I have a 1981 Ford F150 Trailer Edition I was wondering what kind of rear do I have in it the rear end has all the bolts towrds the front of the truck and I was wondering why my vin would say I have a 351W when my engine compartment says its a 5.8LM/6.6L and How can you tell the diff between the 351W the 351M and the 6.6L

 

9 inch rear axle.

351M/400 = 8 valve cover bolts. 6 valve cover bolts = 351W

 

Thanks for the info but how can you tell between the 351M and the 400

 

If the valve cover sticker is gone, I think the only way to tell is to open the motor up. They are the same externally, the differences are in the bore and stroke. You can put a 400 crank in a 351M to make a 400.

 

if you have an rpm gauge, cant that tell you guys, i think thats how i told mine was a 351M, it tach out at 5000, even thought i have the red pointer on the sunpro tack at 4500

 

you can crank any engine any rpm (within logic) if built right, or it can be limited anywhere, if built or runnin wrong, your diff is either a 9" or an 8.8", if you can get a socket on the bottom 2 bolts, it's a 8.8, if not, thank god it's a 9".

 

Just what is the 8th VIN character?

 

8th VIN digit of H should be a 351, S should be a 400, at least that's the way it is in the cars offered with 351 and 400 motors.

 

Another way to tell the difference between a Windsor and a Modified is where the T-stat is located. The Windsor engine has it located in the intake, the Modified has no water in the intake, so the stat is located on the block.

Dan Harriman 84 F150 lwb
Orange, Texas

 

My 6th digit is an H, but anywhere else on the vin there is not another H or S, but also mine is an 80, so i can get a socket to the bottom 2 bolts, but i cant not get a socket rench in their, so i have an 9 inch right, i can only get a 9 16 rench in their, thanks guys, but my 6th is an H. So if you can clear me up.


Taylor

 

youve got a 9 inch if the bolts are pointing toward the front, a 351m is a big block even though it doesnt look it, the 351 windsor and 351 cleveland are small blocks, and if you have 8 valve cover bolts its a big block (351m or bigger) if it has 6 valve cover bolts its a small block (351w or 351c or smaller), how you tell if its a 351m or 400 i dunno, i thought that 351m meant 351 modified to a 400 because every sticker on the valve cover ive seen for a 351m says 351m/400

 

f_balla you are right about the 351m/400 bein' a 400 cid motor, but not all forward bolt rears are 9", ford also made a 8.8" that looks exactly like the 9, but the lowest 2 bolts are not accessible with a socket.

 

thank you for tellin me that now i know and ill try not to confuse anyone else...lol

 

You are a little confused I believe. The 8.8 rear is a totally different looking rear with a sheetmetal cover on the back. It was used in trucks and cars starting in the mid 80's.

The ones that are hard to tell the difference if they are not side by side is the 8 inch rear and the 9 inch. Those are the older style rears that look the same, and you can use the socket test. They also made an oddball 9 inch in some of the cars that won't interchange. But the 8 inch and the oddball 9 inch were never used in trucks.