dannypio

On my 1996 stock GT, I have the Z code 3.07 gears which I understand is the std for automatic cars. I know that the car doesn't have enough horsepower, so considering a tuner. While I'm thinking on that, I don't want to go to the expense of changing gears, but I thought if I could reduce the tire size a bit it might help the axle ratio. I was thinking 245 45 R16 which would reduce the tire diameter about an inch and bring the effective axle ratio to about 3.19. Would this be a noticeable improvement in short line acceleration? Any other ideas? I don't have any shops in my area that would do a gear swap and I just serviced the differential. Thanks.

proeagles

You won't notice that IMO. You could do a gear change for the price of tires all around.

dannypio

Thanks that's what I was afraid of. I don't know of anyone that does that for that kind of price. What gears are recommended BTW? I'm not concerned about mileage, or top end speed since I don't want to drag race.

Z28KLR

For what you would spend on a new set of wheels and tires, why not consider doing something to increase power instead? PI swap comes to mind.... And will make a much more noticeable difference in your car's performance than what you're proposing and assuming you're able to get your hands dirty and diy could probably be done for what you would have spent on wheels and tires. Keep in mind that a +/- 0.19 difference in final drive ratio will be barely noticeable.

dannypio

Thanks. My dad actually had a garage at one time so I am able to do some work, and I saw these but didn't know it would make a lot of difference. Probably not a bad idea since I have the old-style (recalled) plastic intake with plastic coolant runner.

WhiteFoxGT

if you dont plan on cracking in to the motor, go get a set of 4.10s and have them installed. You will also need a tuner to accompany it to correct the shift points in the transmission

odypilots

4.10 would REALLY wake that car up, but the exhaust may drone a bit on the highway. Anyone know what the revs at 75 mph would be with an auto?

Z28KLR

First pic should be what OP's car is doing currently w/ 3.08's. Second one is w/ 4.10's. Both with 4R70W trans and assuming stock 245/45-17 tires. If you want to play around with things a bit, go to www.paladinmicro.com and click on "calculators".

imp

Why not figure it out? First, what tires? BTW, my '94 came from Ford with
245-45-ZR-17s. So, let's use that size.


First, 245 x .45 x .03937 = 4.3 inches, the sidewall width. Got 2 sidewalls plus the rim diameter, so,


4.3 x 2 = 8.68. Add 8.68 to 17 = 25.7", the "rolling diameter". Need Circumference, so 25.7 x Pi = 25.7 x 3.1415 = 80.7", the DISTANCE the car moves for one tire revolution. Change that to FEET, 80.7 divided by 12 = 6.7 feet, distance car moves in one TIRE REVOTION. How many revs per mile?


5280 feet per mile divided by 6.7 feet = 788 tire revs per mile. At 60 mph, (1 mile per minute), tire speed is 788 revs. per minute. DRIVESHAFT turns 3.08 (rear axle ratio) x 788 = 2427 revs perm minute = DRIVESHAFT SPEED @ 60 mph.


Now, the gearing. Call O/D ratio 0.67, close. Engine will be turning 0.67 x driveshaft speed = 0.67 x 2427 = 1626 rev. per minute. AT 60 mph.


Wait, he asked for 75 mph, so 75 - 60 = 15. 15/60 = .25 = 25.% higher. Eng. speed @ 75 WITH 3.08 gears = 0.25 x 1626 = 406. Add 406 to 1626 = 2032 rpm @ 75 mph.


With 4.10 gears? 4.1 divided by 3.08 = 1.33 = 133%. Eng. rpm @ 75 mph with 4.10 gears = 2032 x 1.33 = 2705 RPM!! AT 75 mph.


It's simple arithmetic, fellas. imp

odypilots

Arithmetic, yes. Simple, for some, I guess.

2705 are livable rpms.