Not if you are running blower motors that you need to change the oil out every 15 - 20 hours because of how rich they run, other than if you are running the pi$$ out of them constantly.

That's about $100 in round numbers using SilverCap M-1
15W-50 and a M-1 oil filter fo the twin blower engines.

Blowers benefit most as the high film strength of synthetic oils protect them most when gasoline shears the oil down.

Think it over..

Just purchased 2 five QT. jugs of M1 15-50 from Wally for $26.00 each.

I have a 500EFI with about 40 hours on it (after re-build) and can't decide which Amsoil product to use in the engine. I am trying to decide between the 20/50, 10/40 wcf, and the 15/50 RD50. I have been running the 25/40 from Merc in the past.

http://www.amsoil.com/storefront/aro.aspx
http://www.amsoil.com/storefront/rd50.aspx
http://www.amsoil.com/storefront/wcf.aspx

It seems that most people are running the 20/50 from reading this thread. I boat mostly at Havasu and the pacific ocean.

The 20W-50 ARO is similiar to SIlverCap M-1...excellent choice.

The 15W-40 is a nice oil ofr diesel applications....the Racing formulation is good if you race.

The Racing formulation is good period.

Hydro,
after reading a bunch of your posts, I'm sure you've got a solid answer as to which one I should use. I don't actually race, but my boat is always pinned down the lake!

Is that what you are running?

[QUOTE=Racerngr1;2842506]Hydro,
after reading a bunch of your posts, I'm sure you've got a solid answer as to which one I should use. I don't actually race, but my boat is always pinned down the lake!

Yeah, as I said in your other post, that is all I run, and that is what AMSOIL INC would recommend too. Run the Racing Oil. Pair it with the Marine Gear Lube, oil filters and Racing grease, and you won't be happier. No you don't race, but running about 5000 RPMS for a duration of time, to me, is classified as racing.

I just called teague and he said the 50wt was too thick for the ocean and Havasu. They are only selling the kendall 40wt and that's what he would recommend for my engine. I think I'mgoing to run the WCF.

Yeah, that will work too.