Quote:
Originally Posted by Big Dave
Back on topic.
Gearing changes allow you to fully realize the fruits of aero and weight improvements.
Aero & weight reduce the engine torque required at a given road speed. Changing gearing reduces the air flow through the engine (in itself a major cause of engine friction) and in a gas engine that means a lower fuel burn, all this at the same road speed. If you don't regear the vehicle yopu have to use a more closed throttle to acheive lower air flow and a throttle plate is nothing but an entropy generator.
You would think regaring would be more effective on a gasser than a diesel but the high compression of the diesel is another good reason to minimize air flow. Unfortunately, gearing is expensive. These arehigh-precision bits of machinery that require complex manufacturing tecniques which means high cost. Still, if you really think oil is going to $200/bbl, your choice may boil down to coughing up the cash for gearing or just not going.
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This engine is a monster in it's class. A 2.2L beasty with good old fashioned torque. The average size engine in this class is 1.8L (a full 20% smaller), and I believe there is a 1.6L contender. Despite this, the cobalt gets very good highway fuel economy. Part of that is lower gearing, but they didn't go far enough from the factory for my tastes. Even without considering any other modifications, there is NO reason for this big engine to be turning over at 2500 RPM and sitting at 20% engine load on the highway. This thing is desperately asking for longer legs. My calcs predict that it would be much more comfortable sitting at 2200 RPM, which is still higher then an XFE final gear swap would put me. This would up engine load to around 30%
If oil does hit $200 / bbl, I fully expect that i'll be pushing my car to work on all the inclines, then coasting down the declines.
Either that, or i'll have the first cobalt with a full boat tail.
-Steve