Hello all, first off I am somewhat limited as my truck is a 68 with the truck 12 bolt. I believe I can only find 3.08, 3.42 (maybe aftermarket) and 3.73.
So a little history, the truck weighs right around 4000 pounds with a turbo 5.3 with a T56 I had 450 RWHP with a 4.11. I have worked the tune and am a little better now. I recently swapped to the 4l80 with a 2400 TC from the T56 so the rear gears need a change from the double overdrive.
I do like to drive this truck and take it on a few trips so I would like to bring my cruising RPM down and I understand the turbo likes the load from the numerically lower gearing. Right now with the 4.11 the first 2 gears fly thru very quickly and are not very useful.
I do go to the track on occasion but not too much.
What are your thoughts?
Thanks
Dave

 

Turbos don't "like load", that is one of those internet rumors that wont go away. Gear it just like you would an NA car. Steeper gear for more aggressive performance, lower numerically gear for better highway mileage and more top speed.

 

but I read it on the internet... Ha
Ok thanks for that. My turbo is a smaller T70 so it spools very quick and easily. I will do some more digging.
thanks

 

Just go with a little taller tire for the street and keep it the way it is imo. Otherwise 3.73's if you must. Sweet ride!

 

You can only go up to a 3.73 if you have 4.11 gears now with out changing the carrier. The 3.73 and numerically higher gears are a series 4 carrier in the 12 bolt and the 3.42 and lower are a series 3.

I have a th350 with 3.08 in my turbo 5.3 69 c10 but really wanting to swap everything out for a 200-4r and 3.73's but I really don't wanna buy a new carrier and gears! lol I'm running 295/50-15 26" tall tire too though.

 

That's a short tire... Mine are 285/50 18 at about 29.25 tall.
If I remember correctly I swapped to the series 3 and used the "thick" gear but I don't remember for absolute it has been a while. Originally I had a 4l60 with the 3.73 then the t56 so I swapped to the 4.11 which was great for the hwy driving.

 

Sorry to highjack , but I have never heard that. My 3.42 gear and 30" slicks are killing me then! I need 3.90's then!!!

 

Yea, heres a rambling post I made about it on my website if you want to read some http://atomicfabandperformance.com/i...ing-low-gears/

 

Nice link Atomic,
Thanks guys for the input. I have yet to make any changes as I was in the process of seeing how this runs with the current setup. I do know it will rev very quickly as it is.
Thanks
Dave

 

I just read this and stuck my finger in a spinning turbo like you suggested.