Right off the bat please forgive me for asking stupid questions. Im new to the game of old mustangs. I just got a 351 block from a buddy and he couldnt tell what exactly it was. It came out of a 1977 merc. couger. I would like some help on firguring what exactly it is? Also what is the difference in 351c or 351w? I have even read the term 351m in some local parts books. Is it just head design or something much more then that? Thank you for you time.  

Here's a quick rundown - the 351C was produced between 1970 and 1974.  It's a 9.2 deck block with a cast in timing chain housing on the front.  The intake is dry (meaning no water routed through it) and the thermostat housing sits right center (right being from the driver's seat) in front of the intake, pointing up.  It shares the motor mounts and bellhousing pattern with the "Windsor" type motors.  

The 351M and 400 are the same basic configuration as a 351C, produced from somewhere around 1971 to maybe the mid 80s.  It has a taller deck (10.3) and uses motor mounts like a 429/460 - 3 bolt bosses on the side of the block.  It also uses a 429/460 bellhousing pattern.  A key identifier of the 351M/400 is a big cast "fin" near the distributor.  Can't miss it. The heads on the 351C, 351M and 400 are big and square.  The 351C/M/400 heads feature canted valves (laid back or forward, not in a straight line) with 8 valve cover bolts.

The 351W is a tall deck version of the 289 /302.  It's a 9.5 deck block with the same aluminum timing chain cover as the 289/302.  It uses the same style cylinder heads as the 289/302 with 6 valve cover bolts, with a "laid back" exhaust port area and inline valves.  The intake has water routed through it with a thermostat mount in the front right side facing forward.  The motor mounts and bellhousing pattern are the same as the 289/302/351C engines.  It looks like a big 302, basically.

So - the 351C is out because it's a 1977 engine.  From the big merc, you've probably got a 351M.  Might be a W, hopefully this info will help you get an ID on the engine.  There will also be a casting number and a date code on the block in the starter area (lower right side) near the oil pan rail.  That can help narrow things down.  

Well Thank you very much for the info. That was really helpful. I looked at the block and found the 3 bolt bosses and the fin by the distributor. I found this casting on the block itself D7TE-A-2B. So its a 351m. Now here is another question, Since its a 351m and i have read on some web sites that the 351m is just not worth making a good power plant out of. So should i scrap that motor and go with my other choice of a block which is a 302?  

You can hot rod anything - just depends on whether you want to spend the money.  Before we toss the 351M, what car do you propose putting it into?  

I have a 66 mustang. With the I-6 in it right now. This is my 2nd 66 mustang. Young and stupid was the reason for the loss of my 1st. But out of that car i kept the 302 and c-6. I had got the 351m block from a buddy for free and just though bigger is better lol. I just started stripping the 302 the other day, down to the block to have it checked.  

IMHO - Put the 302 in it.  The 66 engine compartment is smaller than the later models.  The 351M is as big as a 460, which is a tight fit in a 67 up.  The hassle to make it fit, adapt/build mounts, then fix the shortcomings of the 351M as delivered by Ford really don't make the swap worth the time, effort and cost.  The 302 will go in easily and without nearly the hassles to overcome.  

Alright thank you. Im looking for a mild to hot street rod. I was shooting for about 350-400 horses? Do you think that i can make that number out of the 302?  

With the right equipment, yes.  It won't exactly be mild.  A 331 with a good set of AFR heads and a roller cam would get you there and the extra displacement would help.  In just a 302, a "mild" combination with good heads, 9.5:1 and a decent cam is going to produce around 300, somewhat more.  You should get a good focus on what you want to do with the car and build accordingly.  A high HP engine stuck in a street driver with 3.25 gears and a stock converter will just be a pile of expensive junk and no fun.  Look at the package - a 350+ 302 is going to want 4.11s and a 3500+ converter.  Nothing wrong with that.  

I have done some research on trying to get those numbers out of the motor and edelbrock makes a complete package ( heads,intake,cam,carb,valve spring kit,) That produces about 387 hp. This package does sound good. What are your thoughts on this? Good or bad.  

Edelbrock makes some nice pieces.  The package you mention is a Performer RPM package, so it will still require the appropriate gearing and converter (if auto).  You'll also want to have a fresh short block with the pistons set right on the deck to get the full advantage of the cylinder heads.  Or, at the very least no more than .01 down in the bore.  With the pistons on the deck and the cylinder heads from the kit, you'd be right at 9.5:1 which is a pretty good number.  Note you'll also have to buy hardened pushrods - required but not in the kit.  

More quick hits on the 351M/400:
The "fin" discussed above -like just about everything Ford- doesn't show up on ALL 351M/400s.  I believe it's the early, early ones that may be missing that tell-tale.

Parts - see T Meyer, Inc for a strong line of "big C" performance parts, including pistons to cure the "down in the hole" deck syndrome.  Tmeyer Inc

CHI now carries - new for 2007- a real live single place performance manifold for the 400.  

Link to CHI article

Also check with
TLI Racing Engines
Medina, TX 78055  

Falcon is right.  Run a 302.  Look into the stroker 347 from Coast High Performance, or similar manufacturers.  Lots of these have been built (check out any late 80's-90's 5.o mustang mag) and you'll see these all over.  If your going to run 4.11's (as I have) you will probably want to run a 5 speed out of a newer mustang, this way you can drive on the highway.  Otherwise run a 3.50 gear with a 3500 stall and trans cooler (very important).  If you try to squeeze in the 351M, you will have header clearance problems and parts selection is not as great.  There are tons of combos for the 302.  You also will want to run a set of 351 Windsor heads (69 70) are the best.  They bolt right up to your 302 and the have the bigger valves.  If you can afford to run aluminum heads do that, this will solve the bigger valve problem on stock 302 heads.  Remember to have your block balanced and blueprinted, as a good machine shop is very important.

john