Here's an example (simulated using Car Test 2000)...

RX-7 w/~320 RWHP and 4.10 gears, P275/40-17 tires
0-60 mph - 4.17 sec.
0-100 mph - 10.27 sec.
0-60 ft. - 1.91 sec.
0-1/8 mile - 8.17 sec. @ 90.80 mph
0-1/4 mile - 12.59 sec. @ 114.15 mph
0-150 mph - 24.29 sec.
Top speed - 185.06 mph
40-70 mph - 3.29 sec. (3rd gear start)
60-150 mph - 19.65 sec. (3rd gear start)
100-150 mph - 14.02 sec. (4th gear start)

RX-7 w/~320 RWHP and 4.33 gears, P275/40-17 tires
0-60 mph - 4.12 sec.
0-100 mph - 10.24 sec.
0-60 ft. - 1.85 sec.
0-1/8 mile - 8.17 sec. @ 90.94 mph
0-1/4 mile - 12.61 sec. @ 114.91 mph
0-150 mph - 23.90 sec.
Top speed - 181.40 mph
40-70 mph - 3.08 sec. (3rd gear start)
60-150 mph - 19.21 sec. (3rd gear start)
100-150 mph - 13.73 sec. (4th gear start)

Basically, a little lower top speed, a little quicker (0.2-0.3 sec.) on the high end, and very little improvement below 100 mph and in the quarter mile.

If you're drag racing, you'd be better off with 4.50s or 4.77s, probably, but 4.33s aren't worth the performance gain, in my opinion. If you're not a drag racer, stick with the 4.10s. They're "free".

RX-7 w/~320 RWHP and 4.50 gears, P275/40-17 tires
0-60 mph - 4.10 sec.
0-100 mph - 10.18 sec.
0-60 ft. - 1.82 sec.
0-1/8 mile - 8.17 sec. @ 89.05 mph
0-1/4 mile - 12.61 sec. @ 115.35 mph
0-150 mph - 23.59 sec.
Top speed - 178.39 mph
40-70 mph - 2.95 sec. (3rd gear start)
60-150 mph - 18.89 sec. (3rd gear start)
100-150 mph - 13.48 sec. (4th gear start)

RX-7 w/~320 RWHP and 4.77 gears, P275/40-17 tires
0-60 mph - 4.70 sec.
0-100 mph - 10.05 sec.
0-60 ft. - 1.79 sec.
0-1/8 mile - 8.19 sec. @ 86.78 mph
0-1/4 mile - 12.61 sec. @ 115.49 mph
0-150 mph - 23.25 sec.
Top speed - 173.32 mph
40-70 mph - 2.76 sec. (3rd gear start)
60-150 mph - 18.57 sec. (3rd gear start)
100-150 mph - 13.26 sec. (4th gear start)

First thing you'll notice is that the 0-60 mph for the 4.77 gears jumped back up towards 5 seconds... that's because there would then be two shifts before 60 mph, instead of one. Car Test recommended shifting from 2nd to 3rd at 7,450 rpm at 59 mph. Holding 2nd gear a little longer would result in a lower 0-60 mph time, if that were all you were worried about, but note that 0-100 is down to almost 10 seconds flat with the 4.77s.

Second thing you'll notice is that the car gets noticeably quicker without any increase in horsepower in the higher speed range. 4.77 gears would gain you over a second (1.10 sec.) from 60-150 mph over 4.10 gears without any other changes. From 100-150 mph, you'd gain almost 0.8 seconds. Not bad for no increase in horsepower, and on a track with higher speed corners and straights the car would be substantially quicker overall.

And third, you'll notice that quarter mile performance doesn't really change. And won't, on street tires. The advantage of the shorter gears is lost on street tires, and would only increase the chances of tire spin on the launch. The Car Test recommended launch points for each gear set for maximum acceleration and minimal tire spin are:



4.10 - 1,600 rpm
4.33 - 1,300 rpm
4.50 - 1,200 rpm
4.77 - 1,200 rpm


If the car were on slicks, then you could take advantage of the gearing. Simulating 26x10.50" slicks on the same car, you'd get the following...

4.10 - 12.09 sec. @ 115.31 mph, 6,100 rpm launch
4.33 - 12.07 sec. @ 116.15 mph, 6,200 rpm launch
4.50 - 12.04 sec. @ 116.70 mph, 6,100 rpm launch
4.77 - 12.03 sec. @ 116.67 mph, 6,300 rpm launch

The results would be more noticeable with more horsepower, obviously, but you'd probably pick up a tenth or so and about 2 mph in the traps, just from the gearing change, all other things staying the same.

So how does a gearing change affect normal cruising rpm and highway mileage? With P275/40-17 tires...

Cruising - 30 mph, 3rd gear
4.10 - ~2,241 rpm
4.33 - ~2,367 rpm
4.50 - ~2,460 rpm
4.77 - ~2,607 rpm

Cruising - 70 mph, 5th gear
4.10 - ~2,700 rpm
4.33 - ~2,855 rpm
4.50 - ~2,967 rpm
4.77 - ~3,145 rpm

Mileage (estimated)
4.10 - 16.7 city, 26.2 highway, 19.9 combined
4.33 - 15.9 city, 24.9 highway, 19.0 combined
4.50 - 15.3 city, 24.1 highway, 18.3 combined
4.77 - 14.5 city, 22.8 highway, 17.4 combined

Originally posted by scratchjunkie
4k feather clutch then quickly but gradually floor it.