Quote:
Originally Posted by cbaber
We were originally comparing the 2.7 Cayman to the C7 because jamesqf claimed it could get 40 mpg at 70 mph. But the 2.7 and 3.4 Cayman S are rated the same (30 mpg) according to the Porsche website. C7 is 29 mpg, which is pretty much the same thing. The original conversation wasn't to compare the cars, but rather compare the engines.
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Nah, I was the one who claimed the 40mpg. I said that because I drove a Cayman with a brand new engine (not broken in) and got 40mpg lol.
The 2.7 is rated 32 EPA, the 3.4 is rated 30, with slightly longer gearing. This is the PDK versions, which I think is fair because the C7 vette uses a 7 speed manual which Porsche only offers on the 911.
No doubt the cylinder deactivation helps, but the extra pistons it's lugging around definitely hurt the gas mileage. There is simply no way that a hypermiler would be capable of squeezing more mpg out of a C7 at lower speed than a Porsche driven by another hypermiler because the engine is just so big.
Freeway mpg is moot, the right gears means every car can get decent mpg. In the real world very few people get to drive all freeway miles, and the Cayman will whoop the Corvette in fuel economy off the freeway. If you want to talk horsepower to mpg ratio, the newer turbo engines do much much better, but again that's not relevant.
In my book the Porsche 9A1 engine is still better, because in its highest tuned state the 3.4 makes 350hp (the Cayman is limited to 325), and the X51 package on the 3.8 shows that you can easily increase the power of the 3.4L up to perhaps 380hp. This would not affect driveability the way fatter cams would on a Vette because they have a 2 stage lift system. If you really want to compare specific power, the 3.8L engine in 430hp form gives the LT1 a run for its money for sure, because it barely weighs any more than the 3.4, and Porsche could've given it the gearing to get 30mpg instead of 27. They don't use cylinder deactivation for smoothness reasons, but if they did the mpg would be even higher.