Drilling Exhaust on 25HP Tohatsu - 2ST - 2Cyl - 2004

[thibodeauxba]

Where can I find information on how and where to drill holes in my outboard midsection to make my exhaust louder and less restrictive. I hear that many guys with these Tohatsu 25hps have done this and gain a little performance. Anyone have any experience with this? Pros/Cons? A picture with measurements would be nice.

Thanks

 

[pvanv]

Re: Drilling Exhaust on 25HP Tohatsu - 2ST - 2Cyl - 2004

That's an old-school trick to improve reverse thrust. Been done on everything from Mercs and Johnnyrudes to modern jap motors.

I personally have modified a few old 9.9/15 OMC OB's that way, back before high-thrust props were available. It is considerably louder. You bore a 3/4" hole clean through the leg, side-to-side (the drill is run port-to-starboard) just below the anti-ventilation plate, directly in line with the exhaust passage. To get the correct location, you drop the LU so you can judge the center of the exhaust passage. You end up with two 3/4" relief holes (one on each side) above the smaller factory holes.

Does not measurably improve forward thrust, and is unnecessary with today's HT props.