00Formula

I see that a lot of people have swapped the rear gear ratio to a higher numerical gear like a 3.92, but has anyone gone the other way?

I was shocked when I got this car on the interstate and at 75mph the tach read 2500rpm.

For reference my mom had a 4.6L Northstar in her Cadillac and it loped along at ~2000rpm at 75mph. This car probably weighed more and got 26-27mpg on the interstate.

I have a motorcycle and a pony car to go fast in, the Lexus is the daily driver and I'd like to get better gas mileage on the interstate.

Does anyone know if a ~2.73 ring and pinion is available for a 04' GS430?

That would put the car at 2100rpm at 75mph, and hopefully get up in that 26-27mpg range.

kit cat

iTrader: (6)

did you just pull that 2.73 and other mpg/mph/rpm out of the sky or something?

00Formula

2.73 is a standard ratio in other cars I've worked on like F-body's(Firebirds and Camaro's).

I used a gear calculator to get the rpm/mph.

Stock 3.23 gear

http://www.car-videos.net/tools/spee...B1=Recalculate

2.73 gear

http://www.car-videos.net/tools/spee...B1=Recalculate

The gas mileage is an estimate on the GS, but I've driven the Cadillac on trips when I was younger with the parents.
Real world it averaged around 26-27mpg if you drove 75mph on cruise control.

A 2.56 rear end would be even better, but I don't know if the engine would make enough trq to lock up the converter at 75mph in 5th gear. It would only be turning 1975rpm at 75mph.

jcat_350

your best bet is a 3.76 supra tt auto. 3.92 came stock on GS300's to make up for the lack of power. The Gs4 comes with a 3.26, because that's what it was intended to have.

Honestly, that 500rpm is not going to save you much gas.


And no, nobody makes gearsets for these cars because the engineering was not meant to be messed with. This is not an fbody or a mustang.

Even if you could find those gears, without FI the car wouldn't get out of it's own way...which is why the lexus engineers got paid tons of money to put that gear ratio in the rear end.

00Formula

As an engineer myself, I'm kind of at a loss.

The "engineering was not meant to be messed with", yet you just recommended a swap to a 3.76 rear gear?

I'd wager the car has plenty of torque to push a lower numerical gear, but it will reduce the acceleration. As I said, I'm not concerned with going fast in this car. I'd rather it get better gas mileage at the expense of reduced performance.

Frankdorn

iTrader: (7)

Buy a Kia.

sakataj

iTrader: (182)

hahaha.


OP what part of tn u in?

00Formula

East TN, south of Knoxville.

jcat_350

I think you misunderstood...the 3.76 is a full on limited slip differential swap, engineered by the same people for the supra that engineered the lexus.

The gs4xx would be a DOG with gears as low as you are suggesting. The GS300 has a 3.92 in it....at 80mph in 5th gear it sits at 3000rpm. And yet still gets the same mileage as the 8 cylinder GS at around the same speed.

If you're looking for more traction because of added power, a 3.76 lsd is in your best interest. Adds a bit of top end for the 300, and quickens up the 4xx a good bit as long as other mods are there (torque converter etc.)


But, the answer to your root question, again, is no. Nobody makes ring/pinion sets for these cars.

00Formula

If what's been posted is true about the Supra differential being directly compatible with the GS430, then the gears for a Supra should be identical also. I think it's only the NA supra's, not the twin turbo's, as they had a larger ring gear.
Given that's true, it apprears there are some manufacturers that make individual ring and pinion gears for the Supra's differential.

Per Richmond Gear's site they call it a Toyota 7.5" Rear and IFS Front Differential Ring and Pinion.

If this is the correct size and description for the ring and pinion, they may be able to make other gear ratios. On their site they only list really deep gears like 4:10, 4:56, 4:88, 5:29, 5:71.

I'd like to email Richmond Gear and Motive Gear as they both make Toyota 7.5" IFS ring and pinions, but need someone to confrim that's the correct model before I ask about 2.73 gears?

jcat_350

the only diff that will work with the GS (regardless of model) is the MkIV supra TT auto differential.

As for custom building gears, absolutely can be done, but not cheap and quite honestly it wouldn't save you enough gas to be worth it.

4.10s will hang the RPM wayyyyyyy higher. even the 3.76 will raise it, but the benefit there is the limited slip.

My cobra had 3.73s in it and it was putting down 380rwhp, 80mph in 5th (t45 trans) was around 3k rpms. My buddy had a 500hp cobra with 4.10s in it and 80 in 5th was about 4k rpms.

00Formula

As long as they don't charge a huge amount over normal gears it might pay for itself in a year.
Stock gears are $166.25- $225.00.
http://www.jawsgear.com/Ring_And_Pin...7.5-IRS_Supra/

I might be driving 80 miles total each day, almost all interstate.
Going from 22mpg to 27mpg, that's about 0.67 gallons per day difference.
Drive to work 252 days a year, 252 x 0.67 gallons = 168 gallons a year.
168 gallons x $2.80 = $470 a year in gas if it stays at it's current price.

jcat_350

113 days off per year?! **** I need your job.

plus all those gears are MUCH higher than stock...so go completely in the opposite direction...i see 411, 456, 488 lol those gears would SUCK