It seems to be well known on the forum and in the community that a 4L60/70/80 transmission can be made to fit into the tunnel of a Third Gen without modification to the tunnel of the car. Less well documented are cases where a 6L80 has been mounted without modification. The same story persists with the 8L90 and 10L80/90, getting less and less documented as the transmissions get newer.

Dimensions to compare these transmissions directly have been hard to come by. How does one measure these if they do have one to measure? From the underside of the base to get an extra inch? I am aiming to provide some pictures for comparison. I have created these images by lining up the bolt patterns at the front of the transmission as best as possible, and trying to align the output shafts as well. This should allow you to see where on transmission has additional material that would need to be clearanced for, and will show whether the 10L and 8L really do "Fit where a 6L does". Any help verifying the similarities is appreciated!

Comparing the 4L and the 6L:
The 6L80 is very clearly the larger transmission between the two. Where the Bell Housings end is where the similarities end as well. The 6L80 appears to be slightly shorter, though that appears to only be due to a shorter tail shaft housing. The mounting face for the tail shaft appears to be a little longer than on the 4L, but I doubt that this is enough to cause issues. The diameter is clearly the issue, as well as the notably MASSIVE pan on the bottom. This can likely be mitigated with a different pan, but not completely solved.


6L80 in Red, 4L80 in Green

Comparing the 4L, 6L, and the 8L:
Here is where things get interesting. Conventional wisdom would say More Gears = Bigger Trans, but the 8L90 seems to be smaller than the 6L80. Shorter again in overall length, and this time, it looks like the tail shaft mounting face could line up with the 4L80's. It has a shorter pan, and appears to cut size slightly all over. It is notably still larger than a 4L however.


8L90 in Blue, 4L80 in Green, 6L80 in Red

Adding in the 10L:
The 10L appears to have a deeper pan, and appears to have a longer tail shaft housing than the 8L, but the overall size of the top of the unit seems to match up. The length of the 10L and 6L are almost identical, but the casing for the 10L and 8L are almost identical. The 10L appears to have a larger pan than the 8L or 6L, but the 6L has the tallest pan.



4L in Green, 6L in Red, 8L in Blue, 10L in Yellow

Conclusion:
All of this together appears to me like the 8L and 10L transmissions offer an easier swap into our cars than a 6L transmission would, thanks to shorter pans and not increasing in diameter all that much. I would personally very much like to swap out my old 700R4 and 2.8L with a modern Gen V small block paired with a 10L80, but I have had a hard time finding information. Probably years away from starting still, but I'm working on gathering information... Hope this helps someone someday!

 

Neat overlays. Where did you find those drawing models?

 

Each of the images was just found from Google. Ideally, I would have a side view, front view, and rear view, but the angles each of those were taken at was very inconsistent. The isometric views I overlaid and posted are just a common angle that I was able to repurpose. Links below for each picture I used.

4L60
6L80
8L90
10L80

 

Of note, the 10L80 image I used has "10R80" cast into the casing... It CLEARLY isn't a 10R80, so I don't have an explanation for that.

 

I did a 6L80 swap into a 91 camaro about 10 years ago. First with an LC9 5.3 and then an LS3 infront of it. After test fitting I did not think I could get the ground clearance or the correct drive line angles with out raising the tunnel. I raised the tunnel , including the top of the bell housing area about an 1.5 inches back to just infront of the floor brace. I put about 40,000 miles on the car after the swap. I sold it in Nov. of 2021.

 

was your interior made to look stock, or was it more of a race interior? I personally would like a 6 to 10 speed in my ‘89 firebird, but I was to keep the stock interior look

 

Stock look ,even the stock shifter. Because I raised the tunnel the radio area became a single din.

 

that does look absolutely fantastic. Might be a little more challenging with the odd structure that is the radio pod in a firebird though…

 

I'm getting ready to swap an L99/6L80 out of a 2013 Camaro SS. its going into an 87 IROC Z. My question is, could you have gotten away without cutting the trans tunnel? I have looked at your thread and could not locate photos of the trans tunnel cut out and re welded back in. Do you have any of those pictures?
thanks for your time.

 

I have seen other people on this forum say they were going to do it without raising the tunnel but their threads seem to end without a finished car. I understand Hawks did it but I don't know how much torch and hammer work they did. Remember that you have to get the trans high enough to get the drive line down angle right and keep enough ground clearance. Look though some of my old posts from 2013-14 I posted pics of the cut out. Note that I left the floor brace intact , I then made 2 slits in the bell housing area of the tunnel about 10 inches long so that I could raise that area up to meet where I wanted the tunnel level to be. I then Screwed scrap metal pieces to temporarily hold the tunnel top/cap in place while I welded in to fill the gap between the original floor and newly raised tunnel top/cap.I would recommend that you remove the DOD cam and lifters. How are you planning to do the drive shaft? The camaro has bolt in yolk that is not compatible with a u-joint. If you would like to talk on the phone PM me a number.

 

I re watched LSXMATT video of him installing the 6l80 out of a 16 Yukon in his 3rd gen firebird and his transmission has the Yukon tail shaft if I decide to do the 6l80 swap I'll have the tail section swapped and use the slip yoke he used. I'm not sure it the 3rd gen firebird has a larger trans tunnel and that's why he didn't have to modify the tunnel. if I get it up there and figure out, I can't make the swap ill just rebuild the 700r4 to handle the added HP and TQ.

 

Has anyone already installed an 8HP70 automatic or thought about it?