mercury 3.0 exhaust relief.

[Chaz]

Both sides and the hole saw hole at the bottom rear.

[trivialpursuits]

Thanks Chaz... on my 2005 250EFI there's those "cats eye" slots but it doesn't look like they lead anywhere - are those cut through on the 300x?

[Chaz]

They go thru the outer skin of the inner can to the inside , where the exhaust logs live.
I have never seen them on anything other than a 300x inner can, but I wrekkon there's a first for everything.

And yes, one each side.

If I was going to do a full length can , I would make the holes/slots twice as big .. thats just me ..

[trivialpursuits]

Here's what my can looks like. I'm debating about just leaving it alone as it's a fairly heavy 28' twin engine boat and it likes mostly open vent holes on props to get on plane... I don't want to end up with inadequate exhaust flow through the prop...

[Aaronhl]

Chaz please post pics of the underside of the DRIVESHAFT HOUSING where you drill holes, or if you have one of a 300x that is drilled from the factory post that thank you

[Chaz]

Here's what my can looks like. I'm debating about just leaving it alone as it's a fairly heavy 28' twin engine boat and it likes mostly open vent holes on props to get on plane... I don't want to end up with inadequate exhaust flow through the prop...

Those are well below the water line. The cats eye's that are drilled up higher, help the motor to idle easier .. and come up cleaner when you get in the gas. Once that point, a couple little holes will be inconsequential , compared to the total amount of exhaust gas looking to get out.

Aaron .. I'll look see what I have laying around ..

[Aaronhl]

I got a cheap enough 20" mid in the spirt of making things a little louder without the merc racing products prices, I was considering hacking it up a little to make my 3.0 sounds like my carb 2.5s...

Even as cheap as the 20" driveshaft housing was, still tough decision to considering modifying it...

Let me know what you think about the plan,

Drill a few holes in the housing, below the cowl skirt, and plug the square hole in the exhaust plate...I'd run a cut skirt and throw away the rubber cowl boot...
Do you think a lot of water will get in there? Seems to me it would run right down the back of the housing and empty right above the lower unit cuz im exposing the tuner...

I would also cut the outside section of the exhaust "tube" to expose the tuner, see pic for the cut mark...the exhaust would have a clear path to behind the water pump just like on the 2.5s...

***********Chaz approved???*******

[Aaronhl]

U guys gonna let me do this !! ??!!

[Chaz]

A couple way's to go about it.. you can just drill the two cats eyes holes .. the motor will idle much better and come off of idle cleaner.

If you want to leave the inner can in place .. but want a little more exhaust relief .. then you can cut the back side of the bottom off ... drill the hole like the second photo .. then either weld the piece back on .. or leave it off.

Or just cut the inner can off @ the casting line nearest the cats eye slot .. and be done with it ..

[Aaronhl]

OK So what about the holes in the back upper side of the mid section housing ??? A little nervous abut putting those in....

[Chaz]

Ifin I ain't show'd it ... you ain't need it ...

But hey .. be a trend setter ...

[Aaronhl]

Ok I am doin it no turning back
only need to drill a few slot in the driveshaft housing