318/8 Speed Swap

-
wish4hemi

wish4hemi

Well-Known Member
Joined
Aug 26, 2009
Messages
881
Reaction score
191
Location
62450
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.

IMG_9418.JPG
 
The 70 in 8HP70 means it's rated for a max input torque of 700 Nm (516 lb-ft). That number is a little misleading because of the torque converter, spikes during shifts, etc., but can be used as a guideline. There are plenty of 5.7/6.4 Hemis out there putting way more power than that through a stock 8HP70.
 
RAT ROD AL said:
How does it compare in length to say a 904
Click to expand...

Length isn’t the issue. This isn’t like older overdrives where the extra gears are added on the back. Rather, the 8HP70 is bigger in height and in width at the top. Tunnel modifications are absolutely necessary.
 
My van doesn't have a tunnel. But the drive shaft is only 18" long as it is. Is why I asked.
 
You may be getting the cart before the horse, here, AKA what is the status AND COST of a controller?
 
67Dart273 said:
You may be getting the cart before the horse, here, AKA what is the status AND COST of a controller?
Click to expand...
It'd be awesome if someone nailed a stand alone controller...but the aftermarket's inability to even master the 545..the nag...even the 45/42r.. whatever doesnt have much aftermarket support... at this point it's easier/cheaper to bolt a 4l70e or 4l80e into a mopar...that makes me sad :/ lol
 
I like what you're attempting to do, but realistically, I think getting an 8-speed transmission to operate off a stand-alone controller is a very tall order. They were designed around drive-by-wire applications, where the ECU is already receiving enormous amounts of data. I'm not trying to be a naysayer, but from an engineering/software point of view, it's going to be a tough nut to crack.
 
Keystone said:
I like what you're attempting to do, but realistically, I think getting an 8-speed transmission to operate off a stand-alone controller is a very tall order. They were designed around drive-by-wire applications, where the ECU is already receiving enormous amounts of data. I'm not trying to be a naysayer, but from an engineering/software point of view, it's going to be a tough nut to crack.
Click to expand...

Actually, that isn't at all correct. The only absolutely necessary inputs are RPM and throttle position (easily added to a carburetor or pulled from an EFI ECU). Drive-by-wire has nothing to do with it. Sound German Automotive already started shipping standalone 8HP70 controllers in February of this year. If anything, I'm a little behind! It's been a few months since I priced the controller with harness, but ballpark was $1,000 - $1,500. I know of at least one other company working on an 8HP70 standalone system, although the product isn't ready to ship yet.
 
OK, I'm glad to hear that. I have an 8-speed in my Grand Cherokee and even the factory didn't get it 100% right. I still think it's a lot to ask, but time will tell how well they're able to pull it off.
 
Here is a video from a guy that put an 8HP70 in a '67 Ch******. To quote him, "I've tried 2sp, 3sp, 4sp od, and a t56. This 8 spd kills them all."

 
You will need a 4:10 gear or better just to pull it in 5th and 6th. Teens don't have that much torque at 500 rpm. Just sayin.
 
Maybe not at 500 lol.
But I ran a GVOD behind an A833od box with with 3.23s one winter. 65 mph was under 1450 in double over drive. Final drive ratio maths out to 3.23x.71x.78=1.789.. Ran that lil smogger-teen with a TQ and the TTI dual 3" full length system. Hey, 3.09x3.23=9.98 starter, lots for winter. Fantastic fuel mileage.
But I think a 6-speed would be lots for most of us who seldom exceed 100 or 110 mph.
An 8speed for an HO 360, whoa; that would be something.
Funny thing Is, I have 7 useable gears in my combo, and most of the time I only use 3 of them; first, second and overdrive,lol. The rest of the time I might max out with 5.
Nevertheless, I'll be following along.
 
Our 2015 Challenger R/T has the 5.7 and the A8. Axle gearing is 3.06. Freeway cruising at 75 is around 1400 rpms with a 20" wheel package. Most A=body cars will have more axle gearing and a shorter tire so you can expect those rpms to be higher.
 
None at the moment. Russ at Sound German Automotive continues to make progress on the swap. I know he was tearing in to the factory floor shifters this week to see exactly how they work.

A Cummins project has sidelined the 8-speed for me, but it’s still in the corner of the shop, waiting its turn.
 
wish4hemi said:
None at the moment. Russ at Sound German Automotive continues to make progress on the swap. I know he was tearing in to the factory floor shifters this week to see exactly how they work.

A Cummins project has sidelined the 8-speed for me, but it’s still in the corner of the shop, waiting its turn.
Click to expand...
Otay...keep us posted!

Jeff
 
wish4hemi said:
None at the moment. Russ at Sound German Automotive continues to make progress on the swap. I know he was tearing in to the factory floor shifters this week to see exactly how they work.

A Cummins project has sidelined the 8-speed for me, but it’s still in the corner of the shop, waiting its turn.
Click to expand...

That video show him running the trans with a cheap controller he made. Have no idea if it is true or not but seems real.
Fiat need to jump on this or even ZF out of Germany. They used this same trans ( Basic setup) with upgrades in the GT4 class at Neuenburg.
I believe they dropped the converter for a clutch. This trans is less than 200 lbs and can handle up to 750 ft lbs I think in the hp90 trim.
Googled 8 speed and got GM stuff engine and transmission controllers for swaps.
JESUS they R quick!!!!!
 
Pretty sad a Chevy guy has an 8hp70 8 speed and mopar guys just argue about how it can't work mopar guys need to step it up
 
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.

View attachment 1715305856
Click to expand...
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.
 
Last edited:
Johnny Mac said:
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.
Click to expand...

1. A junkyard driveshaft is one option. Another option is an adapter flange yoke, Sonnax part number T35-ALFY-08. This gets you to a standard 1350 U-joint. From there, it's as easy as making a slip-joint driveshaft similar to how one would replace a ball & trunion joint (Early Valiant Barracuda Club - ball and trunion U-joint conversion)

2. The 8HP70 torque converter does not have an integrated ring gear. instead, there is an intermediate flexplate that goes between the crankshaft hub and the torque converter. By my measurements, the fix looks simple enough; just get a standard stick-shift flywheel for an LA motor, drill 6 holes in it, and bolt it to the 8HP70 torque converter. Picture attached of the torque converter. The 6 outer holes are threaded and would allow for a flywheel to be bolted to it.

3. Not sure on this one as my plan had this 8HP70 destined for a 3,740 lbs B-body.

4. You are correct. The tight gear ratios of the 8-speed would mean that you'll always be in the right gear at the right time. And you're able to jump on the laptop at any time to fine-tune shift points, firmness, etc.

8hp70front.jpg
 
You must log in or register to reply here.
-

Back
Top