Competition stacks and mpg

[lumberjack98]

I think i must of hit something wrong when i calculated my mileage today it was 23. 2 mpg. last week (17. 6 mpg). I did install a 4" pipe and kenworth stacks last weekend but did not think they would give a mpg increase. more flow i guess ( stock exhaust before). anyone else have similar? thanks

 

[bmoeller]

I got about a . 5mpg gain when I went with a 5" exhaust. No better and no worse with the stacks.