6 Speed Automatic (6R80) retrofit onto a FE

Picked up a low mile 6R80 in an attempt to replace my blown C6. Here’s the progress. In four days I’ve reshaped the tunnel. My initial conclusion is that I’ll need to make two access holes directly behind the highest bolts on the new bellhousing in order to install and torque those bolts. This assumes an adaptor plate thickness around 1.25". Another option may be to remove the engine bolt on the transmission and reinstall the whole thing. I don’t have the garage setup for that however.

Here’s the description of the new transmission. Multiple versions of the 6R80 were made. Adaptors and electronics are only made for the 2011-2014 2WD V8. 2015-2017 are almost the same but have a different cooling setup.

In general the bellhousing is smaller and overall the trans is shorter than the C6. However the body is larger and more deep.

One area of contact is the very top ridge of the 6R80. This transmission has a 1 year warranty so I am reluctant to grind down anything on the transmission itself. I have the console and can use that to hide any small changes to the tunnel shape. I am using an old conduit bender and a floor jack to “massage” the top of the tunnel for more room. Similar process used around the bellhousing using smaller tools. Keeping the hammering to a minimum.

Some initial videos. Pardon my complete lack of editing. Amateur for sure.



Pretty amazing! I take my hat off. Taking this on is bold!


Very cool! Keep going, can’t wait to hear the results

Good for you, what flex-plate will you use?

On Monday I put in an order for the Speed Gems adaptor. This kit allows the FE 390 to bolt up to a Ford Modular trans. A flexplate and starter w/solenoid are included. I confirmed that all the kit parts are made in the USA. Interestingly enough Speed Gems is located in Wisconsin whereas I am in Illinois. The starter they use is made one town over from where I live. Small world.


This cool. What rear gear do you plan to run?

I know you will have problems along the way, but that Kit $$$ looks like it will solve a lot of them. Good luck and keep us posted

Unsure at the moment. My feeling is 3.73:1 on the steep end or maybe 3.27:1 on the tall end. The 6R80 has a very steep 1st gear. So much so that the controller I bought allows for launches in 2nd gear. I’m not looking to make it a drag car or anything. Just an available option. I have a 2.75:1 open rear end. I’ll debug everything else and deal with that a little later along with new wheels for more traction. Even the hottest newer Mustangs that I have researched only have 3.73:1 and my guess is taller tires.

Thanks. Problems happen but finding a trick solution (hopefully) makes it all worth it. The plate thickness is 1.5" whereas I was considering only 1.25". So will need to massage the trans tunnel a bit more.

Does that adaptor actually measure 1-1/4"? If so, I wonder why it needs to be so thick.

Oops, just saw you last post that is it actually 1.5". Do you see why? Was it designed to position the trans for a different vehicle application?

No worries. I had a small tour of the facility and was shown some prototypes for a SBF. That adapter was pushing 2.5" - 3" thickness. The design and relationship of the starter and ring gear seems to affect the needed thickness. Also practical things like raw stock aluminum thickness etc… That’s only what I gleeaned from the conversations.

Just an FYI. The flexplate is a common Ford design. While I don’t have the need, it would be possible to upgrade to an SFI rated part.

I am watching close, I run a TKO-600 and LOVE it, but as my supercharged motor comes to a close, it would be so nice to “point and shoot” at launch

I just can’t give up my 2.63 final drive in 5th, so normal Ford ODs haven’t looked strong enough and a C4/C6 is out of the question due to the miles I put on the car

Very cool project

Quick update on the 390 & 6 speed auto retrofit.


Great post. Keep the updates and videos coming!

Here’s my latest videos. :thumbup:

Huge sense of accomplishment happened on Christmas Eve as I was able to get the 6R80 to sit flat on the alignment dowel pins.

A considerable amount of tunnel bending and cutting was needed. More than I anticipated due to an offset of the tunnel vs powertrain. As my transmission has a 1 year warranty I was very reluctant to remove any of its tabs. In the end I had to trim a couple of spots on its housing helping move the project to the next stages.

Here’s the firewall where I had to make access for the top bellhousing bolts. The driver’s side has been stamped out to support the gas pedal linkage. This general shape allowed for bolt access once I pushed everything in and up about an inch or two. The passenger side was less cooperative. After a week of deliberation I decided to make a hole. Unless I removed the engine I couldn’t think of an alternative. Now it is servicable and will allow for a torque wrench to be used. So 5 out of the 6 bell housing bolts will get a correct torque specification whereas the top driver’s side bolt will just be snugged up based on feel.

I made a pocket above the vent of the 6R80 transmission. The whole powertrain with shake at idle and shift/twist under load. I wanted to make sure the vent wouldn’t get smashed shut.

Another modification to the factory cross member to accommodate the rib that goes down the 6R80 housing lengthwise. This may or may not be needed depending on the final pitch of the transmission. I see 2° downward angle as a starting point but need an aftermarket cross member and mount for this adjustment.