More questions ---GT350R gearing

Cassidy · Sep 25, 2007

Thanks to all who responded to my question regarding gear ratios for the GT350R.

Shlby66 responded with the following:
“R-Models received a 3.89:1 gear ratio as standard. Other ratios (i.e.: 3.50:1, 3.70:1, 4.11:1, or 4.30:1) were available”.

For the transmission dummy like myself!
1) What does 3.89:1 mean?
1) How does 3.89:1 compare to what was standard gearing for a 65 street Mustang?
2) Is 3.89:1 considered low gearing for short tracks and low-end torque? Or is it high gearing for that long straightaway?
3) Was there anything else that made the R model transmission different?

Thanks again for your input
Richard Cassidy
GT350R recreated, 5R102

Jerry_Moss · Sep 25, 2007

Hi Richard

All this has nothing to do with the transmission ratio! Only rear end.
3,98:1 means simple that your driveshaft has to make 3,98 turns to turn
the rear wheel one time. Wich means 4,11 is a shorter rear end ratio.
If you have a standard 3.00.1 ratio means that going 60mph the cars
rpm is about 2500 wich will be maybe 3200 with a 3,89.
Acceleration is faster with higher gears. Just ride your mountain bike and you
will find out.

Bye Jerry

rsimkins · Sep 25, 2007

Richard,

1) 3.89:1 referes to the ratio of the rear end. For every 3.89 revolutions of the drive shaft, the wheels will turn once. A 3.89 is considered to be a ratio suited to acceleration, though not as much as say a 4.11 or 4.30:1 gear. 3.50:1 is much more of a highway gear.
2) A standard Mustang might have a ratio of 3.00:1 for economy. Rear end ratios were chosen by the factory based on the intended use or market for the car. Some options in gearing might be possible when the car is ordered. Case-in-point would be a later car (1970 era) with the "Drag Pack" option which would get you 3.91 or 4.30 gears.
3) Yes 3.89:1 is considered to be low gearing though not so much as 4.11:1 or 4.30:1.
4) 3.89:1 pertains to rear end ratio not transmission ratios. Transmission ratios for the Borg Warner T-10 installed in the R-Model were: 1st - 2.36:1, 2nd - 1.62:1, 3rd - 1.20:1, and 4th - 1.00:1. The optional transmission had the following ratios: 1st - 2.20:1, 2nd - 1.64:1, 3rd - 1.31:1, and 4th - 1.00:1.

Hope this helps.