Hello I have recently purchased a 81 f-100 custom and the guy couldnt get the hood open and had issues in putting a few things together when the hood was open. But for 400bucks and the immaculate shape it was in, i could not pass it up so i had bought it. After cleaning it up and getting the hood to regularily open; I had noticed that the motor definately was not the motor that came from factory allthought it was covered from sitting the past few years in dirt and mud and a recent flood last year I had tackled the job. Getting it cleaned up and running again I noticed the block numbers etc and the aluminum valve covers. This motor was out of an older 302 High Output car.. and there was a tag.. a rebuild tag.. Right before it was put into storage(in someones backyard) the motor was rebuilt said the guy who I called the number on the tag in on. and the motor was punched .30 over (306 now) had some new internals put in, and also had a mild cam put in. In my head I am thinking this is unbelievable.. I paid $400 for this truck that I thought was gonna just be a good body.. well here the motor is next to new.. next thing is getting it a tune up and cleaning up the engine bay and the little rust on the body so I can rebuilt this beast. So if anyone has any input or anything to hand down to me I am new to the ford scene as I am a mopar guy turned ford after buying this beautiful beast. and come Beginning of july it is going to be my project truck.
Thanks, and yes I am new to the Forums.

 

Welcome to our forum! It sounds like you have a very nice start to something special! Keep us informed as you sort it out.

 

thank you very much, so welcoming. and I will.

 

sounds impressive man!! post up some pics of your work!!

 

thanks, i did have a question though, It seems the motor and trans are from a mustang, but as for the differential it is just a bone stock one. I am just a highschool student but am looking at going for 3.73 or 4.11 gears how would I go about doing so, because the motor just howls horsepower and the truck goes like a bat out of hell.. but the gearing just throws it off so bad and she can only do a 1tire fire if you were to try.
This trucks going to be my summer project as I graduate and start as a welder mid-summer.

 

im there with you man..im a senior in highschool...
what i would do is, since you have a HO engine, go to the junk yard and find yerself a nice rear axle!! last thing you wanna do it torque it and bend..

gearing is also an issue...its up to the driver..in my truck i have 4.11 gears and i have a detroit locker for the rear. granted i have a near stock 302 and by no means enough power to burn tires all day..

as for the car...the 79 trans-am was my first and its my love!! haha..the gearing is relatively low (3.23) but its also because of the engine haha..if it had 4.10 gears..itd be all over the place!!

basically..id go for 4.10s for your truck and you can sqipe an axle off of a truck at the yard...look up door date plate codes for axles and find one to your licking...

 

okay thanks, yards around here are slim pickins, but il keep on looking around. im by all means not a 4x4 nut haha i am more of a street truck person hence why i like the high gearing, but thanks I definately will look around and see what i can find.

 

4.10's if you have a overdrive trans, 3.25's if not. I have an '89 Mustang 302 and a C6 in my 81 F100, with 3.25's. With 225/75R15 tires i turn 3000RPM @ 70mph.

 

What gears does it currently have?

Does it have a C6?

If it has 2.75 gears (likely since it is a 1981 F100) and a C6 then you can pull it down into 2nd gear on the highway and see if you are comfortable with the cruising rpms. 2.75 rear axle and the 1.46 second gear on a C6 equates to about a 4.03 final drive ratio; not far from the 4.11's that you are considering.

The stock 9 inch rear axle is just fine for you truck, it will make swapping gears easy and even in stock form a modified 302 isn't going to hurt it.

 

The stock rear end in that truck is a ford 9", it is very easy to just pick up another diff assembly and swap it out to one with desirable gearing. If it does indeed have an overdrive transmission, I'd suggest 3.73 gears.

 

ah..haha, i dont know much about truck axles, so ill listen to the other guys about the 9" rear. do what they say!! lol