Blakenz

I sort of don't feel right doing that
I've been keen on sourcing a 4.27 because i think it will improve acceleration(i like drag racing) and it makes sense that a heavy car (soarer 1600kg/3500pound) combined with a smallish capacity motor (2500cc) would benefit from a lower ratio(numerically higher).
However , some drag race programs suggest that as i increase power, the diff ratio has far less effect. Am i right in thinking that a 4.27 may shave .3 sec off a 2jzge sc300's time, but maybe only .1 off a 2jzgte or turboed NA sc300?

Blakenz

in which case i'm better to spend money on power improvements rather than a diff ratio change.

maynanator

iTrader: (1)

you are correct, as the power goes up the time spent changing gears vs going with a longer ratio will really start to show. in a slow car the time between shifts is longer thus going with a shorter diff ratio to make power makes more sense. i think you should just save to go na-t or to swap a motor.

KahnBB6

iTrader: (5)

^^ This.

Blakenz, I think in the turbocharged Soarer 4.083:1 is a good ratio at or close to the stock power level. For stock 1JZ's it has to have been a good balance between acceleration and highway economy. The 4.272:1 ratio is better than 4.083:1 for NA 2JZ-GE cars (I have no experience with 1UZ gear ratio changes). My setup revs very quickly and requires me shift more frequently through the gears but this more ideally matches the stock power level of the 2JZ-GE and I don't find it troublesome to drive in the least. It's the same exact ratio used in NA Supra 5-speeds in the USA. That's why I went with this ratio. It feels very matched to the NA engine's powerband.

It wouldn't be ideal at all if I had a 1JZ-GTE(TT or VVT-i), 2JZ-GTE, or NA-T kit with far more horsepower and torque. The car would reach the top of the first two if not three forward gears too quickly to build speed in an efficient way.

I went with this setup with full knowledge of the tradeoffs and of the minor improvement in acceleration in an NA car compared to turbo JZ cars. The change in NA powerband delivery (plus an LSD) was what I was more interested in because I find myself on more mountain roads than I do straight highways where I live and as such I focused on my SC's handling and control. As long as my car is NA this made the most sense to me since my stock 4.083 really is more suited to a stock/BPU-only 1JZ engine.

KahnBB6

iTrader: (5)

Blakenz, this may be of interest to you if you are still considering a 4.272:1 ring and pinion. I may have read this thread incorrectly but I think they are saying that some years of the Toyota Hilux came with the 4.272, namely 2002 4WD models. Another great vehicle we happen to not get here in the States.

Apologies in advance if I am wrong on this but if you get those in NZ you may have a source.

http://www.jzx100.com/forum/topic/67...o/page__st__40

Blakenz

thanks for your suggestion....the hilux is very popular here in NZ, however, the jzx90/jzx100/jzx110 series of diffs are not compatible with the soarer/lexus coupe/ jza80/aristo series of diffs, so the hilux crown and pinion are not a bolt in option for me.
I've done some computer drag racing calculator scenarios, and whilst the 4.3 is about perfect, the 4.1 is so close it's negligible, so perhaps my money/time/efforts are best spent elsewhere. thanks.

KahnBB6

iTrader: (5)

That's fair enough. I wasn't aware that the JZX diffs weren't compatible with ours. Aside, I found it interesting that from the factory the manual Chaser turbos run 3.77 for manual and 3.92 for automatic. That was surprising considering the Soarer 1JZ manual ratio is much higher.

For what it's worth, some folks in the thread I posted seem to prefer 4.11 or 4.30 ratios with their 1JZGTE JZX cars but they didn't specify auto or manual transmission choices.

I'd go for the 4.083 but if you really want to get a 4.272 from here I'll help find one.

aaaadoor

i have a 92 sc300 5 speed i dont know if it was factory or not. when driving you go 1st 2nd 3rd 4th pretty quick.im looking for a lsd that will bring down my rpm when im at 70 mph on the turn pike.i can get a sc 400 v-8 auto diff will that do anything for me.can some one help thanks

KahnBB6

iTrader: (5)

There are a few things that can help determine if you have a real five speed or not: unless it was swapped out, you could have an auto cluster with the drive gear indicators in the center and you could also have a swapped car if you do not have to depress the clutch pedal to start the engine. Both of those things can be changed however.

If you have a 5-speed swapped car you probably still have the 4.272 open diff. The car will feel as if it has a close ratio transmission and 70mph cruising should be at about 3,000rpm. Your speedometer will be incorrect unless someone hooked up a Yellowbox. The rpm I stated also assumes a stock OD tire or close to it. Factory tires for SC300/400's are 215/60R-15 or 225/55R-16. If you are running TT rims front and back the tires would be 255/40-17 rear and 235/45-17 front. Supra NA rims would be 16-inch and I forget the correctly matched tire size for those.

If your car has the stock non-turbo engine I actually don't recommend changing the rear end ratio to less than 4.083 which came stock on 5-speeds... But personally I feel that is too little gearing considering that 93-96 Supra NA 5-speeds came with 4.272s from the factory. But 4.083 is decent if you want to cruise at 70mph @ 2,800rpm in 5th gear.

If you have an original 5-speed that is unmodified you will already have a 4.083 open.

3.92 open-diff from an SC400 will fit but you won't have much acceleration with that ratio as long as you're naturally aspirated. A 3.769 Supra TT Auto Torsen LSD diff is the only drop-in you can get without doing diff surgery but that is only advisable if you are going turbo. It will give you a far better cruising rpm at 70mph but you really won't have any acceleration AT ALL unless you are going turbo.

You could find a 97-98 Supra NA diff which is 4.083 and which has an LSD (which was standard on most NA's from those last two years and a very rare option for 93-96 NA's) but they likely are NOT Torsens (which means they need rebuilding every so often). Those are extremely rare and hard to find, however. You'll have better luck locating a TT Auto LSD rear, having the Torsen removed and installed into a pumpkin with the ratio you do want. That's what I did.

There are also JDM Soarer 4.083 Torsen T-2 LSD rear ends but those are so incredibly rare and in such high demand they make Supra TT Auto LSD pumpkins look plentiful.

You could also find the diff with the ratio you want and install a TRD, KAAZ or another 2-way clutch-type LSD.

Basically, there is no easy way to get an LSD into an SC, especially one suited for NA 2JZ-GE application. It is worth it and improves handling and power delivery (especially with 4.272's) but if you're looking for acceleration improvement on par with a turbo AND lower cruising rpms it's not worth it if you want less than a 4.083 and won't be touching the engine.

For most owners, both the acceleration and cruising issues are solved via an NA-T conversion or a 1JZGTE or 2JZGTE swap paired with 3.769, or 3.92 gearing. 4.083 gearing also matches to the factory 1JZGTE engines but is probably too much for a 2JZGTE or NA-T or 1JZ with a large single turbo.

Since you're in Florida, you could easily take the turbo route for a bit more investment and have the best of both worlds... although the only drop in LSD will still be the TT Auto diff.

Hope this helps.

DoomLight

iTrader: (3)

Love this thread! Should be stickied.

frankdms

iTrader: (1)

I want to give my experience on the 4.08. I have an original 5 speed car swapped in a 1jzgte VVTi 5 speed (re-used the w58). I have made 25 mpg when driving it on the highway (averaged @ 70-80 mph, neutral idle down hills- from Vegas to Denver 255/40/17). In town I did not keep track. On the track it was bad. (Fuel consumption at the track is always bad...)

I would say to all of you racers keep the 4.08 or go with the 4.27 for the benefit of grabbing another gear (especially in drifting). I thought about going with a higher rear gear ratio but it would actually slow my wheel speed overall while drifting. To me I would rather use 2nd-3rd-4th with a lower gear ratio then have a much longer 2nd-3rd with a higher ratio rear diff. I have used tires from size 245-295/ 35-50/17-18's and with the 255/40/17 and the 4.08 if feels like a good match with the 7400 rpm band/ power of the 1jzgte VVTi.

With a 4.27 I could use the larger 18's with the same effect as the larger 17's.

I can see why you would want to use a taller rear diff ratio, but for what I have built my car for the lower ones work better.

KahnBB6

iTrader: (5)

^^ Thank you for this! It gives a fresh perspective on gear ratios for the 1JZ engines. Since you have a VVT-i engine, are you on the factory CT-15B turbo or something else?

frankdms

iTrader: (1)

^ All stock* original ct15b with Mk4 SMIC @ 16-18psi with manual boost controller.

KahnBB6

iTrader: (5)

Frankdms, you're describing my ideal setup. Do you have any future plans to get Driftmotion to upgrade your CT15B to steel blades or to use the Tomei turbo kit on your VVT or do you find the power is where you want it given how you use the car?

KahnBB6

iTrader: (5)

Fuel economy update:

Just this last week I made a very long drive from Southern California to Florida in the SC. It was loaded up like a sardine can with belongings including my having filled the passenger seat up to the height of a full size person. Pretty much no room whatsoever in the trunk or cabin other than giving myself rear windscreen visibility. I have no idea how much extra weight this added but it was very heavy, possibly to the maximum carry load.

Highway passing power was still very much unaffected other than my wanting to stay between 3100-4000rpm on hills depending on the grade. Fuel economy for my first leg of the trip was 23mpg. Throughout the rest of the trip I averaged out to about 21mpg but I was traveling well above 70-75mph at that point. Until I hit the deep south I was averaging about 80-85-90mph. I just tried to keep the car at or below 4000rpm.

Not bad for a car loaded down with too much stuff over a long haul. I'll post fuel economy numbers again if I can replicate that 23mpg figure without the weight.