Best spark plug for the 355?

Hotter/colder heat range should not result in more/less of complete burn. That's a function of combustion chamber design, air fuel ratio and of course enough spark energy.

Heat range isn't any correlation to spark potential, just need it to be the correct heat range to not become a glow plug.

Easy to see if you look at the heat mark on the ground strap (especially after a wot pull).

With stock ignition and fresh plugs/wires on my car and how clean the dyno runs are, I don't think there's any power to be found with ignition upgrades.

Not to say coil on plug isn't a benefit (no possibility of plug wire degradation/interference) but power? Nothing there in my opinion.

 

PMR8B

 

So much reading and information. My heads spinning. After all of that reading, i still cant decide between PMR8B's and the PMR7Bs for my 95' 2.7 haha

 

There are no PMR7B’s, only PMR7A’s. If you’re gonna go with 8’s, go with the 8B’s. So really only 2 choices. PMR7A’s or PMR8B’s.

 

17 years and the argument goes on. What I'll add if that when I bought my car it had a top end rebuild at a very reputable shop and they put PMR7A' in it which lasted for 11 years and 14k miles. Never had an issue, driving, cold start, hot start. SO I stuck with them and the car continues to function perfectly.

 

If I can chime in with 348 .

Took one out on my ( new to me 94 , U.K. spec 320 Hp ) .
No symptoms just curiosity for future procurement reasons , and note they are “9” so hot.

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That is a Champion racing plug, heat range 59 which is equivalent to heat range 4 of standard Champion. This plug is more on the cold side, like NGK 9. Champion racing plug heat ranges are 50 to 65.

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Plugs ave been in my '98 spider for around 13k miles. Changing them out in a few weeks and I'll see what they look like.