Autolite Plugs: APP3924 Double Plat & Plat Pro

[Racer X]

I was under the impression the AGSP32FM had finewire platinum-nickel centerwire electrode with nickel plated shell, and they are not actually double-platinum plugs.

That's the same info I have for them. Of course I discovered this long after they were installed and shortly after they started missing in my car. I wish I'd saved them when I pulled them to show everyone, but one bank was showing more wear than the other.

All the same, I have about 12,000 miles on the Autolite's and I couldn't be happier.

I put them in a friend's ATX SHO (Jamal, you remember Jeff, right?)[snip]

Sure I do. How's that alternator treating him?

 

[sdpatt]

Any spark plug in the SHO engine that does not have platinum on both electrodes is going to erode the cathode arm on three cylinders very quickly. There is no way that those plugs will reach the 60,000 mile service interval of the OEM spark plug.

Are the Denso PK16R11 plugs the direct replacement for the AGSP32PP?

 

[SeanMc]

I'm running copper top and platinum bottom'd autolites on my car with no reported problems.

 

[shobote]

Any spark plug in the SHO engine that does not have platinum on both electrodes is going to erode the cathode arm on three cylinders very quickly. There is no way that those plugs will reach the 60,000 mile service interval of the OEM spark plug.

Are the Denso PK16R11 plugs the direct replacement for the AGSP32PP?

Longevity vs. performance; I'll take the smoother running / performance advantage of the Rapidfires since mine's not a daily driver. Same fit as OEM too; I recently pulled the plugs for a look (after 4 years), cleaned them up and no visible wear can be seen on any, but mileage is probably less than 5k (most of those miles are with a heavy foot) in that period too; I doubt I'll ever put 60k more miles on mine since the SHO only sees the road when the sun shines. If I was putting a lot of miles on it, I'd stick with the double plats for convenience sake.

 

[1slickRED89]

The Motorcraft AGSP32PP was the ONLY plug designed for the SHO engines. These plugs were manufactured for Motorcraft by Nippon Denso.

The original AGSF32EGM and AGSF32PM where manufactured by Allied Signal in Fostoria Ohio, the same company that made Autolite brand, now named Honeywell. I have talked to the technicians who did the application testing back in the day to confirm this. there are many Ford cars that use plugs other than Honeywell's, such as the some Lincolns, Mazda and jaguar, but NGK has those cars, not denso.

I believe the differences height are due to the gasket material (annealed vs non-annealed), which is different for the autolite, and batch to batch variations in terminal stud manufacture.


also, I would stay away from champion right now as their quality has really been suffering lately, and you may get hosed. most brands of the finewire design (Bosch, NGK and denso) will wear down and open up the spark gap in a surprizingly short amount of time (as little as 100 hours of run time). this increases chance of misfiring and is ******* the ignition wires and coil.

in my opinion the best plug, and best value, for the V6 SHO right now is the autolite XP3924 and XP104 for the V8 (both gapped to .03 to .04 NA and .02 to .03 for F/I). I make this recommendation based on test results that show very little gap erosion over 600+ hours of run time, low price for an Ir ($6 plug), the finewire is good for performance, and they are available in a decent heat range spread for N20/boost.

 

[roswell998]

The Motorcraft AGSP32PP was the ONLY plug designed for the SHO engines. These plugs were manufactured for Motorcraft by Nippon Denso. The Autolite APP3924 plugs have the correct double platinum electrodes, heat range and threads, but are 1/32" too tall to let the plug boot seal at the valve cover surface. This will eventually allow foreign debris into the plug wells. If the plug well seals leak, and eventually they will, that grit will make a very difficult to clean soup that can score the cylinders if allowed to enter through an open spark plug hole.

I am using the Autolites now, but have added an O-ring under the boot seal to attempt to minimize the entry of road grit in to the plug wells. Can anyone tell me if the new fine wire Motorcraft plugs have the correct insulator height to allow the design fit of the plug boots at the valve covers?

I had some old plugs and just made the following measurements:

The Original M/C AGSP32PP's are 1/8" shorter than both the replacement M/C AGSP32FM's and the Autolite APP3924's.

I bought the Autolite APP3924's today from AutoZone for $3.99 each and will replace the M/C AGSP32FM's tomorrow. Couldn't get the FM's and after reading this post decided to try the Autolites. I got all of the plugs types out under good light and compared them. Indeed, the Autolites do seem to be identical in appearance to the original M/C PP's except for the length. HOWEVER, I now have the Delco wires and they fit the FM's perfectly and will also fit the Autolites since the length is the same.

Bottom Line........It appears that the Autolites are the best answer today since they are double platinum and appear to be identical to the original OEM plugs specs except for the length and the Delco wires solve that. I assume that Scott is using Motorcraft wires and perhaps his o-ring addition will solve the debris problem. However, I have been well satisfied with the Delco wires to date.

Also FYI, the reason I'm replacing the FM plugs after only a few thousand miles is that I'm in the process of rod bearing preventive maintenance replacement (Clevite) and had the plugs out to release compression and thought why put the old ones back in. Also, all the posts on this site seem to steer toward using double platinum plugs because of the 3 coil firing arrangement of the design. After all, these cars didn't come from the factory with double platinum plugs for no reason. The fine wire single platinum plugs appear to be a cost savings compromise substitution by Ford and they don't appear to have the life expectancy of the originals.

 

[revhardSHO]

The Motorcraft AGSP32PP was the ONLY plug designed for the SHO engines. These plugs were manufactured for Motorcraft by Nippon Denso. The Autolite APP3924 plugs have the correct double platinum electrodes, heat range and threads, but are 1/32" too tall to let the plug boot seal at the valve cover surface. This will eventually allow foreign debris into the plug wells. If the plug well seals leak, and eventually they will, that grit will make a very difficult to clean soup that can score the cylinders if allowed to enter through an open spark plug hole.

I am using the Autolites now, but have added an O-ring under the boot seal to attempt to minimize the entry of road grit in to the plug wells. Can anyone tell me if the new fine wire Motorcraft plugs have the correct insulator height to allow the design fit of the plug boots at the valve covers?

I have heard of this problem as well but I have never actually encountered it when using APP3924s. They seem to work fine with my motorcraft wires.
As for the grit, which can develop over time in any SHO with leaking plug wells, I stick a straw on the end of my shop vac and clean the wells out first before removing them.

 

[sdpatt]

I have a set of WR-4033 wires on my car. I too use the "suction pump through a tube" method to remove the soup from the plug wells before removing the plugs.

 

[SHOkid13]

For what it's worth, RockAuto.com currently has the XP3924 for $4.82 each, and an Autolite mail in rebate worth $1.50 per plug.

Cheers!

 

[Storm-Chaser]

So, what's the difference between the Autolite APP3924 and XP3924? Both are double plats...

 

[1slickRED89]

APP3924 = "necked down" platinum on the centerwire

XP3924 = .6mm "finewire" platinum on the centeriwre, and trimmed ground wire

overall they are very comperable, but if you care enought to ask, go with the XP's because they are slightly better.

 

[SHOkid13]

http://autolite.com/

Answers to all your questions.