For faster, more precise shifts, the linkages were altered for shorter throws, and triple-cone synchronizers were used on First and Second gears, replacing the old T56's double-cone design, while the remaining forward and Reverse gears got double-cone synchros. The synchros are all larger in diameter, too.
These changes significantly increased the amount of power the new T56 Magnum can support. It's rated at a validated 600 lb-ft, and remember, this is a stringent testing regimen that the OEs require to make sure the parts will last throughout at least the life of the powertrain warranty. In reality, the Magnum could likely handle quite a bit more power depending on a number of factors, such as the car's weight and what type of clutch and tires are being used.
Racing Cluster Gear
Next up the rung of performance is a street/strip or road racing box--one that laughs off high torque and rough shifting but may have crude manners for street driving. This is an excellent choice for a high-performance street machine that is not your daily driver but something you may want to cruise around on weekends or take to work on Fridays to thumb your nose at the man. While on a trip to Charlotte, North Carolina, a few months ago, we talked our way into a tour of the Jerico Racing Transmissions manufacturing plant and witnessed firsthand what goes into a narrowly focused racing transmission.
Jerico was founded in 1978 by Jerry Hemmingson, an NHRA A/Gas racer who took to modifying Ford Top Loader four-speeds for better performance and lighter weight. He did this by developing his own gearsets and an aluminum case. It didn't take long for other racers to take notice and ask Jerry to build them transmissions, too. Jerry's Company (get it?) took off from there. Jerico transmissions can be found in NASCAR race cars and in many Stock and Super Stock drag cars. They are still loosely based on the old Top Loader design and up until a few years ago, used Top Loader shift forks until they depleted the supply.
Jerico's chief gearhead and assembly guy, Scott McManus, tells us the company's transmissions can easily support 750 hp in a 3,200-pound car. "A lot of it is in the materials," McManus tells us. Jerico uses aircraft-quality 9310 alloy in all its gears and shafts; "9310 is pretty much the industry standard. All the good transmissions run it."
Racing transmissions also differ from street transmissions by running straight-cut gears. Straight-cut gears are stronger than diagonally cut helical gears found in most street transmissions because engine torque is spread out over a larger contact area between the teeth. The downside to straight-cut gears is they generate a lot more gear noise than helical gears. "Most of our customers aren't concerned about creature comforts, though," McManus says.
Racers demand fast, accurate shifts. "Synchronizers can bind and hang up between shifts. You can't have that happen during a race," McManus says. So most racing transmissions don't run traditional synchros and blocking rings. Instead, sliders directly engage dog rings attached to the gears. The dog rings' teeth are much wider and are spaced farther apart than in street transmissions. Lugs on the slider engage and lock the dogs very quickly, allowing lightning-quick shifts without the pause in Neutral you feel in a street transmission. It's even possible to upshift a dog box without using the clutch. A quick lift off the gas unloads the gears, and you can pull the lever directly into the next gear and get right back on the gas. Clutchless downshifts can be executed as well but require the ability to heel-and-toe or rev match the engine to the desired gear's speed while braking and downshifting.
 Jerico assembler Dan Cordier...  Jerico assembler Dan Cordier checks the shifting action of a transmission he just finished putting together. Jerico makes all the parts for its gearboxes in-house except the cases. This transmission is Jerico's best seller, the DR4-4--a drag race four-speed. |  These are straight-cut gears...  These are straight-cut gears waiting to be installed in a Jerico gearbox. The input shaft is in the foreground, the cluster gear is in the middle, and the mainshaft with the driven gears installed is partially out of the frame in the rear. |  Jerico's dog rings and sliders...  Jerico's dog rings and sliders are clearly visible in this picture. Note that this is a drag race box with the angled-ramp slider lugs.
1 Dog ring
2 Slider
3 Slider engagement lugs
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 Here is a technical drawing...  Here is a technical drawing of a Lenco CS3 transmission. | | |