George/Land O' Lakes
05-12-2010, 07:28 AM
I guess there is nothing more dangerous to your fun budget than saying to your airboat mechanic "What if we...." Well that's what I said and here's where we ended up.
I had asked Chuck Rackley if extending the exhaust pipes on my boat would quiet it down some. He added about 24 inches to each pipes, putting some real neat mandrel bends in them to terminate near the center of the boat. With DB meter in hand the result was about a 1 DB reduction in the sound level. Not a big reduction but now we know.
The next "what if" was to replace the stock B&S intake and carb with a Mikuni that Chuck had on hand. The custom high rise manifold and carb look real nice. We gain over 300 RPMs just with that mod. Chuch then added about two full turns of pitch into the three blad IVO prop to where the engine would turn about 3850.
I took her out the next day and the engine would only turn about 3550! I think what happens is that when you adjust the IVO, it takes awhile of the entire blad to accept the increase in pitch. I've since dropped it back one full turn and am turning 3850 again.
During the trip my GPS went Tango Uniform (bad fuse connection) so I couldn't get any accurate speed results. I'll take it out this weekend and see what she'll do now.
I'm attaching some pics (including one of the reds we caught that day)
As you all will see in the pictures, Chuck sure does nice work. Believe me when I tell you that I made these mods sound much easier to do than they really were.
George
16 Ft Dixon Twister, Stage One B&S, Three Blade IVO Prop, Stainless rigging by Ned, Chuck Rackley:Chief Engineer and Mad Scientist
I had asked Chuck Rackley if extending the exhaust pipes on my boat would quiet it down some. He added about 24 inches to each pipes, putting some real neat mandrel bends in them to terminate near the center of the boat. With DB meter in hand the result was about a 1 DB reduction in the sound level. Not a big reduction but now we know.
The next "what if" was to replace the stock B&S intake and carb with a Mikuni that Chuck had on hand. The custom high rise manifold and carb look real nice. We gain over 300 RPMs just with that mod. Chuch then added about two full turns of pitch into the three blad IVO prop to where the engine would turn about 3850.
I took her out the next day and the engine would only turn about 3550! I think what happens is that when you adjust the IVO, it takes awhile of the entire blad to accept the increase in pitch. I've since dropped it back one full turn and am turning 3850 again.
During the trip my GPS went Tango Uniform (bad fuse connection) so I couldn't get any accurate speed results. I'll take it out this weekend and see what she'll do now.
I'm attaching some pics (including one of the reds we caught that day)
As you all will see in the pictures, Chuck sure does nice work. Believe me when I tell you that I made these mods sound much easier to do than they really were.
George
16 Ft Dixon Twister, Stage One B&S, Three Blade IVO Prop, Stainless rigging by Ned, Chuck Rackley:Chief Engineer and Mad Scientist