4l80e installed, what rear gears
 

I installed a 4l80e in my 1967 GTO a couple months back and I absolutely love it!
I’m currently running 3.23 rear gears with 275/60/15 Nitto drag radials. I feel like the gears are a little too tall. On the freeway I’m turning 2k rpm at 70mph. Which is nice when traffic is clear, but when traffic hits and I’m around 60mph I feel like I’m kinda lugging the engine. I have talked to a few guys with similar setups and it seems like 3.73 gears are the way to go.

I jumped on Wallace racing calculators and ran some numbers. Looks like about a 300rpm difference for the 3.23 vs 3.73.

Curious what your thoughts are and what you guys are running for gears with a lock up OD transmission.

3.73`s would be my choice.

Id go with a 3.73 or 3.89.

4.10 unless you are racing, then go with a 4.30 or 33. On my one car I run a 4.86 and its very happy on the street.

Curious as to why 4.10? These engines make enough low end torque to shred the tires through 2nd gear even with 3.23’s. Wouldn’t that deep of a gear just make it worse?

Too low of RPM in O.D. is not good. 2000, as you found out, lugs. I found a good sweet spot between 65 - 70 MPH is between 2600 and 2800 RPM.

My 05 LS2, stock 400 HP/400 ft.lb. GTO has 3.46 from the factory, 4L60E, I bought the car new, and it has 141,000 miles on it. That ratio works very well for me for a street car.

Based on my experience with that car, my next project is a 84 GP with a 455 in it, I'm going to run 4L80E, with 3.50, 9 inch ford, based on how the GTO works with the 3.46 ratio. I'll keep the tire diameter very close to the GTO to keep the results as close as possible.

That's my experience, FWIW, :2cents:

Final drive in my GTO in OD is 2.42, the GP will be 2.60. Many of the Pontiacs over the years ran a 2.56 final, and I'll be right there with my combo.

For what you're doing SJ, I'd do 3.73. That's roughly just a little over 300 rpm difference from where you are now, and the 3.73's really help the 2.48 first gear at the same time. 70 mph will be about 330 rpm more if you keep your 28 inch tires. Of course I don't know what rear you're running, ratio choices might be a bit limited if still using the 8.2

I'm doing a 4l80 in a car that already has 4.10's with a 400 turbo and has been that way for 35 years. At this point I'm likely going to stick with the 4.10 since the 1-3 gear ratios of the 80E are the same and I've already got the car suspension wise dialed in with that setup and like how it runs.

3.90s should put you right at 2k @ 55mph cruise at the slower highway speeds and still lightly throttle to increase speed. It'll also give you a nice launch in 1st.

Think you were considering a Tremec when the 3.73's were talked about. With the 4L80e I'd go 3.55:1 since your overdrive is a somewhat mild .75:1. I went with 3.73's with the TKO-600 but it has .64:1 overdrive ratio. My final drive ratio is 2.40:1 and yours would be a little lower at 2.66:1 with the 3.55's. Almost a coin flip between the two for you, but I would stay with one or the other and not go lower or higher.

I'm still seeing 2,400 RPM when out in the fast lane keeping up with traffic -- those soccer moms have a tendency to haul the mail.

I run a 28” tall tire and a 3.90 gear with my 4l80e. I would say it’s going to depend on several things including your cam and how low it lugs, what your intentions are for the car etc. my car is raced as much as street driven so I am actually looking to go to 4.10’s or even a 4.33 gear. I find myself cruising at 80 on the highway often once into lockup because that kind of feels like it’s where the engine wants to be rpm wise and she cruises right along. I have also ran a 200-4R behind a 428 with a 3.55 gear before that was a lot more “streetable” and it worked well too. All this being said I would think the least amount of gear I would go with a Overdrive would be a 3.55 and likely if more “street” still a 3.73. If your into racing get on a calculator and figure your trap speed and what rpm your engine likes and you can figure out your best gear.

3.54:1 is fine when run by a 455. In the TQ band huh

The first question needing to be asked in terms of what rear gear is at what rpm does the motor start to pull hard and then at what rpm does it feel like it's making peak Torque in whatever gear 1 to 1 is, then you want to gear for a normal cruse rpm of about 500 less.

Peak Torque rpm will usually coenside with the point in rpm where the fast gain in seen in rpm levels off.

For comparison sake, if cruising is what you're after, I have one here with a .64 overdrive and 3.55's out back with a 27" tire.

It makes absolutely no torque at all and it still lugs around just fine in overdrive at low speeds. I cruise through town all the time at 35 mph in overdrive, and it's just above idle, and will easily pick up speed pushing on the throttle. Basically anything above 35 is overdrive in that car when cruising around and it works fine.

A Pontiac with loads more torque in a very low rpm range should have no trouble what so ever pulling any car around in overdrive.

But......with that said I'm still a big fan of running some gear in the car.

Guys, thank you for all the information. This is great stuff.
The cam is 238/243 at .050. The engine make plenty of torque at low rpm to pull the tall gears. In fact there is road near my house where the speed limit is 50 with some hills, the engine has no problem pulling OD with the converter locked turning about 1600rpm.

This car is pretty much a cruiser. I drive it every chance I get. Living in Southern California means I’m driving the freeway pretty much everywhere.

2000 rpm, 3.23 gears = 68.80 mph
2200 rpm, 3.55 gears = 68.86 mph
2300 rpm, 3.73 gears = 68.51 mph
Seems like I’m splitting hairs between the two. Probably won’t even notice a difference.

Exactly, 3.23 to 3.55 isn't a big change, and going to 3.73 from 3.55's is even less of a change, making the 3.73 an easier sell. So generally when I'm doing stuff like this, spending $500+ for gears and a setup kit, plus my time setting up a rear, I tend to want to make a change that is at least a little bit noticeable. Which is why in your case with 3.23's, I'd go straight for 3.73's. When swapping gears I like to at least jump a 1/2 point in ratio or it's not worth the effort.

4L80 Installed, What Rear Gears
 

I'd leave the 3.23's in there, all things considered. You pretty much answered your own questions. "It's pretty much a cruiser". "Live in SoCal and do a lot of freeway time". If you venture into some of the states to the east of you where speed limits are 75,80,85 and no limit on interstates you'll appreciate those 3.23's. I live in Missouri but, I've been out there with my 700R4, 3.23 equipped 69 GTO and it's pretty nice zipping along at 80,85 and still be under 2800-3000 RPM. You start putting some "gear" in it you'll be defeating your purpose IMO. Plus, I don't know what rear end you have but, if it's the 8.2 any move above 3.23 will require a carrier change. More $. Also, you already said when "putting" around the torque of your engine does just fine. My vote, leave it alone use the money you would have spent on a rear gear change to buy fuel and take some trips. Believe me, the more you drive it, especially in the "wide open spaces" out west the more you'll like it. I know I do mine. Just my opinions. Enjoy.

Besides "lugging", running with too low of RPM will cause the engine to load up and run hot. A higher RPM will allow for a cleaner burn resulting in cooler engine temperature. I have been dealing with O.D.'s in old cars for 20 years which, back then, people would say "they won't work" or "you can't do that". I have raced them as well as drove them on the street which is where I found what the sweet spot RPM is that makes everything happy.

I always like to do the math before committing to a gear.... Opinions / experiences are very subjective when it comes to gears due to variables in engine torque produced, tire heights and intended / applied usage of the vehicle.

Its important to remember that RPMS alone do NOT dictate fuel economy. One of the biggest misconception is that lower RPMS get you the best fuel economy... and that is absolutely not true. The "LOAD" on the engine at any given RPM has everything to do with fuel economy. So increasing your RPMs does not always mean worse fuel economy... of course there is an RPM point of diminishing returns.

When using OVERDRIVE transmissions, I have learned for heavy vehicles (GAS Trucks) that anything under 2000RPMs@60MPH indicates the need for more gear. A rule of thumb that I start with for best all round performance & fuel economy I initially target 2000RPMS@60MPH. The amount of torque you are making at your chosen/set cruise speed and the weight of the vehicle need to be taken into consideration. For a light weight car, I would aim closer to 1500RPMs@60mph as the lowest cruising RPM and select my gears to get me 1500< RPM. The amount of torque you are making at those lower RPMs will assist in efficiency at a lower RPM point when in OD and allow you to chose a taller gear in order to take advantage of that lower RPM efficiency. My general rule of thumb (2000RPMs@60MPH) advice applies to applications using an overdrive transmission. Non overdrive transmissions should gear for Top end RPM performance on 3rd gear...


I like to apply the formula below for every gear in the transmission so I can see where my WOT shift points will be. If my car is going to be a street strip car, I like to be at the top of 3rd by the end of the 1320... so the math is NOT applied to the overdrive ratio and more for 3rd gear... overdrive lands where it lands... this tends to trade off some potential fuel economy. So knowing how you plan to use the car is important to determine before choosing the gear. So there is a lot to take into consideration... the math will help you determine what will be best for YOUR application. The formula I use is found below.

The Math-
Step 1) FIND YOUR OVERALL GREAR RATIO-
Transmission overdrive ratio x rear gear ratio = OVERALL GEAR RATIO

Step 2) FIND YOUR RPMS AT ANY SPEED (Useing your OVERALL gear ratio) - For fuel economy, I use 60MPH as the target. For racing, use your targeted trap speed to determine if more or less gear is needed.

- SPEED X OVERALL GEAR RATIO X 336 / TIRE HIGHT = RPMS


Perform this formula for every gear position in the transmission.

SPEED SAFE, NICK

Been running 3.42 gear set with my 80e for several years. Seems like a nice balance to me.