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Phil S
09-04-2010, 10:27 AM
Sorry for such a dumb question, and perhaps non-Donzi related.

On some old mahogany boats I've seen at antique / wooden boat shows, the thru-hull exhaust exited the transom either right at the water-line or slightly below, as opposed to the height of most Donzi's where it exits at least above the drive height.

Is there a name for this type of exhaust exit / location ? I just love the sound it makes at idle speeds, etc...burbling their exhaust thru the water.

Anybody have their exhaust routed this way on their Donzi ?

Just curious....

Regards,
Phil S

BUIZILLA
09-04-2010, 10:44 AM
i'm with you 100%... I much prefer low exit exhaust, especially corner exit. with a balance tube beforehand... doesn't the Volvo IPS exit the exhaust UNDER the hull?

h20loo
09-04-2010, 11:02 AM
My ski boats exhaust is at water level with passengers and I love the sound as the boat rocks up and down. My wife doesn't think I will ever grow up.

Dr. David Fleming
09-04-2010, 11:12 AM
Mahogany boats of the earlier time depended upon what was available for engines. The speed boat craze after World War I used surplus aircraft engines - The Liberty - which was a state of the art twelve cylinder overhead camshaft 400hp - aircraft engine that was used for pleasure boating or racing - when raced they used individual exhaust pipes or stacks for each cylinder - in pleasure boats they worked into manifolds with bronze or brass pipes, water mufflers and the waterline exit. Fire safety was the main concern here. When the Liberty was gone - manufacturers used what was available from cars or marine manufacturers such as Sterling or Chrysler in line 8 - Chris Craft made their own - nothing like the aircraft engines - performance went way down. In the 50's the new V-8 car engines returned the performance level. 45mph was considered a great speed for the best commercial mahogany boats.


Headers as we use them today - 4 tube into a collector were developed by Chrysler Corp. in the 1950's and 60's to explore the concept of "inertial wave tuning" - sort of like organ pipes all tuning in at a particular engine speed. Before 4 tube headers the design was sort of a tubular manifold design called "try Y" in which two cylinders were "Y" tied together on each head then the tails of the two "Y" were again "Y" tied together - this design was very free flow but with out the tuning effect of the 4 tube -

The "inertial wave tuning concept" is the creation of suction on the cylinder that clears exhaust and in some cases pulls some fuel into the exhaust pipe - it is a concept that is based on the idea that a pressure wave going down a tube creates a vacuum behind it - make the tube the right length and you have cylinder scavenging - long tubes do this at lower engine rpm - short tubes at high engine rpm - this is the reason CMI offers long and short tube headers. Transom exhaust went high as a performance modification - shortest distance out of the boat.

Rodger
09-04-2010, 10:25 PM
Anybody have their exhaust routed this way on their Donzi ?
Just curious....
Regards,
Phil S


My 22 has the exhaust exiting at the water-line...original setup from the factory in 78.

gcarter
09-05-2010, 08:32 AM
i'm with you 100%... I much prefer low exit exhaust, especially corner exit. with a balance tube beforehand... doesn't the Volvo IPS exit the exhaust UNDER the hull?

Yep.
Out the back side of the pod and in the slipstream of the props.
Actually, out the bottom of the hull at about a 45* angle works very well.