Best rear end ratio for my LS swap Monte SS posi upgrade.

[Texas82GP]

700R/60E 1st gear ratio is 3.059

3.059×3.42=10.46 final drive ratio in 1st. Pretty steep for launching. The 27" tire helps though.

3.059×3.08=9.42 better but still a bit steep.

700R/60E overdrive ratio is 0.696

That gear with a 27" tire should turn 2370 RPM with a 3.42 at 80 MPH. This is good.

With a 3.08 it should turn 2134 RPM at 80. This is a little low. At 60 it will turn 1601. A bit luggy.

1st gear in a 4L80E is 2.48.

2.48x3.42=8.42 will launch well with a good high stall speed converter.

2.48x3.08=7.64 too high in my view

Overdrive in an 80E is 0.75

3.42 should turn 2554 at 80 which is quite acceptable.

My vote is a 3.42 with an 80E with a quality ($$) converter with a stall speed somewhere in the 3400-3600 range.

Hopefully this post will help you see the math side of looking at it and help you find the compromise you want. In the end, it's a compromise and it depends on what you want the car to do.

I didn't look at this from a 1/4 mile RPM going through the traps perspective. Not my area of expertise.

My daily driver (truck) has 4.10's with 31.9" tires, an 80E and a 3600-3700 RPM converter (small cam). It's fun. It doesn't launch though. It will light those 12" tires right up with ease.

It just depends on what you want but the more you tune the combination to that, the happier you will be with the car

 

[Jason14x]

Texas....man thank you! Knowing the stats makes a HUGE difference. I was leaning towards 3.42s with the rough "Jason math" in my head. My wife calls it that because I can come pretty close to ratios and percentages and averages.in my head the "wrong way"!! Lol Thank you again !!

 

[64nailhead]

Jared hit the biggest issue for anything performance with a 700 or 60E - 1st gear is stupid low, which in turn makes the 1st-2nd shift rough.

At your HP level both a 700 and 60E will live if in good condition. But a stock built 4L80 will be in that car when you die. Alot of guys never figure to really turn anything up and are more than happy with making some tire smoke, but......if you ever decide to throw a 100 or 200 shot of nitrous at it for fun, then the 700/60E program will be lucky to live to the second shot whereas the 80E will be asking you 'is that all you got?'

From my understanding, you southerners find 2wd 80E's everywhere. Up here in snowland they are not easy to come across because every truck around here has been a 4wd for the past 35 years.

 

[Jason14x]

I just went treasure hunting and found 2!!

 

[oldsmobile joe]

i see no votes for 3.23. good compromise between 3.08's and 3.42's. had these in a cutlass with a 406 sbc and th700. this is what i'm going with in my next build of a 6.0 ls with 4l80e.

 

[Texas82GP]

Texas....man thank you! Knowing the stats makes a HUGE difference. I was leaning towards 3.42s with the rough "Jason math" in my head. My wife calls it that because I can come pretty close to ratios and percentages and averages.in my head the "wrong way"!! Lol Thank you again !!

You're welcome. I hope it helped. If you want some 60E/80E perspective, check out the early portion of the thread on my GMT900 (linked in my autosignature - if you're looking on a phone, turn it landscape to see the autosignature). I detail the swap from 65E to 85E. Just look at the difference between the output shafts. 700R/60E's are ok for stock output levels with no abuse. No more, in my opinion.

 

[Texas82GP]

i see no votes for 3.23. good compromise between 3.08's and 3.42's. had these in a cutlass with a 406 sbc and th700. this is what i'm going with in my next build of a 6.0 ls with 4l80e.

My intent was just to show a range, not necessarily to exclude the 3.23. That may well be the compromise.

 

[oldsmobile joe]

My interent was just to show a range, not necessarily to exclude the 3.23. That may well be the compromise.

no offense taken.

700R/60E 1st gear ratio is 3.059

3.059×3.42=10.46 final drive ratio in 1st. Pretty steep for launching. The 27" tire helps though.

3.059×3.08=9.42 better but still a bit steep.

700R/60E overdrive ratio is 0.696

That gear with a 27" tire should turn 2370 RPM with a 3.42 at 80 MPH. This is good.

With a 3.08 it should turn 2134 RPM at 80. This is a little low. At 60 it will turn 1601. A bit luggy.

1st gear in a 4L80E is 2.48.

2.48x3.42=8.42 will launch well with a good high stall speed converter.

2.48x3.08=7.64 too high in my view

Overdrive in an 80E is 0.75

3.42 should turn 2554 at 80 which is quite acceptable.

My vote is a 3.42 with an 80E with a quality ($$) converter with a stall speed somewhere in the 3400-3600 range.

Hopefully this post will help you see the math side of looking at it and help you find the compromise you want. In the end, it's a compromise and it depends on what you want the car to do.

I didn't look at this from a 1/4 mile RPM going through the traps perspective. Not my area of expertise.

My daily driver (truck) has 4.10's with 31.9" tires, an 80E and a 3600-3700 RPM converter (small cam). It's fun. It doesn't launch though. It will light those 12" tires right up with ease.

It just depends on what you want but the more you tune the combination to that, the happier you will be with the car

great info.

 

[Texas82GP]

no offense taken.

Thanks. I didn't think so. Me neither.

 

[Jason14x]

Compromise is good !