L99/6l80 swap
 

Doing some planning on a Camaro SS pullout swap for my 77 C10. Got some questions on the swap regarding how the transmission will interface with my 3.73 gears and 29" tall tires. I'll be using an all-stock donor drivetrain, complete down to the ECU tuning and exhaust manifolds.

Looks like the tire diameter of the donor Camaro would be pretty much identical (29.5") to what I have. However, an L99/6l80 equipped Camaro came with 3.27 rear gears. Assuming I drop in the combo as is with my 3.73's, will this cause the transmission shifting to be completely out of whack?

Re: L99/6l80 swap
 

Since you are using the Camaro engine/trans ECM/TCM the tune/shift points can be modded in the ECM/TCM using HPT tuners.

Re: L99/6l80 swap
 

Short answer to the last part of your question is yes. The gear ratio and tire size should be able to be changed in the ecu by someone with the proper tools and knowledge. I have read in the past that the 6l transmission shifting is torque based and not by rpm. Some stories of transmissions that were smoked in very short time when shift parameters were altered by less competent persons. While I do have HP Tuners I am not to that point yet. I do have a local guy to work with who uses a dyno to dial everything in.

Re: L99/6l80 swap
 

Yeah that’s what I was afraid of, and why I was trying to stay away from any trans tuning. Well I’m going to be changing the rear differential anyway to a limited slip, so I could always go down to the donor car’s rear gear. With the tire diameter being the same, it should behave exactly like a Camaro. (At least from a tuning standpoint.)

Not to mention, the 3.27:1 rear gear would be a welcome change. With the 6L80 having a 4ish:1 first gear, the 3:73’s would be a handful in a pickup with no weight in the rear

Re: L99/6l80 swap
 

If you just change the rear gear and/or tire size setting I would not really call that "tuning" As far as the low first gear. I am running 5.13's with 37" tires. LSA and 6L90. yet to see how it does. Puts me around 2200 rpm @ 65 mph. Right where I want it.

Re: L99/6l80 swap
 

yes, any non oem part will need to be tuned and accounted for... In my 5.3 6l80 3.73 swaped truck, i used HP tuners and used the quick tire change calibration, it did a good job, but still needed to be tweaked for ideal mph in each gear.
clint

Re: L99/6l80 swap
 

I have 3.73 gears in my truck with a 6l trans and 28" tires. Shifts fine with no issues. I do not have any traction issues either unless you mash the pedal to the floor on takeoff from a stop, but that is to be expected.

How are you going to run a speedo? GPS set-up? The 6l has no provision for a speedo unless you tap into the OBD port and pull it from there.

Adjusting the trans with HP Tuners takes like 2 minutes. No tuning required.

Re: L99/6l80 swap
 

So the 6L doesn't have VSS on the trans output shaft? So where does the ECM get the speed signal?
One thing I have the tuner do trans tuning wise is program the ECM so the trans doesn't go into OD or converter lock until I hit 40-45 mph so the engine doesn't lug.

Re: L99/6l80 swap
 

The VSS is internal an can only be picked up through the OBD2 output for an external speedometer. You would need something off this page to interface:

https://www.dakotadigital.com/index....cat/cat287.htm

I don't know if the car transmissions are an issue, but on the trucks, the first thing you do is replace the converter. They have a habit of grenading and sending shrapnel throughout an otherwise good transmission.

I have mine programmed the same way. No lock-up until 5th gear. 1-4 doesn't lock-up.