this rear axle stuff is confusing, but I have to go posi

[LockDoc]

Originally Posted by Slowguy

Is 3.73 a good ratio for the 4l80e trans?...but I guess that wouldn’t matter if I convert to limited slip?

Yes, the 3.73 should work good for you. I run a 3.73 with my LS1/4l60e combo and it works good.....

LockDoc

[Mike C]

Originally Posted by LockDoc

Yes, the 3.73 should work good for you. I run a 3.73 with my LS1/4l60e combo and it works good.....

LockDoc

As LockDoc says, it will work, but the 2.48 first gear combined with the 3.73 gives you a 9.25 overall first gear ratio while his 4L60E with its 3.06 first gear gives him an 11.41 overall first gear ratio. IMO, the 4L80E really needs 4.10 gears to maximize low speed performance, but it suffers on the highway because it only has .75 overdrive instead of .70 of the 4L60E.

The one feature of newer vehicles that makes them performer so well is the much better chosen and implemented gear ratios and transmission speeds. They accelerate like 60's muscle cars and cruise like 70's sedans with 2.56 gears.

[LockDoc]

Originally Posted by Mike C

As LockDoc says, it will work, but the 2.48 first gear combined with the 3.73 gives you a 9.25 overall first gear ratio while his 4L60E with its 3.06 first gear gives him an 11.41 overall first gear ratio. IMO, the 4L80E really needs 4.10 gears to maximize low speed performance, but it suffers on the highway because it only has .75 overdrive instead of .70 of the 4L60E.

The one feature of newer vehicles that makes them performer so well is the much better chosen and implemented gear ratios and transmission speeds. They accelerate like 60's muscle cars and cruise like 70's sedans with 2.56 gears.

I was hesitant to answer his question not knowing anything about the 4l80 trans. That difference would pretty much make the 3.73 a no-go for that transmission. I originally had a 3.08 behind the 4l60e in my Panel Truck and that did not work for me. It made the transmission overheat when it was in OD. Thanks for the clarification. I will keep that in mind in the future.

LockDoc

[truckster]

There are alternatives to the posi, such as the Tru Trac.

What is your intended use for the truck, and what are you hoping to get by adding traction?

[Mike C]

Originally Posted by LockDoc

I was hesitant to answer his question not knowing anything about the 4l80 trans. That difference would pretty much make the 3.73 a no-go for that transmission. I originally had a 3.08 behind the 4l60e in my Panel Truck and that did not work for me. It made the transmission overheat when it was in OD. Thanks for the clarification. I will keep that in mind in the future.

LockDoc

I was not implying you were wrong just that he might want to think about his final application. You were absolutely right that it would work, and it would be a BIG improvement over a 3 speed trans. The 4L80E has the same first 3 gears as a TH400 plus a .75 overdrive. The big drawback to the 4L80 IMO is the expensive electronic controller required to run it.

These trucks came with 3.08 and the TH400 so the 3.73 would be a big improvement compared to the 6.776 ratio in first gear that application has!

[Slowguy]

I'm not really into burnouts; as many are. I'm the guy that hates to see hard earned money needlessly sprayed all over the side of my car and painting on the asphalt.

I am going to turbo this truck. So it will have at least 500-550 to the wheels...with the boost at a minimum. It could have much more if the truck could apply it to the road. I don't want racing slicks. I want normal performance tires. Probably only 275 or so in the rear.

I think it would be very important at this power level to have both wheels apply torque to the ground simultaneously or I'll just be driving around spinning one wheel everywhere I go. It probably won't do much but I'd imagine adding the rear gas tank, battery, and the air compressors near or over the rear axle will help with traction as well.

I'd call it a hopped up daily driver. Cam is light to keep the power a little lower in the band but tons of power up top when i want it. The 4l80 should be a good dd from what I've read.

[Mike C]

It will be. And turbo cars don't like a lot of gear. You will be happy with the 3.73 most likely. It may even want LESS gear than that, but the 3.7 are a good start. BUT the carrier break is at 3.73 and up on a truck 12 bolt. So if you wanted to run 3.42 that would require a different carrier.

If you want new car driving characteristics on the highway with the 4L80, the 3.42 gives you a 2.565 final drive and a overall first gear of 8.48 which may be better for the turbo. Additional load helps build more boost faster.

Everything should have a limited slip IMO. No matter how little power it makes. All I can say is learn as much as you can about the power characteristics of your motor and what the final goal is. Nothing hurts more than buying things twice.

And at those power levels, you are starting to reach the limits of the truck 12 bolt. Depending on if it is going to spend anytime with sticky tires at the strip, a custom axle housing might be a good idea. A Dana 60 with Big Ford housing ends and custom axles with 3.54 gears would be slick.

Speed costs money, how fast do you want to go as they say.

[Slowguy]

I know all too well about purchasing what I don't need or will end up not wanting and then it sits on a shelf. I've already done a little of that on this build. It's why I ask so many questions and spend days searching. LOTS of info to read but sometimes difficult to find EXACTLY what you are doing that someone has already done. 67 c10, with a 3.73 ratio, lq4 engine with a custom tune boosting to about 500 hp, 4l80e trans with a 3200 stall circle d converter, a transgo shift kit, and an elgin 1839p cam....see what I mean? That's more variables then just searching "ls swap 67 c10". Then on top of that, you get many opinions and what has worked well for "person 1", then "person 2" says something completely opposite (and that opposite opinion obviously worked well for person 2). So all that just adds to my confusion.

Unfortunately, what usually ends up happening, is exactly as you described. I end up buying what I think may work, I don't like it but it gave me a perspective to know what or how I want to change it, and I purchase a new option.

I just know I want posi. I'd like the first gear not to crawl like I've read many stock c10 are from factory, and I'd like to cruise down the road at 70 mph somewhere in the 2-3k range. This build is like many others I've done....I go all it, without ever even spending time driving the original vehicle. I bet I have a total of 10 miles driving the original truck. I can tell you, in comparison to any vehicle 1980 or newer, it was super unstable-feeling and sounded like it was fully revved at about 60. It would clunk and felt like it would sway off the road with any sudden movements.