On the back of an oil bottle you will see the API symbol and then the SM rating if it is a low ZDDP oil for "today's automobiles" that require less phosphorus to decrease catalytic converter damage.

Fine for cars...not for Offshore Boats.

Thus the need to stick with a beefy Motorcycle oil like M-1 V-Twin which has a tough synthetic base and lots of ZDDP....extends engine life a ton over an SM rated oil to be sure.

For the past several years with a flat tappet cam I have used the Amsoil 15/40 diesel/marine oil. I switched to a roller cam last year and I am trying the Amsoil 10/40 marine. I alway use the Amsoil AO filters.

Have respected your recommendations on Oils and Filters. What do you think (for marine performance use) of the new Dominator racing oil from Amsoil?
http://www.amsoil.com/storefront/rd50.aspx

http://www.goldenmotorguard.com/cart/

We always used straight 40w oil in our old 502. Still used some oil, but not a big deal. Just keep an eye on the oil.