Mr Johnson

Have to echo Jacob's point! The install of the TRD piece is pretty easy and should require no setup/shim. But if you feel better about it take it to someone that has done it before.

I've owned both types of differentials now (on different cars) and would say that for day-to-day driving the Torsen unit is an excellent unit. If they were the same price and I didn't have serious horsepower concerns I'd stick with the Torsen. That said, I own the TRD clutch-type now.



You are correct that the TRD has a "lower", numerically higher, ratio of 3.76 vs 3.26 and you are also correct about the result (performance, less top end) but I don't think I understand your example. If the driveshaft spins once and you have a 3.76 differential ratio you need to spin the drive shaft 3.76 times to get one revolution of the wheels. With a 3.26 it only turns 3.26 times for every wheel revolution.

You want lower gearing to a point. Then as your car makes more and more power you want to start moving to higher gearing to extend the amount of time your engine spends in the peak power band.

As I've said before in response to your making this statement, "It just aint so!". Straight line, full throttle, TC kicks in wheel spins. LSD makes a difference. Straight line, partial throttle, rainy day, wheel spins, LSD makes a difference.

RMMGS4

iTrader: (5)

Bit,
think of it this way. A car burning rubber with no LSD lays down only one black streak on the road, while an LSD car lays down two black streaks. Your traction is doubled if both tires are grabbing.

Ive got the the RMM LSD, TC and valve body upgrade. On a grippy surface launching at around 1500 rpm I will still spin the tires for a few feet before grabbing. On a smooth asphalt surface and a little more launch rpm, I can spin "both tires" for about 15-20 feet.

I have Michelin Pilot Sports 285/30-19's w/10 inch rims out back by the way.

As far as the gear ratio debate is concerned, I'd be curious to see how easily someone with similar mods as me can break the tires loose with the main difference being the TRD 3.26 gearing. Who out there can compare launching results with what I just described on my 3.76 geared car?

One of these days, I will try to get my car to the dragstrip as soon as summer rolls around and will post my 60 ft. times.

cyclemax

This assumes the the GS is rpm or speed sensor limited. Most cases with higher gearing will just result in slightly higher revs at a given speed. If the car is drag-limited, you may get more top end, depending on where you peak hp is. A classic example of this is the late 80's Mustang GT's that would go faster in 4th than 5th. 5th put the engine below it's peak power, so it couldn't push it thru the wind at that speed.

Is the GS4 speed, rpm, or drag limited? Also, did anyone recalibrate their speedo when they changed their gearing?

Mean Gene

It's not necessary to recalibrate the speedometer as it reads off the ABS sensors & not the tranny. As long as U don't alter the rolling diameter of your wheel/tire combo ( roughly 25.3", I recall ) by more than maybe 5%, things will be OK. I've verified my speedo after the RMM LSD install by several other methods ( mileage markers, another car's speedo & lastly by a State Trooper's radar ). Fortunately, the last method was via my friend who happens to be a Trooper & NOT by a ticket ( but that's another story!! ):eek:
FWIW - the GS is speed-limited via a 149 mph governor ( soft limitation engineering ).

FWIW #2 - I've been asked to compose a writeup of the RMM LSD by LS400 & hope to have it to him by the end of the month ( deadline's Valentine's Day ). It's been over 2 years since I installed it so there'll be no pics but I'll have some subjective views on things as well as some objective data from the G-Tech Pro & the dragstrip.

JacobT

Rominl,

True or false. RMM 3.76 gear ratio can light up your rear wheels easily but the different gear ratio will confuse the tranny ECU, so you may hit 6500 rpm rev. limiter during hard accelerations.

I was wondering if anyone has opened up the RMM unit and swapped out the ring gear with stock 3.26 gear? By doing so, you'll get a Torsen style LSD without worring hitting the rev. limiter

tomtnc

If you swapped the stock 3.26 ratio ring gear into the 3.76 ratio TRD/RMM center section, you would destroy the gear set very quickly.

If you're interested to know why and a little gear tech, read on:

The majority of hypoid ring and pinion gears for automotive differential applications are designed and manufactured as unique, matching sets. These gear sets are machined and "lapped" together and assembled as a unique pair. In this case, a different ring gear with identical specifications as the "orgininal" ring gear could not be installed in a differential with the "original" pinion gear; if it was, the result would be excessive gear noise and premature failure. A select few higher-end automotive manufacturers such as Jaguar (I don't know about Toyota/Lexus) employ a more sophisticated and flexible hypoid gear manufacturing process called gear grinding. This process allows any pinion to be matched with any ring gear but oinly within a specific manufacturing lot of identical specification / ratio ring and pinion gears. Regardless of manufacturing method (lapping or grinding) for a hypoid gear, a ring gear could not be swapped into a carrier than contains a pinion gear of a different ratio gear set.

JacobT

Thanks for clearing up for me. Now I know why no one has ever done this. In order to do this swap, you'll need to swap out both ring and pinion gears which is too much...

Anyway, I'm happy with my TRD 3.26 LSD

tomtnc

Interestingly enough, the stock 3.26 gear differential ratio is fairly "optimal" for a stock or mildly modified GS4 quarter mile dragstrip run given the transmission gearing / transmission shift rpm / drive tire diameter / differential ratio.

In general, most serious drag-racers set up their vehicles to run through the end of the track at or just past peak HP (which occurs ~5800-6000 rpm in the GS4) while in the 1:1 transmission gear ratio (4th gear in the GS4) for optimal ET. The input variables include transmission gearing, transmission shift rpm (associated with usable engine rpm) / drive tire diameter / differential ratio.

It just so happens that most stock / mildly modified GS4 run through the end of the quarter mile right at the top of third gear (1.424:1 ratio) which saves a timely shift into fourth gear. For comparitive purposes, a 3.76 differential ratio-equpped GS4 will run through the end of the quarter mile ~5100 rpm (close to intersection of hp and torque curves) in fourth gear.

In my relentless pursuit of often useless information, I put together an Excel spreadsheet that will calculate mph in any transmission gear and engine rpm given an input of tire diameter (or tire sidewall info) and differential ratio for the GS4. This spreadsheet also reveals what rpm the engine will move to after a transmission shift for the GS4. If you are interested in obtaining a copy to play with or host, PM me and I will email it to you.

bitkahuna

iTrader: (20)

Ok ok guys I get it - an LSD is useful in all situations! Thanks for clubbing me over the head with it. I feel much better.

And a mighty fine LSD it is sitting in my basement!

SC300T

One of the things that nobody really hit on with the LSD is how much better the electronic traction control works in slippery situations with an LSD.

Here is the situation:

At a stoplight turning right, slight snow cover (or rain) on inside of turn. You hit the gas, inside tire spins, traction control brakes right rear brake, evectively putting forward torque on the outside (left rear) tire due to the way an open differential works. The actual result is that the traction control puts very little usable torque to that outside tire that has traction, you end up lighting up the traction control, without making much forward progress, despite the efforts of the traction control.

With a LSD out back, the inside tire starts to try to spin, LSD torques outside tire, evening up the rpm of both wheels. If the torque is too much for both, sliding both tires will set off the traction control. The car with the LSD will accelerate around the turn much better than without the LSD any time there is a difference in left to right weight distribution and any time there is a difference in road surface traction from left to right.