Gear Ratio (Final) Selection?

[assassin10000]

So, since my motorswap has been sorted, I've been considering changing my rear end gear ratio to make the most of the new power/torque.

The transmission is a W58 and I currently have 4.88's in the rear end. That ratio choice was made with the old motor, an almost stock 4age that probably barely had 100whp. So it gave me just enough to have fun .


Using the gear ratio's of my transmission, I did the calculations to see where the RPM's drop to on each shift. The shifts into 2nd & 3rd fall right into the torque band of my motor, and 4th/5th gear right at peak torque. So the transmission gear ratio's seem ok for the motor, given that I'm not willing to spend the money on a custom/short gear set.

4600 rpm into 2nd
5400 rpm into 3rd
6250 rpm on both 4th & 5th


I can basically get anything from a 3.73 to 4.56 relatively easily. I used an online calculator to get the MPH each gear would top out at with the different ratio's and my current tire size.

W58 & 3.73 = 42.6 / 73.9 / 109.8 / 140.0 / 178.8
W58 & 3.90 = 40.8 / 70.7 / 105.0 / 133.9 / 171.0
W58 & 4.10 = 38.8 / 67.3 / 99.9 / 127.4 / 162.7
W58 & 4.30 = 37.0 / 64.1 / 95.3 / 121.5 / 155.1
W58 & 4.56 = 34.9 / 60.5 / 89.8 / 114.5 / 146.3
W58 & 4.88 = 32.6 / 56.5 / 83.9 / 107.0 / 136.7


Right now 1st gear is almost completely useless, I basically blip it in 1st to get it started rolling and almost immediately shift to 2nd. Cruising it around I have no problems with it in 5th by 30mph, which IMO is pretty damn low. Despite that, 5th is at almost the same RPM on the freeway as if I had the original stock motor (4AGE) & trans (T50).

T50 & 4.30 = 65 mph @ 3700 rpm (80 @ 4525)
W58 & 4.88 = 65 mph @ 3800 rpm (80 @ 4675)


My car IS built for drifting, which isn't too far off from setting it up for track. With the old motor, I had JUST enough juice that I'd hit rev limit in 4th just before the main straight ended and I'd be ready to bring it sideways. I could get it to step out then, and make the turn sideways (barely) but wouldn't be able to maintain tire spin at that speed after the turn. Top of 4th was basically dead on 100mph. Now that I have more power, I'm fairly sure I could go faster and keep the tires spinning.

Any recommendations on how to choose one over the other?


Andrew

[Skylar]

Pick a final that puts you in a good spot in the powerband for all/most corners so that you aren't bogging in 'gear+1' or redlining in 'gear'. You know how the z33 6MT on SR gets rid of those bog-in-3rd, redline-in-2nd corners. Same deal. I wouldn't worry about picking a final to get the most acceleration since you have more power now but still on the shorter side so you aren't dropping a heap of revs on upshift.

Or get a built LS1, leave it in third and never change gear.

[assassin10000]

Hard to pick one based on the corners as I haven't been to the track with the new setup. Without that it becomes a little harder to decide. Good advice, but not much help to me at the moment.

Most acceleration = best use of engine torque (as long as traction is there). Gearing it just right will do this. With the 4.88 it feels like the gears (1-3rd) go by way too fast... even though it definately puts a smile on my face .

Andrew