Difference in Spark plugs?

[shobote]

I've had my 89 SHO for 22 years and have put in 5 types of plugs; OEM, Splitfire, AC Rapidfire, and E3. They all worked with no problem, but the OEM seemed to have less kick via butt dyno than all the others. I do like the E3's and been running them for 3 years.

 

[turbo79]

+1 for the Motorcrafts. I learned the hard way. Aftermarket replacement plugs are slightly longer than OE Motorcrafts. Because they are slightly long, the plug wires won't seal correctly against the valve cover, and water and other debris will find its way into the plug wells and cause a misfire. Motorcraft is the ONLY option for plugs, IMO.

You can also successfully use Denso or NGK plugs. From SHOTimes:

...the Motorcraft AGSP32PP spark plug was not designed or manufactured by Autolite (that's why the APP3924 plugs don't fit), it was supplied by Denso, formally known as Nippondenso. Because of this, there are other spark plugs out there that will fit the SHO engine and the well seal spark plug boot and still run perfectly. This is good for several reasons. ... just in case you can't find the Motorcraft spark plugs you can use either a Denso p/n PK16PR-L11 or a NGK p/n PFR5G-11, both are double platinum equivalent spark plugs.

http://www.shotimes.com/php-bin/mod...le=article&mode=thread&order=0&thold=0&sid=62