Ok, I've got this '81 F100 Sidestep 2wd pickup 300 I6, all stock, except it's got a 3 on the floor..
I'm in the middle of swappin' in a 4 spd. 4x4 transmission off of an '85 Bronco.
Gonna switch over the front end and all the power/hydraulic stuff (breaks, steering, clutch.) I had just dropped all the stuff off the Bronco and decided to drive to Payson from Phoenix, and when I get back to Phx, It's got a horrible knock, and is ready to throw a rod. I don't wanna bother with takin' the 300I6 outta the bronco, I bought it for the 4x4 and power parts, and I don't think the engine is in very good shape. So I wanted to get a 302, 351, or something like that.
So, if anyone has done an engine swap from a 300 I6 to a bigger engine, and could give me some insight on it, I'd greatly appreciate it..

Thanks in advance.

 

Meilichios...I went the other way, 302 over to a 300 I6. I had to get the motor mount plates to bolt on the frame and do some radiator hose figuring (the hose connections are different) and I used the same starter and the plate between tranny and engine(mine is an auto). Do the exhaust and the other small stuff you should not have a problem. If I remember the 302 block is shorter than the 300, may run into needing longer drive shafts?

 

From my experience with the 300, let me give you my honest opinion;

If swapping to a 302, you're not going to notice any more power unless you put a cam or do some serious upgrades. The only way that you will be able to tell a difference will be on top end. That's not going to get you anywhere in a 4x4. The 351W has better torque numbers by a bit than the 300 out of the box, but they do drink quite a bit of fuel, which is something that you need to watch out for these days.

I'm not trying to get off topic or anything, but I just wanted to get you prepared for what you have coming when swapping engines. Some people will agree that the 300 is one of the best engines for a 4x4, some will not. I guess that it's personal preference. If I were you, I would either rebuild the 300 that's in your truck now or I would rebuild the one in the Bronco that you have. These things can be mighty engines with the right upgrades. A 4bbl carb intake, header, performance exhaust, upgraded ignition system, etc. would put you right on top in torque.

But, to answer your question, a small block Ford of anykind should swap right in, except for maybe the mounts and the driveshafts. Those are what you will have to watch out for. Since the wiring is minimal on my 1984 F-150, I know that it has to be at least as good or better on your 1981 F-150. All that you will have to do when rewiring the engine for the gauges or whatever is just know what wire color means what. It's not that hard.

We'll be here to help you along the way, so feel free to ask .

BTW, aren't you going to have to do some driveshaft mods anyway when swapping to the 4 speed trans and the 4x4?

Nightrain