A-Body Autocrossing

[Captain]

Rear tire temps were even across tread width- so I can add some there. I could feel the fronts rolling over and the chalk line and the high tire temps on the outside of tread width confirmed what I felt- so I need to add atleast 5 pounds to the front, which would mean I need to add even more to the rear to change the balance like you are talking about.

Yes I can feel the transfer front to rear easily even in street driving, nose raises easy and settles slow on 60/40.

All 4 shocks are less than 6 months old. The rears are plumbed individually of each other.


My experience from the two events I've previously ran were as follows:
Event 1: Tire pressure at 44# all four corners. Neutral entry, less sidewall rollover on exit, less understeer on exit.

Event 2: Tire pressure at 36# all four corners. Slight oversteer on entry, more sidewall roll over, more understeer on exit.

I talked to 3 guys about tire pressure settings at event number 2, a SRT8 Challenger, a new GT350 Mustang, and a '67 Mustang that is caged with coil overs- all 3 told me they are running 34# pressure in their cars. I chose them because they all have heavy RWD cars that are as close as I could find to mine.

I really am learning as I go, people say "oh yeah, we're to help, just ask anyone if you have any questions." But I haven't found that to be the case. People want to come over and look at my car because it's different, but they're all very tight lipped when I start asking these kinds of questions. I like to think I have a pretty good feel for what the car is doing handling wise after my experience circle track racing.

[UMI Tech]

Oh, I meant add air to the rear air shocks. Although yes, we can add spring rate via tire pressure.

Nice job on taking tire temps. That kind of attention to detail is important.

How much shock are you planning on buying? What are you planning on doing to your car over the winter or beyond?

[Captain]

Between now and next season- I see 4 new shocks on the car and a dedicated rim/tire for autocrossing. I've got a camber gauge sitting around, so I'll start playing with camber and spring rubbers too.

I do not see tubular control arms or coil overs or air ride in my future in the next 5+ years.

I asked a bunch of my car guy friends about changing spring rate via pressure in the shocks and they told me I was crazy.

[UMI Tech]

It's nice to put adjustable shocks up front but the adjusters get in the way of a standard coil spring. I'd lean toward adding a quality damper up front like a Bilstein or a Hotchkis HPS-1000 Bilstein.

[Captain]

I forgot to add the shocks I was planning on getting:

http://www.summitracing.com/parts/HSS-71010009/
http://www.summitracing.com/parts/HSS-70010012/

[UMI Tech]

Between now and next season- I see 4 new shocks on the car and a dedicated rim/tire for autocrossing. I've got a camber gauge sitting around, so I'll start playing with camber and spring rubbers too.

I do not see tubular control arms or coil overs or air ride in my future in the next 5+ years.

I asked a bunch of my car guy friends about changing spring rate via pressure in the shocks and they told me I was crazy.

There's no doubt air shocks would be a bit crazy on an autocross car, but lots of times life is about playing the cards you're dealt...

[UMI Tech]

I forgot to add the shocks I was planning on getting:

http://www.summitracing.com/parts/HSS-71010009/
http://www.summitracing.com/parts/HSS-70010012/

Great minds think alike...

[Captain]

I know, but like you said I'm playing the cards I dealt. If I could go back in time I'd do a lot different. So in talking it out with you- it sounds like the best bang for my buck this season is to swap the fronts for a set of Hotchkiss, and add some psi to the rears.

[UMI Tech]

From what we've talked about, changing out the fronts and tuning a tiny bit with the rears would be my plan if it were my car.

Have a great day.

ramey

[CFster]

Fix that backwards camber curve and it will stick a lot better.

[Captain]

Fix that backwards camber curve and it will stick a lot better.

Please explain.

[CFster]

Well Marcus Savitske sums it up pretty well here --> http://scandc.com/new/node/674

The fact is early A-body suspension geometry is completely backwards. Akin to a horse drawn carriage. You can bolt on all the tubular A-arms, springs and swaybars you want, but that isn't fixing the problem.

Getting that camber corrected puts more rubber on the ground, it's as simple as that. There are several ways to do this - some a lot cheaper than the way I went, but with their own disadvantages. There's a lot of info on these boards about it, or you can talk to Marcus (actually more like listen to Marcus - he'll talk your ear off for about 2hrs and that's before you've bought anything).

[UMI Tech]

Agree as above.

The downward angle of the upper a-arm makes the tire move the wrong way for the first half of its cornering life. Once it finally goes over center and good things start happening, the turn is over. Just by lowering the car an inch and adding 1/2" ball joint height up top, you can make a moderate improvement for a moderate cost. After that comes tall lower ball joints then after that, spindle upgrades...

[Captain]

I'm at work now, I'll read this when I get a few minutes- but it looks like we're talking about more than shimming the upper a arms, you're talking about changing the entire geometry with different balljoints and spindles.

[rockytopper]

I'm at work now, I'll read this when I get a few minutes- but it looks like we're talking about more than shimming the upper a arms, you're talking about changing the entire geometry with different balljoints and spindles.

No you don't have to take it that far. You haven't really wasted money on the parts you have already invested in they needed replacement anyways except maybe the OEM springs. Read the list I mentioned above I believe that is all you need for what you want to achieve on a tight budget. You can keep your lower arms invest only in the upper adjustables and tall ball joints it is amazing what that will do to your handling. Like CFster mentioned above I went beyhond that by installing the lowers but was told by Marcus himself we could work with keeping the factory lowers but I said what the hack and threw in the towel after the 2 hour lecture and said send them too. Check out these videos of my A-body running autocross. Watch the hood line how it stays flat threw out the course and then watch yours again. I am on no commission just a very happy customer who got exactly what I was told. If you can only afford shocks then just buy shocks and pay as you go as you can afford. Ax is addicting isn't it?

[Captain]

What would be the advantage of getting the Hotchkiss valved Bilsteins versus finding an oval track street stock front shock that is stiff rebound soft compression? If keeping weight at the nose of the car for as long as possible would help it turn- wouldn't that be better than a sport tuned shock- or is that what Bilstein has created?

[marolf101x]

ideally you want an adjustable shock so you can use it to tune the vehicle. If you have a non-adjustable shock with a ton of rebound damping it will help keep the nose planted while autocrossing, but it may "pack" while driving down the road (if you hit multiple bumps in succession the suspension is not given time to return to ride height, so it will keep lowering each time it hits a bump until it's sitting on the bumpstops.

Shocks are huge. . .even if the suspension geometry is not "perfect". There's a reason serious race teams will spend $1-2 GRAND per shock.

[Mingus]

Cool car and nice to see you out enjoying it. I'm no expert by any means, but I do autox an A-body. To answer your original question (which kind of got lost in there somewhere) I think your best bet for the rest of this year would be new front shocks and tweak your alignment. Don't let the shop just punch in stock '72 Skylark specs. My wifes' '72 LeMans has all stock suspension plus the "regular" yellow Bilstein shocks (not Hotchkis revalved) and a "performance" alignment (or as close to one as you can get with stock parts). I haven't tried auto crossing it but it drives way better than it did when she bought it with no-name shocks and a stock alignment. It doesn't drive as nice as my car, but there's not near the dollars dumped in the suspension either. The rear air shocks probably aren't hurting you near as bad as the front drag shocks. Like Ramey said, you can even use the air shocks to tweak your spring rates (can't understand how your friends don't think an air shock can do that). The 225 front tires could also be part of the understeer problem. I've heard people say the difference between autocrossing with 245 and 275 front tires is huge. I know my tires (245 front 285 rear 420 treadwear) are definitely not keeping up with the rest of the suspension. I'm torn between spending the money to get a separate set of wheels and race tires to see what it can really do, or wait until I wear these out and get a sticky set of street tires. Keep upgrading it when and where you can, but keep driving it no matter what.

[Nicks67GTO]

Well Marcus Savitske sums it up pretty well here --> http://scandc.com/new/node/674

The fact is early A-body suspension geometry is completely backwards. Akin to a horse drawn carriage. You can bolt on all the tubular A-arms, springs and swaybars you want, but that isn't fixing the problem.

Getting that camber corrected puts more rubber on the ground, it's as simple as that. There are several ways to do this - some a lot cheaper than the way I went, but with their own disadvantages. There's a lot of info on these boards about it, or you can talk to Marcus (actually more like listen to Marcus - he'll talk your ear off for about 2hrs and that's before you've bought anything).

That's no kidding. When i called him i expected a 15 minute conversation. When i got off the phone i felt like i had the knowledge to start a successful indy car team. I have never in my life been given so much good information in one sitting and had it explained to me in terms i could understand. He never asked if i wanted to buy anything either. I was on the phone with him for a good 1.75 hrs. It was all him too. I just let him talk and absorbed like a sponge. Right there he earned my business. I think i'm going with his stage 2 kit featuring some UMI rear suspension pieces and the optional SPC lower A arms.

[Nicks67GTO]

I forgot to add the shocks I was planning on getting:

http://www.summitracing.com/parts/HSS-71010009/
http://www.summitracing.com/parts/HSS-70010012/

I bought and installed the standard bilstiens on my 67' GTO a few weeks ago and i'm here to spread the gospel. Its like driving a different car. control, handling, everything improved in the 1.5 hrs it took me to change them. The only other mod i have is a ws6 1.25" sway bar on the front and a Jeep 12:1 steering box. The car handles very well for a street car now. I cant believe how big of a difference 4 bolt on shocks made.