NGK spark plugs 9 or 8??

[MX MadMann]

hey guys i was wondering about the NGK 400ex spark plugs , the stock is a dpr8z and they " hotter plug" is the dpr9z , i have both and i was just wondering if any of you guys use the 9. should i use it with my pipe and new jets? or should i stick to the stock one?

casey

[VegasEx'r]

The 9 is for extended high RPM's. I use it, haven't noticed any huge differences (either good or bad).

[Ex'rMike]

I have had nothing but problems with the 9. The hotter plug is the 8. I have found with the jet kit it works much better.
Ex'r Mike

[twisted threads]

I also use a 9 and I have not had any problems with the change.

[ChadEXer]

The 8 is the stock plug and it is a "hotter" plug than the 9. The 9 is a colder plug and most engine builders recommend you running a 9 because it lowers the head temp by about 5 degrees. The plug on the 400 is so close to where the valves seat and the colder plug will keep them from warping as easy and your motor will last longer in the long run!!!