JBCO
10-11-2011, 05:51 PM
So the time is sneaking up for me to put together my rear differential on the Mustang.
Intended plans for the car are primarily street driven with no real track or race time. Just a really quick, fun to drive cruiser.
I've gotten used to driving my shop 2011 Subaru STI -- love the gearing, drive-ability & overall power band.
Optimum driving and power band on the STI is 3250-6000 engine RPM's which should be nearly identical for the Mustang (possibly even lower depending on spool).
With the above mentioned plans for the Mustang I wanted to post up my rear differential gear thoughts and make sure I'm not missing any big picture stuff. I know they are two entirely different cars...but I'd like to obtain a similar feel regarding shifts & powerband. The calculated RPM's and specs below I got from various online calculators.
2011 STI Specs
Tires : 245/40-18 (25.7" diameter)
Rear Diff : 3.545
1st gear = 3.636
2nd gear = 2.235
3rd gear = 1.521
4th gear = 1.137
6th gear = .756
Engine RPM
1st gear @ 35mph = 5898
2nd gear @ 55mph = 5697
3rd gear @ 75mph = 5287
4th gear @ 95mph = 5006
6th gear @ 65mph = 2277 (cruising)
Mustang Specs (planned/tentative)
Tires (Rear) 345/30-19 (27.2" diameter)
Rear Diff : 4.30
1st gear = 2.98
2nd gear = 1.99
3rd gear = 1.35
4th gear = 1.0
6th gear = .62
Engine RPM
1st gear @ 35mph = 5540
2nd gear @ 55mph = 5814
3rd gear @ 75mph = 5378
4th gear @ 95mph = 5046
6th gear @ 65mph = 2141 (cruising)
I understand from searching around on here a bit that an overall optimum ratio (trans gear x rear gear) should be around 10 -- and both cars/spec sheets above violate that by about 2 points...but I genuinely enjoy the driving set up this way.
The 4.30 rear gear just seems crazy to me -- but looking at the numbers and given the large rear tires it does make sense.
Thanks for input and feedback...
Intended plans for the car are primarily street driven with no real track or race time. Just a really quick, fun to drive cruiser.
I've gotten used to driving my shop 2011 Subaru STI -- love the gearing, drive-ability & overall power band.
Optimum driving and power band on the STI is 3250-6000 engine RPM's which should be nearly identical for the Mustang (possibly even lower depending on spool).
With the above mentioned plans for the Mustang I wanted to post up my rear differential gear thoughts and make sure I'm not missing any big picture stuff. I know they are two entirely different cars...but I'd like to obtain a similar feel regarding shifts & powerband. The calculated RPM's and specs below I got from various online calculators.
2011 STI Specs
Tires : 245/40-18 (25.7" diameter)
Rear Diff : 3.545
1st gear = 3.636
2nd gear = 2.235
3rd gear = 1.521
4th gear = 1.137
6th gear = .756
Engine RPM
1st gear @ 35mph = 5898
2nd gear @ 55mph = 5697
3rd gear @ 75mph = 5287
4th gear @ 95mph = 5006
6th gear @ 65mph = 2277 (cruising)
Mustang Specs (planned/tentative)
Tires (Rear) 345/30-19 (27.2" diameter)
Rear Diff : 4.30
1st gear = 2.98
2nd gear = 1.99
3rd gear = 1.35
4th gear = 1.0
6th gear = .62
Engine RPM
1st gear @ 35mph = 5540
2nd gear @ 55mph = 5814
3rd gear @ 75mph = 5378
4th gear @ 95mph = 5046
6th gear @ 65mph = 2141 (cruising)
I understand from searching around on here a bit that an overall optimum ratio (trans gear x rear gear) should be around 10 -- and both cars/spec sheets above violate that by about 2 points...but I genuinely enjoy the driving set up this way.
The 4.30 rear gear just seems crazy to me -- but looking at the numbers and given the large rear tires it does make sense.
Thanks for input and feedback...