76 115 merc tuner

[carmex234]

I searched this site for exhaust mods, but cant find anything relative to that year. Can someone shed some light on the subject? From what i understand, i can remove the powerhead,and pull out the exhaust tuner,but at the risk of discoloring my mid section and possibly melting my WP houseing. If i remove the tuner, and drill 4-5 1/2'' just above the cavitation plate will that keep the mid section cool enough? Another idea is cut/modify the very bottom of the tuner,then drill the 1/2'' holes.

Just looking for clarification before i go to cutting and drilling on my stock LU.
thanks

[crazy horse]

All you need to remove is the ext. liner. When you remove the ext adapter the can will be below it and go all the way down into the gearcase. I removed mine for a super speedmaster, I was wondering why you are? I don't think you will melt your water pump and my center section hasn't discolor yet and I'll never drill holes in it:eek:.

[Raceman]

As Crazy Horse pointed out, you're confusing the exhaust liner with the tuner, which bolts on the bottom of the plates.

All of that trouble won't add any power AT ALL to that engine and will just make it louder. Another thing to consider is that the bolts holding the plates on top of the inline mids don't always come out without wringing off, and there's no good way to put heat on em. This is even true on freshwater engines. If you go drilling in the wrong place you may weaken it to the point of causing cracks. On some engines it may help the boat get on top a little better, but since the old 1150's didn't suffer from lack of low end, there's no real reason to do it unless you just want to annoy the old man who calls the water cops and complains about everything.

[carmex234]

Thanks for the mercury fast response! Im not loking for more power it wont happen with this motor,but im in love with the sound this mod makes. The hard to remove bolts you are talking about, are these the 2, one on each side of the drive shaft? If i just remove the liner,where does the exhaust gas flow out? Just beneath the cowling at the 2 rectangular shaped ports or does it exit through the prop hub?

[Raceman]

Removing the liner in itself doesn't really allow the exhaust gas to go anywhere new. What it does is keep the holes you're cutting in the outside from being blocked by the liner. Drilling through the outside area AND the liner accomplishes virtually the same thing.

The two upper plates that surround the motormounts are bolted to the midsection with bolts going downward. This is just from memory, but I believe there are about 2 from the upper plate into the lower and 7 from the lower into the mid.

If you're determined to do it, you can drill above the cavitation plate in the side of the gearcase, right below where it splits from the mid, and directly through the exhaust liner. I've seen em done with a couple of holes on each side, probably 3/4 inch in diameter. Many of the mids I've seen drilled on inlines have broken. This area in the gearcase may be less likely, since it's supported ahead of and behind this area by the studs.

[carmex234]

Sounds like a plan,i saw a tutorial on here wish i could find the link but this guy didnt remove the liner, he left it in and back cut it leaving the front half of the can intact to protect the water pump, then 1/2 holes were drilled. Raceman, what are the 2 rectangular ports just below the cowling looking at the back of the motor? I always see water coming out of there,its not the pisser, its cast into the mid section. If the can was removed would exhaust flow out these rectangular ports? One more ? and thank you very much for advising me, this is a great forum for OB gearheads. What type of line/tubing is used to route a water PSI gauge? will white nylon tube with brass fittings/ferrules work? Thanks again

[Raceman]

I can't remember exactly how the square holes are routed without looking in a housing, but they aren't directly opened to the mid, but rather through tunnels. They're intended as a little bit of exhaust relief when the boat is off plane and the exhaust outlet (propeller) is completely underwater.

I've used hard plastic tubing for pressure guages and haven't had failures. I prefer small rubber hose because of the constant flexing since the motor isn't fixed on the transom.

[Sorry Dog]

inline... exhaust mods??

Hhmmm.

Maybe make a custom header to bolt in the place of the exhaust plate and attach a T3 turbo to that- plumbed to a custom intake box with some fuel injectors spraying at an angle at each set of reeds. Might need an intercooler too.
Don't forget to run race gas.

[carmex234]

Actually SORRY dog....im gonna take th garret turbo of my powerstroke,then if time allows propane injection..jealous yet?