5.0 Mustang & Super FordsHow To Drivetrain
Modified T5 Transmission - No Time To Lose
Pro Motion Performance Powertrain's New T5 Modifications Offer Durability And Shave Time Off Your E.T.
Horse Sense: The two main gear types offered in the Pro GF/T5 are straight cut and helical cut. The straight-cut-or spur-gear is strong, but it isn't the most streetable as you can't downshift the box easily (it's possible to do, but some people find it difficult). The helical-cut gears offer quieter operation for street use, and the angle-or helix-of the gear is adjusted for optimum strength while offering a possible alternative for Factory Stock, Pure Street, and Real Street NMRA racers.
Strong and light. These two words don't often go together in a performance environment such as drag racing. But that's exactly what Pro Motion Performance Powertrain has to offer racers who will row their own gears in Factory Stock, Pure Street, and Real Street next season. Pro Motion has devised a modified Tremec T5 (yes, we said T5) that can handle high-nine-second e.t.'s in a 3,000-plus-pound race Mustang. How is this possible when your buddy can crack his T5 like a two-minute egg in his bolt-on '87 GT? Simple-build it strong with the right parts.
We spoke with Walt Leaman of Pro Motion to get the skinny on his new T5 baby and find out all the juicy details. Walt started Pro Motion more than 14 years ago, specializing in high-performance manual transmissions. A stocking Tremec distributor, Walt's company is well known for its Pro-Shifted Tremecs used in FFW, NMRA, and WFC racing events. These transmissions feature straight-cut-or spur-gears. Straight-cut gears offer superior strength by having the gear teeth parallel to the axis of rotation.
While the gears are strong, give a racer a chance and he'll figure out how to break a part. So, in 2000 Walt teamed up with Leonard Long and his affiliate company G-Force Transmission to make the T5 better and stronger (cue the Six Million Dollar Man theme). What the duo came up with Pro Motion now calls its Hi-Alloy, Straight-Cut-Gear, Face-Tooth, Pro-Shift Transmission. If that's too much for you to remember, just call it the Pro GF/T5-S (for straight). Debuting at the '02 NMRA finals in Bowling Green, the trans was ruled illegal for "stock-type" classes including Factory Stock, Pure Street, and Real Street, where a production transmission with a helical-cut gear was required.
Walt told us that while they could have put a 1-degree helix into the gear and been legal, they instead went through the entire transmission, determining the best helix angle for each gear. For example, the First gear of the T5 is generally the strongest gear, so a small helix angle adjustment was made, whereas on the Second and Third gearsets, the helix angle is slightly less than First gear's. The high-nickel alloy content-made from 9310 steel-did not change, nor did the additional width of 31/416 inch on the gears for added strength.
This transmission is known as the Pro GF/T5-H (for helical). Common to both transmissions, Pro Motion upgrades these T5s with 26-spline input shafts, a cluster support plate, and high-alloy shift link plates. As an option, they can be fitted with bronze shift forks and a high-alloy 28-spline output shaft. They can even have the Fifth-gear assembly removed.
This all sounds good, but you might still be thinking, Why use the T5 and not the beefier models? You just answered your own question there, Sparky, with the word "beefier," as in "heavy." The typical Tremec 3550 TKO has a rotating mass of approximately 50.52 pounds (without Fifth gear installed), whereas the T5 weighs in at a mere 34 pounds, a savings of 16.5 pounds of rotational weight. The weight savings is especially evident in non-power adder cars, where it's usually good for 1.5 tenths e.t. and 1.5-2 mph.
We thought this would be an interesting--if not different--reason to throw some parts on a test car and dyno the outcome. We had Rick Anderson at Anderson Ford Motorsport (who is also a Pro Motion stocking dealer) stick a Pro GF/T5-S with a helical Fifth-gear option into his red coupe and make before-and-after runs to see what kind of improvements one could expect with a transmission such as this in the tunnel. Check out the following captions for an overview of the trans and the dyno results.
Walt also brought us a complete, straight-cut, face-tooth-shifted gearset and installation kit. At the top of the picture are the ultrastrong bronze shift forks, flanked by the high-alloy shift link plates. Below, the shift forks are First through Fourth gears, along with the input shaft, At the bottom is the straight-cut countershaft. The gears are machined with teeth on the face of the gear for engagement since there are no synchros in the transmission, hence the terminology "face-tooth-shifted" used in the description.
For comparison's sake, Walt provided us with pictures of a stock T5 internal gear set, as well as his straight-cut and helical-cut versions. This is a shot of a stock T5 with the stock helix angles on the gears and countershaft.
Shown here is the helical Pro Motion modified T5. Compare this photo with the previous one and you can see the helix angle differences. While it's difficult to see, the gears are actually wider than the stock gears.
Here's the straight-cut version. While it's the noisiest, it's also a bit stronger. With the helical Overdrive gear, the noise does abate some once shifted into Fifth. The straight-cut version of the Pro Motion modified T5 is not NMRA legal, though it can be used in some Fun Ford classes.
We asked Rick Anderson for his opinion on the real-world use of one of Pro Motion's modified T5 gearboxes.
"During drag racing," he says, "the Pro GF/T5 feels super smooth and positive. It shifts so light, you'd swear that you are not moving anything in the trans. When street driving the Pro GF/T5, it is somewhat interesting and not for the faint of heart. Our model has the straight-cut gears in First through Fourth gear and whines loudly like a camshaft gear drive. With each slow gear change, it clunks too, and it also makes some other interesting noises till you get into Fifth, which is a helical-cut gear, and then it quiets down. Downshifting is another matter. It's best to downshift like you upshift and not skip gears (example 4-3-2-1)-which is a lot better than no downshifting, as with the Pro-Shifted TKO."
Even if you've read this magazine only once before, chances are you know about Rick Anderson's infatuation with dyno testing. Though we don't have any photographic proof, rumor has it he once dyno tested himself by running on the Dynojet rollers as fast as he could. We have a feeling Robin Lawrence might have been behind him with a whip, but again, there are no pictures to prove it!
What's more important to this article than overall horsepower and torque gains is time. We can see a solid improvement in shift times by looking at the Time column. If you take the total time of the run and subtract the start time, you come up with these figures: 5.02-0.58=4.44 and 4.88-0.52=4.36, which is almost a full tenth faster (0.08) from 4,200 rpm to 7,000 rpm. Of course, there are improvements in the other columns as well. Ignoring the highlighted peak differences, you can see improvements of up to 11 hp and 12 lb-ft of torque (depending upon the rpm) under the peaks. When it's speed that counts, the Pro GF/T5 will shave down your e.t. and net you some power to boot. You can't complain with that kind of deal.