I am hoping to get some input. I bought my first ford and it's blowing white smoke and has no power. The motor is a 351m, I am wanting to get some more power with the rebuild, intake, heads... would I be better off putting in a stock 460 instead of rebuildingrebuilding the 351m for more power. I have found a low mileage 460 for $400. Cheaper than the parts required for the small block. How easy is the swap?

 

Mounts, some cooling, exhaust, accessory drives, some linkage, may have to fiddle with transmission as even though they are the same pattern there are differences between the 460 and the 351m/400 crank/flexplate etc.

"Low mileage" for $400. OK, what year is it?

Easy for me to say, but I would rebuild the 351M as a 400 with 9.5ish compression, a decent cam and a few other goodies.

 

It is out of an 81 motorhome. Mine is an 80. What kind of fiddling with the transmission could I expect?

 

As I understand the 351M flywheel / flexplate is closer to the block than a 460. So the 460 with the trans from the 351M might work, or it might not have enough room (which would probably wipe out an automatic when you started it, or wouldn't even let you tighten the bolts with a manual).

By the way, for thoughts on rebuilding the 351M I'd suggest you go to the '80 - '86 truck forum. There are a few very knowledgeable 351M / 400 guys there, and there's a lot of traffic (probably get more responses than on the appropriate engine forum).

 

Thank for the responses. Maybe I'll see if they will trade transmissions to avoid any problems. When I read online that these age of engines were smogged to reduce HP ratings, what exaclty does that mean? What is needed to "desmog" them?

 

They weren't "smogged" to reduce power, they were "smogged" to reduce pollution. Reducing power was an unfortunate side effect (at times).

Personally I don't think there's much power you can gain by "desmogging" them. There's a lot to be gained by building them. Heads tend to be pretty poor on engines of this vintage, and you can do quite a bit with a new camshaft as well. But it's not just a matter of taking a few parts off to really wake up a sleeping giant.