Re: Spark plug type for 502 EFI
 

Stock plugs are RV15YC4 or MR43TS at .045.

Re: Spark plug type for 502 EFI
 

You may want to use a projected nose plug (such as NGK BPR6FS) instead of standard nose (NGK BR6FS). From Dennis Moore's BBC Performmance book;

"Spark plugs are an area of the ignition system where an increase in performance is available for very little expense. The increase in performance comes from switching from a standard nonprojected nose to a projected nose spark plug. Most professional high performance marine engine builders and tuners automatically switch to a projected nose plug as a matter of course, but for some reason, this is still a big secret to a lot of amateur or backyard mechanics. Projected nose spark plugs are more efficient at igniting the air/fuel mixture because the nose of the plug projects further into the combustion chamber".

Dave

Re: Spark plug type for 502 EFI
 

The MR43TS are extended tips.

Re: Spark plug type for 502 EFI
 

The 'M' marine have been discontinued.

The 'C' commercials are available.

So instead of MR43TS get the CR43TS.

Some places still have the marines, but it is typically what they have left in stock.