LQ4 tranny compatibility . . . Newbie from Texas

Filbert Sam · September 30, 2014

I just purchased a 1999 6.0 Litre LQ4 motor with harness and computer, plus an extra set of aluminum heads. I thought it was a really good deal. Trumping a likely response, I'll just say it first. "You can always tell a Texan. You just can't tell him much".

The donor vehicle was a 1999 Silverado 2500 4x4. Since it was a 4x4, it most likely had a 4L80E tranny, but I'm not certain about that.

My intent was to do a "LS swap" for my 57 Bel Air. I'm NOT building a 400HP+ muscle car; strickly a street driver. My hope was to build a reliable and efficient driver, no DC generators with leaky PS pumps, 15 MPH, slack steering, etc.).

However, I just learned that the crankshaft for the 1999 & 2000 LQ4s are a little bit longer than the standard LS or LQ cranks for later years (don't know about years prior to 1999). The fix as I can best understand it is some sort of spacer, or a new concaved flex plate, or a new custom made torque converter, or some combination of all of these.

I'd like to go with the 4L60E if possible (size, weight, cost, etc.). If necessary, I can go with a 4L80E if that's my only option.

Q1) Is there a 4160E that will mate up with the LQ4 without the necessity of some exotic solution?

Q2) Is my only option to find a 99 or 00 4L80E?

Thanks in advance

Filbert Sam

darkfox1 · September 30, 2014

Welcome!

Great selection of motor you got there.

I did an LQ4 build a while back. I used texas speed machined Ls6 heads, an LS6 intake, and a 228R cam (also TSP.) It pulled ~450 at the wheels in a 99 silverado RCSB 4x4 before his tranny exploded.

So.. you have 2 options really and it depends on your flexplate. A 5.3 or other 4L60E mated motor will have different bolt patterns as I understand it on the flexplate vs an 80E.

Yes, if you have an LQ4 that came out of a 2500hd, chances are VERY good that it was mated with a 4L80E.

TBH, my recommendation is that you try to source an 80 anyway unless you're doing a mild build. An 80 is pretty darn near bomb proof stock. 60s are great trannies, but if you're gonna be putting 500FWHP to a stock 60, it won't last.

you and I have a lot in common too. I've got a 4 door belair sedan in my shop right now. Leaky 283, ironglide that vomits fluid every time I drive it, rear diff leaking, leaf spring on the pass. side cracked, tires dry rotting. I drive it anyway.

Buddy of mine says he knows a guy here local with a 4 door that's been "pushed back up in the woods" that he may give me cheap. If the frame is straight, I'm planning to do what you're doing. Restore his frame, part out the rust bucket, drop a 5.3/4L60e stocker (ok, maybe a mild cam for some lope) and some disc brakes, move my body onto it and make it a cruiser/casual show car.

Check out these guys:

http://www.brphotrods.com/products/55-57%20Chevy/index.html

I have met them in person years ago at the super chevy show in commerce GA, and I've talked to them on the phone many times. They're a little on the busy side (business is booming apparently) but they're gonna be who I am going to for all my parts.

Apparently you can run the truck front accessories AND stock low mount a/c with a slight frame modification.That's my goal. I'm not into chromed up high maint. engine bays. I want it to look like a stock truck under the hood, and a stock belair everywhere else.

Hope this helps!

Actually, let me add something here to clarify. You don't need a different crank. You just need a different flexplate. The difference is where the flex mates with the torque converter.

LSX swappers, if any of this is wrong PLEASE chime in and correct me. Its been about 2 years so I'm a little rusty on my swap knowledge.

Chris · October 1, 2014

Flex plate and a 4L60E will "work". I have the LQ9 6.0 and really should have at minimum a 4L65E. I have the 4L60E still. It is an LS engine spcan LS 4L60E will bolt up to the block

Filbert Sam · October 2, 2014

Thanks "darkfox1" and "chris" for your feedback,

So, the 4L80E looks like the way to go so long as I can fit it under my floorboard. The 4RL80 makes sense since the harness is very likely already set up for the 4L80E. Plus, the LQ4 is an engine that puts out a lot of torque. I've seen several articles about the '60 not holding up to the torque as well as the '80.

From everything I've read, the 4L80E is roughly the same external size as the TH400. Do you agree? Thinking about the transmission tunnel . . . . will I have to enlarge it.

Thanks again.

Filbert Sam