AC Delco P/n AC41-983. Available at Autozone . Last time I purchased (a couple of years ago) they were around $6.00 or $7.00 a piece. '06 340DA.

 

Merc 33-863622001
AC Delco 41-983
NGK pztr5a-15 (7862)
NGK TR55IX (7164)
gap .060

take your choice.

 

ACDelco GM Original Equipment 41-983 Double Platinum Spark Plug (Pack of 2)

Amazon.com: ACDelco GM Original Equipment 41-983 Double Platinum Spark Plug (Pack of 2) : Automotive

Buy ACDelco GM Original Equipment 41-983 Double Platinum Spark Plug (Pack of 2): Spark Plugs - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

www.amazon.com

 

These are what I'm running now with great success.

 

mr43lts also work very well

 

I have purchased the AC delco 41-983 from Rock Auto

ACDELCO 41983 Spark Plug | Shop Now at RockAuto

ACDELCO Ignition Parts and More for Your Vehicle at Reliably Low Prices. Fast Online Catalog. DIY-Easy. Your Choice of Quality. Full Manufacturer Warranty.

www.rockauto.com

 

I have to change them every 2-3 years, and I run the boat on plane mostly.

Maybe should try something other then AC delco. but normally get a rebate.

 

I hate to say this but I will since I built race cars and done all that stuff before and I know a lot of MSD parts were made fake in China so don't take this the wrong way. A lot of parts on Amazon that say genuine GM or ACDelco are not .You're better off going to the dealer because Chinese knockoffs for every part imaginable are out there