440 -
I had a '71 Gran Coupe a couple of years ago that I was selling. I had restored it, painted FE5 Red, Rallye Hood, Rallye Rims, Cuda Exhaust, new interior etc. It was 100% RUST FREE. It had a 440 in it but developed a knock while I had it for sale. I told people about the knock and they still offered me up to $20K for the car. I did not feel good selling a car I knew had a problem, so I decided not to sell and to yank the 440 out.
I just happened to have a freshly rebuilt 383 at the machine shop and figured it'd be perfect for the Gran Coupe especially since it was originally a 383 car to begin with. So I pull the 440, drop in the 383 and cruise around in it to break it in (after proper cam break in of course) because I wanted to make sure it was 100% before I tried to sell it again. Well, long story short, I ended up only getting $17K for the car despite all of the extra expense & time I went through to put a FRESH motor in it.
BTW - The 383 was no slouch, it had a nice cam, steel crank, new rods, bored 30 over, fully race balanced & prepped etc. BUT people want those CUBIC INCHES!