Merc M8 drives not standing up to the HP of the 1350 Q4, heard merc is having issues with M8s, and are going back to the #6 for reliability. Is this true, anybody else with issues with M8s.

I thought the M8 was a beefed up version of the #6? What is the difference between the two?

I believe a 35% strength increase.

It may have been just a price increase

The #6s make the boats faster-less drag.

The 6 is not rated for 1350hp so it wouldn't be Mercury doing this and the 1350 is sold as a motor/drive package. Im not positive whats avail today but the M8 has / had(?) limited gearing options. Some guys went back to the 6's for gear ratio selection.

The gear ratios they offer are intended to keep the speeds down.They do have a new ratio for the M8 taller than the current 1.30 and 1.43.
As to the #6 horsepower ratings-i am living proof that they do live at 1800 plus.Several M8 owners have switched back to the #6 and gained substancial top end numbers thru lower slip.

Gary, what type of oil do you run in your #6's?

...and how long can the #6's live at 1800+ hp survive on your Skater before service or major failures?

Amsoil synthetic 10w-40w motorcycle oil that Bob Teaque turned me on to.