A good transmission must do three things. First, it must transmit the engine's torque to the ground without blowing up. Second, it should have the proper gear ratios to put the engine's powerband to work in whatever conditions in which the car is driven. And finally, it should be able to shift quickly, minimizing the time the engine isn't doing any work.
Tuners, however, rarely touch a car's transmission. The reason is simple. In most real racecars, the transmission is the single most expensive component, more expensive than even the engine. Case in point: The Quaife sequential-shift, six-speed, dog-engagement transmission, which is rated to handle 350 lb-ft of torque, is worth about $20,000. That means it's a completely pointless piece in a relatively mild street car like Autotech's GTI, but we're testing it anyway. Why? Because it's cool. Plus it's a unique opportunity to compare a piece of real racecar hardware against a conventional gearbox. But first, some background.
Synchro Or DogSynchromesh gearboxes were a dramatic advance in automotive technology 50 years ago. The term synchromesh refers to components inside the transmission called synchronizers. Synchronizers are one or more metal clutches that engage smoothly as the gear selectors slide into position. As the clutches engage, they bring the input and output shafts to the correct speeds so the selected gears engage without grinding. In the absence of synchros, as in first gear on many '60s-era transmissions, revs must be matched very closely by double-clutching and manipulating the throttle.
Synchros are not perfect, however. They take up space, make transmissions larger and heavier, and leave less space in a given case size for big, strong gears. Synchros also take time to do their job, and time spent not delivering power to the wheels is time spent losing races. Because of these drawbacks, motorcycles and many racecars use dog-engagement transmissions.
Dog boxes use really big, axially oriented teeth that engage suddenly. The teeth, or "dogs," have plenty of lash (free play) so they can engage when the shafts are at different speeds. As soon as they come together, however, the shafts are instantly brought to the same speed.
Dogs also allow clutchless shifting, which saves time, effort and allows the driver to left-foot brake more often, but clutchless shifting also means everything attached to the transmission (flywheel, clutch, crankshaft, rods, pistons, pulleys, cams, accessories, etc.) changes speed almost instantaneously, which generates huge forces. Reducing the inertia of all those parts is critical to maximizing durability.
H Or SequentialAt each gate, a standard H-pattern shifter actuates a separate shift fork, which engages one set of gears. A sequential shifter, on the other hand, uses a pattern of grooves wrapped around a drum or cut into a disc, like grooves on a record. The shift lever becomes a ratchet mechanism, and rotates the drum one step at a time. As it rotates, the grooves actuate the shift forks, engaging and disengaging each gear in sequence. Move it one way and you shift up. Move it the other way, you shift down.
This design makes it impossible to shift from, say, fifth to second, without actually engaging fourth and third along the way. This prevents accidental five-two downshifts and the resulting engine carnage, but can be a chore when puttering around town.
A sequential shifter could be used with synchros, but using the clutch would eliminate its speed advantage. On the other hand, dogs can be used with an H-pattern shifter.