Merkur, with 600+ HP and 500/450#/in. wheel rates front and rear works best with less than 10% anti-squat.

If you run soft springs, you might want more, but I'd start low and add it in small steps. The instant weight transfer through the links can make the car kinda stiff-kneed...

[englertracing]

Well... I I think it may need to be soft because its more of a (shitty) road race car. The canyon roads I intend to use it on here angeles crest, glendora mountain road and azusa canyon. Aren't exactly perfect road race courses and I'm planning on running about 4" bump and 4"rebound travel. There's even a "jump" on my favorite road.

Also there will be a shock to take up the shock load of the antisquat.

What suspension setup exactly do you run on that car?
I like it Verry much is the entire body fiberglass?
My ministock is a mercury capri

[englertracing]

That's not a turbo 2.3 is it??

[MadBill]

Certainly a shock link can help. Even though it's one more thing that can be misadjusted, there's a lot to be said for sticking with the familiar.

Our car is a flat floor tube frame with tubular LSA front with double adjustable Koni coilovers and a small (1") anti-roll bar. Rear is a Ford 9" with Koni DAs, a 1' bar, horizontal Watts link on the bottom of the diff and medium length ((22") 3 link. We have ~ +/- 2" travel and run 2-1/2" F. 4" R. ride height. It makes a lot of downforce on our fast home track (Mosport, average speed for us ~110 MPH) and is proving to be pretty hard on the rub blocks, so we'll likely step the wheel rates up to ~ 650/550.

The car is one of several Roush-designed ones from ~1986. This one ran originally with 300 HP normally aspirated and a 650 HP turbo Cosworth 4 cyl. in the IMSA Series plus SCCA Trans Am, but we put in the 306" SBF from our old 1984 Mustang Trans Am car. The body is mostly Kevlar honeycomb, with a stock steel roof.

[Bubstr]

As I see your plan developing, I see some things that would be over kill or hard to make work.

First the mumford lateral control is not going to work well with a Zlink. You will have turned the Z Link into a 6 link if there was such a thing. If using a quick change get the front plate and use a J bar. You'll like the weight you saved and it can adjust roll center much better.

Speaking of the quick change rear. If you go to a Z link you will have to have birdcages for mounting to the axles. Better measure width on that GT and compare to the quick change. I've put a small block chevy in one and a ford rear that had to be narrowed quite a bit. Are you going to have enough room for bird cages and brake mounts and not have to bubble the rear quarters? If you have to do this then you will have to widen the front to get any kind of neutral handling car. A car wide in the rear is an invitation to over steer. It would be a lot of work, but a wide Opel GT could look neat. One other thing on the rear end. Spool Locker or ratchet? They make different length tubes used in LM sprints or midgets.

Unless you already have the Pinto engine, a crate SBC could offer more H/P and dependability for less money.

I'm not trying to rain on your parade. It's a neat idea. Just pointing out some pitfalls.

[englertracing]

As I see your plan developing, I see some things that would be over kill or hard to make work.

First the mumford lateral control is not going to work well with a Zlink. You will have turned the Z Link into a 6 link if there was such a thing. If using a quick change get the front plate and use a J bar. You'll like the weight you saved and it can adjust roll center much better.

Speaking of the quick change rear. If you go to a Z link you will have to have birdcages for mounting to the axles. Better measure width on that GT and compare to the quick change. I've put a small block chevy in one and a ford rear that had to be narrowed quite a bit. Are you going to have enough room for bird cages and brake mounts and not have to bubble the rear quarters? If you have to do this then you will have to widen the front to get any kind of neutral handling car. A car wide in the rear is an invitation to over steer. It would be a lot of work, but a wide Opel GT could look neat. One other thing on the rear end. Spool Locker or ratchet? They make different length tubes used in LM sprints or midgets.

Unless you already have the Pinto engine, a crate SBC could offer more H/P and dependability for less money.

I'm not trying to rain on your parade. It's a neat idea. Just pointing out some pitfalls.

Well I bought a qc center and and nonqc center for 350 bucks I have the aluminum tubes ready to install and a lathe to fit them. As they sit they are farrr to wide.

I do plan on using the non quick change for weight reasons.

Going to keep the width just as you see it. And we will see what happens with the floaters. I'm using 12inch wide wheels with 7inch back space to allow me to place the bird cages wide as possible.

The diff is a gleson type. Id like a varilock also Im running cambered spindles and a crown spoons.

As far as the pinto I have one sitting in my ministock (my track closed) I just need to discard my holley and install a set of webbers.
I also have the makings for something close to a midget engine in my shed.

And I can bring the pinto far through the firewall.