I/O exhaust, have to go out the outdirve?

Hi.<br /><br />I am contemplating an engine swap. I currently have a 3.0 OMC i/o in my boat, but have room for a 5.7. I might be able to get my hands on a V8 sterndrive (complete minus exhaust and some other minor details) relatively cheap. <br /><br />I was thinking about the exhaust. I'm looking at about $600 for manifolds, bellows, etc. Is there any reason why I could not run stainless shorty headers and pipes out through the upper part of the transom? (new holes with flappers maybe a foot above the waterline?) Is there any reason that there NEEDS to be water flowing through the exhaust and out the outdrive?<br /><br />Honestly I want to do this primarily for the sound, as it will only end up saving me a couple hundred bucks. Any thoughts?<br /><br />Thanks.

Re: I/O exhaust, have to go out the outdirve?

you mean water jacketed headers/exhaust pipes right...the water mixing with the exhaust cools it so it can be safely discharged without starting the boat on fire.

Re: I/O exhaust, have to go out the outdirve?

Well, that sure sounds important. Yes that is what I was talking about. So is there a safe alternative or should I stick with the jacketed headers? I was really hoping to maybe route the exhause out the upper transom above the water where it would be louder. <br /><br />Thanks!

Re: I/O exhaust, have to go out the outdirve?

You can block off the exhaust at the drive, by installing a block off plate on the inner assembly, thus eliminating exhaust "Y" pipe and bellows, you can use stock manifolds and risers, and run exhaust strait out the back, you can obtain nice looking ss exhaust tips off of eBay, almost anytime to install thru transom. A few tips if you decide to go this route. 1} install motor,and manifolds and risers, hook up all linkage including steering, then make sure you don't have any obstructions between exhaust riser and transom ( you only get one chance to cut holes in transom) 2) know what dia. exhaust you have example 3" or 4" that can be easily determined by measuring the stock exhaust boot used to connect riser to Elbow to 'Y' pipe, be sure to measure that for I.d. since riser and tips will be o.d example 3" riser is O.D will use a 3" I.D hose to fit and 3" O.D. exhaust tips. this will also tell you what size exhaust hose you need to make connection from riser to tips. 3) always double clamp exhaust connection using non magnetic SS clamps. 4) when making cutouts in transom measure 50 times, cover area to be cut out with heavy masking tape, so gelcoat does not chip, determine centre of circle to be cut, drill a small pilot hole this will allow you to measure the thickness of transom you'll need to know later , use a really sharp good quality 3" or 4" holesaw (whatever size exhaust is) with a 1/2inch drill,centre pilot bit from holesaw, with smaller pilot hole you pre drilled (this helps align holesaw), once ready hit gel coat with a fair amount of drill speed, just enough to cut through gel quickly( help avoid chipping) then with short blast with the drill cut slowly, until about about halfway, ( do not go right through) Now from inside boat. you should be able to line up holesaw again with pilot hole, continue drilling using same method as above until complete, the purpose of drilling from both sides is to avoid shattering and splintering the fiberglass, once done sand edges smooth, install tips using 3m 4200 sealent, don't use 5200 they will be bear to remove., cut exhaust hose to length and clamp in place , then you done.

Re: I/O exhaust, have to go out the outdirve?

I'm in the market for a new inboard boat from the '70s, it's hard to find one that doesn't have exhaust like that.

Re: I/O exhaust, have to go out the outdirve?

Northern, that was exactly (just about) how I would have done it. The drilling from both sides is a good idea I hadn't thought of. <br /><br />So, do I have to worry about excessive heat as WWYC suggested or should I be OK? I understand it will be significantly hotter under the 'hood', and I was considering wrapping the pipes in that ceramic coating to contain some of the heat. I really want to do this as I simply love the sound of a small block chevy. <br /><br />I have another question as well. On the outdrive, can I disassemble and replace the gears with ones suitable for a V8, ,or do I need a whole new unit?<br /><br />Thanks!!!

Re: I/O exhaust, have to go out the outdirve?

If you do the conversion, you should consider a drive shower, because there will be no water flow to cool the drive. This could be a problem depending on your boating habits.<br /><br />Steve

Re: I/O exhaust, have to go out the outdirve?

Ahh Heck why don't ya just go with OTE <br />Over the transom exhaust <br />just kidding!<br /><br />Just be careful with your plan <br /><br />Rich

Re: I/O exhaust, have to go out the outdirve?

Northern Eclipse's post is Exactly how it Should be Done...<br />And, Yes, you Must use Water-Jacketed manifolds, or headers.... You'll be building a Bomb, if you use Dry-pipes under a hatch......<br />I Sort Of followed Northern Eclipse's advise....<br />When I pulled the 140hp out,+ dropped in a 4.3LX in it's place... After building the motor/outdrive, Completely, Wiring,Plumbing,Steering,Trim,etc.... I took a straight-edge off the mercruiser 4" risers to see Where I wanted to Drill my holes.....<br />I then built straight pipes out of 4 1/2" SS, Because that's what I had... Angle-cuts, 12" behind the transom.... It sounded Really Cool..... But it didn't take to many 12/14hrs days of fishing for that to get Real Old....<br />Since then I've gone + Rebuilt them for the 3rd or 4th time.... <br />Now they exit the transom,+ turn down + out.... At Idle the tips are 12" Underwater.... Dead Quite.....<br />Drop the throttle, Pop on to plane, The tips are Breathing Fire about a Foot above the trim tabs.....<br />And, Ya, She Really Sounds Pretty Cool......

Re: I/O exhaust, have to go out the outdirve?

Cool Bondo. My only concern with the swap is really the engine mounts. How do you get them placed perfectly so that the engine can be set in alignment. Right now it is set up for a 3.0 with the single forward mount, and I understand that for the V8 I will have to glass in somewhere to mount the 2 side mounts on the SBC. Is there an 'easy' way to do this? My main concern is getting the height and width correct. (notice the quotes, I know it's not easy but you know what I mean).

Re: I/O exhaust, have to go out the outdirve?

Bondo is correct about dry pipes, as far as engine mounts go I think its a hard question to answer, since we cannot see your boat live and in person, I would think thats something you'll need to wait and figure out, once you place motor in boat, be prepared to remove and install motor several times, or if you can obtain an old stripped down block to use as a 'dummy model' it might be easier to man handle until you get mount placement correct, also be prepared to do some stringer work also, you may have o beef them up in order to handle a V8 or even cut them down to lower engine etc., and yes a gear ratio change will be required, if you have a good outdrive it may be possible to trade it for a V8 drive, Anyway your project is possible, good planning and patience will get you done..

Re: I/O exhaust, have to go out the outdirve?

EBay has an engine alignment tool right now, $150. Or you can bolt the engine to the existing transom, with mounts attached, mark new holes where the engine mounts wind up. Remove engine, drill holes, reinstall engine.

Re: I/O exhaust, have to go out the outdirve?

Probably what I was going to do. Just wondering if there were any tricks to it.

Re: I/O exhaust, have to go out the outdirve?

do a search online or ask a mercruiser mechanic, I believe there is an "X" pattern you use by measuring off of the ears of the gimble assembly.

Re: I/O exhaust, have to go out the outdirve?

The way I did mine was to set the engine on the rear mounts,on the transom plate, then used an Alignment Tool to find a Sweet Spot with the overhead hoist... Then Built Hull Mounting Points for the motor mounts to bolt too.... Mine are .090 Alum. sheet, Bent for strength,+ rigidity... Then Mounted with a Bunch of Pop-Rivits.... + some plywood blocks for spacers....<br />Did it All with only 2 Sinentific Tools.....<br />The Alignment Bar,+ a Tape Measure....<br /><br />If you've got a Plastic Boat, You'll need to Epoxy in some blocks of wood to bolt too...<br />The motor mounts adjust about a half inch, so that's how Close you've got to get.....<br /><br />While yer at it, Put a Black Outdrive on it... You'll be Happier Later....

Re: I/O exhaust, have to go out the outdirve?

It is a black outdrive!

Re: I/O exhaust, have to go out the outdirve?

Sorry, When you Hi-jacked Catfish1's thread(LOL) I had OMC on the brain...<br />Go for It... You'll also need to change the upper gears in the drive.... You've got 1.98s, You'll need 1.50s....

Re: I/O exhaust, have to go out the outdirve?

It is an OMC, it's a black one. Just messin with ya.