Hub to thru hull exhaust conversion

O.K. guys,I think this one has been up for talk many times before,so I will try to keep it simple and brief. I have an 88 OMC 5.0 that is currently thru hub exhaust. I am at least investigating the idea of thru hull exhaust. Here are my questions;

1) Can I just cap the Y pipe ends or must I remove the Y pipe and put a blocking plate in ??
2) Will the stock OMC risers allow me to run exhaust hose straight out to the collectors out the hull??
3) Has anyone made a home made set up that just caps the Y pipe??

I know that performance is minimal with thru hull and noise is more but this is something I want to do if it does not cost me to much. Any help is appreciated.

Re: Hub to thru hull exhaust conversion

I am trying to do the same thing except my boat has thru hull and was change to prop exhaust but as i have found out they make a y pipe that hooks up to both the through hull and the prop exhaust a company on ebay sell them they call them tripple exhaust. As fas as making thru hull exhaust as long as you keep them high enough or put in flappers there really isnt any special instructions just make sure you glass resin the areas that you cut out in the hull so it wont crack later. And i myself are going to cap my y pipe and run it back thru my hull be cause the y pipe has flapper in it so water wont come up in to the engine. Hope this helps

Re: Hub to thru hull exhaust conversion

I was thinking about using a test plug in each side of the Y pipe and then covering the test plug with a furnco cap. That way I have a double seal to keep water coming in the Y pipe. We dont dock our boat over night but I understand that this issue not being taken care of properly would sink the boat quickly. Is the flappers on the outside of the hull enough to protect the motor. My fittings would be above the water line at rest.

Hey Mikdee,I caught an old thread about your thru hull conversions. Can you help me out. Would my stock OMC risers work??? They look to be 4 inches tall and the exhaust hose would slope down hill to the thru hull fittings.

Re: Hub to thru hull exhaust conversion

I agree with doing it right and installing the blocking plate. I am just kicking around for ideas right now. The boat sure does sound nice out of the water on the muffs though. It would be nice to hear that on the water too.

Re: Hub to thru hull exhaust conversion

peanutbay1 said:

I was thinking about using a test plug in each side of the Y pipe and then covering the test plug with a furnco cap. That way I have a double seal to keep water coming in the Y pipe. We dont dock our boat over night but I understand that this issue not being taken care of properly would sink the boat quickly. Is the flappers on the outside of the hull enough to protect the motor. My fittings would be above the water line at rest.

Hey Mikdee,I caught an old thread about your thru hull conversions. Can you help me out. Would my stock OMC risers work??? They look to be 4 inches tall and the exhaust hose would slope down hill to the thru hull fittings.

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I've never done it on an OMC, but on 2 Mercruisers yes, but I converted them both to the later center rise exhaust manifold, & risers, I think the latter one needed 3" spacers as well. I don't know what you got?, but mine went straight out the back on a slight angle down with tips, just above the steering assembly. My boats were rack stored, and launched off a fork lift, and docked for the day, or week, so I never bothered capping the Y-pipe.

If you got the room, clearance, & height, just run them straight out, 3", or 4" marine exhaust hose, with double hose clamps (as required) at every joint. In the future I planned on capping off the Y-pipe with a test plug, & furnco cap, we pipefitters all think alike Now, I was told by a 1/2 azzed mechanic at the marina, if you cap off the Y-pipe or remove it, & cap off, you will lose a few mph because of the suction on the prop, but I don't know if this is true? Maybe if you remove the exhaust boot this would break the suction, (but this is pure conjecture here, even if it is true? ) By the way, I never had a problem running them the way I did in the famously occasionally furious Great South Bay L.I.

Next, my 305/228hp in the old 20' SeaRay bowrider wasn't very loud, but on my 24' SeaRay 350/260 I put rubber baffled marine mufflers on it, and it was not bad, kinda mellow like glasspacks.

Re: Hub to thru hull exhaust conversion

You rock Mikdee!!! You always have good advise and good home grown ideas. I love inventing things and modifying past off the shelf aftermarket items anytime I can. I will have to take some pics of my motor tonight and post them to see if you think my risers would work as well as where I want to have the exhaust pass thru the transom. Out the hub my boat has just a nice tone and it is not very loud,from what you stated it sounds like your 305 mercruiser was in the same league. Where I run you here a wide variety of boats and no one seems to mind including the PAFB most times. Thanks again!!!