Michael, thanks for the info and the links. I found that the diff for a 6 Speed MT MK4 Supra after 1996 is smaller in size witha a diff ratio of 3.2:1.

From the NZ supra site, the got the following spec for my diff centre. Just to remind you, I got this diff of a 1997 MK4 Supra TT RZ 6 Speed MT (highlighted in red).



The crown wheel size: 8"(200mm)
Pinion Teeth: 15
Axle Code: A03B
Helical Gears: 8
Diff Ratio: 3.2:1

So it being 8" should fit into my open diff casing, but what about the diff ration 3.2:1? Will this be useful for my soarer?

 

Won't be useful unless you have a turbo or a manual trans swap. You will be loosing a lot of torque.

Swap out the ring gear for your stock 3.94 ring gear. It will reduce the amount of labor by a lot also. Once you swap pinions you've opened up a whole can of worms. There is a lot more setup time involved.

3.26 vs 3.94 means a 18% torque loss. So if you had 250 ft/lbs to the wheels... you'll now have 205 to the wheels.

This page should help you with the rebuild: https://www.clublexus.com/forums/per...madness-4.html

 

Man you are genious! Thanks for your help and the links. They are very useful.

So following steps in the link and using my open diff's ring gears on this LSD should effectively give me the right diff ratio?

 

Also Michael,
I am getting a little confused about the gearing ratios with the gearbox and the ratios of the diff.

Even if I change the diff the gearing on the gear box should define the final drive ratio (or atleast this is what I thought). What is the correlation between these two ratios?


Thanks

 

wow guys... this is a great thread. Nice to get good info like this posted up.

 

Yeah if you use your open diffs ring gear, you're not changing the ratio at all. You're staying stock, lexus put that ratio in the car in the first place for a reason. Combinations of torque, top speed, fuel efficiency, etc.

The larger the number like 4.27 will give you more torque, but less top speed.
A small number like 3.27 will give you less torque but higher top speed.

A 3.27 ratio would make the car feel like a slug. But if you kept the pedal down to the floor and had a long enough stretch of road, you could probably hit 200mph. (unless you had turbo, 500hp or trans ratios that are lower, then it wouldn't be sluggish, because you're making up for a lack of gearing by having MORE TORQUE!!)

A 4.27 ratio would give you fast acceleration, due to the increase in torque, but in top gear on the highway at 100km/h you'd be revin the motor waaay out. You'd get worse gas mileage too.


Blizzy, the guy in the thread I sent you, changed out his auto trans for a 5 speed manual. So he's showing COMBINED overall gear ratio. And he's trying to get his gear ratios to be in a USEFUL range.

There's an internal transmission ratio for each gear.

For the auto trans it's

first = 2.804
second = 1.531
third = 1
fourth = .705

You're not going to change those ratios. Those are the ratios of engine vs transmission rpm.

In first gear the engine turns 2.804 revs to make the trans spin one complete rev. That gives you torque to take off. As the vehicle speed increases you'd quickly max rev the motor, so you shift to second (the revs drop and torque drops but it's OK you're already moving you don't need as much, then third where it's 1 to 1 (engine and trans spin together in unison), and then into 4th where the engine is turning slower than the transmission by a ratio of .705 to 1.

SEEEE??????

The Final Drive ratio or Axle ratio is the gear ratio in your diff. If you gear the final drive low (4.27) it shortens all those gears. If you gear the final drive higher (3.27) it spreads those gears out over a longer range.

You need a good balance between the two... I recommend you stay with your stock ratio, by swapping the ring gears and calling it a day.

The pinions have differing number of teeth to match the ring gear they correspond to.

So by staying with the stock 3.94 ratio ring gear, you won't have to change the pinion and that makes the setup of the whole diff 100 times easier. And in the end you won't be disappointed that your car accelerates like a turd or just the opposite revs too high on the freeway.

 

Michael thank you very much, the replies you put in this thread are a good reading for any body working on diffs. Thank you once again for clearing the things up.

 

No problem. That's the idea... put good information out there that is easy to digest. That way the next time someone has a question, they can search, find this thread, get the answers they need, and add good information that we missed.

Now it's up to you to keep this thread going with pictures and info from your diff swap as it goes along!!

 

just got the answer i needed from another thread.