On Monday, I decided I would purchase a new Tremec T-5z transmission for the Mustang. It is something I've considered a while primarily to benefit from different internal gearing which work better with rear gears like my 3.80's. Since the transmission is out of the car and I received a 10% discount code at the Goodguys show this past weekend, I decided now was as good of a time as any. I'm sure I will appreciate the improved gearing on Power Tour.
The following compares my current T5 gears to the new T5z:
Gear New Current
First Gear: 2.95 3.35
Second Gear: 1.94 1.99Third Gear: 1.34 1.33
Fourth Gear: 1.00 1.00
Fifth Gear: 0.63 0.68
According to BF Goodrich, my rear tires are 25.7 inches in diameter. At 70, the engine is currently at 2,365 RPM which will change to 2,190 with the new transmission.
What is more significant is the first gear ratio changing from 3.35 to 2.95. When driving with the current gear, I normally switch to second gear at 3,000 RPM which is 18 MPH. After the shift, I drop down to 1,500 RPM in second gear. First gear seems to low and the difference between the gears makes it a weird shift change.
With the new transmission, I'd be at 2,500 at 17 MPH. If I shift then, I end up at 1,646 in second gear. If I shift at 3,000 RPM as I do today with the new transmission, I'll be going 21 and end up at 2,000 RPM after the shift. Presently, second gear is the best gear in the car, I'm thinking first gear will be so much better after this change as it moves it in that direction.
The part number for the transmission is 1352-000-251. It's produced by Tremec. It should be here by Friday.
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