Guest Post: Porsche 7-Speed Gearbox

Although it was introduced earlier this year, the Porsche 911 7-speed manual gearbox is still a feature that gets a lot of press.  Although most journalists believe that whatever the engineers at Porsche develop is well thought out, the 7 speed transmission raised a few eyebrows when it was first introduced.  Some frankly wondered if 7 gears are absolutely necessary.

To gain a further understanding of the whole “number of gears” thing, we need to discuss how the speed of an engine relates to the engine’s power. As the graph below illustrates, the turning speed of an engine is not directly related to its horsepower. Most engines have a sweet spot where the turning speed of the engine combines with the resultant torque to create a maximum horsepower.  In the case of the hypothetical engine below, the peak horsepower occurs at some 2500 revolutions per minute (RPM). This is why cars have different gearing ratios in their transmissions.  The object is to keep the engine rotating at the peak horsepower speed as much as possible for performance and efficiency.

Well, the engineers at Porsche have been building cars for over 100 years so they know a few things about gearbox design.  The introduction of a seven gear box is just a way to optimize the power of the engine as it flows through the drivetrain to the wheels.  Although it takes a little more work to shift all these gears, the result, all other variables being equal, is that the car will accelerate quicker than a “numerically-challenged gearbox”.
It should be noted that the Porsche engineers did not design the 7 speed gear box with equally spaced gear ratios.  This is unnecessary. The Porsche 7 speed transmission is really a close-coupled 6 speed with a 7th gear that is essentially an overdrive.  It is designed so that ordinary driving utilizes the first 6 gears, and when one desires, the long ratio 7th gear can be used for lower engine speeds and improved fuel economy when desired.  
OK, but what is the 7 speed shift monster like? We visited our MD-based BMW/Porsche/MINI dealer and they told us that most 911 owners now report that they love the 7 speed transmission in their Porsche.  They feel it offers the best of both worlds; the first 6 gears deliver brisk performance and the 7th is great to have on the highway.  But don’t take our word for it, visit local your local Porsche dealer and find out for yourself!
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