KJ Jones Senior Technical Editor
January 26, 2010
Photos By: Patrick Hill, Steve Turner

Horse Sense:
How good are ProMotion's pro-shifted Tremec transmissions? So good that no other transmission made it to the winners circle in Real Street at any of the '04 NMRA events. ProMotion's winning ways continued in 2005, as its transmission's win-total by midseason was an unprecedented 14 wins in 14 races. Is that good enough for ya?

The idea of owning a Mustang that puts out serious street horsepower (thanks to various bolt-on upgrades and maybe a little nitrous or a blower for good measure) is a thought that's common to many people out there who share our interest in these cars. "What type-coupe or hatch-of 'Stang should I get?" "What engine combination should I build?" "What transmission should it have . . . a stick or an automatic?"

Let's focus on that last concern-the transmission-the mechanical vessel through which all the engine's horsepower passes, en route to the driveshaft, the rear wheels, and hopefully, the ground. At this point, it's no secret that the stock T5 (especially a pre-'90 transmission, as it had a weak 265 lb-ft torque rating) is a prime example of a part that's "living on borrowed time" even if the car is making good power and if you're doing a more-than-fair amount of flogging it and power-shifting, on the street or at the track. Before you know it, the Third-gear synchronizers are shot, the gearbox is making ugly noises, and you're totally unable to shift it.

Your chances are slightly better with the T5 "Z" five-speed. This version of the T5 was standard equipment in the '93 Cobra and could handle 310 lb-ft of torque. Ultimately, though, if your street Mustang packs a hard performance punch and is capable of putting down 500 or 600 horses, you need a seriously stout transmission if you want to continue to play in the stick world.

Transmission Technologies Corporation is the company that brought us the Tremec TKO-series transmissions that have been mainstays on the Mustang scene since their introduction in the mid-'90s. The Tremec 3550 five-speed was the initial offering for Mustangs, but it's the TKO transmission-the follow-up unit to the 3550-that took 'Stangbangers by storm when it hit the market. The TKO was heralded by many enthusiasts as the must-use, most-reliable Mustang manual transmission of its time-then and now. While similar to the 3550 in terms of gearing and material, the TKO featured larger input and output shafts and was capable of handling 400 lb-ft of torque. As Mustang performance grew, it became almost unthinkable to not use a TKO behind 300 or more horsepower.

The quickest way down the dragstrip with a stick Mustang involves "power-shifting"-basically ramming the stick from gear to gear while keeping the hammer matted for the entire run. Prior to Tremec's arrival on the Mustang scene, power-shifting usually meant certain death for your transmission, probably a lot sooner than you'd expected-especially if you raced the car on a regular basis.

Last year, Tremec introduced its new TKO 500 and TKO 600 five-speed transmissions as next-level, direct replacements for the tried-and-true TKO. The new TKO 600, while similar in terms of appearance and dimensions to the TKO with its 83mm center distance and Toploader bellhousing bolt pattern, is capable of handling torque amounts of more than 600 lb-ft. The TKO 600 features gears and shafts that are made from a higher-alloy (4615) steel, a huge 31-spline output shaft, and a radical one-piece countershaft (TKO's countershaft was a three-piece unit).

ProMotion Performance Powertrain has been the force behind many of the most successful Tremec-shifted cars in Ford drag racing today. Company owner Walt Leaman Jr., a longtime drag racer, built and drove a hard-hitting, nine-second Pinto with a pro-shifted Toploader that he shifted at 9,000 rpm. Naturally, the Pinto was one of the most talked-about cars at the track, and fans' interest in the car was one of the catalysts for Walt starting the business in 1990, after working several years as a marina developer. Walt's unique "face-tooth" method for pro-shifting stick transmissions has been applied to the race versions of Tremec TKO and Pro G-Force T5H trannys that his company makes race ready.

ProMotion gearboxes are capable of consistent shifts at more than 8,000 rpm inNMRA Real Street cars. Realizing the time had come for our own Real Street LX coupe to undergo trans-replacement surgery, we reached out to Tremec and ProMotion for assistance. They were both more than happy to help us with the operation. Tremec sent a TKO 600 to ProMotion, where Walt and his crew upgraded the new transmission into what he calls a Street Pro version (PN TCET 5008; $2,590), and made it ready for us to install in Real Street.

The thing that makes the ProMotion-modified TKO 600 so special is that despite it being a full-on, pro-shifted "race" transmission capable of withstanding such a high rate of torque, the unique design of the face-tooth keeps the tranny somewhat manageable on the street as well. One of the bad raps previous pro-shifted Tremec models constantly received is they were a challenge-almost impossible to negotiate under normal street-driving conditions. The shifting in the early trannys had a clunky, no-nonsense feel and distinct sound that gave the impression all hell was breaking loose inside the case. When it came to getting through the gears at lower rpm and when trying to downshift, the race-bred, pro-shifted Tremecs definitely weren't street friendly.

The main upgrade for ProMotion's Street Pro is the pro-shift treatment the gears receive. ProMotion magnafluxes and shot-peens each gear for stress relief. The face-tooth, pro-shifting process involves cutting the synchronizer ring off each gear in the TKO 600 and replacing those synchro rings with nine-tooth engagement rings that Walt refers to as "face-tooth" engagement. Each tooth on this custom ring is separated by a 31/48-inch gap, and the ring itself is cut back by 7 degrees and positioned on the gear for maximum engagement. Walt says that because of this design, the ring does not compromise actual gear width in any way, and he believes this method is the key to positive high-rpm shifting because there are no synchros involved with gear engagement whatsoever. "Because of the high level of inertia created by engines making 700 to 1,000 horsepower, the key to 8,000-rpm power shifts, which our Street Pro is quite capable of handling, is eliminating the synchros," Walt says.

ProMotion also upgrades the shift fork pins in each Street Pro to quarter-inch, high-alloy pieces, and Tremec's shift fingers are replaced with ProMotion's custom and absolutely massive 4130, hardened tool-steel custom fingers that allow for high-rev, foot-mashed gear banging by NMRA and Fun Ford shift maniacs. "It's the best advantage of shifting you can get," Walt says. "You're least likely to miss a gear with our Street Pro. It features the best overall style of pro-shifting for the track, and is quite capable of seeing some street use. Fifth gear is actually retained in each Street Pro transmission and can be deleted for track-only race cars upon the purchaser's request."

Walt was kind enough to personally deliver Real Street's new gearbox to our Tampa facility. Tech Editor KJ Jones also happened to be visiting the home office, and the two teamed up to install the Street Pro and move our Real Street Mustang another step closer to seeing some "real" street (and hopefully track) action.

What Is Pro-Shifting?!
Synchronized stick-shift transmissions can generally be power-shifted at nearly 7,000 rpm with proper clutch disengagement. That's usually the threshold, due to the high-rpm inertia on the brake side of the synchro ring. The synchro simply is unable to stop the gear into which the transmission is shifted. This blockage or binding results in a missed shift or the transmission just not goinginto gear.

Many racers and transmission builders have modified the stock internals, grinding every other tooth from the sliders, synchros, and engagement teeth as a way of hopefully getting around this problem. This helps some. But, as the power and shock loads continue to increase with today's high-performance stick Mustangs, breakage and failure of the stock parts become more prevalent.

Contrary to popular belief, pro-shifted transmissions are not the clutchless-style crash boxes many stick-jamming 'Stangbangers dream of abusing. According to ProMotion's Walt Leaman Jr., all pro-shifted trannys require clutch disengagement in order to shift from gear to gear. Sorry to burst your bubble on this, but the long and short of it is, you'll still have to kick your left leg with a pro-shifted transmission. The important thing is that you kick that left leg quickly and use a clutch that's up to the task of reacting to things happening quickly.

What is pro-shifting a transmission? Pro-shifting is a process that involves removing the stock synchros and installing parts that make up what are known as pro-ring-style (developed by Joe and Craig Liberty of Liberty's High Performance in Taylor, Michigan), or face-tooth/dog-ring-style, pro-shift systems.

At ProMotion, custom alloy six-, eight- or nine-tooth faceplates are mounted on the tranny's drive gears and mated to custom high-alloy, face-tooth sliders. A Tremec synchro has 36 engagement teeth that must be lined up. At higher rpm, it becomes difficult for the sliders to engage this large number of teeth. The eight teeth on the faceplate of a pro-shifted transmission (nine, on ProMotion's plate) give the sliders a much bigger window for engagement at high rpm, so a racer is more likely to make a shift as opposed to missing a shift or being locked out of a gear.

ProMotion has found that faceplates can have as few as six teeth and still be effective for shifting. But the six-tooth faceplate, despite also having a bigger engagement window than a synchro ring, generates more backlash in the transmission. This backlash can increase the shock load imposed on the gears, which in turn generates fatigue and breakage. ProMotion's face-tooth, pro-shift system is custom made to exact requirements for producing wider gear and face-plate engagement, less shock load, shorter shift stroke, and most of all, reliability.

On the whole, the face-tooth, pro-shift system has proven to be the more-durable method of setting up a race transmission and can be used to upshift or downshift between gears without the transmission disengaging.

Power-Shifting 101
As mentioned earlier, power-shifting is one of the key ingredients in the racing-a-stick-car mix. In order to really understand the pro-shifting concept, we think it's important that you first have a good grasp of what power-shifting really is.

Simply put, a power-shift happens when a racer leaves the accelerator wide open/mashed to the floor during each shift. When power-shifting, the racer must try to consistently go through the following motions with each shift, in order to effectively get through the gears and down the track as quickly as possible:
• Precisely time each shift at the peak of the engine's rpm band or shift point.
• Kick the clutch pedal at the point required for proper clutch disengagement (according to Pro Motion, this point is achieved generally at 0.050 clutch air gap), in order to ensure the transmissionwill shift cleanly without dragging from gear to gear.
• Shift quickly! Remember, although the engine is high in the revs, the clutch is also disengaged when you hit the pedal. So, momentarily,the car technically isn't moving under power, so don't lollygag. Once you feel the shifter hit the stop for the next gear, reengage the clutchquickly.

That's Power-Shifting.

One of the most common mistakes a racer can make is trying to be the "quickest shifter on the street or at the track, and yank the shifter into gear without first focusing on the timing of the clutch disengagement as the first action in the power-shift," according to Walt. "The driver's arm is quicker than his foot." In most cases, these drivers will experience many missed shifts and eventually will damage transmission parts, even if the tranny is pro-shifted. Walt adds this insight about the art of power-shifting to let you know the procedure is far from the proverbial rocket science and doesn't require hours of thought in order to do it properly. "Power-shifting is like riding a bike. If you have to think about it too much, you're probably going to screw up." We agree!