Originally Posted by CHILLZ HEMI
I agree with all the above with the exeception of using higher octane level of gas...using premium gas does not give better mpg, in fact it damages the engine...Im speaking for vehicles that are not recommended by the manufacturer to use premium...Using premium, unless recommended by the manufacturer, is as much a waste of money by using fuel additives from auto zone, and advanced auto...Now it may seem you have gained more mpg, maybe cuz you have lost more hp by using the premium gas...And yes, you can lose hp by not using the correct fuel in any engine...
I have no idea how it would damage an engine. I have seen gains, felt gains, and that would mean that the 91 tune on a programmer is simply destroying your engine. 91 simply burns slower, if I remember. That would mean that power is being created for a longer period of time. I have heard both sides of the argument many times from experienced techs and Chrysler training videos, but in my experience I calculated a increase in MPG over an entire tank, in both vehicles I have owned. I drive the same few roads every day, and my habits never change. If anything, I was harder on the gas with 91. And I know a "butt dyno" isn't reliable, but mine tried to tell me I was going a bit quicker.