I'm currently working on 1989 Iroc for autocross purposes and I'm concern with the T-Tops. The car right now is in great shape 80K and it has all the options I want for autocross except the hardtop roof. I have been looking for a hardtop but I have not come across one, in better shape that the one I have now.

Having said my questions are the following.
1. Is a hard much stiffer than a Ttop?
2. Are sub frame connectors really necessary for twisting forces? (I see a lot of debate on this one here)
3. Will the body of a TTop car eventually fail if used just for autocross and track days?
4. What can I do to protect the integrity of the body?

I'm ready to start modifying the car but I don't want to fix up a car that eventually the body will fail.

I appreciate any help or suggestions.

Thanks

 

A lil bit.
yes, they should be standard and the 1st thing you do to ttop and hard top cars.
not in your lifetime unless your car is rusty.
weld in subframe connectors and cage.

Search around on here for mods to fix the flex. It can be done.

 

Strut tower brace as well.

I haven't auto crossed, but these cars are pretty weak. I am not sure that enough bracing exists to make sense as you will be adding a ton of weight back in.

Don't want to rain on the parade, but for all that you will have to do to get any car to autocross, plus the additional work without a guarantee that you won't still have flex issues, doesn't it make sense to start with the right foundation?

 

I've 3 wheeled my car with Spohn SFC's that were welded along the pinch weld and stock WS6 suspension up a very steep slope out of a parking lot. There is a pic somewhere on the site of Vetruck/ STG's old car doing the same thing on a smaller curb but his suspension was far from stock. I haven't tried flexing mine since I did everything to it but I'd imagine it doesn't have much give.

IMHO, Spohn SFC's welded along the pinch weld, a wonder bar, and an STB should get the body plenty stiff. Tubular rear control arms and a tubular panhard bar will stiffen the rear end up too, and for the STB to really be worth it you'll want Spohn or J&M strut mounts. You can run an "inner" set of SFC's too but I'm not sure they'd be worth the weight; if a car can float a wheel it's pretty darn stiff already.

As far as adding weight, removing the spare tire will offset the added weight of the SFC's which are down low on the car anyway. Some nice headers and an AIR delete if you don't have inspections will offset the weight of the STB.

 

I've run my car stock for 2 years with no ill effects. Except for a crack in the frame behind the steering gearbox, but your iroc should have the wonderbar to prevent that and its not ttop related. Like these guys say, good sfc's and any other reinforcement is always good for the not so rigid cars

 

I have not see a debate on this forum yet that did not recommend sub frame connectors. I think everyone on this forum thinks they should have been installed at the factory.

EXCEPT FOR AUTO CROSS.

Some SCCA clubs stick to the rules and you will move up in class with them. Make sure your competitive in what ever class allows them.

 

Agreed... with one addition.. be sure to not only check the rules about allowing subframe connectors but also about how many attachment points. certain classes only allow a certain number of attachment points which kills the idea of welding it to the pinch weld. Just food for thought since i have first hand seen this issue.

 

Thanks guys for all the input,

Also apologize for not explaining myself better on the sub frame connectors question. What I meant was that I have found different views as of which set is better, the inner or the once run the out side the pinch rail.

Well I will start with the Koni's yellow new set of tires for the next event and see how it goes. Also

Thanks,

 

Exactly. Also welded in VS bolt in. There is a difference in the auto cross world.

Welded in will move you up to a higher class than bolted in.

 

Thanks guys for all the input.

Got a set of Koni's on the way can't wait, especially since the next event is next weekend. Also one last thing, should I run with the T-tops or without them on the car?

Thanks,

 

I noticed a major difference welding the interior when I had it gutted, over the 99 cheesy spot welds used to hold the car together.

 

You can run welded SFCs in SCCA ESP as long as there are only 2 points welded per SFC. This eliminates the perimeter SFCs like Spohn and UMI and limits you to the Alston ones sold by Top Down Solutions.

If you use the perimeter ones that weld in more than 2 places per side (front,rear, and out to the front subframe on each side plus the pinch weld if you do those welds) will put you in CP even if you don't do any other mods.

The advantage of the perimeter style at the track is more jack points to lift the car to change tires but they do put you in a very rough class in SCCA.

As for t-tops or not, we run the GTA with the t-tops in or out depending on the weather. We've also run the IROC vert and the SS vert at autox events with the top down. Some road course events have different requirements, but most autox events don't care.

 

Great info guys. I will go ahead and get the Alston's and have them welded in.

On a side note do the 4th gen have to much of an advantage over a third gen?

My car right now sits around 3360. lbs not including me and it has the following factory options
FE2 36mm 24mm Front -rear sway bars
Aluminum drive shaft
PBR rear brakes
Not power options (windows & seats)

I have thought going the 4th gen route, but I really like and enjoy the iroc z.
Thanks

 

Run with the t-tops off. 1)they do not support much and 2) the car weighs more with them on. Its more upper roll weight.

The car will be fine with Spohn outer perimeter SFC's welded to it. On a scale of one to 10, ten being stiffest, if a hradtop car is a 10 I would put the t-top car a 9, and a convertable a 7. Now with SFC's installed, I would put them a 10, a 9.5, and an 8.5 in comparison to eachother. The t-top car, albeit not being an optimum choice, will work just fine. you have far greater issues of flexing joints and bushing that will cuase you WAY MORE havoc that a flexing chassis. You are not building an all out caged racecar with solid link bushings everywhere and wide sticky R compound tires. Flex is relative to use- your usage on soft street bushings and average DOT tires is not that critical in a flexing t-top chassis.

 

Alstons are nice, weld a cup to the center of each that fits your jack, for a quick nascar jacking

 

The Alstons let give you more flexibility under SCCA SOLO rules for Autox. Depending on your local competition in FS, ESP, and CP it might not really matter which category you go into. Especially if you don't intend to compete nationally and just have fun locally, mod away with whatever options you want. CP cars at the national level are gutted dedicated racecars. ESP is owned by the new Mustangs, and I'm not sure about FS since I never leave anything stock.

As for which is better, that depends on your aspirations and goals. If you're planning on having fun locally, keep the IROC and enjoy the driving. Some courses really favor a TPI setup with the low rpm torque. If you're thinking about national titles, start by driving what you enjoy to get a lot of seat time and then build a car purpose built to go after the title.

 

Alston SFC's are not at all good for cornering. they are a straightline drag racing style SFC. They do not help hardly at all with chassis torsional twist. That is why the SCCA doesnt care so much if you have them

 

Use the outer ones, then use seam sealer along the pinch. I put seam sealer in after the pinch welds just to keep things clean and prevent rust, pockets for gunk, etc. It meets the rule requirements.

 

Please elaborate.

 

What about welding the front and rear of the connectors and then using panel bond along the rocker pinch weld? That stuff is stupid strong, its how most truck bedsides are put on these days. Is that legal??

 

Rather than responding with new text and diagrams, I will search tomorrow morning for the post where I did extensive sketches and text on this issue/ Keep tuned

 

https://www.thirdgen.org/forums/susp...-question.html

 

Thanks to all for all the great info.

I was almost set on the inner style for SFC, but I will put that on hold and take care of the wheels first.

I currently have the 16x8 iroc's on the car, but I have a set of 17x9 SS wheels that I will get a set of spacers for. With the wheels and the Koni's I'm looking to a better weekend at autocross track.

I will post back the improvement with the Koni's and the wheels change.

Thanks again for all the help.

sac

 

My biggest suggestion to you if you plan on running SCCA sanctioned autox events is to talk to the local guys and read the rule book. There is a big difference in the class you will end up in when you go from a SFC that welds in 2 points to a SFC that welds in more than 2 points.

If it's going to be more of a track car than a daily driver, look at cage options for a chassis stiffener. Cages fall into safety equipment in SCCA and have more allowances within the classes than SFC's.

And don't wait to add parts to get out there and drive it at events. Get behind the wheel now and do mods as you get the time to do them.

 

Thank you. That was interesting to read.

 

I have a t-top car for autocross but I haven't raced with it yet. Try a couple runs with the t-tops on and then try with them off. Their may be some aerodynamic drag with them off but you may need to talk to an expert to know for sure.

 

I've auto-x'd a few times in the past year in my t-top. I agree with what I found on this board before I started. It's all about the tires. Granted I've got WS6, poly swaybar bushings , aftermarket panhard and trans to diff brace, Tokicos. I do not have SFC.
Sack if you are just starting you've got plenty to work with already. Are you going to Homestead? I would like to check it out. OCCC in Orlando is June 9 with SCCA.

 

Didn't have time to read everything so sorry if this was already said. I would agree SFC and wonderbar are a must. I have seen and heard inners are speedbump catchers. Spohn is a nice unit. I went umi for reasons like if I need to add or just plain Jack up car square. Seems easier to me to use.

How serious are you planning on taking your car? A simple no class to stay in just for fun? Keep t tops. If not there are several things to look at.


I would do a 3pt stb check to see if you have the other factory braces as well. And if other things are not tuned for it stiffer is not always better. These cars are designed to flex if you put these SFC in there is the possibility of it only cracking somewhere else. I once read something about all that but was awhile ago over on frrax.com.

Check that site out for actually used info(people that regularly race their f body's)

 

Once again thanks for the great info posted here. I installed the Koni's yellows and now the car handles amazing and definitely the weakness is my driving. I will be attending as many local events as I can here locally to practice and I will hold for now on further modifications.

Talltim, yes I will be going to homestead in June let me know if you can make it.

Sack

 

OK Sack we can continue via PM thx.