spark plugs for gt40 aluminum heads

[88GTtom]

i have autolite 3924's in right now, i copied and pasted this from another thread and am wondering if i should change to what it says. you guys let me know.
GT40 Heads:
AUTOLITE
stock--765 (Heat Range - 5) [14mm, .708 Reach, 5/8" Hex]
1 step colder--764 (4) or 104 (4) [14mm, .708 Reach, 5/8" Hex]**
2 step colder--103 (3) [14mm, .708 Reach, 5/8" Hex]**
-----AR473 (3) [*recessed tip, racing plug]
-----AR472 (2) [*recessed tip, racing plug]

now this person had info for stock e7 heads and said to use 3924's for them.
SO... what is the difference between the 3924's and the 765's, 764's or 104's like posted above. If i can remember, i think the reach was different between the two..?? Does that matter and which one is better to run. thanks tom

 

[50bomber]

Ok, this may not be helpful, but I have GT-40Ys and I run Motorcraft AGSF-32C, as per Ford Racing catalog. I have actually mocked up different spark plugs, Bosch, Motorcraft AWSFs, Autolites and none of them stuck out into the chamber enough, only the AGSF series did, in fact everytime I tried one, it perfectly indexed itself, so that it was pointing towards the exhaust valve . I think AGSF series has a longer thread than the regular AWSF, 32 is colder than 42? Am I wrong?

 

[88GTtom]

AGSF... who makes them...

 

[88GTtom]

oh... Motorcraft makes them.. now i see. if anyone else can chime in on this, i would like to know what i should be using...

 

[2000xp8]

I had gt40y heads that never went on the car, and my mustang mechanic (highly reputable) had me buy the autolite 3924's.
They are also used for x's.
You can take my word on this.

NON supercharged applications

 

[50bomber]

If you have the heads off the car, I highly reccommend, just threading one or two in just to see if it fits....If not, maybe buy one of those Motorcrafts AGSF-32C (they are like $10 for set of 8 at PepBoys) and compare the threads with Autolites or whatever...Cheers

 

[Insane3D]

If you have the heads off the car, I highly reccommend, just threading one or two in just to see if it fits....If not, maybe buy one of those Motorcrafts AGSF-32C (they are like $10 for set of 8 at PepBoys) and compare the threads with Autolites or whatever...Cheers

$10 for a set of 8 @ Pepboys??? I went to my local Ford dealer, and they were like $30 for 8.

I didn't know PepBoys sold Motorcraft plugs...

 

[88GTtom]

i am going to try them out, i know ford would charge an arm and leg for some, i wonder if pep boys does have them that cheap. I am installing an Accel 300 ingnition, what gap do you guys suggest i gap the plugs to? I also have new ford 9mm wires as well as a new accel cap and rotor. thanks tom