A-Body Autocrossing

[Captain]

I recently started autocrossing my car and have a great time doing so but I'd like to improve my times. When I rebuilt the steering/suspension/brakes recently I did so with more of a daily driver theme in mind- so few aftermarket parts. I'm happy with acceleration, braking and corner entry but my corner exit really suffers due to a heavy understeer. I'll give you some stats on the car to show you what I'm working with.

1972 Buick Skylark
361 ci 375hp/4100ftq
th350 (leave in 2nd on course)
Eaton posi 3.23 10 bolt
Right Stuff brakes 4 wheel power disc kit
225x45x17 Cooper Zeon ZPT
Moog center link, tie rods, idler arm
Stock spindles, front control arms, bushings, ball joints
OEM replacement front springs
3 way adjustable front drag shocks (60/40, 70/30, 80/20)
Front 1.25" sway bar
Tubular non-adj trailing arms
OEM replacement rear springs
split valved rear air shocks
1" rear sway bar

I really struggle with setting my air pressure in the tires. For the fronts I've tried everything from 35-44 lbs, and the sidewalls still roll over a ton. The rears I've tried the same 35-44 lbs and they don't roll over like the fronts but the car handles much better with all the tires in the lower 35 range- with the exception of when I feel the fronts rollover. Once the fronts reach their threshold I might as well stop the car, turn it, and take off again.

I know the rear air shocks need to go- that's first on my upgrade list, but what other tweaks can I do to make the car handle better?

[shep]

I would give Marcus at SC&C a call tell him what you want it to do and he will point you in the right direction. I would guess his pro comp kit stage 1, 2, or 2+ and a set of performance lowering springs perhaps Hotchkis with the Bilstein shocks valved to match the springs all around would be a good start.

[UMI Tech]

Give us a call as well. We can help stick that front end.

[Captain]

Give us a call as well. We can help stick that front end.

Thank you UMI, I'm using a very nice set of tubular trailing arms that bare your name.

Having just replaced the entire suspension/steering and braking system I am not in a position to be able to throw more new parts at the car. Other than replacing the shocks- most things are going to be out of my price range. I'm most interested in working with what I have and tweaking it: camber adjustments, toe, air pressure, rear spring rubbers.

[ProTourGSX]

Some pics of car, and/or video would be nice! Sounds like a fun car!

[rockytopper]

Your closer than you know. About 1500$ more and a call to Marcus will get you what you want. You should consider adjustable uppers with tall ball joints along with lowering springs and a good set of performance shocks. Your car will handle night and day ahead of what you have now. Good luck with it.

[Captain]

My baby
https://static1.pt-content.com/images/pt/2012/08/VvkGE-1.jpg

The before
https://static1.pt-content.com/images/pt/2012/08/XPE7o-1.jpg

The after
https://static1.pt-content.com/images/pt/2012/08/Y0mRg-1.jpg
https://static1.pt-content.com/images/pt/2012/08/5kWh2-1.jpg
^ You can see the beautiful UMI trailing arms peaking out from the wheel arch

Getting ready to head to it's first autocross
https://static1.pt-content.com/images/pt/2012/08/Zgyx0-1.jpg

Autocross Video:
http://youtu.be/zlQ9gXIHMcU

[Captain]

Also, here is my RF tire at 36# start pressure and 39# hot pressure- significantly more heat on outside of front tires than the middle. The chalk line started up an inch or so into the tread.

https://static1.pt-content.com/images/pt/2012/08/Sc6Kd-1.jpg

[ProTourGSX]

Cool car! Watching the video made me feel like I was in the passengers seat, too cool!

[UMI Tech]

Nice! Thanks for choosing our trailing arms.

From a car standpoint I think you're looking pretty good to run a first season and get some seat time. The nut behind the wheel (Ha!) is actually the most important part of auto-x. At our local events there is a father and son team with Honda CRX Si's. The dad has a stock one where the son has a slick tire blingmobile. The dad wins by three seconds every time.

Smooth inputs go a long way.

Camber can be decided by using a tire pyrometer.
http://www.longacreracing.com/catalog/item.asp?id=200&catid=7

It's a little different in auto-x than in oval track, however, because your corner radii are quite often all over the map.

1/16 or so Toe out might help turn-in.

A spring rubber in each RR is a good way to get the back end to rotate a bit. Also, with a radial tire, adding air in the rear will add a bit of spring rate. Adding too much air will also help the back end rotate by decreasing rear grip at the expense of reducing overall grip.

At least I think that's how it all goes.

ramey


Thank you UMI, I'm using a very nice set of tubular trailing arms that bare your name.

Having just replaced the entire suspension/steering and braking system I am not in a position to be able to throw more new parts at the car. Other than replacing the shocks- most things are going to be out of my price range. I'm most interested in working with what I have and tweaking it: camber adjustments, toe, air pressure, rear spring rubbers.

[Captain]

I have a background in circle track, other than iRacing, turning right is new to me.

I use a digital IR gauge for tire temps. I'm just not sure what camber setting I need, getting my hands on a camber gauge is not a problem..

Thank you. Turn in is good, apex out it understeers heavily.

I race against a gutted Civic with full aftermarket suspension and slicks, he's in the top 3 every race. In a course where the winning car has 55 second time- I struggle to run a low 62. I'm not totally out to lunch- but with a little tweaking I know I can make the car much, much more competitive than it is right now. And that's my goal.

[Captain]

Also- this nut needs plenty of tightening, only been in two events so far.

[bret]

On the road right now myself, but take a look at our Level 2and level 3 systems. I've not run across a faster Chevelle than ours yet...and it's driven to the events.
I'll have britt post a link shortly.

[Captain]

Thank you for your input Bret- beautiful Chevelle by the way. I drive this car all over the place, road trips to Chicago, Indy, back and forth to work most days when the weather is nice... to the events I race. It's no show car or trailer queen, I built it to drive hard- and that's exactly what I do.

I'd like to reiterate to anyone who may not have read everything that I previously posted- that at this time I am not able to spend more money on a bunch of new parts and am currently needing set up advice on how to make what I currently have work better. Spring rubbers, camber adjustment, tire pressures... that kind of thing. Not realizing how much I was going to enjoy throwing the old girl around in corners I spent all my money on mostly stock parts.

[marolf101x]

I realize you don't want to buy new parts, so I'll just post a link to this video demonstrating what can be done with a parts swap.
Should you find some funds in the future please give us some consideration.
http://www.ridetech.com/tv/2010/11/ridetech-3-hour-suspension-install/

Now, on to tuning. . .
There are a few general rules you'll want to keep in mind (and they typically don't cost a ton):
1-lower center of gravity
2-equal weight distribution: you want the car to react the same when you step on the brakes or the gas, or turn left or right.
3-shock tuning: the idea is to keep the weight on the tires that need it. So when you turn you want more weight on the front tires. When you are on the gas you want more weight on the rear tires. This can be accomplished with shocks by slowing down or speeding up pitch and roll
4-tires: no matter how good the suspension is it won't stick if the tires are rock hard
5-compromise: remember a good handling car is one that compromises the least

[Captain]

Do you guys get paid on commission or something, lol?

Beautiful kit and parts. At the time of the rebuild I didn't plan on getting as involved in autocrossing as I've become. Not to mention I did quite a bit more than upgrading the suspension when I did all the work, and I don't have deep pockets by any means. I'd like to think with new oem style parts that I've put on the car I'm in no where near as bad as shape as the "before" video.

Maybe in the very distant future I'll be able to afford a kit like that, but I don't see it happening for quite a few years. Until then I'll keep tightening the nut behind the wheel and put on a show for the crowd, the car is a crowd favorite for sure.

[marolf101x]

I don't get paid on commission, I just design parts (though selling parts does ensure I have a job when I get up in the morning!)

As others have said the nut behind the wheel is a BIG part of this. I drive quite a bit and the biggest change that made me faster was to "slow down". Calm and smooth is typically faster than a "drift show".

Keep working on the car, changing one thing at a time and it will eventually get quicker!

[Captain]

In thinking over my current suspension, how bad are my front "drag" shocks hurting me? They're designed to transfer weight to the rear wheels upon acceleration. I'm thinking that even on the 60/40 split setting that this could be a major reason for my understeering from the center off... thoughts?

[Captain]

I have 3 events left this year and enough money to change either the rear air shocks or the front drag shocks- which is going to show more improvement?

[UMI Tech]

Can you add a few psi to the rears to help fix the understeer from the center off? Keeping in mind you're actually reducing traction out back in favor of balance.

Can you feel the car transferring a lot even with the shocks on 60/40?

How are the "ages" of each set of shocks? Clapped out or relatively new?

[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?

https://static1.pt-content.com/images/pt/2011/10/th_IMG_2336-1.jpg (http://s282.photobucket.com/albums/kk243/rockytoppers1/?action=view&current=IMG_2336.mp4)

https://static1.pt-content.com/images/pt/2011/10/th_IMG_2264-1.jpg (http://s282.photobucket.com/albums/kk243/rockytoppers1/?action=view&current=IMG_2264.mp4)

[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.

[Captain]

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...

UPDATE:

Ran short on money to upgrade the shocks before that weekends race, the only changes I made were psi in tires and air shocks. In my class (Street Mod Street Tire) I finished 10th out of 18. However, comparing my lap times to cars in other classes I beat: new (stock) Camaro RS/SS, Mustang GT, Cadillac CTSV and Challenger SRT8, Trans Am, C4 Vette. I was very happy with I ran this weekend. Remember the only real "upgrade" on the car that wasn't a factory option is the rear disc brakes and headers (even at that my disc kit is all off the shelf gm parts). The current rear air shocks and front drag shocks are probably a downgrade over an oem shock. Everything else is just new oem replacement parts.

Having said that, increasing psi in the rear air shocks is what helped me the most this weekend, on corner entry the car actually wanted to rotate and turn in, it didn't just lean on the front tires until they begged for mercy. Front end geometry is what is hurting me the most right now- I'm destroying my tires because they are rolling over on the sidewalls so far.

I have a camber gauge and shims- looking for some help on what kind of adjustments to make for track driving.

[UMI Tech]

Max out the camber as far negative as you can (put a bunch of shims in it). Depending on your tolerance for vague feeling steering, you can get more max camber if you sacrifice caster. On second thought, put a bunch of shims in the rear of each cross shaft and a moderate amount in the front of each cross shaft.

1/16" toe out will help turn-in but you'll have to "drive" the car since it will tend to not self cancel on corner exit.

If you're low bucking the end of the season, add some 1/2" taller ball joints. Rumor has it we are going to have some 0.9" taller in the upcoming weeks but maybe not in time for your race.

http://www.umiperformance.com/catalog/index.php?main_page=product_info&cPath=13_262&products_id=676

Adding ball joint height is a way to increase spindle height and help it gain camber.

ramey

Oh, and it sounds like you were driving well. Good job.

[Captain]

I have a gauge, so loading it up with shims is a little less scientific than I was hoping for. What kind of degrees should I be looking for?

[UMI Tech]

I'd choose around 2.25 degrees.

[Captain]

I'd choose around 2.25 degrees.

Wow, that's a lot of negative camber. I am chewing the **** out of the outer sidewall though.

[Captain]

To increase negative camber I'm going to add an equal number of shims to both mounting points on the upper control arm, right?

[UMI Tech]

Yup. Since the factory geometry doesn't allow for much negative camber gain (?!) we have to start with an aggressive static amount.

With the tall spindle and geometry upgrades we can run a tire wear friendly static alignment and still have the proper camber during cornering.

ramey

[Captain]

Static means wheel relative to ground, right? My camber gauge is one like this:65312

[UMI Tech]

Static means "car is not moving". Dynamic is how the camber changes when the suspension is traveling in compression or extension.

That may be the exact gauge we have. Nice choice.

[Hotchkis]

If you are looking for a complete suspension solution with proven results in autocross competitions then I would definitely suggest taking a look at our Stage 2 Total Vehicle System (TVS). It comes with absolutely everything needed to completely transform your A-Body with just bolt-on parts. Every part of this system was designed to complement the others so you can rest easy knowing that the matched components in this kit will work correctly. The incorrect front suspension geometry of the A-Body that was brought up earlier in this thread is corrected with our Geometry Corrected Upper and Lower front A-Arms that increase caster, improving the camber curve, and give you additional camber/caster adjustment. This kit also comes with custom-valved Bilstein shocks that are matched to the spring rates and vehicle. There is a lot more adjustability built into this kit beyond just camber/caster. The new rear sway bar is adjustable so you can tailor the roll-stiffness to match your wheel/tire combo, the layout of the autocross course you are driving, and your own driving style. Our billet upper trailing arms are also adjustable so that you can get the correct pinion angle to improve your launch. For more information on our Total Vehicle System please visit our website: http://www.hotchkis.net/stage-2-tvs-system-19711972-gm-abody-small-block-.html

65347

FrptyCumg5A

[Captain]

Lets talk tires now

Remember I'm on a shoe string budget. 15" stock car style rims are cheap and easy to come across, but mostly in 8"W versions. 10" are available for slightly more. I'd like to have a set of rims/tires dedicated to autocrossing and I think the brake kit I've put on the car will allow me to downsize wheels to 15" and clear everything. If I can get a set of 10"W wheels to fit on the car- is there any draw backs to running a 17" wheel versus a 15" wheel?

Ideally I'd like a 15"x10" set up- which would probably be something like 275x45x15, right? Handling wise, how much different would it feel on track versus the current 225x45x17?

[SSninja]

I think that the tire options for 15" wheels are pretty limited.

Did a 30 second search for a 275/xx/15, and this was the only result with an aspect ratio less than 50:

http://www.tirerack.com/tires/tires.jsp?tireMake=Hoosier&tireModel=A6&partnum=735ZR5A6&vehicleSearch=false&fromCompare1=yes&wtpackage=true

It's also available in a 275/50ZR15, as is the BFGoodrich g-Force T/A Drag Radial

[Captain]

I just threw the camber gauge on for the first time a few minutes ago- it won't thread on 2 turns before I bottom out on the wheel bearing nut. There is little to no vertical slop in the gauge though, it threads on enough that the free spindle on the end starts spinning.

RF: +1 degree
LF: +0.75 degree

Does that split seem right? Or is my gauge not threaded on far enough?