Hi, recently My 91 F-250 with a 460 V-8 engine siezed up, and every thing else works perfectly, and I dont want to sell it for parts. I was wondering if I could put a smaller engine in it with better gas milage for cheap as posible, or get a rebuilt 460. Thanks

 

I would think it would be cheaper to pickup a rebuilt 460 then it would be to swap down to a 351. Unless you can find a donor truck that has all the emissions, electrical connections, computer, motor mounts, transmission (bolt pattern is different on a 351W. I would also evaluate whether going to all that trouble and expense is worth the small gain in mpgs?

 

To make a certain amount of horsepower, you need a certain amount of fuel and air. Doesn't matter all that much if the "certain amount of fuel" is at higher RPMs with a smaller displacement or lower RPMs with a higher displacement. Most engines are only 15% efficient at best, so using that as a guideline...

I can assure you that the smaller engines won't give you any obvious increase in mileage.

The smaller engines have to rev more to make the same power as the 460. The 460 makes that same power at lower rpms, using its vast displacement.


Among my friends and I, we've sorta agreed that my 351W truckd oesn't get any better (or worse) mileage than my friend's 460 powered bronco. The difference between the two is I have to rev mine more to get some acceleration, whereas his has a really nice snap off the line, but maxes out a bit earlier. Of course broncos are not equal to crewcabs in weight so maybe that's skewing our "agreement".

Putting another 460 there is going to be by far, the least amount of work for you.

 

Agreed - considering the amount of additional work it will take you to swap the 351 in, you're better off sticking with the 460.