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Old 09-23-2013, 11:13 PM
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gsxr gsxr is offline
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Join Date: Aug 2001
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It takes a pretty substantial axle ratio change to move an engine far enough out of the optimum efficiency window to make a big change in fuel economy. It also makes a difference if you are talking about pure city, mixed, or pure highway economy; and how much of a lead foot you have.

That said... when you figure out the difference in MPG, also calculate the current cost of fuel per gallon, along with the miles driven per year. I find it comical that many people freak out over MPG when the car in question gets driven under ~10kmi per year. I went through this calculation when we switched out my wife's 300D 2.5T (30mpg average, mixed driving) with an E420 (20mpg average, mixed driving). Even with the massive difference... the 300D got 50% better economy compared to the gas guzzler... the actual DOLLARS PER YEAR difference was far less than expected. With fuel around $4/gal and ~10kmi annually, it was ~$500. Nothing to sneeze at, but having nearly triple the horsepower on tap was worth every penny.

Now if you drive a huge amount of miles per year... say, 30k-50k per year... then every MPG can make a big difference in the wallet. If it was going to cost us a couple thousand dollars extra per year to drive the funner car, we probably wouldn't have done it.

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