Heres the deal. I bought a set of used heads for my porting etc, and they happen to have a heli-coil in one of the spark plug holes. The problem is that the heli coil that was put in before I got the heads, happens to be set too far down in the hole, and therfore puts the standard spark plug too far into the combustion chamber. When I tried the platium TR55's that I have, the plug sits too far down in the combustion chamber. We tried using an Autolite racing plug # AR3910 with a washer and was non tapered seat, and it worked perfect for fit, but I dont know the heat range of it. I need to find a plug that has a heat range close to that of the TR55, but fit like the AR3910. Is there anyone out there that can help me figure out what I need to do.

Brian

 

The AR3910 is the same as Champian C59YC and NGK R5672A-9

 

My question is, will the AR3910's work with my setup, or do I need to find another plug with a different heat range?? Doew anyone know what the heat range of these plugs so that I can get a close match to the TR55's I was previously going to use. OR, should I use the TR55's in the other 7 holes, and use one of the other NGK plugs in the hole with the heli-coil?? Thanks

 

See if this chart can help you:
http://www.clubplug.net/auto_ngk.html

I know the AR series plugs are non-resistor, and I think the 3910 is 2 heat ranges colder than stock, but don't quote me.