ZFR5N plugs too long?

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standup303

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Went to replace my plugs today with the NGK ZFR5N and they are a good bit longer than the Champions I pulled out. Are the NGKs the incorrect plug? This is for a 225 slant 6

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They are correct and will fit and work fine. The electrodes are longer, yes, but will not hit anything. If you're installing these in a '63-'74 head, remove the metal ring washers first.
 
They are correct and will fit and work fine. The electrodes are longer, yes, but will not hit anything. If you're installing these in a '63-'74 head, remove the metal ring washers first.
Awesome thank you
 
My NGK catalog specifies BP5FS for the 225 Slant 6.
 
The BP5FS is the listed plug for the slant six. The consensus of using the ZFR5N plug is to get the gap further into the cylinder, for a better burn. My personal opinion is that I have seen no change in performance/mileage.
PS: I haven't tried them on a 170 engine, but I would be careful, as the piston comes up to the top of the block, and MIGHT hit the plug. 198/225 engines do not have this potential problem.
 
Apart from the possibility of mechanical contact using the Z plug, I would be concerned about pre-ign from so much real estate being exposed inside the chamber. Just because the Z plug works in XYZ engine does not mean it is the best choice in another brand......In my NGK catalog, Z plugs are only specified for a few engines.
 
PS: I haven't tried them on a 170 engine, but I would be careful, as the piston comes up to the top of the block, and MIGHT hit the plug. 198/225 engines do not have this potential problem.

They do not hit in my 170 and it seems to idle smoother with them.
 
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