Originally posted by adamnygaard1: even with the 3L hybrid i wouldnt say you "need" one.
I do.
Upping compression by over a full point is one very good reason for choosing colder spark plugs. As is running forced induction or nitrous. Basically anything that increases cylinder pressure (and thus temperature) requires a colder plug. Don't want to get pre-ignition at high RPMs because your plugs are hot enough to ignite the air/fuel charge before spark occurs - on the engine hard is a BAD time to get uncontrolled combustion.
That said, going colder without good reason will get you a set of fouled spark plugs right quick.
With the above warnings, I run APP103 plugs, which are one Autolite step colder than stock.
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