I own a 1995 Lexus SC300 that has been manual swapped with a R154, I only ever drove it once to get it home but the speedometer read very high, it would read 90 mph when i'm only going about 65 and my tuner warned me that the revs will sit pretty high at highway speeds(tach doesn't work yet), I know that it still has the stock diff from the factory and i'm curious if anyone knows what ratio the stock diff is with the automatic transmission and what ratio would match better with a R154 transmission. Also any differential recommendations, ideally something more on the budget side.

 

First off, after doing any final drive ratio change, transmission type change or overall rear tire diameter change your speedo will be slightly off one way or another. The fix is a Yellr YellowBox V5 with their (upon request when you purchase) SC300/Soarer/MKIV plug-and-play harness.

My old install DIY for that (with pictures) starts on this thread post:
https://www.clublexus.com/forums/per...ml#post7250024

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All 1992-2000 SC300 Automatics came with a stock final drive ratio of 4.272:1. This is good for the stock auto 2JZ-GE configuration, good as an upgrade to an SC300 NA manual car if it will be staying manual *and will also be staying NA*

Stock 1992-1997 SC300 factory 5-speeds came with a factory 4.083:1 final drive ratio. So did 1991-2000 Toyota Soarer JZZ30 1JZ-GTE factory manual cars (Soarer JZZ30 factory autos came with a 3.92:1 final drive ratio as standard).

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It sounds like you have a boosted and built 2JZ-GE NA-T or GTE swap with your R154.

The 4.272:1 ratio is too aggressive even for a 2.5L 1JZ-GTE high revving engine but a 4.083 is good since it is technically a stock Toyota configuration.... with a 1JZ + R154.

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But with a boosted 3.0L 2JZ engine of any type bolted to an R154 the better final drive ratios will be:

3.92:1 (from a 92-97 SC400) -- It will allow boost to build up and actually be usable. A good ratio but it will feel a bit aggressive around town and on the highway.

3.76:1 (from a Supra TT Auto, Lexus SC430 (some model years only) or Toyota Aristo 2JZ-GTE) -- This is the most ideal with a boosted 3.0L + R154 and is a very good all around balance between having enough gear off-boost and good room in each gear to use boost effectively. Highway revs are reasonable with a 3.76:1 ratio. This is the ratio that most people with boosted 3.0L's with R154's want to use. I have this ratio in my SC and I'm quite happy with it.

3.615:1 (ring and pinion only harvested from a 1989-1995? LS400. The ring and pinion have to be used in a full SC/MKIV/GS/Soarer 200mm differential rebuild job but it all fits and works) -- This is a slightly more relaxed alternative to the 3.76:1 option. It takes more work to get it set up but if the math works out for what you want in your car's setup then it is another solid option so long as you planned to rebuild a differential anyway... to get an LSD installed for instance.

3.266:1 (from a 98-00 SC400, 98-? GS400, 98-2000 LS400) -- This is what some people go with but it is a very long ratio. More suited for a CD009 or V160/161. It will make your response feel lazy compared to the other higher ratios listed above and isn't going to provide the best overall drivability with an R154. Highway fuel economy should be great with this however but you don't want to cruise with your engine below 2100 RPM or so (which would lug it).

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One other thing to note is that sometimes the instrument cluster speedo and tach gauges need service. If yours does then Tanin Auto Electronix are the people to call for that repair.

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Your tach isn't working you say. Assuming the gauge motor is not experiencing any issue what ECU are you using? If you have any GTE ECU installed then you will need to solder a jumper wire over the R109 resistor pins on the back of your cluster's circuit board because the GTE ECU's tach signal is output at a lower voltage than the GE ECU's output their tach signal at.

 

My car is currently at First State Motorsports where my 2jz ge na-t is getting a ecumaster emu black with a patch harness, fluidampr crank hub, billet tensioner, audi r8 coils, bti guage and along with that he said he would rewire the tach to work. If I remember correctly my tuner told me that I should go for a 3.76:1 diff, do you know which sc430 model years, same question for the aristo and supra tt as well. What aftermarket options are there too?

 

There are NO aftermarket diff ratio options available.

You just need to get one of the ratios I mentioned above from whatever Toyota or Lexus model has it.

Remember that if you are planning to swap over an entire diff pumpkin from another Toyota/Lexus model you will need to swap on an SC diff companion flange (the three-pronged propeller thing at the rear). Follow the SC or MKIV TSRM procedure for replacing one of those-- don't use an impact gun to torque down a companion flange as if could upset the delicate alignment of the gear teeth meshing between the pinion and ring gear internally.

You can get a 3.76 ratio from any 1993-2002 Supra MKIV TT Automatic (93-98 only for U.S. models) and from any JDM Supra MKIV SZ-R 6-speed (JDM factory Supra NA with a V161 6-speed and 3.769:1 diff from the factory). The Supra TT Auto diff had a standard or optional Torsen T-1 LSD depending on the model year so some of these will be open diff and some will have a Torsen LSD inside. Always have the seller confirm which diff is inside with a picture.

If you are already starting off with a build greater than 450-500whp then skip the Torsen T-1 and invest in an aftermarket LSD as the T-1 doesn't consistently or reliably handle power above that level very well. The rarer factory Toyota T-2 Torsen LSD is much better in this regard but it is extremely rare even compared to the already rare T-1 Torsen.

The 3.76:1 is also available from all JDM Aristo 2JZ-GTE models.

You can also find the 3.76 ratio from 2007-2010 SC430 models.

 

Good morning Craig,
Question, I thought the SC430 that you mention had a 3.26 diff. Please enlighten me. Oh by the way did any have a limited slip?
Have a good day,
Bill

 

Hey Bill-- The 2001-2006 Lexus SC430 came with a 3.266:1 open differential. The 2007-2010 SC430 switched to a 3.769:1 open diff from the factory along with its switch from a 5-speed automatic to a 6-speed automatic.

Unfortunately there was no factory LSD available on SC430's. To the best of my knowledge this was also the case with the Japanese market Z40 Soarer equivalent which was later rebadged as a Lexus for the Japanese market as well until all production ceased.

Some Canadian market SC400 model years reportedly did have a Torsen LSD optional or standard in their 3.92 (3.916:1) diffs... but no 1992-2000 U.S. market SC got that option. Only the JDM JZZ30 Toyota Soarer and some trim levels of the JDM UZZ30 or UZZ31 Toyota Soarer.

 

I found this 3.76 diff on ebay, how would I go about fitting axles because these dont use a stub style axle, is it even worth the hassle/money to do so, I am also tempted to install a 3.92:1 from a sc400 just because its so affordable and I can always add a diff down the line when I increase power but how rough would that be on the car and the drive? I'm only gonna be making ~400 whp for the forseeable future

https://www.ebay.com/itm/16604354783...QaArD-EALw_wcB

 

Craig,
Well I knew that if anyone knew the answer to that question it would be you. Thanks so much for sharing your vast knowledge.
Bill

 

That is ALMOST the same differential but the casing will not work in our cars since our cars use diffs with axle stubs built into each carrier housing. Internally it has been speculated that the internals and rest of the diff are the same as the older 200mm SC/Soarer/MKIV/GS/Aristo diffs but that hypothesis has not been fully tested yet by swapping parts from one to another.

Bottom line, for an SC application you do need to get an SC/Soarer/MKIV/GS/Aristo 200mm diff or at least custom build one with one of those carrier pumpkin housings.

So no, you shouldn't use that diff that you found. Keep looking for one that is compatible with an SC that has a 3.76 ratio.

But also if you're already getting set up with a turbo engine it is highly recommended that you also get some LSD installed into whatever diff you plan to use. Your steering inputs will be a little more erratic to keep the power under control with an open diff.

Yes, a 1992-1997 SC400 stock diff can be a good starting point if you need something affordable and more available right now. And you might even like that ratio. But keep your ebay searches saved and on the alert for a compatible 3.76:1 diff even if you can't fine one right now. One or more will come up for sale if you keep looking.

 

I learned and continue to learn from all the contributors before me and always defer to the senior forum members

In this case the biggest repository of information about our differentials is on Supraforums in this thread:

https://www.supraforums.com/threads/...l-info.608545/

 

I'd like to update this thread with a discovery I have made, I turn out to own the sc300 with the R150 swap done by user Crevasse https://www.clublexus.com/forums/bui...-the-r154.html and my car is not a r154 as the previous owner told me which unless they swapped it to a r154 while in their ownership, i asked my tuner dan at fsmoto to check as he has the car rn. I read the crevasse planned on doing a 3.26, would that be more viable? I do plan on doing an lsd but given im gonna be making about ~400 whp im not in a rush to get to that as I wanna do ls400 brakes first.

 

would a 3.266 from a 98-00 sc400 be a direct bolt in?

 

Oh, you have THAT SC! Very cool! I wondered what had happened to his project and now it is in your hands!

Yes, a 1998-2000 SC400's stock 3.266:1 diff will be a direct bolt in. No change to the companion flange required. Just swap your old one out and swap that one in.

It will be a very long ratio for any of the R-series transmissions so if your turbo setup is large and laggy it will probably not be a great match. If your turbo setup is very responsive then it will be better but will still be long gearing. Many people have run a 3.266 with an R154. It all comes down to preference of setup.

The R150 has a shorter 1st, 2nd and 3rd gears compared to an R154. 4th is the same 1:1. 5th is slightly shorter. Strength should be the same. Clutch options should be the same.

A 3.769:1 ratio is probably still the most ideal in the long run but given the difference in transmission gearing your R150 setup might be a good candidate for the totally custom built 3.615:1 ratio combination I mentioned in my earlier post.

Any LSD option is going to be a chunk of change so by all means focus on upgrading the brakes first

 

Can you outline every car that comes with a 3.26 diff I can swap into the car, I found a guy who is willing to sell me the diff out of his 2003 sc430 in new york for $100 if I come pull it which is the best deal I have so far, that should be a matter of just switching the flange and the axle stubs out right? Are there any other diffs beside the 98-00 sc400 diff that will bolt right in with no change? Lastly i'm deciding to do a 3.266 because it is a fairly similar to set up to the r154 with a 3.76 besides 4th gear, see below

 

^^ In my previous posts above I listed most of the other cars above that come with a 3.266 gear ratio in our common diff housing above.

You can add *some* model years of the JDM MKIV Supra Turbo 6-speed M/T's to that list since not all of them came with a 220mm "Big Diff" but rather the 200mm size instead.

Also add *early* model year Lexus LS430's and GS430's which also got a 3.266:1 ratio with the axle stub type 200mm diffs. All open diff from the factory. Roughly these 3.266 diffs range from 2001-2005 2001-2003 model years for those three early 2000's Lexus models.

Basically any diff that did not come from a 1992-2000 SC300/400 or 1991-2000 Soarer will require an SC or Soarer diff companion flange swap.

Axle stubs should not need to be swapped in nearly all cases. The only time that is really needed is when you install some model aftermarket LSDs such as an OS Giken. The axles themselves are all equally strong and there were only a couple of very minor variations between all the cars that got these axle stub type RWD 200mm diffs.

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Also the diffs from the 1st generation IS (and Altezza) and 2nd generation IS are not compatible. Their diffs are more in line with those from the MKIII Supra, Cressida, Chaser, Mark II and FR-S/BRZ/GT86/GR86.