Why are we considering an automatic for our ASA stock car?

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Update by J.G. Pasterjak to the American Speed Association Stock Car project car
Oct 30, 2023 | BMW, transmission, stock car, ASA Stock Car, Seems Legit Garage, ZF 8HP, ZF Transmission

Actual wrenching progress on our former ASA stock car project has been slow.

Honestly there’s a LOT of research to do before we break out the socket set and the welder, so most of our effort toward the car has been in the conversation and study department.

So, for our transmission: Which way to go?

The space where a gearbox lives in our ASA stock car needs a new tenant. Photography Credit: J.G. Pasterjak

Most tube-frame road course cars will use a dog ring-style, straight-cut four-speed, like a Jerico or a G-Force. These durable transmissions allow clutchless shifting and have a long history of being the right tool for the job.

But there are options, and we’d be crazy not to explore them. Since we’re not building the car to a specific ruleset–it will be an unlimited-class time attack car with the ability to run some wheel-to-wheel in regional classes like our local SCCA’s Super Production Over division, where pretty much anything with four wheels and fenders that tries to look like something OEM is welcome–we don’t really need to worry about how it’s always been done, only how we want to do it.

So putting a modern five- or six-speed synchro box in there is on the table, as is a sequential transmission–although that particular table costs a LOT to sit at.

But on a recent road trip, all that windshield time had our minds wandering to what transmissions we really liked, and we kept coming back to one in particular: the ZF 8HP automatic.

Photograph Courtesy "Seems Legit" Garage

Yeah, we said it, automatic.

Not familiar with the ZF 8HP? It’s the automatic box currently specced in cars like the Toyota Supra, BMWs of all varieties, Dodge Challenger and Charger, Alfa Romeo Giulia and Stelvio, Porsche Cayenne, a mess of Aston Martins and, well, you get the idea. Then add in a bunch more stuff not even imported to the U.S.

It’s a quick-shifting, eight-speed automatic that feels more like a dual-clutch than a traditional auto: snappy, well-timed upshifts and crisp, controlled downshifts.

It seemed to us–at least while cruising down the highway–that there should be more than a few of those in junkyards, or at least more of them than there are Jericos or Sadev sequentials. And wouldn’t it be cool if you could hack the control module and somehow adapt one to an LS like we plan to use in our ASA car project?

Indeed, it would, and it turns out “Seems Legit” Garage was one step ahead of us this whole time.

Seems Legit” Garage is a Michigan shop with a bunch of former OEM engineers–more than a couple formerly of FCA and/or Stellantis–and racers who list among their specialties swap solutions for the 8HP.

Oh yeah, my philosophy now is ‘8HP the world,’” says CEO Mike Pagano after we made the initial “Hi can we be friends?” call to them. “In stock form it’s already a great transmission, but with just a little tuning it can be turned into a truly excellent track transmission.”

The ZF 8HP comes in a few common flavors, the most common of which are the 8HP 50 and the 8HP 70. The 8HP 50 is used in a lot of BMW applications, while you’ll find the higher-capacity 8HP 70 variant behind Chrysler Hemis and in modern turbo BMWs as well as in Jags and Astons. The 70 variant is rated at 516 lb.-ft. of torque.

How much? Used ones go for less than $2000 from auto recyclers.

Adapting an 8HP to several popular drivetrains involves the physical connection–“Seems Legit” Garage has adapter plates and kits for GM LS, Honda K series, Toyota 1UZ, Nissan RB and a host of BMW applications–plus the necessary electronic hacking.

Photograph Courtesy "Seems Legit" Garage

Basically, when you’re choosing an ECU, if you choose something that utilizes a drive-by-wire throttle, that makes the tuning much easier and more seamless,” Pagano tells us.

From there, “Seems Legit” Garage has basically hacked the control system for the transmission. A programmable control unit from HTG allows nearly any function desired, as well as options for controlling shifting. “From full-auto to sequential-style stick to paddles, with varying force and full tuning options,” Pagano says. He’s making this sound like a no-brainer.

Photograph Courtesy "Seems Legit" Garage

So now we come to the objections. And, truthfully, on our end, we’re not seeing a huge downside here.

The price seems right, and every new car we’ve driven with a ZF 8HP has impressed us. And with “Seems Legit” Garage’s promise to make the experience even better, it’s hard to put a lot of checks in the “against” column.

Still, due diligence demanded we ask some questions before we just had them wrap one on a palette.

Will it fit?

I’ve put these things in Z3s with almost no body modification,” Pagano replies.

Since we’re dealing with a tube-frame car that we can just cut and restructure to meet our needs, this seems like an easily overcomable issue, if it even exists in the first place.

Why not a DCT?

BMW DCT swaps are becoming increasingly popular, and “Seems Legit” Garage has parts and software to facilitate those as well, but Pagano still prefers the 8HP for most situations.

The DCTs are more expensive to purchase on the secondary market, and the programming can be a bit more complex. “With the DCT you sometimes have to go in and tweak the shift programming for specific tracks,” he says. “The computer is always anticipating the next shift, and pre-loading the next expected gearset, but if you have a certain situation where you aren’t selecting the gear the computer is expecting, it really doesn’t function optimally sometimes.”

The 8HP, he says, is a better tool for more situations with less need for specific programming, and at a lower cost.

It's an automatic. Aren’t there tons of parasitic losses?

The whole 8HP lineup was designed around minimal parasitic loss, for performance and economy,” he tells us. “With tuning, parasitic loss is on par with most manuals since there’s almost no slip inside the gearbox.”

Having driven more than a few cars on track equipped with 8HPs, we can confirm that manipulating the throttle in a corner to balance the chassis–which is usually where manuals excel over automatics–is just as precise in an 8HP automatic equipped Supra as it is in the manual version.

So, what’s your opinion? Does our tube-frame track monster need a paddle-shifted modern automatic. Or are we committing some sort of automotive blasphemy? And, even if we are, is that bad?

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wvumtnbkr GRM+ Memberand PowerDork
10/30/23 2:15 p.m.

Do eet.  Let us go on the journey with you.


Sounds awesome honestly.

RonnieFnD New Reader
10/30/23 2:20 p.m.

I was just thinking about this the other day wondering if it was still around.  Glad to see it getting some love again.

Tom Suddard
Tom Suddard GRM+ Memberand Director of Marketing & Digital Assets
10/30/23 2:27 p.m.


David S. Wallens
David S. Wallens Editorial Director
10/30/23 2:41 p.m.


(Okay, I knew this was coming and edited the piece but just wanted to join in.)

NY Nick
NY Nick GRM+ Memberand Dork
10/30/23 2:53 p.m.

I like the idea, everyone knows what this looks like with a 4 speed. I think this is really innovative for this application. It also made me think about this trans for a circle track application, we race vintage which has basically no rules. This could be an option...

JG Pasterjak
JG Pasterjak Production/Art Director
10/30/23 3:02 p.m.

Yeah I'm not really seeing much downside here. this seems to scratch a lot of itches that are practical as well as editorial.

I just kind of got the idea while driving home from UTCC and putting my Tundra in tow mode, which gives you some manual control over thr automatic's shifting. "Hey, sequentials are stupid expensive, but what's wrong with a good automatic with a manual valve body?" I thought. "Ooh, those 8HPs that are in the Supra are awesome. I wonder if they're available from boneyards and hackable?"

Literally googled for info while I was sitting in a rest area on I-75 in Tennessee and found that a) 8HPs are cheap and b) SLG exists. So thanks Tennessee DOT for making your highway men's rooms both comfortable and WiFi enabled.

Tom1200 PowerDork
10/30/23 4:26 p.m.

In reply to JG Pasterjak :

Seeing as you've already raced one car with an automatic (F500) I see know reason not to do it again. Automatics have come a long way since the Powerglide.

chaparral SuperDork
10/30/23 6:15 p.m.

I'm interested in how well this project goes, mostly because Seems Legit Garage has the right background to do something cool. 

madmrak351 Reader
10/30/23 7:12 p.m.

Very interesting! 

Floating Doc (Forum Supporter)
Floating Doc (Forum Supporter) GRM+ Memberand UltimaDork
10/30/23 7:37 p.m.

I'm all about manual transmissions, but I think you have made a good case for this. I say go for it. I'm looking forward to following along.

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