Drilled midsection for exhaust

[Deeredude64]

Hello again merc guys. I’ve been doing some work this winter to the ol 2.5l. I bought a different prop to try and upon taking with the prop builder he asked if anything had been done to my engine. So I had explained to him that I was told from the previous owner that it had been rebuilt and had aftermarket reeds, stainless motor mounts, and drilled midsection for the exhaust. He said I may lose some performance with the mid being drilled. So I’m here just to get some insight on this subject as to why they would have drilled and tapped 5 holes on each side of the midsection just above the cavitation plate and how does/will it affect my performance. Engine is 1991 carbed 2.5l 12” slidemaster jack plate current prop is a tempest plus 25p with 3 large hole plugs running 62 mph at 56-5800 rpm. Serial number is 0d062795

New setup is a 25m Yamaha worked by josh Edwards of Steve’s custom props with a 8” rapid jack magnum at 3.25” prop to pad but I haven’t been able to run it with this setup yet.

[JOE54]

the exhaust system in your engine WAS designed to direct flow thru prop upon acceleration ,with relief holes drilled on a heavy boat you may loose a lil low end power or acceleration,removing ex bucket inside mid makes it worse on some boats, lighter boats mostly don't notice this , also now all know where your at and sounds cool but doesn't help ,dout it will hurt any top end performance at all

[OnTRAK]

I have read that drilling a mid can weaken its structure. For safety purposes, inspect it frequently for any cracks that may form around the holes.

[Deeredude64]

the exhaust system in your engine WAS designed to direct flow thru prop upon acceleration ,with relief holes drilled on a heavy boat you may loose a lil low end power or acceleration,removing ex bucket inside mid makes it worse on some boats, lighter boats mostly don't notice this , also now all know where your at and sounds cool but doesn't help ,dout it will hurt any top end performance at all

I guess I should have mentioned it’s on a 1990 champion bass boat. So not real heavy. Would it do any good to plug the holes off since they are tapped? My hole shot wasn’t bad with the tempest but could be slow with a full livewell. My other concern would be the need to rejet the carb if I plugged them off. I have no idea if the carbs were re jetted when they rebuilt the motor and did all the work to it.

[JOE54]

try it , jets should be fine if still stock, carbs should have adjustable idle mix screws, mains are fixed

[Deeredude64]

try it , jets should be fine if still stock, carbs should have adjustable idle mix screws, mains are fixed

I will do it and see. So was there any purpose in doing this mod Other then for the sound

[JOE54]

not in my opinion or results from requested drilling and bucket removal

[Merc2.4]

I will do it and see. So was there any purpose in doing this mod Other then for the sound

My understanding is when drilling mid is for reduced slip #s , but may slow hole shot a little ,but gain a mph or 2

[blackboat]

A couple guys I knew did this because they heard that it would help with plug fouling issues during long idle times in no wake zones... and run a bigger prop and still have a decent hole shot. About all I could tell it did was make them noisier.

[JOE54]

^^^^^^ agree when complete exhaust is blocked from propeller and mid is cut out in rear for all ex to exit above water line and none thru prop,,DRAG BOATS and champ series ultra lights, 300 hp on a roofing shingle