Spark Plugs for 1973 351C Q engine

[1973stang]

Hi Folks,

I am looking for Heat Range (HR) 4 spark plugs for my car.

1973 351C Q engine.

According to engine specs...Spark plug is BF-42 or Autolite 45 (HR 5; 18 MM pitch).

Autolite 24 has HR 4, but 14 mm pitch thread.

I searched and then called Summit Racing...they say for my engine it is 14 mm pitch thread.

1) So which is it ??

2) If it is 18 mm pitch...which spark plug would you reco. for HR 4

Rush

 

[mach1000]

Can't say the thread pitch but pretty sure 99% all 351C engine plug threads are the same. Try looking up a 71 351 M code or 2 engine.

 

[jeff8877]

According to the 1973 car service specs you need an Autolite ARF-42. This is also the same plug that the sticker on the valve cover calls for with a Q code 1973.

Jeff

 

[Don C]

I'm sure the confusion lies in the differences between Windsors and Clevelands, 351W takes 18mm plugs, 351C takes 14mm.

In Autolite's new numbering system you would take a 24 (or XP24, APP24, or AP24):

http://www.autolitecatalog.com/Application.aspx?b=A

 

[jeff8877]

Don C...

If you put the correct original plug (ARF42) in the search from your link it returns a 25 plug not 24...

Jeff

I'm sure the confusion lies in the differences between Windsors and Clevelands, 351W takes 18mm plugs, 351C takes 14mm.

In Autolite's new numbering system you would take a 24 (or XP24, APP24, or AP24):

http://www.autolitecatalog.com/Application.aspx?b=A

 

[Don C]

That's correct, however 1973stang wants a heat range 4, which makes it a 24, and is the same as a 1971 351C.

 

[73StangCoupe]

I have a 73 Q code. I replaced my plugs with these...

http://m.summitracing.com/parts/ngk-6630

 

[Don C]

I'm going a different route than most, with my plug choice. I'm going to try Bosch +4 plugs (#4449) in my 351C. Whenever they have been available for my vehicles I have put them in and have generally noticed an improvement in performance and gas mileage. I like the 4 electrode design (must be from my flying days), no worries about the electrode shadowing the fuel/air charge.

 

[1973stang]

Thanks guys,

You are the best.

Cleared the confusion between W and C

Gave me a few options to try.

Rush

 

[72HCODE]

hey rush the guys cleared it up