Returd

I just picked up a torsen mounted in a pumpkin for my 92 SC400 I counted the teeth on the torsen equipped pumpkin and got 48 teeth on the ring gear.

I popped the cover off of my 93 parts car diff and counted 46 teeth. Theres obviously a gear ratio difference. My understanding is that the stock 92/93 rear diff is 3:26.

What is the ratio in the torsen equipped pumpkin?

I checked the mesh pattern in the torsen pumpkin and it's good so I'd rather leave it as is but don't know how that will affect speedo, fuel mileage etc as I don't know the ratio.

can someone chime in please?

KahnBB6

iTrader: (5)

It's best to keep ring and pinion gears as matched sets. Even though you checked the ring and pinion tooth alignment as okay you're never supposed to mix and match them.

1992-1997 SC400 rear diffs are 3.916:1 (3.92)
1998-2000 SC400 rear diffs are 3.26:1
1992-2000 SC300 A/T rear diffs are 4.272:1
1992-1997 SC300 M/T rear diffs are 4.083:1

The 200mm sized MKIV Supra TT Auto Torsen LSD always came with a 3.769:1 ring and pinion. If you want to remove the 3.76 ratio ring gear from the Torsen LSD then you have to do a procedure involving heat to get the metal to expand just enough to get it off after the non-resuable bolts are broken loose and removed.

Then you would still require a matched ring and pinion ratio of your choosing to be fully installed, aligned and shimmed properly into whatever diff the LSD is going into.

Forgive me if my info is a bit redundant but it's not going to be good if you mix and match differing ring and pinion ratios. You would very quickly destroy the gears.

Now as to the speedometer and fuel economy, if you went with a more aggressive ratio than your stock 3.92 your speedo and odo would read a bit fast. With a 3.769:1 ratio your speedo and odo would read a bit slower. More aggressive, shorter ratio makes for better off the line acceleration but slightly lower top speed in each gear. Slightly less aggressive, longer ratio does the opposite.

Fuel economy would be very marginally worse with a ratio higher than 3.92:1 and very marginally better with a ratio lower than that.

The speedo reading itself should be able to be corrected with a Yellr Yellowbox corrector which is also available with a plug-n-play harness for SC's and MKIV's if you request it from them when you order. Very easy to install and calibrate with a portable GPS such as a Garmin or Tomtom that shows the active speed of your vehicle on the screen.

I covered the installation and calibration of the Yellowbox V4 (with some online calculators) in this thread:
https://www.clublexus.com/forums/per...ml#post7250024

I'm familiar with how it hooks up to the three-wire VSS sensor on the W58 and R154 transmissions. I assume but am not certain from my own experience if the same VSS connector is used on the SC400's A340E automatic transmission.

Returd

I had no intention of mixing ring and pinion (that'd be beyond stupid), but I understand you're offering well intention-ed advice. I've changed gear sets in my Mustang's and can handle the swap, but doing nothing is an easier job. I was hoping to identify the gear sets by the ring gear tooth counts.

I was told by the seller it had 3:26. I believe the gear set is not original Supra but was changed. Identifying gear set by tooth count is still my objective, and I'll then decide if I'll go through the trouble of changing. My car will be gently driven and mostly a highway cruiser so a increased mileage at the cost of acceleration performance would be fine.

I did a quick search and got what appears to be bad info of 3:26 in my 92 & 93 SC400's (go figure, inaccurate info on the web). Looks like that was misguided, your info appears to be more accurate.

My torsen apparently came from a low mileage Supra, possibly the 3:26 is correct (still want to confirm via ring gear tooth count). Thanks to your info 3.92 looks to be what I currently have in my 92 SC400 driver.

I have an in dash Kenwood Nav/Stereo and can get accurate speed info from that. I'd like an accurate in dash instrument cluster speedo/odometer but it's not super important. I'd consider the Yellow box depending on cost. I have a spare auto transmission from my 93 parts car (not sure what the actual model is, I'm new to SC's) on the garage floor and will take a photo of the VSS and post.

So if anyone know's tooth counts for various gear sets I'd know for certain what's currently mounted on the torsen.

gerrb

iTrader: (34)

^^^ Can you count the pinion teeth of your differential and recount your ring gear teeth please. Something does not add up. if yours came from a 3.26 JDM 200mm diff then it should have 49 ring gear teeth

I have torn apart basically all kinds of Supra TT / NA and SC differentials since I have installed TRD LSDs on the differentials of my cars. If my memory serves me right

USDM Supra MKIV 6speed TT Diff 220mm 3.13 gear ratio has 47 ring gear teeth and 15 pinion teeth
JDM Supra MKIV 6speed TT Diff 200mm 3.26 gear ratio has 49 ring gear teeth and 15 pinion teeth

USDM Supra MKIV Auto TT Diff 200mm 3.76 gear ratio has 49 ring gear teeth and 13 pinion teeth
USDM Supra MKIV / SC300 NA Auto Diff 200mm 4.27 gear ratio has 47 ring gear teeth and 11 pinion teeth
USDM Supra MKIV / SC300 NA 5speed Diff 200mm 4.08 gear ratio has 49 ring gear teeth and 12 pinion teeth

GS400V8

iTrader: (4)

Yeah you might need to count that pinion gear.

For example, on the GS400 and Supra, the pinion gear teeth set the final drive, not the ring gear. However the thickness of the ring gear is larger on the Supra, so when you put the Supra LSD unit inside of a GS400 pumpkin (what I will do to retain the 3.266 gearing) than you must swap the GS400 ring gear to the LSD unit.

The GS400 and Supra both have 49 ring gear teeth, but the pinion is 15 on the 400 and 13 on the Supra as stated above

I have a Supra/Aristo 3.77 diff in mine right now

KahnBB6

iTrader: (5)

My apologies It was indeed just well intentioned advice and I probably misunderstood what you were describing you wanted to do when it came to the ring gear on the Torsen. Absolutely with diffs it is easier if nothing needs to be done.


That Kenwood stereo will be a perfect GPS speed reference. The Yellowbox direct from Yellr's website used to be about $50 for the older V4 model if memory serves but it went up to about $93 for the current V5 model. The plug and play harness made for our vehicle application is a little extra but not much more. It is a set and forget aftermarket device. The only time I've ever had to mess with it or even think about it after initial calibration is if I have changed my tire size, final drive ratio or transmission type. The fine tuning in correction that it offers is extremely accurate. I've been running my V4 model for over five years without issue.

Returd

I'll do a recount, I ran out of digits after 21....

Returd

Okay so the torsen equipped diff is 49 teeth so it is a 3.26 Versus a 3.54 from m parts car (rusted housing from parts car). I assum I'll also have the same 3.54 in my driver. So if I don't swap gear sets I'll have a speedo/odo error making my actual speed greater than displayed.

considering I'd like improved mileage and I get my power fix from my supercharged Mustang, I'm going to install as is. Also I'm getting lazy with all the other work also being done.

Once I have the rear end back in I have to install the LS400 brakes, but first all new brake lines. Oh i have to install the rebuilt rack, and sway bar links. Then i have to do valve clearance.

I need a nap.

thanks for the help folks

gerrb

iTrader: (34)

^^^ You better count the pinion teeth of both to make sure of the gear ratio of those differentials . Looks like someone just installed that torsen on that clean differential pumpkin so there is no guarantee it is a 3.26. That is not a JDM Supra MKIV differential pumpkin that had the 3.26 gear ratio and torsen LSD from the factory.

Even the rusted differential , I doubt that has a 46 teeth ring gear and has 3.54 gear ratio cause the differential is not also a Supra MKIV pumpkin found on European MKIVs that had the extremely rare 3.538 ring gears. Besides those had 220mm ring gears so it will not fit into that pumpkin and those MKIV diff with 3.54 gear ratio also had LSD from the factory.

KahnBB6

iTrader: (5)

^^ I'm going to second this concern Gerry has brought up. Returd, I know you have inspected and counted those teeth carefully and I know you are not stranger to setting up differentials but what if the previous owner of the diff actually just installed the 3.76 Torsen ring gear into a 3.26 pumpkin against a 3.26 pinion? It would be a stupid ridiculous oversight on the part of your seller if that were really the case but I would want the possibility completely ruled out before running it.

I don't know the correct tooth counts for each ratio but the members who posted above do. Especially when used with a 250hp stock 1UZ-FE application that Torsen LSD will last forever as-is with normal gear oil changes. This may be redundant advice again but I always feel it's better to triple check any tolerances, torque numbers or specifications before moving forward.

Indeed that diff in the picture is not a factory MKIV TT 200mm diff since it has no cooling fins on the housing. Smooth 200mm 3.26 diffs were used in the 98-00 SC400, GS400 VVT-i and SC430's. Most commonly we get those common 3.26 open diff pumpkins from salvage GS400's. My guess is that is what you may have-- a 3.26 GS400 200mm diff with a TT Auto Torsen installed.

Gerry, correct me if I am wrong but I thought the 3.54 ratio was a Euro-market-only MKIV TT diff? That would be a very rare ratio to have in the USA.

Edit: I'm including the big "JZA80 Differential Info" thread from SF for reference.

http://www.supraforums.com/forum/showthread.php?608545-JZA80-Differential-Info!&highlight=jza80+differential

Double Edit: Looking at that thread I am only seeing the 3.54 ratio listed for Euro 220mm MKIV TT diffs and not the 200mm size.

Returd

both pumpkns are from SC's. I personally removed the rusted housing from my 93 SC400 parts car. The painted housing is identical. I will do a recount on the rusted housing ring gear as now I'm questioning myself on that count as well.

Judging from the mesh pattern in the torsen equipped diff its highly unlikely the wrong pinion is in place, but I'll do a recheck and count revs as well..

The logical answer is the Torsen along with 3.26 ring/pinion were mounted in an SC housing.

I do appreciate the info and concerns.

gerrb

iTrader: (34)

You are right , those 3.54 ratio are extremely rare and are found only in some European MKIV TT diff and have 220mm ring gears. So no way it will be in that pumpkin which can only accomodate a 200mm ring gear . Those pumpkins are consistent with Lexus pumpkins.

Those diffs do not have cooling fins that is why the diffs inside the pumpkin cannot be the factory 3.54 from a European version MKIV and the other is definitely not from a JDM MKIV so that torsen was installed on that pumpkin.

Counting properly the ring gear and pinion teeth of each differential is the only way to verify exactly their gear ratios. One thing sure, non of those have a 3.54 gear ratio cause both are 200mm ring gears and a 3.54 has 220mm.

RXRodger

iTrader: (2)

I am going to assume you probably are not running the 15 or 16 inch wheels that came on the car, but I guess it's possible. If so, that throws off your speed off anyway so you have to look at the total picture as far as speed error. Probably stating the obvious so apology up front.

Returd

well it appears I can't count worth crap, so apologies for causing confusion and again, thanks for all the input.

Rusted housing from stock 93 SC400 (Canadian car):ring gear 47 teeth/pinion 13 teeth

Black painted torsen housing, ring gear 49 teeth,/pinion 15 teeth.

as far as wheel size goes I have 245/45/17's with an OD of 25.7" which is the same as stock wheel OD. There should be no additional error from wheels.

gerrb

iTrader: (34)

I don't mean to pick on your counting but the above numbers are not possible

No SC400 ever came out with 3.6 gear ratio .