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Fitting a Dry Exhaust System

petesim

Member
"I'm interested in fitting

"I'm interested in fitting a dry exhaust system to my GI 8.1 and was wondering if there is a blanking plate available to cut off the water between the manifolds and risers. Also would this affect the engine tuning or would the ECU adjust accordingly. I'm hoping to improve fuel economy by allowing the engine to breathe better. As it is now, the exhaust exits via 2x 4" pipes from the risers, through the transom shield and then out through a single 3" outlet at the drive. I don't profess to know more than the VP engineers but it seems restrictive for a 496 cubic engine. I guess I would need to run the raw water from the exhaust manifolds out throug a skin fitting in the hull seeing as the risers would now be blocked off."
 
"I have a simular situation wi

"I have a simular situation with my 5.7 and a 280 Drive, i.e., 2, 4" ports necking down to a too small port thru the drive.
Well.... it will be noisy...very noisy. Here in NJ mufflers are required (more accurately, they have a noise level law that for all practical purcposes makes you install mufflers!) HOWEVER, if noise is not an issue...

There is one technical issue you need to look up for yourself. That engine is basically the same engine as the same CID MERCRUISER. The link below takes you to a page that has downloads for almost all the MRECRUISER factory shop manuals...free... warning the files are huge! Find the manual for the engine closest to yours and search in that manual for exhaust system reguirements for the INBOARD version of the engine. For example, my 5.7L MERC spec says, single 4" or dual 3" exhaust ports. What yours needs ???? Maybe same, maybe not.

Assuming it needs dual 4" ports.

Disconnect the exhaust lines from the elbows.

Buy 4" MARINE EXHAUST service hose
Buy a pair of 4" thru transom ports (with external flaps and internal shutters...Merc has the kit with all these parts.

Connect hose... drill a pair of 4+ inch holes in the transom.
Install the ports, hook up to exhaust elbows with the 4" hose you bought. Double clamp all connections with high quality clamps.

With this setup exhaust and water will exit from each port at the transom... Ports should exit about water line.

If noise is an issue, then there are special mufflers that you can install between the elbows and the transom.

Link to Manuals... could not find it...HOWEVER, If you go on to the MERECRUISER forum and ask "BONDO" if the back door is still open... If not ask if anyone has that manual for you."
 
"I'm thinking that you mea

"I'm thinking that you mean "Thru Transom" exhaust, correct?
To my knowledge, any portion of an exhaust system that is enclosed must be wet. "
 
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