Gearing Options and Diff options
 

Back in the day we would swap out our stock gearing for some TRD 4.56 or 4.88. 4.88 was nuts in a 3TC or 4AGE corolla. The 4.88 would give you crap gas mileage on the freeway but driving it in the lower gears was a blast.
Know the Miata MX5 and s2000 guys do gearing change for a little more acceleration. Thinking about going this route since I live on a island and our freeways are usually full of traffic anyway.

Does anyone know of what gearing options will be available. I am a little confused on the actual rear end in the FRS/BRZ. Have read R160 and some where else Lexus IS rear end. Hope it is the IS300 rear end.

Also anyone got any idea where the speedometer sensor is? Off the trans or off the wheel hubs? Hope for the manual FRS/BRZ the sensor read off of the trans.

Now to look at some BRZ/FRS under carriage pics and diff options...

The vehicle speed is most likely calculated from the wheel speed sensors in the stability control module and then sent along the high speed CAN network to the various control modules. That's how the Rx-8 does it for example; there is no separate vehicle speed sensor. You would have to figure out which module needs to be reprogrammed.

There may be some ring and pinion options available once we can nail down more details on the differential.

Speed sensor could be off the front wheels, the 86 to me looks like it has some sort of ABS/non locking brake setup (my partners current lancer has something similar, stops pretty good actually) and id dare say it would have a sensor of some sort back to the ecu then off too the cluster.

Could probably tell by watching 1 of the drift vid's the speedo doesnt bounce up and down with revs compared to g/box/diff driven speedo. Or maybe it does but i couldn't see that it does.

Also regarding ratios, i doubt we would have any trouble with stock fitment. 6sp would already have a better ratio then we had before and only serious track/racer type would have a purpose for different ratios.

Would ratio matter, well to some it may, at least a lower diff ratio, but then your MPG goes out the window.

I honestly think other then cams and a ecu tweak (along with intake and exhaust, which is almost a given) there wont be much needed done to this car.

It already appears to have light weight (well lighter then the usual) equipment like flywheel, crank etc etc.

The $$ spent vs gains will be terrible compared to the 4age, i mean i cant see any reason why lighter flywheels, ground down crank, lighter pistons etc will have any marginal effect for majority of people. Serious track/racer will see results but the the average Joe Blow it will be a expensive and fruitless exercise.

My 2c

It's the IS housing. So aside from whatever comes standard, figure on being able to swap in:

2.937:1
3.583:1
3.909:1
4.083:1
4.100:1

Differential-wise, there's the OEM torsen (that might be the same unit that's in the ISF), an OS Giken, some other clutch type that I can't remember and whatever crappy viscous/open diff that comes in the vanilla IS.

Found this on the net on what diffs can fit the IS300. Also below is a list of the LSDs available. I guess OS Giken can be added. Also read that MkIII supra diffs fit. Gearing options from supras run from 3.27/3.13 to 4.27. Wonder what the FRS/BRZ rocks?

Differentials:

1. TT supra (93.5 - 98)
2. GS4's
3. Automatic Supra rear
4. MKIII 86-88 ?


LSD's

1. TRD
2. KAAZ
3.OS Giken
4. Torsen
5. Viscus

Really think for the $$$ if the gearing is not stupid crazy priced like powerhouse gearing is ($1300) coupled with a OS Giken you can have some serious fun.

Is there a way to change a single cog, say make 6th gear longer for mpgs, and then use shorter final drive? :O

Educated guess: 4.10 for the manual

My guess is 3.53 or 3.73

I agree with this range, considering the excellent MPG rumors floating around.

Also, I doubt they would go too short, as that would hurt the aftermarket, which they are trying to support.

I am sure 4.10's would be fun w/ more HP

Yes, technically you'd be changing two gears (gear set) but it's totally doable. Assuming no major changes have been made to the design of the gearbox, you should be able to use the 6th gear set from an older AZ6 if one has a taller ratio. Or you could just call up someone like PPG and ask nicely.

Also keep in mind however that you have to do a bit of research on the synchro matching of the 5 to 6 transition.

If you make 5 super short, and then 6 extremely long for highway cruising, the synchro will not have time to slow down the trans during a normal shift between the two, and it will grind on any sort of quick shift, even when in perfect condition. There is a limit to the RPM drop that you can achieve based on the synchros.

You'd have to make a pretty extreme change for that to be an issue though. Even the not particularly impressive synchros in my WRX will handle a 3-5 shift without any issues (2-5, not so much :)).

LOL done a 2 -> 5 instead of 2 -> 3 a few times??:D

Hey it's better than a 4 -> 1 instead of a 4 -> 3.

I promise you this, within a few months of these coming out, there will be a few "I shifted from 4 to 1 on accident and now my engine is making a tapping sound" threads. If the shift pattern is like the s2k, we will see a lot of these.