Spark plugs for the aluminum head?

Mustang_Geezer

Well-known member
Anyone tried to experiement with differant spark plugs? Mike suggested AR 3934 Autolite racing plugs which I have run for the past 3 years. However they tend to foul out after awhile which I thought was caused by my carb.

However I took some of them to work and we matched them up to some other Autolite plugs.I'm running Autolite 3924 plugs in it right now and if they work I can upgrade to platinum or double platinum plugs using this same part number.

Right off the bat I've noticed better starting, no miss fires on a cold engine and the plugs havent had as much of a tendency to foul out.

The plan is to run them for 200-300 miles, pull them out and see what they look like. :)

Later,

Doug
 
Doug,
The AR style plug comes standard with .025" gap. And that's the gap that they are suppose to be used at. They are designed for high cyl. pressures (boost, n2o etc.)
So that would probably explain the fouling.

We run AR3932 Kelly's car. 2 steps colder. But we're running a turbo and we're trying to pull some heat out of the chamber and keep the plug cool.

The standard 3934 plug is the same as the AR3934 except it has the longer gnd. strap and a larger gap.
Later,
Will
 
Thanks Will for the info!

I pulled the plugs out and they look fine so I'm going to keep running them until I install my new motor.

Later,

Doug
 
Gene Fiore":zjqp4qp9 said:
New motor? Details?? ;)

Gene,

More compression, more rpm's, bigger cam than the current motor.... ;) :mrgreen: Plus its a 66 motor so it'll have forged rods.

Its bored .030 over, 0 decked, balanced, flat top pistons, schneider race cam, arp throughout. Aluminum head, holley 4 bbl and all the other classic inline goodies will get swapped from my old motor to my new one. Then the current motor is going to be punched .080 over so I'll have a backup motor.

Machine work is finished and all the new parts are boxed up in my shop. I'll post a couple of pics when I unbag it and start assembling it.

Later,

Doug
 
Gene,

.512 lift, 280 duration, 107 lobe center.

At .050 lift is .310 & duration is 222

Compression is supposed to be right at 11.0 to 1

He did a nice job with the machine work and it is a virgin block. He had to deck it .047 to reach 0 deck and it still had the original FOMOCO stamp main & rod bearings in it.

Hows your engine coming along? Havent been on here for awhile...too many things to do... ;)

Later,

Doug
 
Sounds great...my engine has been done and installed back in March. Runs great but still running the 350 Holley...I still have plans to install the 500 Holley I got from you. Like you, been very busy and right now it's just too darn hot to work out in the garage when it's 112 deg with humidity. My sig has been updated with all the new stuff. ;)
 
After putting over 1000 miles on the plugs they still look great so I'm switching to the platinum plugs next weekend and am switching to Mobil 1 15 w 50 synthetic oil in my old engine.

Autolite plug number 3924 for regular, AP 3924 for Platinum plugs & APP 3924 for Double Platinum plugs.

Later,

Doug
 
I had a couple questions I needed answered, so I called Autolite and talked to their in-house spark plug expert for nearly an hour. I was surprised that he took that much time to talk with me, but he was very helpful. At any rate, here's the plugs he recommended for an average performance build with 200 RWHP. Ha said to start in the middle of the range (like a AP3924) and go from there. And that for each additional 100 HP, we'll probably need to run a plug that is one step colder. In otherwords, if you have 300 RWHP you should start with a AP3923 instead.

When you check the plugs, the tip should be a hazy brown. If they are white, you need to run a cooler plug and/or richen the mixture. If they are dark brown or black, you need to run a hotter plug and/or lean the mixture. Dark black means the plug is too cold, dark brown means the mixture is rich, blackish brown means cold and rich. For more informatio on plug readings, click here.


Naturally Aspirated - Street:
AP3922 to AP3926 (Platinum Resistor - extended tip)
APP3923 to APP3926 (Double Platinum Resistor - extended tip)
XP3923 or XP3924 (Xtreme Double Platinum Resistor - extended tip)
Naturally Aspirated - Strip:
AR3910 or AR3911 (Non-Resistor - extended tip)
Boosted - Street/Strip:
AR3932 to AR3936 (Non-Resistor - standard tip)

PHOTOS: AP3924 - XP3924 - AR3911 - AR3934 (note the differences in the tips)
AP3924.jpg
XP3924.jpg
AR3911.jpg
AR3934.jpg
 
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