moe4541

I have a 5.3 twin turbo build that I'm needing suggestions with on rear end gears. This truck is just a street truck, no racing. 700HP goal.

I have a 83 Shorted truck with a 12 bolt 5 lug posi or the 10 bolt stock one. I was told 3.08 gears would be best for me.

Specs......
5.3 (2002 Tahoe)
Cam-Stage 2 212/218, .550"/.550" (can't remember if its 112 or 114LSA)
stock heads
Brian Tooley double springs .660"
BT pushrods 5/16"
TH350 built for 850HP
3200-3400 stall converter
(2) T4 .68/70
20" rims on 275 tires

If you have any questions to help with responding please ask. This is my first turbo build.......

moe4541

83 Shortbed!!

gsxrred1000

iTrader: (3)

If it's not a race truck go with 3.42 or whatever close equivalent with 12 bolt. 3.08 are pretty tall unless your looking for 2k rpm at 80mph. 700 wheel is a lot for a gen 3 motor also.

dallasbound

Ok, I was looking into 342 gear. I just want the700hp for the dyno. I don't plan to keep the boost high. I want to daily drive it.

gsxrred1000

iTrader: (3)

Yup they will work great. I drove around with 4.10's at 600whp til I felt like changing gears and making it threw the traps at 1/4.

dallasbound

So 342 is ideal. 308 would work.....with the stall and turbo size where would the cruising rpm be amd when will it start to spool

gsxrred1000

iTrader: (3)

To many variables to answer that.

3 window

iTrader: (1)

I had a 3.08 gear in my Nova and it hung on the converter a little too much for me. Didnt have the super low cruise rpms that you'd think (because of the converter). I swapped I a 3.31 and the car's a completely different animal. Spools just as fast, cruises better because it locks the converter up better, has better pickup etc. I'd go 3.42 over the 3.08 for all the reasons mentioned above. BTW, I've got the $450 PTC converter.

moe4541

I got my converter built for about $500 at a local shop.

Ok I'll at the 3.42 gears.....

moe4541

I know

Game ova

2:73 in a 3700# f body, with a 9.5 5200 converter.....LOVE the gear. Th400 btw.

moe4541

Is this a street or race car?

Game ova

Street car in every sense, full interior, heat A/C, extra amps/sub....exhaust out the back. And drive the 1 1/2 hours to the track.

dlandsvZ28

I went from 3.23 (A4) to 3.73, and then back to 3.42, and finally back to 3.23.

My Procharged D1 1998 Camaro is not a race car either, just wanted lots of rwhp (currently 565 rwhp) and excellent street and highway cruising manners.

I want to cruise at 75 mph at a lower rpm (around 2100) than the higher rpms I had with the 3.42 or 3.73 gears. I am running stock size tires - 25.67 tall. Better gas mileage too, at lower rpms at 75 mph.

But the desired rear end ratio also depends upon how tall a tire you will be running.

As said before there are many variables to consider one of which is the stall speed of your converter.

With a truck and with much more weight I certainly wouldn't want a high stall speed along with a taller rear end ratio - 3.42 - 3.73 or higher.

It's no fun cruising at 45 mph with the engine racing at 3 K rpm trying to move 4 K + lbs because you have a high stall speed and a tall rear end ratio.

All around drive-ability is your goal so in my opinion I would choose a lower stall speed along with a lower rear end ratio. You will have plenty of rwhp when and if you need it - all you need to do is stump on the go-fast pedal.

moe4541

Ok, I'm tracking.......That converter cost me almost $500, I stuck with it for now. the stall is 3200-3400. My original build wasn't for a truck, this was a last minute pick.

I ordered 308 and 342 gears. I have two turbos going on and I didn't know how to calculate all of these numbers and what determines what when I would like it to boost.

gsteele

Rear-End Gearing Simplified. ... "Tall" gears and "short" gears are referring to the gear ratios. Tall (high) gears have LOWER numerical numbers such as 2.79, 2.90, 3.00, 3.25. Short (low) gears have HIGHER numerical numbers, such as 4.11, 4.30, 4.56, 4.88, 5.13, 5.36, etc.

Pro Stock John

iTrader: (34)

So you are running a 28.0 tall tire? I'd run at least the 3.08 if you have it lying around. Also if you are trying to hook on street tires (not drag radials) you'll want to go less gear.

dlandsvZ28

I think in an earlier post he said 20 inch rims and 275. A Nitto 275 X 40 X 20 is about 28.62 inches tall. A 50 would be even taller.

275/40R20 106W XL 207040 7.2 28.62

Guess he needs to factor in first gear ratio too in the Th350 along with final rear end ratio + tire height to get final drive ratio.

moe4541

Yes 28. I have a 3.08 and ordered a 3.42. My 3200 stall will hook the tires different from the 3.42.

moe4541

I'll have to call the shop who built the trans to get the gesr ratio