hey lear when you say "old set-up" do you mean when it was carburated. So new would be fuel injected I take it.
If so 15mpg isn't bad on something that isn't a fuelie... just wondering.

 

Yeah it had a Carter Thermoquad on it. Its very similar to a Rodchester Quadrajet. It has small front primaries and 2 1/4" secondaries. I will now feel the pain of a 670 Holley and a bigger cam. Good-bye gas mileage Hello <10 mpg. And if anyone thinks 15 is good... but it did get better mileage than my 440-6 GTX

 

never said 15 was good just said it wasn't bad. 18 mpg would be good

 

15 mpg kind of a joke I know its not good or would ever be considered good. I wish 18 mpg I had a chance to get. But with the right combination and a really conservative driver 18 would be possible But I surely am not that guy and my car is not that temperment. But I wish you could get both and with todays cars you can get close. Power and descent mileage.

 

Without a doubt the 340. I remember embarrassing many big blocks with that screamer!

 

The best mileage I ever got out of my 340 was 17 mph on a long trip. Every day mileage was around 13-14 mpg.