Autocrossing an Automatic equipped car: Grassroots Motorsports forum: Grassroots Motorsports Magazine

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July 14, 2011 2:46 p.m. scardeal HalfDork
I'm creating a Street Prepared roadmap for my car, and I wanted some feedback from someone with lots of experience.

Has anyone regularly autocrossed an automatic-trans equipped car in SP trim? (I hear C4 vettes preferred autos in SP trim.)
1. Have you replaced the torque converter with an aftermarket unit?
2. What was your experience with it in Autox? on the road?
3. Did it have a measurable affect on AutoX times? MPG? anything else?
4. Any other automatic-specific mods?
Thanks in advance.
July 14, 2011 3:15 p.m. ReverendDexter SuperDork

I autocrossed my 5.0 before I did the manual swap. With a good automatic, I don't think it would have been so bad, but the AOD in those cars doesn't have a 2nd gear detent (you hold 2nd by having it in L, winding out 1st, putting it in D long enough to have it shift, then putting it back in L), and the stock shift behavior was economy minded.

It made for some frustrating moments on course, either where the tranny was in too high of a gear, or when it FINALLY downshifted, which then unsettled the car.

There's definitely some advantages, though. Left-foot braking is much easier when there's not a 3rd pedal in the way, and if the car shifts in a properly aggressive manner, well, you no longer have to think about what gear you need to be in or when to be in it.

I wouldn't be adverse to doing it again, just not with a stock AOD!
July 14, 2011 3:21 p.m. jimbob_racing Dork

Rental cars are almost always automatics and they work fine for autocross.
July 14, 2011 3:28 p.m. scardeal HalfDork

The only shifting "issue" that I have is that it doesn't like downshifting into first gear above 20 miles/hour. When I go to the manual rear-end ratio, I don't suspect that I'll want to downshift back into first.

I know some of these performance torque converters claim to more efficiently put power to the ground, but I'd like to know any weight differences and dyno charts of before/after...
July 14, 2011 3:40 p.m. Toyman01 SuperDork

I autocrossed my RX-7 with an automatic. Other than slow launches it wasn't too bad. Most courses were run in first which kept the engine in the 5000-7500 rpm range where a rotary is happiest.

How well it's going to work is going to depend on how the car is geared. Most autos don't down shift to first willingly without slowing way down.

A little left foot braking with throttle will keep the torque converter wound tight for better corner exit acceleration.
July 14, 2011 3:46 p.m. jlm_photo Reader

I autocrossed a 93 Fox body mustang with an auto. Transmission lasted through the first event...barely.

http://www.youtube.com/watch?v=nSWbaJFot-M
July 14, 2011 3:50 p.m. scardeal HalfDork

Thanks for that little tidbit about left foot braking. I'll have to practice that (a lot!). BTW, it's an 07 350Z.

Most courses I'm seeing that top speed is roughly 1st gear + 5 to 10 mph, but I'm seeing ~ 1 second better times by shifting into second before doing any heavy transition sections (eg a slalom).

I'm hitting the top of 1st about 20-25 feet before I have to start braking. Of course, we have a rather limited lot size to deal with. I've never gotten it up past 50 locally, but I know that some places you can get to around 65ish.
July 14, 2011 4:21 p.m. Toyman01 SuperDork

If it blips the rev limiter a couple of time before braking, let it. More than 5 or so, shift. The better slaloms in second gear are probably due to less torque, as in not loosing traction on the rears. You can probably overcome that with throttle control. Autos loose a lot of time on shifts, particularly downshifts, so don't unless you absolutely have to. A course that is open at the beginning (2nd gear) and tight at the end (1st gear) will be the bane of your existence. Figuring out where to do the downshift always screwed me up.

And yes, automatics will puke their guts out on a autocross course. Keep a close eye on them, especially fluid levels. You don't want it to suck a gulp of air at full load in a corner, it will probably melt down. I also let the car idle between runs, to keep the fluid cycling, to shed as much heat as possible. Heat will kill them faster than any other abuse you can imagine.

That's my two cents worth. That's also from driving a 200K miles RX-7 that I wasn't driving home from the autocross. I have 0 experience with a 350Z. Some of the things I recommended, like left foot braking, are probably hard on a transmission. Keep that in mind.
July 14, 2011 4:51 p.m. Will HalfDork

Automatics aren't too bad on autocross courses IF you have enough torque to start in first, shift into second, and leave it there for the rest of the run. I forget what the SP rules say in regard to autos, but a better trans cooler and/or a bigger pan should help quite a bit with regard to fluid temps.
July 14, 2011 7:52 p.m. failboat Reader

In the grand marquis I could lock it in 1st and just leave it there.
July 14, 2011 8:31 p.m. JoeyM SuperDork
scardeal wrote:

I'm creating a Street Prepared roadmap for my car, and I wanted some feedback from someone with lots of experience.

Has anyone regularly autocrossed an automatic-trans equipped car in SP trim? (I hear C4 vettes preferred autos in SP trim.)
1. Have you replaced the torque converter with an aftermarket unit?
2. What was your experience with it in Autox? on the road?
3. Did it have a measurable affect on AutoX times? MPG? anything else?
4. Any other automatic-specific mods?
Thanks in advance.
Mikael Edstrom (MSCC member) drives an automatic 'vette, and he often gets FTD at MSCC events. You could ask him what he's done to the car.
July 15, 2011 8:39 a.m. Ian F SuperDork

Personally, no - but there's a guy in the Philly region who runs a '70 Camaro in ESP with an automatic. The car sounds freakin' awesome and is basically prepped for the class (stiff suspension, fat Hoosiers, trailered to events). I'm pretty sure it's geared fairly tall and runs a high-stall convertor. I'd swear it never shifts out of 1st gear for an entire run, and the course designers in our region like to design reasonably fast courses. He's usually the only ESP car running, but generally finishes well in PAX.
July 15, 2011 9:41 a.m. Jay_W Dork

I remember watching a '65 Mustang at the local autox courses. Every time he put that thing in D you could tell, cuz the tires went and I quote "CHONK" as they got rotated a degree or so. No Idea whatall was done to that car but the autotragic didn't seem to slow him down awful much.
July 15, 2011 12:03 p.m. conesare2seconds Reader

I autocrossed a couple of C4 Vettes for many years, an L98 and an LT1, w/ stock TC's. Both had enough torque to run most courses in 2nd once moving. Left-foot braking was easy-peasey, you can develop really good car control skills w/ an auto. Eventually, I decided to switch to a 6-speed C4 due to the manual's advantage in 2nd gear (lower gearing put the manual car in its powerband earlier), BUT if I had it to do over, would deffo stick to an auto and just revise the rear end ratio for the same effect. Trans cooler might not be a bad idea for you. I suppose whether an auto is a good idea depends on the car, the more torque, the better I'd guess it would be w/ an auto. Lots of NCCC autoxers are regionally and nationally competitive in auto Vettes.
July 16, 2011 12:15 a.m. Vigo Dork

Trans cooler might not be a bad idea for you.

That is a funny way to say you should DEFINITELY put on the biggest trans cooler you can find.