View Full Version : 22zx exhaust, i need help!!

doubleduece donzi
12-21-2011, 10:22 PM
1999 22zx 454mpi. It has the stock exhaust and mufflers.The exhaust is to quiet for my taste,however i dont wont a sound thats just really loud but doesnt sound good or powerfull.Does anyone run this setup without mufflers????what does it sound like?Also how would having no backpressure effect the mpi motor.I also thout about taking most of the guts out of the mufflers but leaving one of the plate in it for backpressure. I really need advice thanks.

Dr. David Fleming
12-22-2011, 04:54 AM

Marine exhaust has recieved quite a bit of attention on this site. Not only is it a performance issue and a sound issue, it also has a practical side. If you look at your 22zx in the water the 454MPI is very close to the water line of the boat. This means that the exhaust outlet is also very close to the waterline of the boat. Marine engineers like those guys at Merc and Donzi have spent a great deal of time trying to keep the water out of your engine.

Water injestion and water reversion are two serious problems that can kill your motor. Water injestion is when for some reason, like a stern wave hitting the back of the boat or the boat coming off of plane quickly the exhaust system is flooded by water backflush. The Corsa Mufflers on your boat keep out the water as do the Salasbury flaps that shut under certain conditions.

Water reversion is part of what we got to into in the cam timing discussion. Recient studies have revealed engineering designs in the riser of the exhaust manifold that keep water from backing up into the engine. Also water is sprayed into most marine exhaust like the Mercruiser which use this water exhausted from the engine cooling system as a spray into hot exhaust gasses of the exhaust manifold riser. This cooling is to keep the exhaust system from setting fire to the boat and to quiet it. The Mercury design is a package system and it is a complicated system that usually works well.

If you and a couple of your friends stand on the engine hatch of your 22ZX while you are swimming off of the back of the boat. You are going to get that exhaust near or under the water. Should another boat send a stern wave at you the air intake openings of the 22ZX hull are going to be letting water flood into the engine compartment openings and your marine exhaust system is going to be doing all it can to keep water out of the engine cylinders.

The Corsa mufflers are a good Donzi design and in some areas of the USA like Lake Oakland in Michigan and areas of Illinois and Kentucky are monitoring the exhaust noise. Local cops with meters who know little or nothing about what they are doing are pullin guys over and giving them tickets for stock Donzi exhaust systems. Some Donzi 22ZX have a Quick Quiet or similar system which deverts the exhaust into the lower unit drive area to silence the engine. This was and option.

Quick Quiet exhaust as a design feature also allows some water from the upper exhaust pipes to have a direct route down out through the lower exhaust pipes instead of into the engine. Some guys think it also allows water to form a "well" to come up into the exhaust pipes. Merc places a couple of small butterfly valves in this underwater exhaust y-pipe to prevent this from happening but sometimes these come apart.

My 22ZX has CMI e-top headers and CMI mufflers which are louder than the Corsa Mufflers. CMI has an air operated exhaust deverter system also. So some guys like me have changed out their Corsa exhaust muffler pipes but always with the water problem in the back of their minds.

Most people who take off the rubber flaps and take out the baffle plates from the Corsa mufflers find little performance improvement and some increase in noise. But remember that anything that keeps out the water is an improvement.

joseph m. hahnl
12-23-2011, 10:09 AM
Doesn't matter what the performance aspect is, what so ever. It is unlawful meaning" Illegal" to disable or modify the muffling device.

That said your just asking for trouble with the man.


This is from Alabama Boating Rules and RegulationsThe exhaust of every internal combustion engine used on any vessel shall be effectively muffled by equipment so constructed and used as to muffle the noise of the exhaust in a reasonable manner. It is unlawful for any person to operate or give permission to operate any vessel powered by an engine or outboard motor in such a manner as to exceed a noise level of 86 decibels measured at a minimum distance of 15.2 meters (50 feet) from the vessel. The use of cut-outs is prohibited, except for vessels competing in a regatta or official boat race, and for such vessels while on trial runs.