This 502MPI is 97 so I'm guessing platinum or a grooved plug was spec then. Now that the irridiums are out can they work well in a 502 at 5K rpm. Since the spark is so small I know there are issues of spark blow out on some iron heads but don't know on this marine stuff how they work. Anyone know or tried it?

You will be changing a regular plug before they wear out anyway. I say stay with the normal plug which I believe was the good old Ac Delco MR43T. Someone correct me if I'm wrong.

the plug will work but you don,t need a plug that was designed to last 100000 miles in automotive use.

Soooooo the marine tune up is more from fouling than wear? If fouling, does grooved help any on this application? What is the recommended interval for changing in this engine? Is the interval short enough that the replacement frequency makes it more cost effective with the standard plugs than irridiums?
I am a tech so I understand mechanical, hydraulic and control systems. My time and expertise has been auto/truck and equipment primarily and my marine exposure is good but not intricate enough for designing and modification. I hope there are not too many questions here but I want to learn more info on these systems and I don't have any marine competition buddies to learn more of this from.
Just before putting the Bird away the starboard engine did not bust off instantly as usual so I started to speculate about tune items and wondered about plug parameters. It could be something from fuel or other but the maintenance was stretched out just before I got the boat so I am mostly suspicious of regular service stuff. I will do a total tune with every component from the plugs to the distributor just because I keep my stuff in optimal running condition and just fishing for improvements and the best running components and service on these engines.

Thoughts?
TIA

Ayuh,..... For marine spark plugs, ya can't beat the marine line up from AC Delco, as they're alloy bodies which take much longer to rust,......
MR43T for most Chevy heads, MR43TLS for the Vortec heads, needin' longer plugs,...

For marine motors, most boaters are anal with spark plugs, 'n coils, throwin' away perfectly good parts, just because they're Easy to change,....

Fancy spark plugs, Any of 'em, are best at helpin' ya spend yer fuel money on things other than fuel,....

Split fire, iridium, platinum, All of 'em are a Waste of money,....

What is a suitable alternative to the mr43t, did some calling and no one in town carries it.

CR43T

M=Marine
C=Commercial

Thats too easy, doh! Thanks sb

Just as a little FYI: the M (marine) series have stainless (or nickel plated) for metal (threads + body) so they won't rust as much as the standard R43T's.

Not sure on commercial, but easy to tell. If threads are black on any AcDelco, they are normal steel. If they are shiny they are SS or nickel plated.

If they are steel (black) just don't let them stay on motor forever....LOL. And obviously, salt water use can make hem corrode real quick.

That's all.

Edit in: Have an Oreilly's ? Online shows most physical Oreilly stores carry the MR43T's.

Tell me about it, I live on a "island" and it took 5 stops to get 8!