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Talking Transmissions Part Two

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Talking Transmissions Part Two covers the Continuously Variable and Manual Transmissions, one increasing in popularity, the other sadly disappearing.

Manual
The “stick shift” is the traditional purists transmission that every driver should be required to learn. It educates a driver on the interaction of the vehicle and gear selection. It is the lightest and most reliable type of transmission. Now cars like the new Corvette Stingray and Porsche 911 offer a 7-speed manual. Interestingly the Corvette has 4 “acceleration gears” ending at 147mph and 5th starts the overdrive ratio “fuel economy gears. The Carrera S has 5 “acceleration gears” ending at 158mph.

Besides weight and reliability, it is the most direct connection to the driver and the performance of the vehicle. For classic cars, it is almost always the most desired transmission and many weren’t even offered any other way. Until recently, it was always the most fuel efficient transmission due to its simplicity and direct mechanical connection to the driveshaft. Now some sports cars such as the Vette, 911 and Nissan 370ZX offer a computer rev-matching for expert downshifts and others like the Chevrolet Camaro ZL-1 a “no-lift” full-throttle upshift.

It is one of the most fun ways to drive car and requires the most skill on the public road, drag strip or road circuit.

Disadvantages are the constant action needed to drive the car which is the biggest complaint. It is not fun in stop-n-go traffic. The car be stalled by not applying enough power or the clutch suffer from excessive wear by not releasing it completely. It is difficult to “launch” at the dragstrip because the clutch pedal determines how much power from the engine is applied to the drive shaft to turn the wheels in addition to managing engine power with the throttle. Some have hill control but starting from an uphill position can be daunting for beginner drivers. A bad driver could mean lurching shifts, stalling the car, excessive wheelspin and almost always a prematurely worn clutch which can be a costly repair.

MPG Comparison:
Corvette Stingray 6-speed automatic 16/28, manual 17/29 Advantage: Manual
Porsche 911 Carrera 7-speed DCT 20/28, manual 19/27 Advantage: DCT
Subaru BRZ automatic 25/34, manual 22/30 Advantage: Automatic*

*This large discrepancy brings up a possible advantage of the automatic being reactive to top-gear acceleration demand by immediately downshifting versus the manual requiring a downshift. Further investigation is needed.

Continuously Variable Transmission
The CVT is one of the more recent offerings that finally broke into the mass market with Nissan as well as hybrid vehicles. The concept of the CVT is the ratios vary within a set range rather than have “steps” like gear sets. Therefore shifting is seamless unless “steps” are programmed due to driver familiarity, and acceleration and fuel economy can be optimized. With the primary exception being Nissan and now the Subaru WRX, it’s perfect for lower-powered, fuel-efficient oriented vehicles.

While climbing a hill may be very smooth, when accelerating, the engine will stay at the rpm that is demanded for the rate of acceleration chosen. For example at wide open throttle, the engine will sit at redline until the driver eases up. So the droning can become tiresome and a bit disconcerting. You won’t find many technicians that are familiar with repairing this type of transmission.

Oddly you can almost compare it to an electric vehicle which has a direct drive without multiple gears and also to a Top-Fuel dragster that uses clutch slippage to modulate power to the wheels while the engine stays at full power. Time will tell if it shows up in racing applications.

MPG Comparison:
Honda Accord 2.4L automatic 26/34, manual 24/34, CVT 27/36 Advantage: CVT
Subaru WRX manual 21/28, CVT 19/25 Advantage: Manual

There are many choices in transmissions now and its best to experience whatever is available in the make and model to determine which one is best for you. Obviously one transmission type may be an advantage in one car and not in another.

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