The numbers I quoted are both 2009 figures taken from the websites today. It obviously has to be consistent company to company to have any meaning. I suppose you could better it by 7MPG but I think I'd have to see actual proof of that instead of just taking somebodys word for it. Like be there at the fillup, be in the car till the tank was emptied and do the math myself. I don't know how you could ever determine actual Highway MPG anyway because you'll never use a whole tank of gas without stopping and starting. If that's just what flashes on the MPG display on the dashboard, then it's the same thing I saw in my Father in Law's old HT4100 powered Cadillac Fleetwood. At least for milliseconds when he let off the gas going down hills with a tailwind. 
The numbers are comparable in a given year from manufacturer to manufacturer. All testing is performed by the EPA, using a given set of driving parameters in a laboratory setting, so that traffic, weather, driving style, etc don't play a part. EPA changed their testing procedures beginning with the 2008 model year to more accurately reflect "real-world" driving habits. Here's a quote from the EPA website:
Beginning with 2008 models, all fuel economy estimates based on new test methods, which EPA finalized in December 2006. The new methods better account for actual driving conditions that can lower fuel economy, such as high speed, aggressive driving, use of air conditioning, and cold temperature operation. The new estimates will give drivers a more accurate estimate of the fuel economy they are likely to achieve on the road. Because of the new methods, the estimates for most 2008 models will be lower than their 2007 counterparts. To aid consumers shopping for new cars, EPA has also redesigned the fuel economy window sticker posted on all new cars and light trucks to be easier to read and understand.
Using EPA estimates for 2009 models, the numbers would be lower than pre-2008 vehicles. For 2008 models and later, the old numbers are attainable, but require the driver to use a light touch, moderate speed, no A/C, etc. Given the gearing in the six-speed Vettes, it's quite possible to get that kind of mileage. But if the drivers are running around town using all that power, you can bet the mileage will fall dramatically, to no better than the the average SRT-8.
Topic: An example of what small block cubic inches can do, and .... (Read 2056 times)
