I have twin 2.5's with standard mid-sections, not the offshore housings. I have heard that you can drill out the exhaust at the point where the mid-section meets the lower unit to improve exhaust flow. Stock exhaust exits over the prop as well as through exhaust holes. Can anyone shed some light on this or point me in the right direction as to where to get more detailed info?

Here are my questions:

1. Does this improve performance or help the engine run any smoother?
2. Where EXACTLY do you drill and is there a template and where do I locate one?
3. What size hole and how many do you drill?

Thanks in advance.

Shane

I drill (5) 1/2 inch holes in the bottom part of the midsection. A big plus also is to take the liner out of it. As for a bolt pattern, I just spaced them evenly. I had a 20" drill manufactured to do this. Drill only through the first "plate" and not through both. It makes it breathe easier. I may be able to take a couple pictures if you need it. Tom

in order to do this correctly you will need to remove your powerheads and look into the midsection. where the mid section gets narrower their is a flat surface, this is where you drill the 5 1/2 inch holes. this will make the exhaust come out between the cavatation plates. ( I am assuming that you are talking about the fishing motors and no the hi-performance 2.5 mercs.)
Do not drill holes in the midsection elsewhere or the mid section WILL break.

RT

As a side note, you will gain nothing but noise from this.

I have 2.5 mid sections. Not the offshore race mids the standard version. From what I have gathered the upside potential is not worthe the downside risk!

Thanks for the help guys.

Shane

Shane,

Visit the Scream and Fly message board. The outboard guys hang out over there and will answer your question. The better way to do this is with a Bob's Unit. I had my 225 Promax done and it helps hole shot. The Bob's unit also comes with a plug, so that if you boat where noise is an issue, you can plug the holes off to quiet the motor. I also love the sound of a 2-stroke with relieved exhaust. By the way-you do NOT have to remove the power head.

SHANE , IF YOU HAVE HIGH PERF 2.5'S WITH THE STANDARD MIDSECTION , THEN THE HOLES HAVE ALREADY BEEN DRILLED FROM THE FACTORY.