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

Jason14x

Not-quite-so-new-guy
Mar 28, 2021
26
3
Okay anyone know the best rear end ratio for best overall performance in my Monte? My Ls swap will be using either my 700R4 or the 4l60E that I got with the 5.3. As I mentioned the plan is 400-450 HP at the crank. I will want to be able to drive it on the highway and cruise comfortably at around 80mph. I am looking for the best trade off between off the line grunt and cruising comfort. I want to make sure so I can get the best posi rear end I can without having to spend more money .changing gearing. So I await you guys and all your knowledgeable advice !
Jason
 

motorheadmike

Geezer
Nov 18, 2009
7,025
113
Ottawa, Ontario Canada
4.88s.
 

Texas82GP

Just-a-worm
Supporting Member
Apr 3, 2015
6,746
113
Spring, Texas
Okay anyone know the best rear end ratio for best overall performance in my Monte? My Ls swap will be using either my 700R4 or the 4l60E that I got with the 5.3. As I mentioned the plan is 400-450 HP at the crank. I will want to be able to drive it on the highway and cruise comfortably at around 80mph. I am looking for the best trade off between off the line grunt and cruising comfort. I want to make sure so I can get the best posi rear end I can without having to spend more money .changing gearing. So I await you guys and all your knowledgeable advice !
Jason
What size tire are you running on the rear? You don't want to hear it but take it easy on either the 700R4 or the 4L60E at that power level. I built my 4l65E twice before I gave up on it and swapped to a 4L85E.

I like this RPM calculator. Use the bottom (manual entry) section....

 

L92 OLDS

Royal Smart Person
Mar 30, 2012
2,487
113
West Michigan
I have 400 HP at the wheels and run 3:73’s. It’s way too much gear for that power level on the street. I’m thinking about 3.08’s or 3.42s. Right now I am traction limited with the biggest drag radial I can fit.

I agree with Texas82GP. You will be ahead in the end if you sell those weak transmissions and go with a 4L80.
 

Jason14x

Not-quite-so-new-guy
Thread starter
Mar 28, 2021
26
3
3.42s? 3.23? 3.08? I would rather give up a LITTLE off the line than be winding the snot out of it. So 400-450 HP, going with the camaro 98-02 posi, 27 8nch tires and the type of driving experience I am looking for ....your suggestions??
 

64nailhead

Goat Herder
Supporting Member
Dec 1, 2014
2,888
113
Upstate NY
3.42

It will cruise great with mild cam with your OD and it will launch hard with the right converter.

If you decide to use a 4L60, then please hold off and get a 4L80. There isn't a good reason to use a 4L60 unless you got it for free and it was freshly rebuilt on someone else's dime. The ony positive thing about them is they are cheap to fix because the repair parts are super cheap due to they get repaired often.
 

-dw-

Apprentice
Mar 15, 2021
51
18
Central MN
I have a 700 behind a 455 with 3.41 and 26in tire. Last trip I made to the track (2hrs one way) the gps said 76mph average.
 
Oct 14, 2008
7,075
113
Melville,Saskatchewan
I have a 700 behind a 455 with 3.41 and 26in tire. Last trip I made to the track (2hrs one way) the gps said 76mph average.
I am surprised your 700R4 has lasted all these years. You must have got a good one and threw every possible upgrade in it. A far as the rear end ratio, what are your plans? You can just add a used 3 series Torsen or a new 3 series Detroit True Trac with Moser 28 spline axles, aluminum girdle cover and use your factory 3.73 gears. Easier set up, basically just set the back lash. It won't be outlandish and rpm will be acceptable on the highway with the .70 OD. Maybe throw a shift kit in the 4L65 or 70E, whichever one it is and keep a search out for a 2wd 4L80E. Crappier gearing and only a .75 OD gear but extremely strong. Of course any truck torque converter will be extremely tight, talking 1500 rpm stall, so that will also need upgraded.
 
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