You might try the SplitFire with the four electrodes, I had a friend who tried these in his boat and they cleaned up the performance and transom all the way around. The boat ran on the Rev Limiter for the first time since it was new. No more black transom either.

MR43T on the shelf @ NAPA every time I go for them!! Cant figure having to order them

I've run NGK UR-5 "V-Power" sparkplugs in big-block, small-block, and small-block Ford marine engines for years and they seem to work very well.

NGK 5672A-9 or 10's, also Champion PN791.

I just changed plugs. I run AC #1's but the new ones are different than my old ones. Same plug # but different ceramic and electrode???????

I just finished building a pair of 540's for my 35 Sonic. Ihad always ran MR43T's from the NAPA shelf. However after talking with Nickerson's who built my carbs and Tommy at Cheif who i purchased the valve trains from they both insisted on the NGK UR5's stock #2771. They do burn much cleaner and do not load up at idle. I am running Merc ignition with the HP module. These two guys convinced me.

I just finished building a pair of 540's for my 35 Sonic. I had always ran MR43T's from the NAPA shelf. However after talking with Nickerson's who built my carbs and Tommy at Cheif who I purchased the valve trains from they both insisted on the NGK UR5's stock #2771. They do burn much cleaner and do not load up at idle. I am running Merc ignition with the HP module. These two guys convinced me.

Nothing runs like the NGK V powers ! I have used them in everything . Everything that used to load up with other plugs will not with these . Also helps on motors that are old and burn oil .Keeps the plugs clean .

Don't use split fires on high energy ignition like an MSD box . It is too much power for the plug .It wil burn tips right off . They even tel you that in the paper work . I here they work good with stock ignition though .

I haven't used the NGK V-Power but I do really like the AC Rapid Fire #1

the TS has a longer tip than the T ....the TS gets the tip farther in the cylinder and more centered. the TS's burn alittle cleaner (less transom soot) in my 365hp.

the M stands for marine and they are corrosion resistant. i change my plugs every couple of years so I just get the R43TS because they are cheaper.