318/8 Speed Swap

wish4hemi said
I finally got my hands on an 8 speed transmission (8HP70) out of a 2018 Challenger this weekend. This particular one looks to be from an SRT 6.4 Hemi car. Supposedly, it only has 5,000 miles on it.

I was able to get it mounted to a spare 318 I had in the shop. There are some custom adapter pieces to be made/purchased, but it can be done. For those that are wondering, this is an electronically-controlled transmission that will require a standalone transmission controller. There are a few guys out there working on that end of it with this and other OEM transmissions (Ford 6R80 and 10R80). The idea is to be able to run a carburetor or standalone fuel injection system on the engine, then a separate system for the 8 speed. Obviously, the advantage of the 8 speed is close gear ratios and two overdrives (0.84:1 and 0.67:1).

For now, my plan is to use it for mock-up purposes, then sell it and pick up a built 8HP70. By then, I should have enough details lined out to pass that information along to the next owner.

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So I have been chatting with sound German automotive, and he seems to pretty confidently have a stand alone harness/controller figured out. $1000 plus shifter. Don't have a ton of details beyond that, but supposed to utilize the internal tcu. And require not much more than a tps and rpm input if I am understanding correctly.

So I do see some issues, and perhaps in your mockup, you came across some of these. I would greatly appreciate some input, as I am beyond intrigued.

1. What's the simple solution for the output yoke? Does that involve a junkyard driveshaft from a a8 car getting cut up?
2. The factory torque converter appears to have some press on/hard attached, "2nd flexplate" what are your plans there for mating that to an LA flexplate? The hemi flexplate has a ring gear...LAs don't. Hemis have a different balance and crank hub. Custom flexplate needed I assume? Or does this mystery plate come off?
3. What is the factory torque converter from a 4000lb car/ 6000lb truck going to do in a 2800-3200 lb car? My instincts say, stall speed will drop way down...hopefully not getting into the infamous "dies in gear" issues of needing more stall. Same will lesser HP...or even more HP...how do these converters react? Would love to know if chevelle guy used an OE Chrysler converter. I do know with so many electric inputs, some of the old school thinking here may be out the window.
4. 8hp70 transmissions in 2wd config with low miles are all over for $1000.... So 1000 trans, 1000 controller, 100 shifter...yoke of some kind...flexplate? Still seems super doable for under $2500. A modern 8 speed with insane OD...stump puller gear, 700hp capacity, a trans brake option even? I mean it's no $800 727 rebuild...but finally a "chrysler" OD trans option that isn't a cobbled together mess of vac lines and switches....I'm intrigued to say the least...enough to have spent the last 2 days burried online researching it.