hey guys im building a mud truck for compitition use.. its a 81 f250.. chassis. frame is shortened, 25 inch custom lift. dana 60 front and rear with 4.88 gears. now it has a 351m engine in it right now. wondering how this engine compares to the 460? i want the most hp to torque i can get. should i try to find a 460 engine for it? if so what is the best year of 460 to have? anyone know the weight of these engines fully dresses? which would have more potential? thanks alot guys..

 

I won't question the 25" lift, nor the 4.88 gears, just state that there's no good reason for the first, and if you're running a 40+ inch tire you should have went with 5.38 gears.

As for the engines, convert that M to a 400 and add some good C heads and you can build very good power, but when it comes to bang for the buck, you can't beat a 460, or 460 based engine. Stock, that '81 351M is 142hp and 262 ft/lb of torque, while an 86, 8.0:1 compression bone stock 460 is 240/380.
Just about any 460 is a good one to start with. If you are out to build power, you want to start with a carbed engine, not a fuellie, as while they have good heads, the stock EFI is quite limited, and if you want to carb it, you are stuck bolting a carb on the stock lower intake, there's no real aftermarket there.

If you want to not do much of anything to it and have pretty good power from a bone stock engine, you want a 71 or earlier engine, as they are high compression out of the box. However, other than the early closed chamber heads, when it comes to building an engine, a 460 is pretty much a 460, yes there are deck height and balance differences, but, post 72-87 low compression engines are all very similar.
If you want real power, take a 79 or later block, or aftermarket, add a 4.5" stroke crank, and some good aftermarket heads... The sky is the limit.