KahnBB6

iTrader: (5)

I've searched a lot and this isn't something that's been addressed directly. I'm looking ahead into diff ratio options for the following setup:

R154 5-speed and USDM 2JZGTE with stock twins at stock power (320hp crank) with a maximum limit of BPU power (350whp?).

Between these three ratios, which would be best for someone who prefers a *close ratio* rather than relaxed feel? Again, the power ceiling will not exceed 350whp-- possibly slightly less.

4.08, 3.92 or 3.77?

I already have 4.08 and a 3.77 spare ratios. I'd pick up an SC400 3.92. From what I understand, 3.77 isn't going to feel like a close ratio setup but correct me if I'm wrong.

For now I'm NA and running a TT Auto Torsen LSD diff with a custom 4.27 ratio plus a speedo corrector and I STRONGLY prefer that combination over stock for NA during all types of driving. I only mention this because many people don't seem to like 4.27 even on a 5-speed NA car and personally I love it for NA. It feels perfectly matched for aggressive driving and the frequent shifting is more my style. Come swap time this will change of course.

Edit: I'll add that I'm running Supra TT size 255/40-17's in the rear and may stay that way or go to 265's or 275's max.

The reason I throw 4.08 into this question is because, as we all know, from the factory all 1JZ Soarer 5-speed manual cars came with 4.08's-- even the torquey VVT-i 1JZ's. Granted, these are engines with .5L less displacement and significantly higher rev ceilings (1JZ 7400 I think vs 2JZ 6800)

3.92 is very similar to the final drive on early MKIII Supra Turbo 5-speeds (86-88?) so I know that's also a proven factory ratio combination for an R154 against a 3.0L.

Any thoughts, guys? I know a lot of you are running significantly more power than I'm planning to. My SC is set up to be more of a driving and mountain road car than a drag racing or roll racing car.

Thanks!

INTIMAZY

iTrader: (5)

None will truly feel like a close ratio gearbox. It's just a widely spaced 5-speed trans. No matter how you cut it, that's the way it will be.

However, if you like shifting a lot, 4.27 would be the 'busiest' followed by 4.08 and then 3.92


My personal preference? 3.3 on a R154.
I get GREAT gas mileage on the highway and don't need to shift much. Boost still gets you going incredibly quickly and you can ride the gear out further.

blk&blu*j

iTrader: (1)

a 3.9 ratio on a r154 1jz will get you to 140 in 4th gear at 7k.

The hell with close ratio these cars are not an 89 Ford gt mustang with 225 hp. with no top end and a 5200 rpm redline.

1jz like to rev so run them accordingly.

KahnBB6

iTrader: (5)

INTIMAZY-- You have a good point. Neither the W58 or R154 are true "close ratio" boxes. A V160 could probably be considered a true one. 4.27 definitely requires frequent shifting on my NA engine but I'm very OK with that. It's too much gear for turbo though. The 4.08 is the head-scratcher to me because Toyota used it against the 2.5L 1JZ but not either of their 3.0L turbos. Interesting you say that 3.92 is still considered "busy" (which I think is what I'm looking for, lol). 3.3 seems a little low for my tastes but I'm curious: what does that gearset come from?

blk&blu*j-- So you recommend the 3.92, then? If I were going with a 1JZ engine I'd plan to throw in the 4.08 without question (factory configuration) but I'm not, much as I'd like to. This will be for a stock/BPU 2JZGTE swap so I was concerned 4.08 wouldn't match the powerband well given the extra torque, power and displacement but I also don't want to go with a gear more suited for 500whp+ because I'm not going nearly that far with the engine or giving it a single turbo.

3.916:1 (3.92) sounds like the safe bet from what you've both told me so far.

Ali SC3

iTrader: (10)

3.3 is from 97-00 SC400 and actually a 3.266 (you might remember from the sc400 gas mileage thread).

I can tell you my stock w58+4.08 feels a little busy with a single turbo but it sounds like that is what you are looking for, a 3.92 probably wouldn't be a whole lot different but is a good comprimise between that and 3.7

INTIMAZY

iTrader: (5)

Also can swipe one from the newest SC430.
1st gear can be a bit hairy to launch from up an incline if you have a lightened flywheel or grabby clutch. On the highway it cruises well out of boost even at 80mph. It's definitely not an 'exciting' gearset but you're just a gear down from boosted fun anyway. Makes 2nd gear useable again even at 20psi on a 60-1. Most people dismiss the gear because everyone says it's a bad match. There was one supraforum guy that inspired me. It's not too shabby at all.

account2x

iTrader: (5)

There are a few factors to consider.

First and foremost the close-ness comes from the transmission gearing. R154 isn't ever going to be a close ratio box.
Second generally speaking the shorter the gearing, the quicker the acceleration and the lower top speed.
As black and blue mentioned top speed in 4th gear is very important. With the R154 4.08 nets a top speed of 128 in 4th, 3.92 ups that to 133 and 3.77 138. If you ever plan to drag the car then that extra 10 mph can be very important.
Another important consideration is traction. Putting in a taller gear can help alleviate grip issues. This won't be much of a issue at BPU levels but trust me BPU is only a phase. Eventually those stock turbos will blow.

Personally I drove a W58/4.08 diff and a 6MT with a 3.2 diff. The difference was night and day.. The first setup requires cruising 2300-2800k rpm range. The later in the 1700-2200 range. Even worse because the gears where so short it required constant shifting. f I didn't shift on time I'd hit 4k rpm like that. @ 80 mph the highway rpms used to be close to 3500, now it is closer to 2800. Even in TTC mod the car hits boost at in the 3k rpm range. it was unpleasant to drive it before, I can't even imagine how much worse it would feel turbo's. Boost hits, time to shift, that would just suck.

KahnBB6

iTrader: (5)

Ali SC3 and INTIMAZY,

Thank you for clarifying. I should have guessed it was 3.266, lol. Still, I think that's going to be far too low for what I'll be doing with the car. A larger single setup would take the car into a whole new territory of power but I'm not going there in the forseeable future or possibly at all even though I know I can down the road. Mild stockish to BPU power range will be enough upgrade and investment by itself. 3.769 is as low as I'd go for the planned setup.

KahnBB6

iTrader: (5)

Very good point and I didn't mean to mislead with my questions in the top post. I know both the W58 and R154 don't have true close ratio spacing. I'm only focusing on the final drive itself to give the overall feel of shorter gearing while not overgearing the engine's power and delivery characteristics. Same thing I did with my older NA gearing thread, only this time I'll be backing off to something much more reasonable for GTE use.


Yes, this makes total sense to me when you consider trap speed. My intention really isn't to get into drag racing so I overlooked that. I'm far more inclined to get into trackdays with the car once all this is completed.

Traction is definitely a concern of mine, especially in inclement weather. As a later project I'm interested in retrofitting the SC/Supra TRAC components and using a RaceLogic traction ECU come swap time since I hear it's far smarter than Toyota's programming. With the car in boost at normal highway cruise rpms, especially in rain I can see the potential for problems, especially with the Torsen T-1 I have.

As far as the stock twin turbos, I'm aware people ditch them but I'm not sure when that point would be for me. Last week I nearly bought a complete USDM set that I intended to have rebuilt given their mileage. They would have gone onto the swap engine fresh. There is also the STU Hagen twins upgrade as another option. Whatever I do I'll be keeping the stock twins and hardware in some form whether I stay sequential or TTC.


I'm really starting to understand how 4.083 really only worked for Toyota in one or two very specific applications, and stock ones at that. 3,500rpm @80mph I'm okay with on my NA engine given the better distribution of the powerband (over 4.083) but I also don't have boost coming on at 3k. As I recall though, my 4.08 was more like 3,300rpm @80mph. Negligible difference though.

I haven't driven but have ridden in a 600whp 2JZGTE V160 with a 3.266 (open) rear. Dare I say more gearing would have been ridiculous. I've read of some Supra TT 6-speed guys wishing to swap in the Swiss(?) export 3.5 220mm ratio but I can't see it's positives at the level of power I experienced in that V160 car.

It makes sense that there can be far too much shifting needed to the point that one or more gears are completely unusable. For a 2JZGTE, it sounds like the 4.083 isn't a realistic long-term option for any reason. I'm sold on that. Done.

KahnBB6

iTrader: (5)

Guys, thank you. Really. I know I ask some complicated questions sometimes but it helps to have a better understanding of why certain combinations of gearing work far better than others once turbos are involved. 4.083 on the 2.5L VVT-i 1JZ has been a head scratcher for me for a while now and I wondered if the engineering logic applied to the 3.0L engines.

3.916 and 3.769 are what I'm going to choose between. The former is easy to try out as a drop-in test. The latter I have waiting to get reinstalled if I need it.

Ali SC3

iTrader: (10)

Kahn sounds like you are on the right track with the 3.9. the 2.5 L gets away with the 4.08 because of the smaller displacement and it is a single turbo so I figure that's why toyota paired it with a taller gear from factory.

KahnBB6

iTrader: (5)

^^ Ali, that does make sense. It's just interesting to me how half a liter less displacement and one turbo versus two makes such a difference in appropriate gearing.

Anyway, yeah, I'm going to try the 3.92 first. Should be easy to obtain. If that feels like too much I can always use my spare ratio.

account2x

iTrader: (5)

On a half-off day the 3.9 is only 50 dollars at a pick a part.

A good single turbo setup can be had for 1500 with quality used parts. I just don't see the point in ever rebuilding the factory twins.

KahnBB6

iTrader: (5)

^^ Thanks for the tip! I've seen several SC400's at pick-a-part yards in L.A. and $50 ballpark sounds great.

I know how cheap the single turbo kits are. It's still cheaper and less troublesome to just get one of those and NA-T my stock engine rather than swap in a full GTE. Still, I'm going that route for smog purposes so I accept it's certainly not the most economical way to go. I already have an OBD1 6-speed ECU. The rest will come after my move.

Ali SC3

iTrader: (10)

believe it or not .5 liter makes a difference, and then take away those twins and that makes another larger difference. The sequential twins are like a completely different animal the boost comes on right away, do a couple of BPU mods and I prefer it hands down to a single for anything under 14-16 psi. look into the spring mod for turbo #1 it will let you get more than 10 psi out of the first turbo up to 4k, and then turbo 2 kicks in and if you put a manual boost controller on turbo #2 you can then control what the max boost is.
It really comes down to what you like, for city driving I would take a stock gte any day of the week with a fun gear like the 3.9 or even the 3.7. If I had to have a highway warrior, I would strap a large single on it and put the 3.7 or even the 3.2 on there depending on how big that turbo is.
this is all assuming a 5spd of course, for a 6spd it is simple you just go with the 3.2.