Last week I took a spare 9" carrier, that I have been dragging around for about 8 years, to a recommended shop to swap out the ring and pinion. This was a Currie nodular 9" carrier that came with a 31 spline True Track diff, but had a useless 4.57 ring and pinion gear.

A while back I purchased a used OEM 2.75 ring and pinion and also a REM polished 2.75 ring and pinion from Quick Performance. I told the guy to use whichever gear set he felt would be the quietest. HE ended up setting up the used OEF Ford gear. I started the carrier swap yesterday and finished it up this afternoon.

I took my first drive and I have to say, that in my opinion, this is the optimal rear axle ratio when using the 8HP70 transmission. The gears are very quiet and I am pretty pleased.

For anyone contemplating the 8HP transmission swap, I would use either a 2.75 or at most a 3.00 gear set, assuming the typical 25.5 to 27 inch tall tires that we all use. With a taller tire, a 3.25 gear would work as well.

Andrew

 

It makes sense. The Chargers and Challengers got either 2.65s or 3.08s from the factory.

 

One more piece to the puzzle has been acquired for me. I just grabbed an 8HP70 out of a 2018 Charger. I have two cars in line for the lift before the Elco gets back on it.

Exciting times.

 

That's exciting. What's the overall plan?

Andrew

 

It's going in the wife's 81 El Camino. The car currently has a mild 355 with a FiTech TBI, 200-4R, and 3.73s in the factory 7.5. The plan is to replace the original wiring, swap to port injection, and change to an 8.5. I have some GM 3.23s laying around that I think would give me the same torque multiplication with the 8HP that I currently have with the 200-4R. The ultimate goal is to keep it a nice street cruiser and gain efficiency. I just need to order the DomiWorks adapter and pick a controller. I'm leaning towards MaxxECU so I can knock out both the switch to port injection and the trans controller. The wife won't need to use a transbrake feature or anything like that. I just want to keep it simple: put it in Drive and go.

I also read the multiple comments about the Adamat adapter not being of the same quality as DomiWorks and to stay away from Seems Legit. I would like to add to those comments as I had emailed Adamat about their SBC adapter, and they sent me to Seems Legit. I had a specific question about their flywheel because GM changed the SBC to an externally balanced crankshaft when they switched it to a one-piece rear main seal, so the flywheel in their kit would need to be externally balanced. All they could tell me was that they used that kit on the specific engine in one of their YouTube videos and could not answer if the engine was internally or externally balanced. So, since DomiWorks offers something that bolts to the existing flexplate, the engine's balance is a moot point.

 

Huge shoutout to Andrew, Dr Efi. We got my OBS up and running today. Got the Ls and 8hp70 driving nicely with Holley Dominator and TurboLamik! Kong LSA2650 up next!

 

I have a 3:15 9” pumpkin. Good to hear your perspective. How far are we from buying a kit end to end to make this work in an fbody?

 

I don't sell any parts, so it would be up to some other company to make that happen. But all the parts are available. You would just have to piece it together.

Andrew

 

Something like this?


Transmission Used Dodge 8HP70 (V8 model) $1,000
Adapter Kit DomiWorks LS to 8HP Adapter (Plate + Flywheel) $1,350
Controller CANTCU? $1,200
Wiring conversion harness? $550
Shifter BMW F30/F80 Electronic Shifter $250
Driveshaft Custom Slip Yoke adapter flange (e.g., Sonnax) $200
Cooling Billet AN Adapter + External Cooler $350
Mounts Fabrication/Universal Crossmember $200
Total ~$5,100

Debating this or a magnum F. I guess they are close in comparison on price.

 

Bump. 2026 looking good for the 8hp swaps! Huge thanks to Andrew, DrEfi.

 

Love it. I'm at the PRI show and everyone is talking 8HP swaps. I'm glad to be a part of it.

Andrew

 

Lots of good info on 8HP mods in this video:

 

this thread keeps me up at night. any idea what kind of RPM these transmissions can handle stock?

 

Calvin actually covers that in the video listed above. His theory is the bigger 90 won't rev as well as a beefed up 70. If all goes to plan, we will find out at Sick Week. I'm rooting for him. He is a prime example of thinking outside the box.

 

“Yeah that’s pretty much been our experience too. Most of the 8HP swaps out there work, but getting them to behave consistently across the board is where things start to show cracks.

A lot of it seems to come down to how the trans is being controlled — especially torque management and how clean the communication is between engine and trans.

Once that side of it is actually sorted, I agree it’s hard to beat an 8HP for a street/strip setup.

We’ve been messing with keeping everything under OEM ECU control instead of standalone, and it’s interesting how much that cleans up the drivability side of things.

Out of curiosity — what issues have you seen the most? Mostly shift quality or more random behavior?”

 

HPA had a really interesting podcast episode about ZF 8HP swaps a couple weeks ago.

It's on youtube, but there's no real video content in it, so it's probably better to just listen to it through a podcast app.


I want one in my C5 now, because fast solid shifts with paddle control sounds really fun. But making it fit without losing the transaxle layout sounds hard...

 

There was a post in one of the 8HP groups on FB about someone trying to put a kit together for C5/C6 Corvettes. It wasn't going to be cheap.

Andrew

 

Yeah, and it was also going to move the transmission to the back of the engine, with a regular driveshaft and a new rear diff. Probably fine for the drag and drift folks, but I'd rather not go that route.

 

I didn't look at the particulars of the kit, but I would not want to re-engineer the whole driveline either.

There is an Austin Martin 8HP70 case that's used in a transaxle application. That seems to be the most viable transmission to adapt for transaxle Corvettes.

Andrew