TOPIC: '84 115 transfer port cover - to modify or not?

I am finally getting around to re-assembling my '84 115 that has had a rebore (after waiting 3 months for the pistons etc. to arrive from the USA! ). I will be going around the ports removing the various casting burrs (clearly visible on the bottom pic) etc but I notice the transfer port covers a) have a flat facing the gas flow which, to my way of thinking would be better if knife edged & b) the covers block off part of the transfer ports themselves so would, again to my mind, benefit from relieving in these areas. Its not easy to explain but hopefully the pictures will help.

What do you 6 cyl builders think? My knowledge is based around gas flowing 4 stroke heads but I would have thought the same theory works here, the easier the flow of gas the more you pack in the cylinders. that makes a bigger bang & the prop goes around faster!

So I'll take a stab where I play with 1500's that are powerported the same way. Anything to smooth should help but any noticable h.p. change will be hard to come by, and flow does not always follow the path that appears it would. I'll bet there is very little to be gained in port matching to the rounded end of the intake but who knows. I have refrained from doing anything as there is a balance between the intake and exhaust that gives the best scavenging, that is the removal of spent exhaust from the cylinder and charging with fresh intake. Two cycles do not do this as efficiently as a 4 stroke it is a major cause of earlier generation two cycle inefficiency.
Port volume plays a role as well as velocity of the flow. Opening things up would reduce velocity and increase volume, generally a two cycle wants the intake volume as small a volume as possible, hence the old method of "stuffing" the crankcase. This gives the best response to the pressure changes as the piston moves. Same on velocity, fast charge velocities are better. It's the difference in volume between piston at TDC and BDC that is what ideally should be available to fill the cylinder. This is a bigger factor than minor smoothing would provide. Compression is another thing, did you get high domes or low domes for your pistons? High domes will give more H.P. but better fuel is needed. Compression builds HP fast. Also the lengthy delivery seems odd, did you get Merc pistons? There are many junk aftermarket ones out there.
I would personally recomend against modifyng as the gain is minimal so why risk disturbing the relation between the intake and exhaust pulse? As an example the intake porting size between a 1150 and a 1500 is pretty dramatic but still only results in an extra 35 h.p. so blending surfaces would not yeild much. That extra 35 h.p. gives maybe 4 to 5 mph on a fast (60mph) hull so even if you found 5 h.p. the speed increase would hardly be measurable.
Your generation 115 is a great runner, I'd leave well enough alone. Just my two cents.
Randy

Short and sweet, I agree with Randy, leave the deflector as is. The casting flaws by all means remove. The intake path is quite convoluted and expands and contracts along its length. Widening the area right at the ports would slow down the charge and change the intake timing.

Short and sweet, I agree with Randy, leave the deflector as is. The casting flaws by all means remove. The intake path is quite convoluted and expands and contracts along its length. Widening the area right at the ports would slow down the charge and change the intake timing.

Thank you gentlemen for all you comments, I will just clean the casting flaws away.

Geoff UK