Hermosa

This is an informational post to those who want to compare the rear ends between the SC300,SC400, and MKIV Supras

92-97 SC300
6 cyl, AT (4.27 ratio)
6 cyl, MT (4.08 ratio)

98-00 SC300
6 cyl, AT (4.27 ratio)

92-96 SC400
8 cyl (3.92 ratio)

97-00 SC400
8 cyl (3.266 ratio)

92-96 MKIV Supra

w/o turbo; (4.27 ratio) Limited Slip
w/o turbo; (4.27 ratio)
w/turbo, MT (3.133 ratio) Limited Slip
w/turbo, AT (3.769 ratio) Limited Slip

97-98 MKIV Supra
w/o turbo; (4.08 ratio) Limited Slip
w/o turbo; (4.08 ratio)
w/turbo, MT (3.133 ratio) Limited Slip
w/turbo, AT (3.769 ratio)
w/turbo, AT (3.769 ratio) Limited Slip


Differential Gear Ratio Changes

Racing Teams use different gear ratios to suit the characteristics of each track and obtain maximum acceleration. Successful autocrossers know the advantages of a quicker ratio, but as a street/highway performance option it is often overlooked. This may be because it seems more difficult than changing computer chips or adding a suspension package. Also, many local shops and even dealers lack the special tools and expertise to rebuild and change gear sets in differentials. With our racing experience we are very proficient with differentials and we have the special tools needed to make modifications correctly. UPS and other carriers have increased their weight limits and can now pickup and deliver your differential at your front door. The usual diff removal or installation time for most is 4.0 hours.

Changing to a quicker ratio provides faster acceleration in all gears at all rpm's. It does not affect engine emissions or idle speed and can make up for changes in tire diameter. Some models were originally geared very long for increased fuel mileage. These cars benefit the most from quicker ratios.

Generally, longer ratios yield better fuel mileage and shorter ratios offer more acceleration and higher fuel consumption. In practice, the fuel difference is often slight. If you have such a long ratio you must frequently downshift to pass or accelerate quickly, then in reality you do not get the theoretically higher fuel mileage that the longer ratio would have you expect. And, if you switch to a shorter ratio for more acceleration, you may not burn much more gas than before, as you are now able to upshift more quickly into the higher gears.

In a similar way, you would expect that changing to a shorter ratio for more acceleration will reduce your top end speed a you would run out of revs in high gear. However, few cars have enough top end torque to pull full revs in high gear. Changing to a shorter ratio will usually enable the engine to pull more revs against the high speed drag resistance. Though you will turn more revs per mile, your actual top end speed may be as good or better than before, especially if you have added some additional performance improvements.

The following formula will enable you to calculate your possibilities, but keep in mind actual results will vary. Drag, rolling resistance, tire characteristics, spoiler packages and engine modifications all affect acceleration and achievable top end speed. And don't forget road conditions, speed limits, and radar! It is usually more practical to gear for greater acceleration than higher top end speed. You can enjoy it more often with fewer penalties.

MPH = RPM/((ring-and-pinion ratio) x (transmission final drive ratio) x 336 / (tire diameter)))

*See Tire Diameter Formula below to calculate above diameter

It recommended to stay within a +/- 7% gear ratio change for most street driven cars. To obtain a percentage change, divide your original gear set ratio by your proposed new gear set. The resulting percentage also equals your RPM change at a given speed.

Hermosa

In an earlier post I mentioned that I felt like my SC300 with the Supra TT Limited Slip Differential was going faster than the speedometer indicated. It looks like this is true once I calculated that at 65MPH on the speedometer was actually 73.64MPH in true speed. Careful when driving if you are unsure of the speed of your car after mods. At 57.37 MPH on the speedometer I am actually driving the legal highway speed limit of 65MPH.

lexcoupe

so i have a 92 sc300 manual. I want to make the acceleration faster. what supra gears can i swap in and get better acceleration?

Kevin

wmulli

The only ones that will give you (slightly) quicker acceleration are the 4.27 gears. I'm looking for a set of these now, but finding them with the limited slip is a real b&*^c!

wmulli

Hermosa, are you offering to supply these diffs? Or even know of a source for them?

wmulli

Great info Hermosa! The .gif of the formula for deriving the tire diameter has one mistake. In the example, it left out adding the wheel diameter as was shown in the formula. I understand it was a link from somewhere else and not your mistake, but I thought it should be pointed out.

Thanks for the great post!

Hermosa

This is an FYI for members to benefit. However I might be able to get one for you from somewhere. PM me only if you are serious about getting one immediately. I do not want to jump through hoops if you are only considering installing one.

The formula was edited and corrected.

I have a torque converter upgrade and a turbo so that should help me get more off the line. If I had the 4.27 LSD then I would be spinning the wheels like crazy.

Miles B

Pretty sure the V8 Soarer comes with a Torsen LSD.... doesn't the SC??

Why don't you just get the gears in your diff changed if you want better acceleration?