351M Headers .... help!

JasonE · Aug 1, 2020

Hey guys, I'm restoring a 1973 Mustang with a 351M engine in it. I'm have all the parts to do an Edelbrock performance upgrade to it. But I'm stuck trying to find the right headers for it. What do you guys recommend?

Don C · Aug 1, 2020

Is it an "M" code 351 (Cleveland) engine, or an actual 351M? Two different engines, but very similar. If it is a 351M do you know how it got in the car?

A 351C "M" code came with 4V heads and requires 4V headers.

JasonE · Aug 2, 2020

It came from factory that way. I was told that when I bought it and I looked it up through the VIN. Its a 351M 2 valve engine. When I read about it, it says it's a tall deck - I'm concerned with clearances if I use a standard 351C header.

Hemikiller · Aug 2, 2020

Step one, make sure you know what you have, note the "wall" on the 351M block. If it's not there, you have a 351C

Don C · Aug 2, 2020

2V and 4V on older engines does not refer to the number of valves in each cylinder, but the number of venturies (barrels) in the carburetor.

The 5th character in your car's VIN (vehicle identification number) will tell you what engine came in your car.

Don C · Aug 2, 2020

This article should help you to understand the differences in the engines

https://en.wikipedia.org/wiki/Ford_335_engine

The spreadsheet in this thread should help you with the VIN numbering, as well as with other Ford codes and numbering systems.

https://7173mustangs.com/forums/topic/33536-ford-code-numbers/?tab=comments#comment-344745

JasonE · Aug 2, 2020

Hemikiller said:
Step one, make sure you know what you have, note the "wall" on the 351M block. If it's not there, you have a 351C

View attachment 43541

Thanks for the PIC, it's helpful! Looks like I have the "wall" you circled on your picture up by the distributor making it a 351M engine.

Hemikiller · Aug 2, 2020

Yep, that's a 351M or a 400 block. Most 351C headers for the 71-73s will not fit due to the extra deck height & resulting width increase

Another member @MeanMachine used Patriot shorty headers on his 400 equipped car.

https://www.summitracing.com/parts/pte-h8435-b?seid=srese1&gclid=Cj0KCQjwyJn5BRDrARIsADZ9ykEGltBT0KuNQfkQoo69FHvIb1_VpTP1shrbZehEjWkdUVhpN1zT-rUaAtoNEALw_wcB

Don C · Aug 2, 2020

Interesting, definitely not from the factory that way. Now, the 64 thousand dollar question, is it a 351M or a 400? If it has a casting number from '71, '73, or '74 (begins with D1, D3, or D4) it is likely a 400. A casting number for '75, '77 or '78 (D5, D7, or D8) means it could be either one. And, then if it's a 400, big block or small block bellhousing?

351M Headers .... help!

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