ITA '7; rear grip help? (few other things too)
 

Okay, per the topic, we're running an ITA prepped car, an '83. The basics are all there; GC coilovers/camber plates, G-Force tri-link/panhard bar and turn-in spacers, Tokico Illumina 5-way adjustable shocks, strut bar, stiffer front sway, etc. I forget what spring rates we're running but it's straight out of the G-Force reccomendations. Oh yeah, tires are currently Hankook Ventus in 205/60/13, pressures... well, we tried down to 34/33psi.

Basicially speaking, wondering about what direction to move for a bit more grip... we're not able to put as much power down as we'd like without kicking the rear end out. The main track we get out on is Blackhawk Farms, which is a 1.95 mile twisty thing, so... putting down power would be kinda nice to move up from mid-pack. ;) Also wondering if there's any glaring omissions from the list; some MGA guys were saying in essence that we're crazy for not running a rear sway and that it would drasticially help weight transfer but I don't think we are having much body roll in the rear.


... also as a minor point, wondering if there's any advice on cooling. The motor kind of, ah, got overcooked on Sunday with my dad driving. Maybe related to the fact that we were experimenting with putting synthetic through it (hey, OMP's disabled) but... well, any thoughts on that? Stock rad/oil cooler (not the beehive) but no additional ducting; also no airdam to get more air in.

Finally... since we're building up a new shell from scratch, where else is there to get weight out? We're well above minimum weight with the existing car and while the noise deadening tar is still in it and the autopower cage might be overweight, I don't know that fixing those on the new one would drop *that* much mass. Plus, the stock wiring harness is completely gone which, come to think of it, might not be strictly IT-legal... :D

Thanks in advance for any help.

So you're kicking the back end out on corner exits? Sounds normal and probably is tunable.

The Panhard bar from G-Force is adjustable and would be the cheapest/easiest thing to change. Basically if you move the roll center closer to the CG you will decrease weight transfer on that end of the car and therefore should be able to get more grip on that end of the car. The Rear roll center is at the center of the Panhard bar. So what you could try is to move the panhard bar UP some. Make sure you keep it level with respect to a known level surface.

Conversly you can increase weight transfer on the front of the car for the same effect. Increase spring rates or possibly raise front ride height, this raises the CG and the roll center though.

There really is no need to have anti-roll/sway bar on the rear of these cars. Adding one will increase roll stiffness which will add weight transfer and make the oversteer issue even worse.

I don't have anything to add to AXer's post, other than say "What he said". We just installed the GeForce 3link/panhard on a customer car and initially had the same troubles as you. Moving the panhard fixed our problem, but it may have been minor in comparison to yours.

As far as actual grip: have you tried any other tires than the Hankook's? Specifically, Hoosiers? I'm curious as to the difference in grip levels between the two tires, but our customer is thrilled with the S04's, so there's no chance of getting him to to try it. ;)

RotaryAXer: You're right that it's normal and probably tunable... just trying to figure out how to adjust the extent. ;) Interesting on moving the panhard around; hadn't looked into it enough to think of that one. And thanks for confirming my suspicions on rear sways.


christaylor: The car came with V700 Victoracers (slightly used) but the suspension was just about stock then so can't really compare. The tires before this were AS303s in 205/60/13 which we got with (supposedly) one race on them (for cheap, obviously :D) and ran for probably quite a lot longer than we should have. Subjectively, the Hankooks take a lot longer to heat up and feel a lot less stable at the limit... the Hoosiers felt the same no matter how hard you were cornering, and even past the point where you were sliding off the track. ;) You could look at this as the Hankooks being easier to learn, but they just feel scary; I'd much rather be running Hoosiers.

Objectively, both my dad and I are turning faster lap times with the Hankooks... but they're newer than the Hoosiers were and I'm still learning how to flog the car. Oh yeah, I should mention that my experiences are in high-speed autocross, so tire warming is a big concern.

We also have a set of used RS303s in 225/45/13. I've personally never run them, but we tried them on a practice session of my dad's and lost 2 seconds a lap so they've not been back on. I might try them next event (if the car's fixed) to see what happens.

What are your pressures on those tires when fully warmed up? I think that is more important then the temps. before heated.

As for cooling you'll be happier if you did put in some air ducting. A larger oil cooler will help as well.

I wouldn't compare tires based on how the used ones perform. I've had three year old toyos that still grip pretty good and I've seen some newer tires that just gave up the ghost after 10 cycles. First thing I would do is to start taking tire temperatures and inspecting the tires after the race. Figure out what is happening before you start fixing something. My cure for the overstter was two fold, I rasied the front suspension slightly and put a slightly firmer spring in the front as well, seemed to cure many of the ills.
As a car, 1st Gens are a tail happy bunch, you might need to adjust your driving style as well. Eevn with a fair amount of tuning I found it best to get the weight on the back of the car with the throttle even before I apex. Once the weight is back, you can push them pretty hard before they break loose.

-Trent

Exactly how big is your front swaybar? How good are the swaybar bushings and end links?

Stay away from rear sway bars on a 1st gen RX-7 road racer.

What kind of diff are you using?

Start recording tire temps. These must be recorded immediately, as soon as the car comes to a stop in pit lane.

What about spring setup, cross weights, and weight on the right rear wheel? Have you lightened the LF of the car as much as possible, and moved as much weight to the RR wheel as possible?

AkariMotorsports: Hot pressures I don't recall off the top of my head, up in the 40s with the LF around 44ish. And yeah, we're going to be doing some better ducting on the new chassis.

TrentO: Oh, definitely the tires are working differently after having a few races in them, which is why I made sure to mention that. Tire temps we've been doing religiously, but again don't have the numbers on me. You're right that some of this is just going to be adjusting driving styles, but we don't quite yet know what we can tune and what we have to live with.

speedturn: Heh, argh... again, don't have numbers on me; need to remember to post from home. Sway is somewhere around an inch, but don't hold me to that. Diff is the stock type LSD, last rebuilt god-knows-when (still works, but... another off-season project) with 4.88 gears. Corner weights... heh, you got me. ;) We've done the best we can, but LF is still way way way heavy. We thought hard about weighting the RR, but... right now we're so overweight that we decided to just leave things be.



Need to come back to this again when I have the notebook in front of me. Sorry about not being able to pin down exact settings, and thank you all for your advice.

Rasie the front of the car or lower the rear further. The first gen cars need the weight equal or more to the rear. I brought my front up a good 1/2" and the results were quite surprising as the rear seemed to dig in and hook where it previously skated.

-Trent

Wow, overweight? I had to do some <cough> ballasting <cough> to the '79 we prepped because it ended up being WAYYYY light. For the first race, we were way over the limit of onboard lead. :eek:

Have you guys tried any track days? I finally figured out they were well worth it when I found out how much more track time you get and how flexible the folks that run them are. I got more tuning done in one day than I would in half an SCCA season.