While fast cars with manual transmissions can be loads of fun, not everyone has the desire and/or coordination to swap gears on their own. There are also instances, such as the one we have here, where the car is just too fast for its own good. MM&FF shootout alumnus Bob Watson found himself in just a situation with his '01 Bullitt Mustang.
Watson's special-edition Pony has steadily progressed from a blower and exhaust to a more potent Vortech T-Trim-fed, poked, and stroked VT Engines' Darton MID 5.0 modular powerhouse, which led its owner to drop in a Tremec TKO five-speed to keep up with the 600-plus rear-wheel horsepower. A switch to a more aggressive clutch took away some of the Bullitt's driveability and fun factor, which are extremely important to Watson as this car gets quite a bit of street use. An aggressive clutch combined with multitudes of horsepower and street tires can make for an eventful driving experience-and a weak left leg should you get caught in rush-hour traffic.
Another problem is the lack of appropriate elapsed times. While the Bullitt's driver can wheel pretty well, the elapsed times just weren't as deep as they could be with a race-style stick. That, combined with the aforementioned driveability issue, pushed Watson to look into the option of installing an automatic in his '01 Bullitt Mustang, a car that was available only with a manual transmission.
Our subject Bullitt Mustang...
Our subject Bullitt Mustang already had its stock Tremec 3650 five-speed swapped for a heavy-duty TKO unit prior to this story. But the aggressive aftermarket clutch took some of the fun factor out of the ride during street driving. The 4R70W/converter combo is marginally heavier than the TKO and its clutch/flywheel setup.
Transmission swaps are nothing new in the Mustang world, though you hear about auto-to-five-speed swaps far more often than the opposite. That said, we decided to follow along with the Tremec-to-4R70W swap and see how it turned out both on the track and off.
The key players in this tech story are Watson; BC Automotive of Carmel, Indiana; and HP Performance of Orange Park, Florida. Darrin Burch of BC Automotive has gained a good rep in the modular arena with regard to stout auto transmissions, and he hauled a fully customized 4R70W down from the shop's Indiana digs. Alan Brown of Dirtydog Performance accompanied Burch and also lent his services on this install. Brown handles all of BC Automotive's torque converters and offered us a custom unit for this application. The converter is a lock-up unit with a stall speed of approximately 3,500-3,800 rpm.
While Burch and Brown handled the majority of the installation, the HP Performance staff supplied its lift, Dynojet, mechanical exper-tise, used-parts finder, and tuning prowess to help get the job done. Also making this happen was Jerry Wroblewski of SCT who supplied an NUX2 automatic ECM, along with upgrading the SCT Pro Racer Package so we could program the new NUX2 computer code.