Rear differential question

finaltable · 11-12-2007, 10:11 PM

I am looking for ways to improve the fuel efficiency of my '90 NA. The code on my door sticker (G282) says my rear end is an open 4.3 ratio. I understand that 3.9 and 3.7 ratios were also available. What difference would I see if I switched to a 3.9 or 3.7 and is this something that would require replacing the whole differential or could they just open up my existing one and replace gears?

supramacist · 11-12-2007, 10:14 PM

Taller gearing gives you more top end.
Shorter gearing gives you better take off.
They should be able to change the gears in your current diff.

finaltable · 11-12-2007, 10:26 PM

Help me understand this. I read 4.3 rear end as "4.3 rotations of the crankshaft are required to get one rotation of the rear axle" so to get 1000 rpm of the tires the engine (via the transmission) needs to be turning the axle 4300 rpm. The bigger the number is, the greater the torque applied to the wheels but the higher the revs will be when cruising.

Did I get this right?

supramacist · 11-13-2007, 12:50 AM

I don't know the specifics on it.

It's like switching tire sizes. If you go low pro. You get out of the hole faster. But you lose top end.

A taller tire gives you more top end. But takes longer to get their.

That's the best I know to explain it. I'm not sure wich series are the tall or short gears.

I'm not sure your wrong or right without further research.

mrnickleye · 11-13-2007, 06:20 AM

Quote:

Originally Posted by finaltable

Help me understand this. I read 4.3 rear end as "4.3 rotations of the crankshaft are required to get one rotation of the rear axle" so to get 1000 rpm of the tires the engine (via the transmission) needs to be turning the axle 4300 rpm. The bigger the number is, the greater the torque applied to the wheels but the higher the revs will be when cruising.

Did I get this right?

Yes.
Cost wise, you will NOT by just gears to replace yours. You will find a turbo car pumpkin (the diff) and replace yours with it.

If yo drive 70% or more at hwy speed, then you will get better MPG. If you drive 'mostly' around town, then you will lose MPG, as it will take more gas pedal to get the car moving up to speed.

The NA gears are higher because the HP is lower than turbo car, and is need to get these fat pigs (3700lbs) moving.

Mine gets 17-18mpg town, and 20-22 hwy.

It would be WAY cheaper to put taller tires on the back.

For a year I ran some 255x50x16's on the back. They are 1" taller, and 1" wider than stock.

I got 24mpg hwy on a 1000 mile trip, without loss of 'pickup' around town.

finaltable · 11-13-2007, 01:24 PM

90% of my driving is highway miles. I commute every day from Athens, GA to Norcross (in Atlanta.) The trip is 55 miles one way and only about 3 miles of it is not on either GA-316 or IH-85.

I am assuming that I also need to lose some weight from the car as well. I know that subject has been discussed in other threads here.

My car is coming up on needing new tires; I'll remember to get taller tires when I get them.

Now where do I get a new pumpkin?

mrnickleye · 11-13-2007, 02:46 PM

Your not gonna want a NEW one, as it may cost more than the car. Toyota dealer.

You can get a used one from the wrecking yard.

There are also a few places that have remanufactured ones. Check the net, and sell section on here.

"I" would spend my $$$ on some 18" wheels, and 50 series tires. That whay, you'd get the taller gearing you want, and some kool wheels & tires, for less than a reman. pumpkin costs.

finaltable · 11-13-2007, 02:59 PM

You weren't kidding. A new 3.7 differential from Toyota is $2,363 which *is* more than I paid for my car. I'll have to look around for a used one or remanufactured.

I'm not putting 18" rims on the car for all sorts of reasons but I will try going with a higher profile tire.

oowee623 · 11-13-2007, 06:04 PM

im always seeing lsd diffs for less than 100 check supramania.com

supramacist · 11-13-2007, 07:49 PM

Yes. Tires.

11-12-2007, 10:11 PM	#1
finaltable 3" Exhaust Join Date: Sep 2006 Location: Texas Gulf Coast Posts: 99	Rear differential question I am looking for ways to improve the fuel efficiency of my '90 NA. The code on my door sticker (G282) says my rear end is an open 4.3 ratio. I understand that 3.9 and 3.7 ratios were also available. What difference would I see if I switched to a 3.9 or 3.7 and is this something that would require replacing the whole differential or could they just open up my existing one and replace gears? __________________ Current ride: Not a Supra :-(

11-12-2007, 10:26 PM	#3
finaltable 3" Exhaust Join Date: Sep 2006 Location: Texas Gulf Coast Posts: 99	Help me understand this. I read 4.3 rear end as "4.3 rotations of the crankshaft are required to get one rotation of the rear axle" so to get 1000 rpm of the tires the engine (via the transmission) needs to be turning the axle 4300 rpm. The bigger the number is, the greater the torque applied to the wheels but the higher the revs will be when cruising. Did I get this right? __________________ Current ride: Not a Supra :-( Last edited by finaltable; 11-13-2007 at 02:30 AM.

11-13-2007, 01:24 PM	#6
finaltable 3" Exhaust Join Date: Sep 2006 Location: Texas Gulf Coast Posts: 99	90% of my driving is highway miles. I commute every day from Athens, GA to Norcross (in Atlanta.) The trip is 55 miles one way and only about 3 miles of it is not on either GA-316 or IH-85. I am assuming that I also need to lose some weight from the car as well. I know that subject has been discussed in other threads here. My car is coming up on needing new tires; I'll remember to get taller tires when I get them. Now where do I get a new pumpkin? __________________ Current ride: Not a Supra :-( Last edited by finaltable; 11-13-2007 at 01:28 PM.

11-13-2007, 02:46 PM	#7
mrnickleye 1000whp postwhore Join Date: Jun 2005 Location: Mojave Desert, Calif. Posts: 1,705	Your not gonna want a NEW one, as it may cost more than the car. Toyota dealer. You can get a used one from the wrecking yard. There are also a few places that have remanufactured ones. Check the net, and sell section on here. "I" would spend my $$$ on some 18" wheels, and 50 series tires. That whay, you'd get the taller gearing you want, and some kool wheels & tires, for less than a reman. pumpkin costs. __________________ Had a Red 1989 N/A. Automatic. Sports Pkg. w/wing. TEMS, and some nice MODS. Sold to a friend 10/08/08.

11-13-2007, 02:59 PM	#8
finaltable 3" Exhaust Join Date: Sep 2006 Location: Texas Gulf Coast Posts: 99	You weren't kidding. A new 3.7 differential from Toyota is $2,363 which is more than I paid for my car. I'll have to look around for a used one or remanufactured. I'm not putting 18" rims on the car for all sorts of reasons but I will try going with a higher profile tire. __________________ Current ride: Not a Supra :-(

11-12-2007, 10:14 PM	#2
supramacist 1000whp postwhore Join Date: Apr 2007 Location: Escape from the Prison Planet Posts: 1,356	Taller gearing gives you more top end. Shorter gearing gives you better take off. They should be able to change the gears in your current diff.

11-13-2007, 12:50 AM	#4
supramacist 1000whp postwhore Join Date: Apr 2007 Location: Escape from the Prison Planet Posts: 1,356	I don't know the specifics on it. It's like switching tire sizes. If you go low pro. You get out of the hole faster. But you lose top end. A taller tire gives you more top end. But takes longer to get their. That's the best I know to explain it. I'm not sure wich series are the tall or short gears. I'm not sure your wrong or right without further research.

11-13-2007, 07:49 PM	#10
supramacist 1000whp postwhore Join Date: Apr 2007 Location: Escape from the Prison Planet Posts: 1,356	Yes. Tires.

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