1 Attachment(s)
2005 Merc 40m mods for river racing
Guys, got a 2005 Merc 40m 3 cylinder (about 1000cc). Runnin on a 14' 44" bottom semi-v aluminum boat. Boat weighs about 300# without me in it nor the motor (another 400#), set up for running fast with all my fishing crap pulled off. The motor has stock reeds, 60hp reed stops and 60 carbs. Rev limiter has been disconnected. A local prop shop shaved the leading edge??? of a Power Tech semi-cleaver 14" and it turns about 6000 rpm according to my Teleflex tach, consistently. GPS shows about 42 mph with a little porpoise. I have the motor up on a 4" setback plate. Prop shaft is running about 2" below bottom of boat. Trim tabs are set to neutral. On a cool day with a little tweaking, I can get about 200 more RPM and about 1 or 2 more mph.
My question is twofold.
What else could I do to the motor? I don't really plan on turning over 6500 or so. I want to cut the tuner and relieve the exhaust but don't really have an idea of where. I know a basic rule of thumb is 2 1/2 times the diameter of your exhaust port for the end of your diffuser cone. Does this apply to outboards as well? Do I need to go with Boyesen reeds? I know alot of guys add a little exhaust duration but I'd rather not cut on ports until it grenades.
For you Ron, what prop works well on these hulls? Most I've seen run anywhere from semi-cleavers to round ear Vengence style props. A few guys with some mods run full on Sport C cleavers. It would seem that I would want more transom lift to minimize porpoising, but some say I need to get the bow elevated? I am planning to send the lower unit to Bob's to get a nose cone installed. So the prop may see a little more surface in the future.
THanks to all and sorry for the big post!
I'd Like To SEE THE BOTTOM
I'd bet there is more speed in the bottom than the motor...
A good flat bottom, maybe with some air traps, and a larger set back, with bottom water pick up nose cone, see Fast Fred's.... then a larger diameter and bigger pitch prop could help...do the engine mods LAST or NEVER!!!!
Take Some More Pictures..
Where do you live?
Take some pictures of the bottom....and transom area...
As Gritch says, "Speed cost money, how fast do you want to go?"
There is a lot of stuff that can be done, cheaply, by yourself...
If you can't boat in the winter, turning it over wold be the first step...PAD bottoms work...