GT-40 M-6049-X303 Plug Gap

[93gtmustang]

I'm using Motorcraft SP-447A Plugs with the GT-40x heads. Was just wondering what you guys that are running these heads are gapping the plugs at?
When I bought the motor, Ford Racing said 0.044. I've seen 0.045, 0.050 and 0.052.
Thanks !

 

[FastDriver]

All will work if your ignition system is strong enough. I recommend .045 with autolite 3924s for naturally aspirated combos. I don't know your plugs but if they're right for the heads and copper core the gap should be the same.

 

[Mustang5L5]

I’m running 0.054” on 3924s on my N/A HCI setup.

It really all depends on the strength of the ignition. For N/A you want to open up and expose the spark as much as possible without making it unsustainable causing misfires. If 0.045” works nice, try 0.050”. If it feels like you are having misfires, close the gap up a bit.

 

[93gtmustang]

All will work if your ignition system is strong enough. I recommend .045 with autolite 3924s for naturally aspirated combos. I don't know your plugs but if they're right for the heads and copper core the gap should be the same.

The Motorcraft SP-447A plugs replaced old Motorcraft number AGSF32C. They're actually a 4 cylinder plug lol! That's weird. The Autolite number is 104.
Yup they're copper core.

 

[FastDriver]

Only difference I see is the .708" length vs. the 3924s at .750". Maybe yours are nickel coated... read something like that while searching around. Anyways, should work fine.

@Mustang5L5 is right. The wider you can gap, the stronger the spark, but the more ignition system it requires. Strong spark means better burn, theoretically. And stock is .054 IIRC. But, I've run gaps all the way down to .028" in high-boost setups and it all seemed the same to me. The only notable thing about too wide a gap is that I've had it break up at high RPM (Not enough dwell time for coil to rebuild a strong enough magnetic field) or higher boost (denser higher resistance air where a shorter gap yields the same resistance needed and just as strong a spark).

 

[93gtmustang]

The Motorcraft plugs are copper core. 0.044 gap. That gap I believe is for a 4 cylinder. That's probably why the guy at Ford racing gave me that spec. He was probably looking at the Motorcraft parts book?
That's right on the stock Gap. I just looked in the 5.0 Mustang tech reference book. 1987-93 5.0L H.O. ASF-42 Motorcraft Plugs .054 gap.
The 93 GT-40 cobra. AWSF-42C Plugs .050 gap. I think I'm going to open them up to .050. I'm running the stock ignition and I'm up to 6000-6100 at the track, so I don't know if I'll have any problems? I read this just recently. " The gap should be set to requirements of the ignition system.
So on my 1993 it calls for .054. I don't know? Makes sense.

 

[FastDriver]

Yeah, just play with it and if you have any high RPM break up, back the gap down. You know enough to figure it out, now.