So I have a 79 Monte that I just LS swapped. Car was an all original 35k mile car with the 4.4 and 3 speed trans, for the swap I went with a 2002 ls1 and 4l60e setup out of a trans am. Now that I have been driving the car I’m noticing I can get the rpm’s above say 3200 (unless I’m in neutral or park) I guessing the factory rear gear is the problem since I have a OD trans now. Has always been my plan to change out the carrier for a posi and new gear ratio, I’m trying to figure out what would be a good gear ratio to go with. Car will be a cruiser and will see highway time also I ride on 205/75/14 tires and don’t see myself changing that out anytime soon I want to keep the original look of the car. I plan on going with a setup from quick performance what would your suggestion be for a gear ratio ? Stock LS1 and stock converter with tire size listed earlier.
Thanks !
View attachment 212152
View attachment 212150
View attachment 212151
I vote for a 3.42 for a fun cruiser. Here's why:
Tire height calculator - This is one of many. It's the one I like.
Tire Height Calculator by Wallace Racing
www.wallaceracing.com
Your tire height is 26.11"
The first gear ratio in the 4L60E is 3.059. 3.059 (first gear ratio) x 3.42 (rear ratio) = 10.46:1 final drive ratio in first gear. I wouldn't go any steeper than that. To put that into perspective, my truck has a 4L80E, which has a 2.48:1 first gear, the truck has a 4.10 rear gear and 32" tires. 2.48 x 4.10 = 10.17. The 10.46:1 you'd have with your 4L60E and a 3.42 will be plenty steep to get her off the line with good responsiveness. If you get onto it, traction will be a problem. With a 3.73 it's going to want to either spin the tires or jump right out of first gear before you can get across an intersection.
Lets look at 3.059 x 3.23 = 9.88. I like that better. Now let's look at Highway RPM for either a 3.42 or a 3.23
RPM Calculator - I like this one. Use the bottom section.
The 4L60E has an overdrive ratio of 0.696:1. With your 26.11" tall tire, with a 3.42 rear axle, it will turn about 1991 RPM at 65 MPH and will turn about 2604 RPM at 85 MPH. This is a good range. At 45 MPH (about when it is going to want to shift into overdrive with a stock tune), it will be turning about 1378 RPM. This is fine.
With a 3.23, it should turn about 1302 RPM at 45 MPH, 1880 RPM at 65 MPH and 2459 RPM at 85.
I think either gear would be a good choice. I still vote for the 3.42. My guess is that's the gear set the Trans Am had in it. Hope this helps.