This might help.

http://www.tciauto.com/tc/gear-ratios/

Note the difference between 1st gear in the 350 vs 1st gear in my 4le60 (1998 Z28). Compare final gear too: 1.0 vs .70 in the 4le60.

 

OD in the 4l60 is .70 but 3rd gear is 1:1 just like a turbo 350.

 

Agree but the OP stated he wants good street and cruising manners, not a race/drag car.

So the TH350 with only three gears will be 1:1 when cruising. So IMO there will be a big difference in rpm cruising at 75 mph with 3.42 gears vs 3.08 or numerically lower gears - 2.73 gears for example since no 4th gear or OD.

 

I'm tracking with gear ratio but when throwing the turbos and the higher stall into the mix I'm lost.


two 68/70s
3200 stall

 

You recommending 3.08 or 3.42 gear?

 

I would go 3.08 if you do a lot of highway driving . You will have plenty of torque to get moving.

 

3.42= 3078rpm@75mph. (28in tire)
3.08= 2700 rpm@75 mph. 28in tire)
3rd gear turbo 350

 

I'll hit the highway every now and then. 90% will be street time. Driving around town.

 

How do I calculate when I'll spool for boost. and what RPM will it kick in....3200-3400 stall. (2) 68/70s.