transmissions

alex.rhodes · 03-13-2006, 10:36 AM

I've searched a bit and can't find this anywhere here. N/a tranny is 3.89:1 and turbo is 3.37:1 in regards to final drive. I understand that putting the turbo tranny in a n/a is gonna make the n/a slower. in terms of real life, how much slower? I don't really understand the math to take gear ratios and make speeds and rpms out of them. The car is stock 85.5, w/ 245/45/16 rear tires. please no flaming, I'm not looking into this because the turbo is faster or any such b/s, i have a line on a tranny and am trying to keep a car on the road before it rots away. thanks

JRMock · 03:26 AM

The Turbo gear set is 'taller'. More mph per gear, but lack of power will make it harder to get going.

To calculate MPH for any given gear...

(RPM * TC) / (FDR * GR * 1056) = MPH

TC = Tire Circumfrence - 245/45/16 = 77.5mm
FDR = Final Drive Ratio
GR = Gear Ration i.e. 5th gear, standard trans = .730

(3,000 * 77.5mm) / (3.889 * .730 * 1056) = 77.6 mph

so...
Standard trans, 5th gear at 3,000 RPM = 77.6 mph.
Turbo trans, 5th gear at 3,000 rpm = 78.8

However, the real differences are in the lower gears. Calculated at 3,000 rpm...

Gear - Standard - Turbo
1 - 15.7 - 18.6 mph
2 - 26.7 - 31.7 mph
3 - 38.8 - 44.8 mph
4 - 52.9 - 63.1 mph
5 - 77.6 - 78.8 mph

Good luck
JM

Zero10 · 03-13-2006, 02:08 PM

If your transmission is broken, and this is your only option to get it back on the road, do it.
That said, I'd be watching for a N/A transmission in the coming months to swap it out with, then maybe re-sell the turbo transmission.

highway · 03-13-2006, 09:00 PM

http://www.clarks-garage.com/shop-manual/trans-04.htm
Pretty good resource, gets down to the gear ratios. There are also some speed/transmission calculators out there that will tell you how much slower your car will be at the same RPM.