4.875 final drive review

[rx3]

Apparently the stock flywheel is dampening some drive-train vibrations (probably occurring in the transmission and provoked by the fact that the engine deceleration forces are varying). Not all cars get it but it appears to be common with other Subaru models too. http://forums.nasioc.com/forums/showthread.php?t=942273
Since this noise is occurring when there's no significant load on the transmission, I doubt it is harmful.
It's not that bad, for instance, if you'd install a differential brace, you'll get more and permanent noise (not something you'd want as a highway commuter).

[rx3]

The LW driveshaft won't add any noise as this is after the transmission.
(The vibration is occurring in the engine and transmitted to the clutch and transmission. The lighter flywheel does transmit more vibration to the transmission and probably depending on some tolerances in the transmission, the deceleration noise will be more or less noticeable).

[mid_life_crisis]

Does anyone know offhand what ratio will get an A/T the closest to matching the overall final ratio of a factory M/T?

[M23]

F it...do the 4.88 on a MT. Let us know how it is on the highway

4.67 would be a nice and DD-realistic middle ground though ..too bad there's no inexpensive/affordable option and I think the only one avail (MFactory) is noisy straight cut teeth and a bit more expensive than Weir. Wish Weir made an affordable 4.67 option.

[kodyo]

Originally Posted by mid_life_crisis

Does anyone know offhand what ratio will get an A/T the closest to matching the overall final ratio of a factory M/T?

I believe the 4.88 will get you just a tad over the factor M/T, which is probably where you'd want be.

[ohnoitsthefuzz]

Originally Posted by ML

Weir Performance also has a FD kit. The Supra FD will fit ours. http://weirperformance.com/finaldrivegears.html

Which year range of the Supra FD fits ours??

[kodyo]

Originally Posted by ohnoitsthefuzz

Which year range of the Supra FD fits ours??

Mark 3 Supra I'm pretty sure.

[KoolBRZ]

Originally Posted by mid_life_crisis

Does anyone know offhand what ratio will get an A/T the closest to matching the overall final ratio of a factory M/T?

Here are the gear ratios for manual and automatic;

Manual transmissions
I=3.626, II=2.188, III=1.541, IV=1.213, V=1.000, VI=0.767
6th gear ratio, Differential ratio, and engine RPM's at 60MPH.
0.767 @ 4.10 = 2575 RPM's @ 60MPH
0.767 @ 4.30 = 2701 RPM's @ 60MPH
0.767 @ 4.55 = 2858 RPM's @ 60MPH
0.767 @ 4.77 = 2996 RPM's @ 60MPH
0.767 @ 4.88 = 3065 RPM's @ 60MPH

Automatic transmissions
I=3.538, II=2.060, III=1.104, IV=1.00, V=0.713, VI=0.582
0.582 @ 4.10 = 1954 RPM's @ 60MPH
0.582 @ 4.30 = 2049 RPM's @ 60MPH
0.582 @ 4.55 = 2168 RPM's @ 60MPH
0.582 @ 4.77 = 2273 RPM's @ 60MPH
0.582 @ 4.88 = 2326 RPM's @ 60MPH
0.582 @ 5.29 = 2521 RPM's @ 60MPH
0.582 @ 5.404 = 2575 RPM's @ 60MPH
0.582 @ 5.71 = 2721 RPM's @ 60MPH

An A/T 4th gear is 1:1, running 3357 RPM's @ 60 MPH. 5th gear w/5.71 FD @ 60 MPH runs @ 3334 RPM's, so 5th gear is still overdrive, barely, even with the highest FD you can get.

They don't make a 5.404 to 1 ring and pinion, so you can't match a manual's final drive. You can totally out-launch a manual though!

First gear, (launch!) comparisons;
3.626 M/T 1st 4.10 FD = 7101 RPM @ 35 MPH

3.538 A/T 1st 4.56 FD = 7046 RPM @ 32 MPH
3.538 A/T 1st 4.88 FD = 7069 RPM @ 30 MPH
3.538 A/T 1st 5.29 FD = 7152 RPM @ 28 MPH
3.538 A/T 1st 5.71 FD = 7168 RPM @ 26 MPH
Showing approximate redline speeds with each FD.

I'm getting the complete rebuild package with 4.88 gears delivered TOMORROW! I just ordered the entire kit, bearings, seals, shims, solid spacer, and etc. from Spence @ Weir Performance and it got shipped Friday. Here's the price I'm paying for all the parts;
FRS/BRZ 4.88 final $268.70 includes pinion depth shims
Install kit $313.94 (includes all diff bearings, solid spacer with shims, axle seals, pinion seal, pinion nut, gear marker)
ship $20.55
Total $603.19
Installation should be about half that, so roughly $900 - $1000 for everything replaced with all-new parts.

I'm getting this installed Thursday the 15th. I'll post here and let you know it turns out. Tire height for stock size tires, 24.62". Gear calculator website - http://www.csgnetwork.com/multirpmcalc.html

[mid_life_crisis]

Originally Posted by mid_life_crisis

Does anyone know offhand what ratio will get an A/T the closest to matching the overall final ratio of a factory M/T?

Originally Posted by kodyo

I believe the 4.88 will get you just a tad over the factor M/T, which is probably where you'd want be.

Originally Posted by KoolBRZ

Here are the gear ratios for manual and automatic;

Manual transmissions
I=3.626, II=2.188, III=1.541, IV=1.213, V=1.000, VI=0.767
6th gear ratio, Differential ratio, and engine RPM's at 60MPH.
0.767 @ 4.10 = 2575 RPM's @ 60MPH
0.767 @ 4.30 = 2701 RPM's @ 60MPH
0.767 @ 4.55 = 2858 RPM's @ 60MPH
0.767 @ 4.77 = 2996 RPM's @ 60MPH
0.767 @ 4.88 = 3065 RPM's @ 60MPH

Automatic transmissions
I=3.538, II=2.060, III=1.104, IV=1.00, V=0.713, VI=0.582
0.582 @ 4.10 = 1954 RPM's @ 60MPH
0.582 @ 4.30 = 2049 RPM's @ 60MPH
0.582 @ 4.55 = 2168 RPM's @ 60MPH
0.582 @ 4.77 = 2273 RPM's @ 60MPH
0.582 @ 4.88 = 2326 RPM's @ 60MPH
0.582 @ 5.29 = 2521 RPM's @ 60MPH
0.582 @ 5.404 = 2575 RPM's @ 60MPH
0.582 @ 5.71 = 2721 RPM's @ 60MPH

An A/T 4th gear is 1:1, running 3357 RPM's @ 60 MPH. 5th gear w/5.71 FD @ 60 MPH runs @ 3334 RPM's, so 5th gear is still overdrive, barely, even with the highest FD you can get.

They don't make a 5.404 to 1 ring and pinion, so you can't match a manual's final drive. You can totally out-launch a manual though!

First gear, (launch!) comparisons;
3.626 M/T 1st 4.10 FD = 7101 RPM @ 35 MPH

3.538 A/T 1st 4.56 FD = 7046 RPM @ 32 MPH
3.538 A/T 1st 4.88 FD = 7069 RPM @ 30 MPH
3.538 A/T 1st 5.29 FD = 7152 RPM @ 28 MPH
3.538 A/T 1st 5.71 FD = 7168 RPM @ 26 MPH
Showing approximate redline speeds with each FD.

I'm getting the complete rebuild package with 4.88 gears delivered TOMORROW! I just ordered the entire kit, bearings, seals, shims, solid spacer, and etc. from Spence @ Weir Performance and it got shipped Friday. Here's the price I'm paying for all the parts;
FRS/BRZ 4.88 final $268.70 includes pinion depth shims
Install kit $313.94 (includes all diff bearings, solid spacer with shims, axle seals, pinion seal, pinion nut, gear marker)
ship $20.55
Total $603.19
Installation should be about half that, so roughly $900 - $1000 for everything replaced with all-new parts.

I'm getting this installed Thursday the 15th. I'll post here and let you know it turns out. Tire height for stock size tires, 24.62". Gear calculator website - http://www.csgnetwork.com/multirpmcalc.html

Fortunately an A/T doesn't need to be as leveraged as a manual, due to the multiplication effect of the converter. I'll be watching to see the results of your 4.88 swap, as I'm looking at doing something similar, but was thinking in terms of something more like the 4.5 range. Now that I see that chart again, I realize that I might not even notice that change.

[Lunatic]

I said it before and I'll say it again, couldn't be happier with my AT 4.88 gearing. It's perfect for the AT.

[CSG Mike]

Originally Posted by mid_life_crisis

Fortunately an A/T doesn't need to be as leveraged as a manual, due to the multiplication effect of the converter. I'll be watching to see the results of your 4.88 swap, as I'm looking at doing something similar, but was thinking in terms of something more like the 4.5 range. Now that I see that chart again, I realize that I might not even notice that change.

The converter locks aggressively, so there's no torque gain there most of the time.

[mid_life_crisis]

Originally Posted by CSG Mike

The converter locks aggressively, so there's no torque gain there most of the time.

...and we can't reprogram the transmission's computer, so no changing that.

[CSG Mike]

Originally Posted by mid_life_crisis

...and we can't reprogram the transmission's computer, so no changing that.

I get frustrated with the AT not letting me downshift the way I want to when I drive the AT on track...

[Teseo]

Originally Posted by CSG Mike

I get frustrated with the AT not letting me downshift the way I want to when I drive the AT on track...

This is when MT shine, exist something to "hack" the cpu to make
the transmission downshifting more aggressive? Idk something like
the pedal dance