Here are the parts that we used in upgrading our 727 TorqueFlite from B&M. To upgrade our automatic-equipped Charger, we tapped B&M for their Transpak calibration kit, a flexplate balance-matched to our 440, a new Holeshot 2400 high stall 11-inch converter, and the SuperCooler to let it live.
Last issue, we began the process of upgrading a 727 TorqueFlite transmission using B&M's Transpak-a valve body recalibration kit which contains the pieces and instructions that allow the trans to be recalibrated to three different levels of performance: H/D Towing, Street Performance, and Competition. In our install, we went somewhere between the Street Performance and Competition settings.
After retrofitting a downshift kit from a later-model TorqueFlite, we were well on our way toward performance-oriented shifting, but that's only one part of the equation. Giving our Mopar an additional off-the-line kick would come from a new B&M Holeshot 2400 torque converter.
Torque Converter
Since making those much needed changes to our trans, we then turned our attention to the torque converter. One of the reasons for Chrysler's success in racing with the 727 was the company's pioneering use of high-stall torque converters. Stall speed varies in relation to two things: the design of the converter, and the load/torque that the unit sees. A given torque converter may stall at 2,500 rpm behind a small block with 300 lb-ft of torque, but provide 3,000 rpm before reaching stall speed behind a 440 which belts out 450 lb-ft of torque at stall rpm. It varies.
Our '71 R/T came with the factory 12-inch (actually 11 3⁄4-inches in diameter) converter, which had a factory stall spec of 2,000-2,350 rpm. While this was a fairly high stall speed by most manufactures' standards of the time, the Hemi converter of the same year was a smaller higher-stall unit, which delivered 2,500-2,850 rpm of stall-outstanding for a factory converter. Chrysler was wise to the advantages of getting specific engines up to an rpm off-the-line where the engine was into its power curve. The less torquey 383s of the same vintage came with an 11-inch (actually 1031/44-inch diameter) converter very similar to the Hemi unit, and delivered 2,300-2,650 rpm of stall. As for 1971, when our car was built, the engineers felt the larger converter was better suited to the low-end torque curve of the 440HP. The HP 383s (as well as some small blocks) got the added off-the-line oomph of the high-stall, 11-inch units. In 1973, Chrysler pulled out the stops on the 440HP torque converters, and backed the engine combo with the 11-inch converter in B-Body applications for an outrageous factory stall of 2,600-2,900 rpm.
For our high-performance 440, the factory 12-inch unit had to go, and rather than scrounge for an ancient factory high-stall of questionable durability, we again turned to B&M, selecting their version of the 11-inch high-stall converter, the Holeshot 2400 (PN 10415). Taking the B&M 2,400 rpm number at face value, it would seem shy of the factory stall ratings listed above for the original 11-inch converters. The B&M converter rating system is based upon an input torque of 230 lb-ft at 2,500 rpm. Going back to what we said earlier, the stall in a particular application will depend upon the actual torque/load the converter will see. It's not that the B&M unit has less stall, it's just the way it is rated-as opposed to the stall listed in the factory literature, where the stall numbers reflect actual input torques approaching 400 lb-ft of torque. The B&M Holeshot unit is a stout street performance converter, featuring a furnace brazed impeller and turbine, needle bearings between the stator and turbine, and new H/D hub, pump drive, stator springs and rollers. For us, knowing it's a time-tested B&M piece gave us much more confidence than some generic rebuilder's special.
When changing converters on some Chrysler engines, balance must be considered. Some engines, such as our heavy-rod 440, later cast crank 340s, 400s, and 440s, as well as all 360s, were externally balanced. To arrive at the final engine balance, some eccentric weight was included in the crank damper, as well as weight added to the converter. Performance replacement converters generally come zero balanced, or without weights. True, weights can be welded on, but the positioning and amount of weight needs to be precise to maintain the factory engine balance specs.
B&M took an alternative approach, providing for the eccentric balance in specially made flexplates, specific to the engine application. They carry a broad range of externally balanced flexplates for Chrysler engines. Once mated to the engine, the B&M flexplate allows for the use of any zero balanced converter-a neat solution. Additionally, the flexplates are heavy-duty SFI approved units, legal for all NHRA and IHRA classes. We picked up a B&M PN 10238 flexplate for our Six Pack rod 440HP.
Easy Cooling
Finally, with the higher stall converter comes more heat. Heat is the quickest way to waste an automatic, so we ordered up a B&M PN 70255 SuperCooler auxiliary trans cooler. The SuperCooler is a high efficiency stacked-plate type cooler (similar to the factory police engine oil coolers), made of aluminum for high heat conductivity. The unit is designed specifically for low pressure drop, and has an internal bypass system to drastically reduce the risk of lubrication system failure. It's true that in most installations, the factory didn't use an auxiliary trans cooler with their high-stall converters (the Hemi and Police Packages being the notable exceptions). We felt that the addition was good insurance to protect our investment. The quick mounting system had the unit installed in minutes, and a few hoses later we were hooked. The only hang-up was the need for purchasing brass fittings to adapt the factory 5⁄16-inch flare lines to the supplied hose. These were sourced at a local NAPA parts store.
Rubber Meets The Road
Although a valvebody reprogramming kit can be installed with the trans in the car, changing the converter meant dropping the trans. In a B-Body this wasn't too tough, even with basic equipment in a true driveway install (a lift would make it a breeze). Was it worth it? From a performance standpoint, the change in driveability in this car was unbelievable. The Holeshot converter behind our high-torque big block provided a full 3,000 rpm of stall in off-the-line launching. With the prodigious torque available at that rpm, even with the Sure Grip limited slip and sizable rubber out back, nailing the throttle instantly boiled the hides-to the point where they couldn't recover and hook without backing off. With the old converter, stabbing the throttle would just give us 20 feet of peel-out and then she'd bite. Definitely a gain in off-the-line launch here. It's just a matter of getting it to hook to harness the gains on the strip.
With our recalibration, automatic shifts now came in at 5,600 rpm-perfectly matched for our combo. While full-throttle shifting was power-shift quick, we didn't experience any of that annoying shift-kit harshness while driving at part-throttle or in low-speed shifting. The trans felt and acted like a factory performance TorqueFlite in normal driving. If all this sounds like a lot of magazine-guy enthusiasm, what can we say? This stuff did exactly what we needed it to. What more could you want?
