Rebuild my tired 240, or buy/rebuild a 300?

My main concern is mileage. Which would get better? A rebuilt 1966 240, or a rebuilt 1970's 300?

I used to have an econo with a '73 300 and what must've been a 3.00 diff. I could cruise down the highway at 70+mph and get 18+mpg. If I could get 20-22mpg with my rebuilt 240, I would do that. It would save me the money of buying a 300 to start with too.

Great question! I was going to get a 300 but you brought up a good point. I hope others with experience on the gas mileage of both the 240 and 300 will chime in.

I dont know anyone getting over 18mpg with a 240.

When I was driving my 64 I was getting 13mpg on a worn out 170 engine with two cracks in the block.
An old friend had an Etruck also he got 22 on his 170 engine
I have a 85 truck also with a 300. The best it got me was 18 mpg.
300's have torquewith longer strokes. They say they eat a tad bit more than a 302 does.
I'm not sure but I think a 240 should get better gas than a 300. It will not have the torque power for pulling or hauling. Someone may jump in the clarify that better than I can.

Personally, I wouldn't even think of another 240,,,, the torque makes it seem like twice the motor, and gearing is much more tolerant, especially pulling a long grade. Like Tim said, the most you can expect out of the 240 is 18 with everyone honking their horn at you>LOL>..
Had a fast 240 in my 65 with 3:50's in it, climbed the long 210 grade without loosing any pep,,, but always looking for another gear at 80. Put 3:25's in it, got weak going up the same grade, almost down to 2nd gear now. crud!!!
killed the 240 and put in a 300,,, now it climbs the same grade the 240 was dying at with the 3:25's,, LOVES TO RUN at 80, now, and now even thinking of dropping in some 3:00's???????? Point is that its a torque monster, and you can grunt with it (foot out of the pedal for grandma), and if geared right, I suspect even better mileage......
Put in a dag 4spd shifter, and use 4th for an OD,,, it WILL pull it, and really get some mileage. I just happen to have a 4spd, converted over to a 65 column,, LOL...
vic
vic
vic

I've got a built 300 in my 67 SuperVan with a 2.84 rear end. I consistently get 10-12 mpg around town and 20 on the highway. Last July, I towed a small trailer with a motorcycle on it from Portland, OR to Bend, OR and back...over a few mountain passes. I was passing other cars and trucks. I'm going with Vic...the torque of a 300 cannot be beat.

My 1975 rebuild 300 gets 14 mpg city with a 2.75 rear.

I love the torque, but would like to trade for a more efficient engine.