drilling hole for exhaust

[42cigrevotrips]

i have a 1984 evinrude 235 crossflow. completely stock. i want to have the exhaust exit prior to the prop. im guessing the only way to do this is to drill ..... where do you drill exacty? how do you go about this? how big a hole etc. thanks

[Fish]

hey 42cig,
I am not a white motor guy, but with the mercs the best recommendation is to drill up from the bottom of the midsection so that the holes are facing towards the water. 5 x 1/2 holes on each side of the mid towards the back. At least with the mercs, "arguably" (since this is an often debated question around here) drilling the holes in the back of the mid (where normal offshore exhaust might exit) weakens the mid structurally in a place that receives considerable stress (I am assuming a surface piercing application). There are also some nasty pics somewhere of some mids that have broken. Hopefully some OMC guys will chime in.

BTW, nice boat in your avatar!

[42cigrevotrips]

thank fish, ya the cig looks nice, but the good ole check is the onyl one ever runnin:D

sorry about my lack of knowledge of outboards. i am not very familiar with the way the exhaust exits. do u want to drill the holes right before the mid meets the lower? shoudl the five holes be lined up parallel to the ground? how far apart? if they are on the side of the case then how far should they be from the front or back? i just got a srx prop (over hub exhaust), will this help from havin too much slip from the exhaust? will much of the exhust stil exit thru the prop? thanks for cooperatin with all these questions

[Fish]

42 cig,
I found a thread that has some more info and some pics by chris lacey of where to do it on an OMC. Looks like it is a little different thatn the merc location. Exhaust Releif (http://forums.screamandfly.com/forums/showthread.php?t=90792&highlight=drill+exhaust)

Perhaps if you could post a pic or tell us more about your setup, I would be willing to bet someone on here has or has had the exact same setup.

[jphii]

I'm hoping you can figure it out from this picture (http://members.cox.net/gecko_europa/DSCN0253.JPG) It's right below the top of the lower, just behind the middle bolt. This one is cut not drilled. I have two drilled ones and two cut ones. If you need better pics let me know. One thing: Drilled is considerably quieter than cutting out the slot. I mean CONSIDERABLY! The other one that's cut is cut about twice as big. The drilled ones have 5-6 holes 5/8" with a chamfered edge.

Like I said, need more pics, let me know.

[42cigrevotrips]

thanks a lot for the links. one more q, whats the difference in cutting as opposed to drilling holes besides teh sound? will more air exit if its cut? would you just cut out the area that you would drill theholes?

[jphii]

I think that it flows more air with the slot cut out. Yes, you cut the same area where you drill. I don't know if there is any solid data to back up the drill v. cut argument. I just think the more air you can flow in AND out, the better.

I'd really like to hear someone like racer's or one of the other gurus opinion on this one. I'm sure it's been covered before, but I'm too lazy to do a search:eek::eek:

[Lockjaw]

I liked the pic Chris Lacey posted for me of his 235, where he drilled four or 5 1/2 in holes into the lower unit. That is how I am going to do mine.

I have seen cut outs, and I have seen 3 nice size holes drilled completely through on a friends 2.6gt, and it did not like having those plugged at all.

The nice thing about drilling holes is you can tap them, and use pipe plugs to cap them if needed. Cut outs are way loud too. Of course my engine is loud anyway.

[Riverman]

The Bob's snout allows you to pop in some rubber plugs to plug the above water outlet if you need to be quiet for a while.

[chris_lacey]

I liked the pic Chris Lacey posted for me of his 235, where he drilled four or 5 1/2 in holes into the lower unit. That is how I am going to do mine.
This one? Drill 4 or 5 1/2 holes upward into the radius at about 45 degrees.
Sorry, I don't have anybetter picture. Phish has this boat now.
I added a thumbnail for the diagram Ralph posted.

[Riverratt]

This is how I did mine also which is the same as Chris is talking about. It did not make mine real loud this way. I have since added the bobs snout also.
http://forums.screamandfly.com/forums/attachment.php?attachmentid=92416

[Lockjaw]

Yep thats the pic.

:D