Stock Spark Plugs - heat range?

WarmAndSCSI

Honestly I've been building and tuning boosted engines for the past 5 years... I really don't think this setup needs 8 heat range plugs. A 13:1 engine might, though. There must be something about the cylinder head design that allows Nissan to get away with running such a cold plug with no fouling issues. That's more of the info I was interested in getting - I just read most of the service manual today, and nothing there.

The heat range of a plug dictates how much heat the spark plug can carry away from itself and the area surrounding the electrode. Really, it's just a way to prevent detonation and pre-ignition by eliminating the spark plug as a potential hot spot in the cylinder. I haven't spent much time looking at stock AF curves, but maybe the motor runs lean enough stock to warrant this extra protection.

I know my Evo X has basically the same plug design, and heat range (8) stock. But it essentially runs 20+ CR (boost PR * combustion chamber CR) under full boost stock (19-ish psi). At 32 psi, I was only needing a 9 heat range plug. Similar modern combustion chamber design, but I know it's not the same engine at all.

But you have a good point with the owner's manual comment and such. A 3.7 L V6 making 332 bhp on 91 octane stock is pretty much pushing the limits to begin with.

This is just a question of curiosity and thinking about boosted applications on the Z, not looking to mess with anything; so I'm not sure how plug gaps are relevant. I don't really like messing with gaps on iridium-tipped plugs anyway; too much room for mistakes and potential broken plugs inside the combustion chamber!

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