RPM's for 3 cyl Merc 90

[MX-14]

Does anyone have a 3 cyl later model Merc that can run higher rpm's and what mods necessary?

[Capt.Insane-o]

To have it worked to use 2.5 pistons. Best to leavi it alone or find a 3 cyl OMc to build, yes I did say that. I've never been a fan of mercs newer mid range motors, unless your fishing.

[Dave S]

Capt Issno is ritteyo:) Try to get a 850Xs, it's what was made for your boat:D Oh oh someone will dissagree.:eek:

[Markus]

I don't think that engine is built for high RPMs. It is the same powerhead as the inline 4 minus 1 cylinder, and the inline 4 is well known not to survive much above its max. rating of 5250.

For serious RPM in a 3 cyl. 90 hp, get a Yamaha or Tohatsu/Nissan. They are used over here for offshore racing and people do all the tricks on them.

[mk30h]

I'm sure -I saw a merc High Pro. Bulletin on the newer 3cly looper 70-90hp a few years back (early 90's)with a SSM II. I wish I had kept the fact sheet which came with a picture- specs and price which to me seemed dirt cheap at the time.
I these engines have a lot more oomph than the OMC 3. The four inline -100-125 have lots of power but
the max rpm is 5200 or so. I suspect this may be partially limited by the 2+2 design which allows the engine shutdown fuel to 2 cly at low rmps. Great for trolling at lowerspeeds - if the engine is tuned right it works well. Designed more for fishing than speed. These engines also have heavy duty gearcases. Always wondered why Merc went for two bolts on the gearcase to access the internals than its one piece design that all other Mercs had.

I have a 115 - never had a problem (except the stator) but I do miss the sound of the inline 6. But then again the new engines use less fuel - but weigh over 50Ibs more.

[MX-14]

The work I have done to my 3 cyl includes Wiseco pistons, Boyesen reeds, and little exhaust work. I ran it at 6500 rpms all day and it screamed, but I was told not to run it over 6200. I then went to a 26" prop and bbrought rpms to 6000-6200 but lost speed? I am curious what is keeping me from running 6500?

[Dave S]

The 4s may not like revs, just do what is good for you.