How do I tell a Ford 351 from a 400?

Question

I am helping a friend work on his truck. The truck is a 1970 but it is a conglomeration of parts from various trucks. The P.O. told him the motor was a 302 and recently it died on him. The truck will only run when you hold the throttle about half way open. The carb is a brand new aftermarket holly that has been on there for less than a month. The truck runs fine with the throttle open. He replaced the plugs, wires, cap, and rotor to see if that was why it would not idle and then it would not run . He called me to look at it and I checked it and found 2 wires were switched so I switched them back. This made it run worse and backfire. We looked in the manual and found that a 351/400 had a different firing order. We tried that order and it runs smoother with the throttle open but still does not idle. We replaced the brain box and coil but it made no difference. We need to tell which motor it is so we can buy a fuel pump for it. There are no stickers under the hood or on the motor.

Some more info...There are only 2 vacuum lines. One for the tranny and one for the vacuum advance. Both have been replaced. The new module and coil are the same for all the duraspark for V8's. (I checked part numbers for both engines) I pulled the fuel line off the carb and stuck it in a bottle. I had him turn the motor over and it spurts gas once per revolution. The filter is new and it is one of the clear ones. I can see that it stays 1/2 to 3/4 of the way full when the motor is running. I put a timing light on it. With the motor running fast enough to be stable (I am guessing aroun 2000 rpm) there are 3 timing marks visible. the center one lines up with the pointer.

The 351 and 400 take different fuel pumps so we need to know which motor this is before we buy one.

Any suggestions would be appreciated. He can't afford to take it to the shop anymore so I would like to help him.

Thanks

G

Answer 1

There are several different V8s made by Ford that will fit in this truck. It may even be a 352, which is a completely different engine class in itself. The easiest way to figure out which class of V8 yours is is to count the number of valve cover bolts.
2 bolts = "Y Block" V8s (like 272, 292, 312);
5 bolts = "FE" V8s (like 352, 360, 390, 427, 428);
6 bolts = Windsor or "W" V8s (like 260, 289, 302, 351W);
7 bolts = "385" V8s (like 429, 460);
8 bolts = "Cleveland"/"M" (like 351C, 351M, 400)
This will help you determine what motor class you have, and the motors in each individual class should interchange external parts with the other motors in the same class, with the exception of the M and C motors, since the intakes and heads are different. The biggest headache you are going to have is that Ford made 3 different 351s, and also a 352, and almost nothing interchanges between any of them. If you use the above bolt counting method, you will have a better idea of what type of motor is in your truck. I hope this helps, and if you need anything else, just ask away!

Answer 2

The blocks are identical on the 351 Modified (M) and the 400. The only difference was the stroke length. Find the firing order on the top of the intake manifold and using a manual, determine the engine.

Answer 3

There's anumber on the block that tells you what you're dealing with. I think that you're problem lies with one or both of two things. First is the distributor installed correctly. You can only be loik one tooth off for it to work right. But, Most likely it's the timing chain. You gotta tear down the front face of the motor, Bring #1 piston to tdc and visually inspect the timing marks on the drive and cam gears. If they're not aligned then you gotta re do it.