Hey automatic tranny guys

[herb fraser]

As you may know I am using a 350 sb chevy , putting out about 310 hp, and a T350 tranny with 3.73 gears in the rear end. Last nite I went for a go cart ride and it was way to easy to spin the tires , I am thinking that I should change out the rears for a set of 3.08s
Most likely to many RPMs at high way speed . Therefore more noise and less gas millage .But mostly concerned about the jumping off from start, kinda want something better to drive, maybe I am wrong?

Any thoughts would be helpful
Thanks Herb

[myjones]

Herb
If you are going to do any road trips like power tour etc. you should use an online calculator and just fill in the blanks.
Think about cruising at 60 70 and 80 as the most common scenarios and look at the different RPMs for those speeds.
You just plug in your tire size, different rear gear ratios and final drive ratio for the TH350, there shouldn't be enough
loss from the TQ convertor to change much unless you get something wild for stall speed. You want to choose the
sweet spot so you aren't lugging the engine much below 1800 or buzzing it much above 3000 for those hwy speeds.

[wallace18]

IMO 3:73 rear gear is a bit much for the street with a 350 trans. You will be turning a lot of RPM's. Lots of guys down here with 350 Chevrolet engines in rods use the 700R4 overdrive GM transmission. With your setup I bet that truck is super fast right off the line though.

[herb fraser]

IMO 3:73 rear gear is a bit much for the street with a 350 trans. You will be turning a lot of RPM's. Lots of guys down here with 350 Chevrolet engines in rods use the 700R4 overdrive GM transmission. With your setup I bet that truck is super fast right off the line though.
Crazy fast off the line Hindsight is great , I would of use a tranny with overdrive, so I guess the cheapest way to go would be to change out the gears, not really worried about lots of speed off the line .

[NAZ]

Unless you're planning to run some large diameter rear tires, even the 3.08:1 rear gear ratio may give more RPM at cruise than you'd like. Run the numbers before you decide.

[herb fraser]

just ran the numbers and with my 32 inch tall tires with 3.73 gears 2300 rpm at 60 with 3.08 gears 1900 rpm , doesn't seem if 2300 rpm is to bad and don't know if it worth changing gears to get the rpm down to 1900

[herb fraser]

Unless you're planning to run some large diameter rear tires, even the 3.08:1 rear gear ratio may give more RPM at cruise than you'd like. Run the numbers before you decide.

Yes I am running tall tires they are 32 inch tall compared to my tires on my cobra which are 26 tall

[GoDadGo]

Herb,

32" tires with 3.08 gears will yield 2,265 RPM at 70 MPH with ZERO slip.
32" tires with 3.73 gears will yield 2,745 RPM at 70 MPH with ZERO slip.
You can pretty much add in 5-10% slip based on your converter choice.
Hope this helps & Good Luck Fellow Chevy Fan!

Steve

[herb fraser]

Thanks Guys, at this point I am going to wait and see how I like it after it all done and on the road , Next build a tranny with an overdrive :)

[Erik W. Treves]

Fwiw... mine has 3.08s