How-To Choose the Correct Plug For Your Cag

First off, here's a list of plugs (not including Iridium) you can use in you cag.

Non-Projected Type Tip (regular) Plugs:
(Left to Right: hot to cold)

NGK: BM6A, BM7A

Nippon Denso: W20M-U, W22M-U

Bosch: WS8E, WS7E, WS5E

Champion: CJ8, CJ6

AC Delco: CS45, CS42, CS41, CS40

Motorcraft: A7NX, A3NX, A2NX

Autolite: 235, 254, 255, 253


Projected Type Tip Plugs:
(Left to Right: hot to cold)

NGK: BPM6A, BPM7A, BPM7Y

Nippon Denso: W20MP-U, W22MP-U

Bosch: WS8F, WS5F

Champion: CJ8Y, CJ7Y, CJ6Y

AC Delco: -

Motorcraft: A22NX

Autolite: 2974



Some basic information about the differences in projected and non-projected style tip plugs:

Projected style plugs protude farther out the end of the plug as opposed to non-projected plugs. But this doesn't necessarily mean the center electrode and insulator is really longer. The length of the center electrode and insulator determines the heat range of the plug. The longer the center electrode and insulator, the hotter the plug. A projected plug and non-projected plug of the same heat range will have the same length center electrode and insulator, it's just that the projected plug's design will sit the center electrode and insulator farther out the end of the plug.

Since the center electrode on a projected plug protudes farther out the end of the plug, this of course brings the tip farther into the combustion chamber. This will increase the plug's tip firing temperature, one of the advantages of running a projected type plug. This allows you to sort of "fine tune" the heat range plug the engine is needed. A projected type tip plug will have a firing temp of 10-20ºC hotter than a non-projected plug of the same heat range.

A spark plug no matter what type of plug it is and no matter what type of engine it is used in must have a tip temp of 450-800ºC for optimal operation.

Too hot of a plug:
If the tip (center electrode) temp is higher than 800-850ºC, the plug most likely will overheat and will damage or overheat the insulator that surrounds the center electrode which then will melt the center electrode. This can cause the spark plug to fire before it is supposed to, which detonation. Detonation is an engine's worst enemy and in extreme cases can actually crack the piston.

Too cold of a plug:
If the tip temp is lower than 450ºC, the insulator surrounding the center electrode (which is made of ceramic) will not get hot enough to burn off carbon and other deposits. This is referred to as "self cleaning". If these deposits are not burned off, this will lead to spark plug failure or fouling and will cause misfire.

Some may think a projected style plug since it will sit farther into the combustion chamber will raise your compression a bit but this is not really true. Since a projected type plug's tip will sit farther into the combustion chamber vs. a non-projected plug, this will act like advanced ignition timing which can be an advantage or disadvantage. The smaller the spark plug gap will also act like advancing timing and a wider gap will act like retarding the timing. In engine performance theory, advanced timing will give you more torque or low end punch. Retarded timing will give you more top end or better for high RPMs.

The key is always in reading the plug. That is the only way you will know if a certain plug is right for your setup. A melted or worn looking electrode can indicate that the plug's heat range is too hot but can also look the same if it is simply just old (high mileage). A plug with built up carbon depsoits can indicate that the plug's heat range is too cold but can also be cause from week igntion. If a plug when viewed under a magnifying glass you see metal deposits can tell you that you motor is suffering from severe detonation and you should check the internals mainly the piston. Reading a plug can be tricky and it takes experience to get good at it. But when your pro at reading a plug, you'll know exactly how your engine is performing. There are many places online that have pictures of various conditions of plugs to help you identify plug conditions.