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1983 Mustang Project - Performance Transmission Comparison Test - C4 vs. Five-Speed
Answering the age-old question: Is there a difference-and if so, how much?
It would be impossible to count the number of times we've been asked what the performance difference would be when switching from a five-speed to a C4, or vice versa. The general consensus has always been that the five-speed-equipped car would be quicker and faster, all things being equal. But the fundamental question remained: how much quicker?
We set out to answer that question by doing a direct comparison between a full-competition C4 from Transmission Specialties and a Pro-Shifted Tremec 3550 built by Hanlon Motorsports. The C4 was equipped with a drag-race-friendly, 4,700-stall speed, 8-inch Dura Sprag converter, an ATI chromoly SFI flexplate, and a transbrake. The Tremec was fronted by a Ford Racing Performance Parts heavy-duty clutch and billet-steel flywheel. The only items changed were the flywheel, trans, and driveshaft. No changes were made to the engine combination, and the initial dragstrip tests were performed using the exact launch and shift rpm. The reason for the driveshaft change was simply because in the past we had always run the stick with the custom Dana driveshaft that came with the car.
Our assumption was that it was stronger, and it clearly fit better with the stick, meaning the yoke didn't hang out of the tailshaft as far as the OEM driveshaft did. The Dana piece is 311/42 inches in diameter versus 3 inches for the OEM unit, yet the factory driveshaft outweighs the Dana by 2-3 pounds. While even 3 pounds of rotational weight can make a difference, we don't believe it's dramatic enough to make a noticeable one on the timeslip or a chassis dyno.
Our tests were conducted in summer weather, all at the same track-Old Bridge Township Raceway Park near Englishtown, New Jersey. The weather varied during our time there, but we were able to test each transmission under similar conditions. Since we were using a vehicle of known quantity, it was easy to compare our tests with prior runs. This helped put our results into proper perspective.
It's also worth mentioning that the tests were conducted during weekly test and tune nights where the track conditions varied due to weather, oil downs, and street-tired cars affecting the racing surface. This only helped to shed light on what it would be like to live with each transmission in the real world. As an added bonus, we were able to dyno the car with each transmission, which not only confirmed some of our expectations, but surprised us as well.
The testbed was our own Project Pro Tree Mustang ("Value-Minded Mustang," June '06), a naturally aspirated, 302-powered combination representative of many street/strip cars. PTM uses a stock roller short-block with mild '71 351 Windsor cast-iron heads and shorty headers. Prior to this transmission comparison, we swapped the FRPP E-303 cam for a Ford X-303, and port matched the Weiand Stealth intake to the heads (we also used Fel-Pro 1250 gaskets). For those following this project, the cam swap made essentially no change, which we attribute to the limitations of the OEM heads. More on that in a future issue.
Our first order of business was to baseline the C4 combo on a chassis dyno. We took the car to PRA Solutions, a division of RIPP Modifications in Staten Island, New York. There, Perry Papadopoulos helped us find the best timing and jetting for our new cam with the C4. I was personally surprised when we made 302 rwhp, considering I didn't believe this engine made much more than that at the flywheel. Nonetheless, this tuning session netted us a full tenth over what we had been running previously with the X-303 cam. At the track, the car ran several 12-teens in some oppressive heat and a best of 12.09 at almost 109 mph.
We were confident the five-speed would put the car into the 11s in the heat, and it didn't let us down. Right off the trailer, we ran an 11.99 at 111 mph. The 60-foot time dropped to an all-time best of 1.54, and that was with the exact same 4,700-rpm launch and 6,200-rpm shift point we had been using with the C4. The only change that was made in deference to the five-speed was the shock settings. Knowing the stick would shock the driveline (and our short-sidewalled 26x10 slicks), we reverted back to the same rear shock settings we had used in the past with a hard-launching stick car-full tight. We also tightened up the front struts to try to control the antici-pated bounce from the big wheelies we planned to pull. Our current strut situation is a bit of a compromise. When one of our old struts blew out before a big race, we were pressed for time, so we installed a new set of adjustable Koni Sport struts. Although they're infinitely adjustable, they're not intended for drag racing. The valving is the same for compression and rebound, which wasn't an issue with the automatic since we ran them soft. But now if we tighten them enough to eliminate the bounce through the 60-foot clocks and after the 1-2 shift, we run the risk of reducing weight transfer to the point where we may compromise traction. This situation is further compounded by the soft spring rate of our four-cylinder front springs. So far, the results have been acceptable, but we'll need to address this if we want to maximize our results.
|Gear Ratio - Comparison Chart|
|Overall First-gear ratio with 4.27 rear gear: 10.50|