40 mpg is good, but out of reach for us Mopar guys. I have a 408 built to 500hp and 11.8:1 compression. I jetted the primary side down a bit to 72 and left the secondary side at 86. I don't drive it nicely very often. I check my mileage all the time out of curiosity more than anything else. When I am tuned for 93 octane I average 11.5 mpg and have gotten as high as 15 mpg when I drove it nice the whole tank. When I tune it up for race gas I obviously drive it harder and get around 8-9 mpg.