Hi Guys,
I'm new to here, and finally joined up so I could write some posts to get even more info than I have already found in others posts.
I don't have a top dollar, super high speed racing boat, and a budget to suit!
However I do have a nice solid 14' wide body aluminium fishing boat with a 3mm plate bottom and a hull designed for stability at high speeds (very deep nose).
I have recently got the bug to get as much speed as I can out of the setup as I use the boat for fishing at night time on my local salt water lake, and have many favorite spots from one end to the other....
However its not a small lake!!
Lake Macquarie in NSW Australia is the largest tidal salt water body in the southern hemisphere. https://en.wikipedia.org/wiki/Lake_M...w_South_Wales)
I have trialed a few different motor/prop combinations on the boat now and feel that I'm on the right path finally with a 1998 Evinrude 40hp 2 stroke (OMC 50 cui 2 cylinder).
I have changed the carbies to a pair removed from a johnson 75hp that are big bore and butterfly, with adjustable mixture screws and have adjusted the timing to 23 degrees at WOT while running 98 octane fuel.
I have also fitter sports fibreglass reed valves from USA, and have ported the reed cages and manifold for smoother unobstructed flow.
But there are a couple of things I cant find enough info about, that I feel can still help get the most out of the engine.
*Spark plugs and gaps?? I have found so many different settings online (.030-.045'') that I would prefer to just ask someone with experience, rather than trial and measure the speed.
*And compression levels? I am currently getting 160psi cranking pressure in both cylinders.
Will I benefit much from increasing to around 180psi? I only ever use 98 octane fuel and it has electric start.
I have 2 different props to choose from, a 15'' and a 17''.
The 15''is almost enough to flip the boat, and even with a full load and 2 passengers tops out at the same speed as it does with just me (55km/h)
But when the 17'' is fitted, the top speed is over 65km/h when empty, but with my usual passenger the top speed is limited to 56km/h.
My aim is to improve torque and power enough to be able to use the 17'' prop, and increase the loaded speed to as close to the empty speed as possible.
A 16'' prop would be ideal, but there is no such size!
Any thoughts or suggestions would be most appreciated.
Cheers Ken
