spark plug
 

Leading is 7 or tailing is 7?

You talking about the NGK part number?

7 is leading.

BUR7EQP for leading
BUR9EQP for trailing

(NGK part number)

I remember reading that some people ran either all 7's or all 9's i can't remember which it was

its 9s all around

your 9s in trailing or just trailing in general are just for emmissions really....look at a rotor housing - its just this little hole going through to the mount for the plug.

if you look at the leading it goes all the way through and is the "more important" part of your ignition.

SO....if you want to run a colder plug (9s or 10.5s or somethin) change out your leading.

leading is bottom
trailing is top


OH...and dont crossthread your spark plug....especially not the trailing!

some say put all 7 in the engine will help pass emission. I already have all HKS all 9's. Just need to find out the part number for the 7's

My car has limited modifications. It's got a K&N Filtercharger and a downpipe, but it runs a whole lot better with 7s and 9s than with just 9s. Plus I failed inpection with 7s and 9s (didn't pass until they did a non-dyno test). That being said, I probably will change them to all 9s the next time I change the plugs. By then my car will probably have 95,000+ miles and you figure that many miles and you wanna keep the rotary gods happy and keep the car as cool as possible.