Here's why I asked this question. I had a 454 in a 1974 Vette. Mostly stock, with the exception of some closed chamber heads to increase compression a bit without having to get into the lower end. A Stock class drag racer did some tweaks to the Quadrajet. I put a slightly higher lift/duration cam in it (I don't recall the specs, so I'll use the ubiquitous term ‘RV cam’ to describe it), and I had a Doug Nash 5 speed. High gear was 1 to 1, and I think I put a 3:55 rear gear in it. One summer I went on a trip and got an honest to God 17 MPG, which I was extremely pleased with. I just cruised; keep my foot out of it. I’ve read about big inch big blocks making tons of torque right off idle, so I thought this might equate to decent MPG. Yeah, I want it to go like that 1974 when I want, but want a bit of economy too. Thus, the bigger engine idea with the new Richmond 6 speed with the OD sixth gear. My co-worker has a new Z-06, and has this luxury. He says if he gets on the freeway and puts it on cruise, he’s in the high 20’s MPG wise. But he has great performance too if he hits the loud pedal. I have a big block Nova. While it’s fun to hit the gas, it’s not so fun to go to the neighborhood Blockbuster in it and return with ½ a tank less gas! Finally, I can pull off a 540 project. I can do the engine, tune up, drop in the engine, etc. I don’t feel ready (or willing) to try a LS1 or LS6 swap to get what my Z-06’s buddy’s got. But maybe the new computerized engine management system is the key to the Z-06, and an old school big block is going to make the HP, but not the MPG. Thanks for all the replies. It's better to talk about now, as it's just theory, than do it, spend the money, and to wind up unhappy and having to start again.