Hi Danny, If the heads on your engine currently use 13/16 gasketed plugs, you can't change to 5/8 taper seat because the heads aren't machined for that type of plug. You need to continue using the 13/16 gasketed plugs.
What you should do is use one of your current plugs as a starting point. Enter the plug brand/number into the search engine at http://www.sparkplugs.com/ to search for comparable plugs. As long as you're happy with the heat range of your current plugs, you can gap them at the gap of your choice as long as the ignition system can handle it. With a stock HEI you should be good for a .045" gap. Also when you're looking at plugs, there are two different lengths to consider, especially if you have headers... ISO (International Standards Organization) The ISO height for a spark plug from the seat to the top of the terminal nut is 50.5mm.(1.98") JIS (Japanese Industrial Standard) The JIS height for a spark plug from the seat to the top of the terminal nut is 53mm (2.086") Obviously if you have headers on your engine, you'll want to make sure you use ISO length plugs for a little extra clearance. Herb -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Danny Wilsher Sent: Monday, September 04, 2006 9:08 PM To: The Chevelle Mailing List Subject: [Chevelle-list] spark plugs Hello gentlemen, I am working on a 70 model 350 and have exchanged the old point type distributor for a HEI from who knows what but it has been so long since I have tackled this little chore that I have forgotten what kind of plugs I used to use. I know if I get some that I can gap wider it will be better. The ones in the motor are the 13/16 with the metal gasket that seals them to the head. The guy at the parts store told me that the ones with the 5/8 would work just fine but I would rather get a plug that seals like it is supposed to, not with the beveled seat that the 5/8 plugs have. What I am asking for is a number for say an AC plug that will work with the HEI distributor. Thanks, Danny Wilsher.... Wilsher Motorsports Inc.
