Guido David, I fixed a friend's 2000 Mustang GT that had the same thing happen. He said it sounded like a gun shot! On a good plug hole it only had 4 threads on an aluminum head (nice). By using anti cease (love that stuff) you can over tighten the plug and pull the threads. If you install plugs that are a bit to0 long in the thread area you will expose a thread or two in the combustion chamber. After time they will cake up with deposits. When you remove the plug it will pull the threads out. TimeSert was the best way as they use a pin to lock it in. I used a far less costly insert to do the job. He never removed the plugs in that car again. He traded it in on a 2016 550HP Challenger. Larry - Cleveland -----Original Message----- From: DeTomaso [mailto:detomaso-bounces@server.detomasolist.com] On Behalf Of Guido deTomaso Sent: Monday, August 08, 2016 7:37 PM To: detomaso@server.detomasolist.com Subject: [DeTomaso] NPC: Ford 5.4 liter engine blows out sparkplugs ? Think this engine is swapped into some Panteras, someone I know had a sparkplug blow out like a bullet, apparently this is a fairly common problem according to brief internet research. Wondering if anyone here has experience repairing a sparkplug hole on one of these, apparently it's a special shaped hole for a special shaped plug. TimeSert make a kit, but it's like $600. Thanks, GD