Spark plugs what do you guys like best?
 

Looking to get the plugs for my fresh 509, it has slightly increased compression to 9.2:1 wondering what plug works best and what heat range would be best? I ran previously an NGK YR5 but I also saw the AC Delco Rapid Fire #1 plugs. Only plug I don't ever run is Champions I hate them.

Factory cast iron heads ?
Delco MR43T or CR43ts.
.035”-.040” gap, no more.

Yes factory cast iron heads. What is the difference between the MR and CR plugs? Googling now lol

https://www.offshoreonly.com/forums/...ark-plugs.html

MR is marine, CR is commercial and the TS is extended tip from what I found. Which is my better choice?

https://www.offshoreonly.com/forums/...ark-plugs.html

The MR's are supposed to be stainless so they dont corrode.....if your in salt then do that...i always boated in fresh and changed the plugs yearly and used the standard CR's with out any issues....

They don’t make MR43TS’s, thus the CR43TS’s.
c = commercial
m= marine = stainless
TS is extended tip vs T which is normal
43 is good heat range for your engine

i like and run ngk ur5 projected tip in our hard charging 540

I've been running NGK's for many years. Never had an issue with them.

NGK plugs are the only ones we use.