4.875 final drive review

[CSG Mike]

Originally Posted by Teseo

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

Not necessarily. I have issues with the FRS AT. I don't have these issues when I'm driving the twin clutch cars.

[GT86_PRAGUE]

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

I wrote Spencer last week, if he replies, I will order 4.88 kit too.
Together with new 2 way LSD.

[mid_life_crisis]

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...

Interesting, there must be some variance between units, because mine downshifts pretty well but upshifts have an annoying lag. That might seem that way partly because of throttle delay though.
In my case that's not on a track under sustained aggressive driving conditions, just on brief backroad runs when the opportunity presents itself, so take that for what it is worth.

[Tye300]

@CSG Mike is right. Sometimes the AT will not let you downshift if you are close to redline in your current gear. This is where the AT is at a disadvantage at the track. Some corners can be taken with a downshift from the MT, while the AT needs that you brake, then downshift to get out of that corner. This costs you some seconds compared to the MTs. Up shifts have almost no lag during the 1-2-3 shifts, but 3-4-5 shifts have a significant delay. It's not really a problem on track though as you don't use 4-5-6 gears often.(on our tracks here anyway) but yes, the downshift program has a significant disadvantage to the MTs.
Now if some company unlocks the programming and let's you do the high-rev downshifts, that would even the field with the MT-AT cars. Especially if the AT has a 4.88 or 5.1 FD.

[Lunatic]

I have not found the down shift to be a problem for me on the track, but I an not as good a driver as Mike. So for now I am very happy with the way my AT shifts both up and down.
I like to shift myself, but you would be surprised how well the AT works on the track in Sport mode, letting the car shift it's self. Later this year when I'm more consistent driving I'll do some comparison laps between manual shifting and sport mode shifting.

[mid_life_crisis]

Originally Posted by Tye300

@CSG Mike is right. Sometimes the AT will not let you downshift if you are close to redline in your current gear. This is where the AT is at a disadvantage at the track. Some corners can be taken with a downshift from the MT, while the AT needs that you brake, then downshift to get out of that corner. This costs you some seconds compared to the MTs. Up shifts have almost no lag during the 1-2-3 shifts, but 3-4-5 shifts have a significant delay. It's not really a problem on track though as you don't use 4-5-6 gears often.(on our tracks here anyway) but yes, the downshift program has a significant disadvantage to the MTs.
Now if some company unlocks the programming and let's you do the high-rev downshifts, that would even the field with the MT-AT cars. Especially if the AT has a 4.88 or 5.1 FD.

That sounds like a gearing issue more than an AT vs MT issue. Regardless of auto or man, downshifting at too high an rpm is going to damage something. The auto's computer simply prevents that. If you can't find the gear you want at the track you go to, then the rear end is the wrong ratio, correct? Interesting about the 123 456 difference, on the street I notice 1234 56, which I always assumed had something to do with the OD.

[CSG Mike]

Originally Posted by Lunatic

I have not found the down shift to be a problem for me on the track, but I an not as good a driver as Mike. So for now I am very happy with the way my AT shifts both up and down.
I like to shift myself, but you would be surprised how well the AT works on the track in Sport mode, letting the car shift it's self. Later this year when I'm more consistent driving I'll do some comparison laps between manual shifting and sport mode shifting.

The downshifts that felt "off" (happening mid-corner) are downshifts that should have been happening under braking. Specifically, Turn 2, turn 6/7, and Turn 17.

Your tune allows you to rev higher while in gear, but it won't let you downshift unless the lower gear will be under ~6.5k RPM or so.

On an unrelated note, I don't recommend you rev to 8k often.

[CSG Mike]

Originally Posted by mid_life_crisis

Interesting, there must be some variance between units, because mine downshifts pretty well but upshifts have an annoying lag. That might seem that way partly because of throttle delay though.
In my case that's not on a track under sustained aggressive driving conditions, just on brief backroad runs when the opportunity presents itself, so take that for what it is worth.

There is a lag, but it is crisp. Downshifts just don't happen at all.

[Tye300]

Originally Posted by mid_life_crisis

That sounds like a gearing issue more than an AT vs MT issue. Regardless of auto or man, downshifting at too high an rpm is going to damage something. The auto's computer simply prevents that. If you can't find the gear you want at the track you go to, then the rear end is the wrong ratio, correct? Interesting about the 123 456 difference, on the street I notice 1234 56, which I always assumed had something to do with the OD.

You are right about the ratios. What I am trying to say is that the MT can downshift to the selected gear before and during braking because you can push the clutch in. With the AT it has to be brake, wait for the revs to come down a bit, then downshift. I have a lot of vids that shows the beep sound the car makes when it says you can't downshift. I have to click the paddle again a few seconds later to get it to downshift to my preferred gear which takes a few secs off my time. Where as in an MT, the downshift is instantaneous.
To simplify it, you can engine brake into a corner in an MT, and the AT won't let you do it in track applications.
To get back on topic, if they make a program change to the AT ecu which will allow you to downshift in high RPMs, then an AT with a 4.88 or 5.1 FD could be a track star. As of now though, the MT is at an advantage. You could play with FD ratios all day but the AT ecu is the weak link. That's coming from an AT owner.

[Lunatic]

Originally Posted by CSG Mike

On an unrelated note, I don't recommend you rev to 8k often.

Whoops, didn't realize I was going that high.

[AJPG]

Originally Posted by CSG Mike

The downshifts that felt "off" (happening mid-corner) are downshifts that should have been happening under braking. Specifically, Turn 2, turn 6/7, and Turn 17.

Your tune allows you to rev higher while in gear, but it won't let you downshift unless the lower gear will be under ~6.5k RPM or so.

On an unrelated note, I don't recommend you rev to 8k often.

The only reasonable fix for that would be playing with the final drive for each track... And yes is the only annoying thing I found in the AT (bip bip) each and every time the computer doesn't agree with the down shift.

[GT86_PRAGUE]

Originally Posted by Dustin

OEM Toyota part numbers that you can use. Obviously you would want under a 4.10 for taller gearing.

41201-80125 : 3.58
41201-80050 : 3.73
41201-80052 : 3.91
41201-19605 : 4.10
41201-29606 : 4.30
41201-19557 : 4.56

You can also give Spence at Weir Performance a call. He has many options available, both taller and shorter, and as I said before, you can not beat his prices.

Where did you get these numbers?
Do you know number for 4.88? Thanks.

[KoolBRZ]

I got my 4.88 FD parts today. They were sent to Maryland by mistake, so they got here today instead of Monday. I'm leaving my car with Wryann of VIP performance in Portland OR. tomorrow at 9:00 AM. I'm also going to ask for before and after dyno runs in 4th gear to estimate the comparative power increase. I'll be giving feedback this weekend after I've driven it a bit. I think this is going to be the best improvement I've bought for my car.

[AJPG]

Originally Posted by KoolBRZ

I got my 4.88 FD parts today. They were sent to Maryland by mistake, so they got here today instead of Monday. I'm leaving my car with Wryann of VIP performance in Portland OR. tomorrow at 9:00 AM. I'm also going to ask for before and after dyno runs in 4th gear to estimate the comparative power increase. I'll be giving feedback this weekend after I've driven it a bit. I think this is going to be the best improvement I've bought for my car.

This will be interesting

If you are running a bicycle (road bike or mountain bike it doesn't matter) and you couldn't go up hill then down shift does it give you more power???
More like mechanical advantage I think.

Anyway I'm with the 4.88 since it release (more than one year I think) and I love it, also due to my short commute and frequent back road use I couldn't stop thinking on how it will behave with a 5.1

Congrats on your mod and enjoy