I have an 08 crew cab 5.3, with a 93 performance tune. I get about 13 to 15 mpg, And was thinking about downgrading to 87 octane. Will I get worse mpg on a 87 economy tune. The reason I am asking is because I have been out of work for a few weeks. And that 10$ Extra 3 to 4 times a week add up.

Thanks for any help

 

At general cruising speeds the MPG shouldn't change if you ran 87 or 93 octane. Likely the 93 tune is more agressive with wide open throttle timing and maybe everywhere else depending on how it's setup.

It could also be setup to enable enichment at lower values and that will use more fuel all over. Bigger tires or other mods and reduce mpg and switching back to a stock-ish tune and 87 won't really help there. Driving style is the other biggest factor.

I drive basically city only and I get 14-15 mpg right now.

 

Yea it shouldn't really affect mileage too much, it's mainly a performance thing.

 

Take off's will kill mpg. The harder you take off, the more gas you use. Try being a little lighter on the throttle from take off.

While cruising, drop your speed by 5-10mph. That'll save you some there. The difference between an 87 and 93 tune is spark timing. You have to run less timing with 87 octane and that could cost you more mpg because you have to use more throttle to get moving.

You might be able to run a few more degrees of timing in the cruise area of the spark map. This can help, albeit, probably minimal.