Dad always got the new models on a memo charge to use for the summer. "We" liked to play with the engineering and see if we could make them run faster. The ’55 Big twin we got was a dog. Very quiet, but not as fast as the ’54 we had the year before. (27 powerhead horse power, 24.7 at the prop shaft) The ’55 Bigtwin picked up speed when you opened the motor cover, so we opened the quarter inch hole in the front lower motor cover to two inches. Then we took it apart and planed off the top of the block to the raise the compression, trimmed and balanced the pistons. I squared the ports and filed the lower unit a bit. We put a spacer behind the intake manifold and radiused part of the reed valve holes toward the carburetor. It was then faster than our ’54 Bigtwin. When we sent it back to Evinrude at the end of the summer, Denny Watkins told dad it was developing 33 horse power, I thought it was the basis for the 30 horse. Altering the port timing changed the power curve. You got your peak horse power at a higher RPM. Those who proped the ’56 Bigtwin at 3,800 RPM did not get even 25 horse power. Those who proped over 4,600, got the full 30. You can also gain speed (as has been pointed out in other posts) by raising the transom hight an inch or two. . . 😀
