6L80/6L90 swaps - trans tunnel mods?

[Jackson's Dad 64 C10]

I know, I need to do a build thread… we just dropped our freshened LY6 into our 64 C10 yesterday. Still have a ways to go on the engine, but the Speed Engineering headers are a perfect fit! I’m sitting on a plane, heading to Alaska for work so it will be a few days before I can touch it again. My 12 year old wanted to see some progress, so we just placed the engine with no trans (supported the oil pan with some wood blocks to keep it from twisting back).

I’m contemplating the transmission install and thought I’d throw this one to the forum… I have the 6L90e out of the donor truck, and I’m wondering how best to make it fit. This appears to be a low hump truck, but the “hump” is a crude patch done by a PO. It has some sheet metal booger welded in, with some fiberglass looking stuff on the seams. I’m going to start by cutting that out, but I’m wondering if a repro high hump will work, or if I’m better off looking at something like the trans tunnels that Bowler, Tin Man and others make.

For those of you who have swapped 6L80/90 transmissions, what clearance issues did you experience, and what was your solution? For reference, I’m running No Limit Wide Ride IFS with their trans crossmember (trans crossmember isn’t installed yet). I think the motor mount locations have some impact on where the drivetrain ends up.

Sorry for the novel, they just closed the boarding door so I’ll check back later. Thanks a ton, fellas!

-Chris

[LS short box]

I haven't done a 6L80 but if you have to repair the floor any way no reason not to put in the high hump. I'd bet money it will give you a better drive line angle. If you are putting in new carpet just order the high hump model.

[Jackson's Dad 64 C10]

Originally Posted by LS short box

I haven't done a 6L80 but if you have to repair the floor any way no reason not to put in the high hump. I'd bet money it will give you a better drive line angle. If you are putting in new carpet just order the high hump model.

My original plan was just to put in a high hump, and that’s still my first choice, but I’m not sure if that will give me enough clearance. People talk about the 6L transmissions like they are just massive. I guess they are when you compare to a Turbo 350 or even a 400. I’m planning to initially cut out the crappy repair, and go from there. I’ll try to cut as little as I can, until the trans fits, then I can take some measurements and find my options. I am still hoping someone sees this thread and goes “hey, I put a 6L in my truck, here’s what worked for me”. If not, I’ll post back with what I come up with for someone else in the future.

[LS short box]

You might check over on LS1tech.com to see if there is anyone else running a similar combo in a C10.

[nsb29]

I put a 6l80e in my 65 I used a high hump had good clearance it’s the only way to go don’t think it’s possible to use a low hump

[Jackson's Dad 64 C10]

Originally Posted by nsb29

I put a 6l80e in my 65 I used a high hump had good clearance it’s the only way to go don’t think it’s possible to use a low hump

Thanks. That helps a lot. I didn’t want to get into a scenario where I bought the high hump and it didn’t fit. I think I’m still going to cut away what I need to replace anyway, and take a few measurements just to be sure.

[raic65]

Originally Posted by Jackson's Dad 64 C10

I know, I need to do a build thread… we just dropped our freshened LY6 into our 64 C10 yesterday. Still have a ways to go on the engine, but the Speed Engineering headers are a perfect fit! I’m sitting on a plane, heading to Alaska for work so it will be a few days before I can touch it again. My 12 year old wanted to see some progress, so we just placed the engine with no trans (supported the oil pan with some wood blocks to keep it from twisting back).

I’m contemplating the transmission install and thought I’d throw this one to the forum… I have the 6L90e out of the donor truck, and I’m wondering how best to make it fit. This appears to be a low hump truck, but the “hump” is a crude patch done by a PO. It has some sheet metal booger welded in, with some fiberglass looking stuff on the seams. I’m going to start by cutting that out, but I’m wondering if a repro high hump will work, or if I’m better off looking at something like the trans tunnels that Bowler, Tin Man and others make.

For those of you who have swapped 6L80/90 transmissions, what clearance issues did you experience, and what was your solution? For reference, I’m running No Limit Wide Ride IFS with their trans crossmember (trans crossmember isn’t installed yet). I think the motor mount locations have some impact on where the drivetrain ends up.

Sorry for the novel, they just closed the boarding door so I’ll check back later. Thanks a ton, fellas!

-Chris

I'm running the same setup (LY6/6L90) on my 66 c10. I fabricated adapter plates for the motor mounts that placed the #8 coil within 1/4" of the firewall. I also fabricated my own transmission mount. I set the engine/transmission down at 3 degrees. With that said, my c10 has the factory high hump and the 6L90 clears with plenty of room. In my opinion, if you need to replace the floor, the high hump is all you need. Most of the height in the 6L90 is actually below the input/output shaft centerline IIRC from my research.

[Jackson's Dad 64 C10]

Originally Posted by raic65

I'm running the same setup (LY6/6L90) on my 66 c10. I fabricated adapter plates for the motor mounts that placed the #8 coil within 1/4" of the firewall. I also fabricated my own transmission mount. I set the engine/transmission down at 3 degrees. With that said, my c10 has the factory high hump and the 6L90 clears with plenty of room. In my opinion, if you need to replace the floor, the high hump is all you need. Most of the height in the 6L90 is actually below the input/output shaft centerline IIRC from my research.

Raic65, that’s really good information. Did you keep the truck pan on the transmission, or did you swap to one of the lower profile pans like a Pontiac G8? I’m just wondering if I’m going to have to deal with a really low pan below the frame rails. Thanks for the input!

[raic65]

Originally Posted by Jackson's Dad 64 C10

Raic65, that’s really good information. Did you keep the truck pan on the transmission, or did you swap to one of the lower profile pans like a Pontiac G8? I’m just wondering if I’m going to have to deal with a really low pan below the frame rails. Thanks for the input!

I kept the truck pan on my swap. I wasn't concerned because I don't plan on laying frame. IIRC, the transmission pan does hang below the frame rails by 1/2"-1". I can double check though if you like.

[Jackson's Dad 64 C10]

Originally Posted by raic65

I kept the truck pan on my swap. I wasn't concerned because I don't plan on laying frame. IIRC, the transmission pan does hang below the frame rails by 1/2"-1". I can double check though if you like.

I appreciate it, but I’ve already got the engine and trans almost ready to go in, so no turning back now! I’ll check the clearance once it’s in, and can swap the pan and pickup if I need to. I have a high hump on order from Classic Muscle (the my are close enough to do pickup and save on shipping), so fingers crossed that it works in our truck too. Thanks for all of the help and input guys!