The old addage comes true again. You have to check..and recheck any part that is given to you for your car!
My story:
Went to NAPA a couple of months ago. Have dealt with them for over 15 years...the the 340 Duster days, thru the Civic SI days, and thru the AMX days. Always good and knowledgeable service. So I go in there, looking for NGKs. The look it up..."Is it an SVT?" I answer yes...they go and get me NGK TR55GP. I install..car runs fine. Begin reading posts about SP extending 5/8" too far into combustion chamber. Get curious..decide to install proper Motor Craft AWSF-32PP ($4.99 at NAPA BTW). They come pre-gapped at .045, so I open them up to .050. Pull NGK plug, and lo and behold...the threads sure enough allow the electrode to extend that 5/8" extra into the combustion chamber. The thing is...the Motorcraft plug they 1st found in their manuals was also the AWSF-32F (which BTW...Bill Jenkins is also recommending!) and just looking at it you can see the extra threads that allow the extra length!!
The moral of my story...do your homework before buying! This board had proved to be invaluable again!
