Muscle Mustangs & Fast FordsHow To Drivetrain
1992 Ford Mustang Project Car - Automatic Overtaking Done Quickly - Part 2
Part 2 Firm Up Your Shifting Plans.
Last month, we left off with our new TCI AOD transmission installed but untested. Our subject vehicle, a '92 Mustang coupe was making plenty of power, but the stock slushbox wasn't getting the job done when it came to efficient and quick shifting.
When you move the shifter at 4,000 rpm and it doesn't complete the gear change until 6,000 rpm, something's amiss. That's what our stock AOD was doing behind our nitrous oxide-injected '92 coupe we've been playing with. To solve this issue, we called the folks at TCI Automotive, who sent us one of their Streetfighter AOD transmissions and Saturday Night Special torque converters.
The Streetfighter AOD is a fully built, high-performance transmission, and ours featured TCI's new constant-pressure valvebody, which is designed to take the guesswork out of setting the line pressure using the throttle-valve cable. The Saturday Night Special converter is a lock-up unit that features a 400- to 500-rpm increase in stall speed. This was of particular interest to us as our nitrous system is set up on a window switch that engages the giggle gas at 3,000 rpm. Anything we can do to get the engine at that point in the rev range sooner should translate into quicker elapsed times.
Given that we expected snappy, precise shifts from the TCI unit, we surmised that our 17-inch drag radials may not provide enough traction for the heavy 150hp hit of nitrous oxide, especially on a fading racing surface. This was evident the last time out with the stock transmission, and the crisper shifts only exacerbated the problem. That being said, we called the folks at Toyo Tires, who set us up with a quartet of their brand-new Proxes drag rubber, consisting of 25x15 front runners and 26x10x15 rear slicks.
To pare some weight from our automatic-equipped equine, we dialed up speed-parts giant Summit Racing for a set of lightweight aluminum racing wheels. Fresh off the brown truck was a set of Weld Racing Draglite wheels, 15x3.5 for the front and 15x8 for the rear, with a 5.5-inch backspacing. Using the Weld's 8-inch wheel width versus a stock 10-hole-style wheel's 7-inch helps make the tread flat and square, and we want the contact patch to be just that.
With the new transmission installed and the slicks and skinnies loaded up, we headed to our local Thursday night test and tune looking for quicker elapsed times out of our modified notchback. For our first pass, we went motor only and utilized the 17-inch Nitto drag radials. We'd hoped that the new torque converter would cut down on the 60-foot time, but our first effort clocked a 2.24-second time, followed by a 13.89 at 101.86 mph. The 2-3 gear change was quite abrupt and broke the tires loose quite vigorously, forcing us to pedal it to regain traction. Our subsequent motor-only pass came in at 14.07 at 100.59 mph, the run plagued by wheelspin at the Second- and Third-gear changes.
With time running out on our track session, we decided to mount up the slicks and skinnies and dial up the nitrous oxide. We had the rear wheels off of the car, and the new Weld Draglites hanging on the studs when yours truly was asked for the wheel lugs. It was immediately apparent that the bonehead behind the keyboard forgot them at work, and a subsequent search of the company tow rig confirmed the situation. We still had an hour and a half left in the session and bolted the drag radials back up. We were determined to spray some nitrous one way or another.
We gave the Nittos a hot and nasty burnout, and staged the black coupe. The converter did its job in getting us into the nitrous sooner, as we recorded a best-ever 60-foot time of 2.15 seconds. The drag radials held traction at every shift, and the notchback went through the traps in 12.75 seconds at 114 mph. Our next run included a great burnout, but the track surface had faded and the nitrous injection overpowered the tires. The timeslip was so abysmal, we threw it away.
Comparing the before and after times, we're about a tenth off of what we ran before on nitrous, and about three hundredths off on motor. Tire spin was certainly a factor, and something we'll most certainly have solved the next time we hit the track. We were expecting a couple of tenths drop in elapsed time, but maybe the tire chirps between gears are giving up more than we think.
Next month, we'll swap out the 3.55 gear for a 3.73, and drop in a new differential from Detroit Locker to make sure we get both wheels planting the power to the pavement. Ultimately, we think the notchback should be able to get into the low 12s, if not the 11s, so come back and find out how it all pans out.