airchomper

Hey I was wondering if anyone knew much about the rear differentials in our cars. It appears as though most of the 90s-early-2000s RWD Lexus cars and the Supra share common rear differential components but have different rear drive ratios.

It appears as though the 2001-2003 LS430s have the lowest final drive ratios of the generation except maybe the 6-speed North American Supras.

The '01 LS430s have a 3.266:1 ratio and the Supra has a 3.16:1. The 2004+ LS430's have a much "shorter' rear differential gear ratio at 3.76:1 although their top gear is much lower at .56:1 whereas the 01's have a .75:1 ratio.

Any how, I really like that I can change the oil in the 5 speed and its internals are so much "figured out" than the 6-speed transmissions are. But I think the 6 speed gets way better milage on the freeway and my commute is basically all freeway, and rather than going to the hassle of selling my car and finding a nice '04-'06, I'd like to change the final drive ratio. I notice that the Lexii which use the 8-speed have a 2.93 final drive.

does anyone know if the LS430 and the LS460/GS350 have the same form factor? I could get one and bolt it in, but I've also seen the pinion and gearset are available. It looks like one can change out the gears relatively easily, anyone have any thoughts?

Thanks!

Gene01

You might try asking PureDrifter in the LS400 forum. He has a lot of experience with differentials.

BradTank

I can't imagine the gas savings would ever be recouped with a swap like that.

The EPA rates a 2004 LS430 at:
16mpg city/ 23mpg on the highway, 18mpg combined

2001 LS430 :
16mpg/23mpg, 18mpg combined

http://www.fueleconomy.gov/

I have a 2004, and I would rate my average mpgs at 19-20mpg. The EPA ratings are definitely conservative, so you can add a bit to that, but I don't think there's a huge difference between the two in fuel economy.

My guess is most drivers would save something like $3 a month on gas, if that. It's more about the performance with the 6 gears than it is fuel savings, it allows a more aggressive gearing.

All the issues with the speedometer and odometer, and a rear gear ratio that's not optimized with the factory transmission, plus the cost of a differential. It just looks like a big headache to me to save a few bucks a year on gas, but let us know if you go through with it.

airchomper

Thanks for the response guys!

I'm getting about 26 mpg now because of my favorable commute, although I only drive my cars on the rainy days because my bike gets ~100 mpg (although is much slower than my LS - I must be one of the few people who has a faster car than motorcycle).

I don't really know what the gas savings might be, back of the envelope calculations (friction increases by the square of an RPM, although there are pumping losses to consider, and the way the force of drag increases with speed) say I might see +5-8% mpg if I manage to get a 2.93 ratio in there. I know I'd only save a few dollars a month, but if I keep the car for another 200,000 miles, it might just be worth it (if I ignore the net present value of the cash I'll use to get the parts). I think it's just something I'm curious about as a fun project. I might have the chance to get my hands on an LS460's differential someday and I'd like to know if there's value in that option.

I thought the 2004s did better on the EPA's highway but I have to update my beliefs in light of this new information.

Thanks again! Happy driving everyone.