I’m looking into which late model overdrive automatic would be the best choice behind the 6.2L LS in my ’70 Nova. Chevrolet Performance has just announced availability of the 6L80E transmission package that will work behind either a Gen IV or Gen V LS engine. This adds two more gears over what might otherwise be a 4L65E. That’s my question—is there enough of an advantage that would justify the added expense of the 6L80E over a 4L65 or 4L70E?
B.L.
There’s a ton of material here to consider so let’s just dive right in. We’ve included gear ratio charts for the 4L60E, 4L80E, 6L80E and even the 8L80E transmissions for comparison purposes. There are multiple advantages to the transmissions with additional gear ratios.
GM Modern Automatic Transmission Gear Ratios
| Transmission | 1st Gear | 2nd Gear | 3rd Gear | 4th Gear | 5th Gear | 6th Gear | 7th Gear | 8th Gear |
|---|---|---|---|---|---|---|---|---|
| 4L60E | 3.06 | 1.63 | 1.00 | 0.70 | — | — | — | — |
| 4L80E | 2.48 | 1.48 | 1.00 | — | — | — | — | — |
| 6L80E | 4.02 | 2.36 | 1.53 | 1.15 | 0.85 | 0.67 | — | — |
| 8L90E | 4.56 | 2.97 | 2.08 | 1.69 | 1.27 | 1.00 | 0.85 | 0.68 |
If we go back in time far enough, the earliest successful GM automatic was really the Powerglide, a two-speed box. As history shows, we’ve evolved from two, to three, to four, to six and GM now has both eight- and 10-speed gearboxes. The advantage is that the engine now stays in its power band as shifts progress with less rpm drop between each gear. The ‘Glide would drop 1,500 rpm between First and High gear (depending upon the converter used) while late model boxes now offer very minimal drops.
This improves even part-throttle acceleration because the engine doesn’t experience a severe rpm drop between gear changes and acceleration is smoother despite the fact that the transmission will shift much more often.
The 6L80E is rated at 650 lb.-ft. of torque which is dramatically better than the 4L70E’s 496 lb.-ft. With the much deeper First gear ratio in the 6L80E, this will have an effect on a rear gear ratio choice.
Let’s look at some examples. With the six-speed’s 4.02:1 First gear, if the rear axle ratio was a 2.48:1, this would be the exact same First gear ratio as a TH400 or 4L80E with a 4.02:1 rear gear! However, when the 6L90E reaches overdrive, you are now faced with an extremely tall 2.48:1 x 0.67 (Sixth gear) = 1.66:1 (which is an impractical ratio).
This means you would need something closer to a 3.31:1 rear gear in order to have a somewhat practical overdrive ratio in Sixth gear. In this case it would be 3.31 x 0.67 = 2.21:1, which is somewhat useful but still pretty tall to be able to pull at 70 mph. As an example, at 70 mph in Sixth gear and the converter locked up with a 26 inch tall rear tire, the cruise rpm would be right at 1,999 or rounded off to 2,000 rpm—which is acceptable as long as your engine isn’t equipped with a big cam.
The advantages to the six-speed trans is that you now have four full forward gears at or below 1:1 while the 4L70E is limited to three gears. With the deeper ratios and the added gear, our simulations show that a typical 430 hp LS with enough tire to eliminate tire spin with 2,400 rpm stall speed converter and a 4L60E would run 12.30 at 110.3 mph. Just changing to the six-speed auto, the additional leverage from the ratios improved the Chevy’s simulated time to 11.93 at 114.30 mph. That’s an improvement of almost 0.4 second and four mph! This shows you what the additional ratios are worth.
This simulation does not take into account the additional weight of the six-speed which is roughly about 50 pounds heavier than the 4L60E. It’s also likely that the 6L80E converter is slightly heavier as well, so these issues might reduce the six-speed’s advantage slightly—but only slightly.
The 6L80E is the only transmission in Chevrolet’s lineup of gearboxes that places the transmission controller in the oil pan where it is subject to high oil temperatures if abused. The later eight- and 10-speed gearboxes moved the ECU back out of the transmission and the six-speed is essentially its own design—completely different from all previous and subsequent transmissions.
Chevrolet Performance part number NAL-19366637 includes a 2,400 to 2,600 rpm converter; part number NAL-19417102 has a looser 3,000 to 3,400 rpm stall speed. These all come with a controller harness and calibration already set up for the street. The harness will also accommodate a paddle shifter.
Overall, the new Chevy six-speed appears to be a fairly strong package, and it’s priced not that much more than the cost of a 4L70E transmission and converter.
Hi Jeff, I purchased a 2003 gmc envoy for an ls swap in my 68 camaro. It has an all aluminum 5.3 which I am going to leave stock, it runs awesome. So I have all the computers an wiring. I have a 2011 6L80E trans I want to put behind the 5.3. Will the computer from the envoy run this trans or what do I have to do to control it? It has a 373 posi rear end. Thanks for your help. Dan
Hi Jeff, I have a 95 C1500 WT I want to swap the V6 out to a V8. It has a NV3500 transmission so I’m not seeing a huge issue other that the clutch is larger for the V8 match up. The computer should be fine right?
Does a 2400 rpm stall converter mean that in any gear – or, let’s say top gear at 70mph in your 2000rpms at 70mph example – if you depress the gas pedal enough to make decent torque, the rpms will go up to 2400? Do they generally lock in top gear? Or other gears?
I would like to put a 6l80e trans into my 07 Saturn sky with my 5.3 ls swap can it be done ?
I don’t understand why no mention of the vehicle its going into was brought up. In a 70 nova a 4l60 will fit without tunnel modification. The 6l absolutely will not fit with out cutting your trans tunnel.
I have a 94 z28 lt1 383 stroker motor. What all do I need to install 6l80e transmission . Currently it has the 4l60e.
Will either 6T75e or 6T80e bolt up to a 2005 3800SC 111 that currently has 4T60e?
Hello, I am noodling on doing a minor restomod on a 1963 chevy 2 that currently has the 6cyl and a 2-speed powerglide and has the floor shifter. I would like to go down the line with at minimum a 4 speed automatic, but the higher the gear the better. I really didn’t want to get to the 600HP sort of LS people are doing, that just not the goal. The goal is to both improve safety, and driving experience, but also to make it a better all around driver. I am open to just about any GM engine combination, within reason of course. So, that said, do you have suggestions and my guess is you’re going to tell me i have to weld in a new transmission tunnel, which is okay, but then I’d ask, any good ideas on classic looking shifters? Think that covers it and thanks!