Tom Wilson
November 1, 2010

Note: Stock baseline set with 10 degrees ignition timing and underdrive pulleys. The X302 figures reflect 13 degrees ignition timing and stock pulleys. Stock torque would improve with more timing; X302 power would gain with underdrive pulleys.

Transmission Upgrade
Because our '91's T-5 gearbox had 198,000 miles on it and was making increasingly more gear whine, we installed Ford Racing's M-7003-Z transmission as a replacement. This is the world-class version of the venerable T-5, a transmission we've come to love for its light shifting and minimal weight.

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Compared to our tired stocker, the M-7003-Z features upgraded synchronizers and bearings; a steel input bearing retainer; more torque capacity at 330 lb-ft; a short-throw shifter (not too short and fun to shift); double-moly second, third, and countershaft cluster gears; carbon-fiber third/fourth blocker rings; and a Cobra-style pocket bearing. The rest is compatible with the stock trans, with a 28-spline output shaft and seven-tooth speedometer drive gear, so it bolts right in.

T-5 Gear Ratios
Gear Stock '91 FRPP
1 3.35 2.95
2 1.99 1.94
3 1.33 1.34
4 1.00 1.00
5 0.68 (0.675) 0.63

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As the chart shows, the gear ratios are slightly different. Clearly the taller first gear combined with our crate engine's lower off-idle torque, choppy idle and stock 3.08 rear axle gears means starting from a dead stop is something of a small event, requiring a touch of technique. We stalled the engine numerous times until we ingrained the slight rpm increase and clutch slip required; now it's second nature. Curiously we find the taller first gear handier in parking lots, on super bumpy roads, and so on, but maybe not as brainless in crawling stop-and-go traffic.

Another consideration is speedometer error. Of course, we can ignore the First gear speedo error, Second and Third are close enough to not count, Fourth is identical, leaving only Fifth as an issue which we're probably just going to live with. In the real world, the speedometer is "slow" by about 6 mph at 70 mph in our pacing tests, so we remind ourselves we're going faster than indicated on the freeway. Ssadly, the odometer no longer reflects the exact mileage, but it's close enough for maintenance work.

What is to like about the ratios is the slightly taller Fifth gear makes flying along with the reality of 80-mph freeway traffic easier, plus it's beneficial for fuel economy at less frenetic cruise speeds. What was unexpected on the freeway-and has nothing to do with such minimal gear changes-is the noise level of the exhaust. The only new exhaust bits are the short-tube headers; the sound quality is the same-there's just a bunch more of it.

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