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Exhaust/collector length for staggered engines

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Old 01-06-2011, 12:08 PM
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Question Exhaust/collector length for staggered engines

First, a bit of background. My experience with exhaust systems has been mainly drag & roadracing with 4-stroke motors and some tuning/design with 2-stroke expansion chambers.

I've noticed that when it comes to staggered engine installations that the exhaust/collector length from the forward motor is (naturally) longer than the rear motor. From my experience I know that how the exhaust tubes collect into the header collector and the collector itself can have a significant effect on scavaging and on a motor's torque curve.

How is the extra collector length compensated for with staggered engines? It seems to me that there would be completely different scavaging/backpressure issues (solutions??) between the two engines.

TIA

Tom
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Old 01-06-2011, 01:23 PM
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Not sure the header collectors are all that much different (except angle) between the forward and rear motors on a staggered setup. Obviously the tailpipes are longer. Even if the collectors where different the difference in peformance between the two motors would not be enough to be noticed in a twin setup.
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Old 01-06-2011, 05:03 PM
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Thanks for the reply.

In the photo you posted (is that really your engine setup in your Chapparal? ) what I refer to as a collector would be the pipe that runs from where the 4 header tubes come together to the transom.

From the following article: http://www.circletrack.com/enginetec...or_design.html

Comes this quote which backs-up my experience in tuning: "For example, had we used a single-plane intake manifold instead of our Weiand dual-plane intake, the results could have been completely different. The same holds true if we had used a different set of cylinder heads, camshaft, and even the length of the exhaust pipe after the header collectors.

In the blown engine setup of your photo, there isn't really an issue with header design due to the forced induction.

As an aside, I'm particularly amazed that titanium isn't being used for exhaust manifolds (this is the aircraft engineer coming out in me) - at least I could not find any with a rather quick google search. I realize that many are rolling their eyes at the thought saying, "Are you crazy? A set of stainless CMI's cost big bucks. Titanium would be outta sight." Here's where I'm again amazed. There are several sources of Ti headers for auto engines that are around $1000 a pair. I realize that marine headers are water jacketed. However, the production cost of a pair of stainless jacketed marine headers just can't be that much more when you consider that Ti cost much more. IMHO, the numbers just don't add up. Maybe it has to do with that "Surgical Stainless Steel" versus "Stainless Steel" thing.

FWIW, Ti has been used in saltwater applications almost since the discovery of the metal in the 1950's. Industry sources indicate continuing usage of the original Ti equipment after 30 years of constant saltwater immersion has produced no measurable corrosion. Other saltwater applications with water temperatures as high as 500F has produced the same result: no measurable corrosion. Titanium's corrosion resistance is due to a stable, protective and strongly adherent oxide film. The film forms instantly when Ti is exposed to a trace of air or water. Some, but not all forms of corrosion that have virtually no effect on Titanium in a seawater environment: Cavitation Corrosion, Crevice Corrosion, Electrochemical Corrosion, Electrolytic Corrosion, Erosion Corrosion, Galvanic Corrosion.

I'm not a stress engineer so I can't talk to vibration induced cracking, but I suspect it would be less susceptible than stainless due to grain structure.

Anyhow, I'll shut up with the engineer nerd sh!t 'cause it's time for me to go home and celebrate the close of another 4 day work week with a Beefeater's martini on the rocks.

Tom
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Old 01-06-2011, 06:26 PM
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Quote:
Originally Posted by tda3 View Post
Thanks for the reply.

In the photo you posted (is that really your engine setup in your Chapparal? ) what I refer to as a collector would be the pipe that runs from where the 4 header tubes come together to the transom.

From the following article: http://www.circletrack.com/enginetec...or_design.html

Comes this quote which backs-up my experience in tuning: "For example, had we used a single-plane intake manifold instead of our Weiand dual-plane intake, the results could have been completely different. The same holds true if we had used a different set of cylinder heads, camshaft, and even the length of the exhaust pipe after the header collectors.

In the blown engine setup of your photo, there isn't really an issue with header design due to the forced induction.

As an aside, I'm particularly amazed that titanium isn't being used for exhaust manifolds (this is the aircraft engineer coming out in me) - at least I could not find any with a rather quick google search. I realize that many are rolling their eyes at the thought saying, "Are you crazy? A set of stainless CMI's cost big bucks. Titanium would be outta sight." Here's where I'm again amazed. There are several sources of Ti headers for auto engines that are around $1000 a pair. I realize that marine headers are water jacketed. However, the production cost of a pair of stainless jacketed marine headers just can't be that much more when you consider that Ti cost much more. IMHO, the numbers just don't add up. Maybe it has to do with that "Surgical Stainless Steel" versus "Stainless Steel" thing.

FWIW, Ti has been used in saltwater applications almost since the discovery of the metal in the 1950's. Industry sources indicate continuing usage of the original Ti equipment after 30 years of constant saltwater immersion has produced no measurable corrosion. Other saltwater applications with water temperatures as high as 500F has produced the same result: no measurable corrosion. Titanium's corrosion resistance is due to a stable, protective and strongly adherent oxide film. The film forms instantly when Ti is exposed to a trace of air or water. Some, but not all forms of corrosion that have virtually no effect on Titanium in a seawater environment: Cavitation Corrosion, Crevice Corrosion, Electrochemical Corrosion, Electrolytic Corrosion, Erosion Corrosion, Galvanic Corrosion.

I'm not a stress engineer so I can't talk to vibration induced cracking, but I suspect it would be less susceptible than stainless due to grain structure.

Anyhow, I'll shut up with the engineer nerd sh!t 'cause it's time for me to go home and celebrate the close of another 4 day work week with a Beefeater's martini on the rocks.

Tom
Then use side exhausts or zoomies out the hatch,We were going to use Titanium Headers in a project, the Italians were going to build them for us @ $30 K a Motor with the tailpipes.
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Old 01-07-2011, 02:02 AM
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Hello;



Car or motorcicle exhaust it is "dry", but boat exhaust is covered with water coat, which cool exhaust gasses.
(I looking for good collector 4/1 exhaust)

Water coat cool gases and they shrink up. It mean, that boat exhaust collector must be shorter than car exhaust collector for same rpm.


Any idea how to define optimum diference of lenght for dry-car and water cooled-boat collector?



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Old 01-07-2011, 02:26 AM
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Quote:
Originally Posted by sinus View Post
Hello;



Car or motorcicle exhaust it is "dry", but boat exhaust is covered with water coat, which cool exhaust gasses.
(I looking for good collector 4/1 exhaust)

Water coat cool gases and they shrink up. It mean, that boat exhaust collector must be shorter than car exhaust collector for same rpm.


Any idea how to define optimum diference of lenght for dry-car and water cooled-boat collector?



bye
Saso
With boat headers, water is not induced intot he exhaust until the very end of the tail pipes right before it goes through the transom.
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Old 01-07-2011, 02:29 AM
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Quote:
Originally Posted by tda3 View Post
First, a bit of background. My experience with exhaust systems has been mainly drag & roadracing with 4-stroke motors and some tuning/design with 2-stroke expansion chambers.

I've noticed that when it comes to staggered engine installations that the exhaust/collector length from the forward motor is (naturally) longer than the rear motor. From my experience I know that how the exhaust tubes collect into the header collector and the collector itself can have a significant effect on scavaging and on a motor's torque curve.

How is the extra collector length compensated for with staggered engines? It seems to me that there would be completely different scavaging/backpressure issues (solutions??) between the two engines.

TIA

Tom
Boat exhaust has much larger tail pipes after the collector than most automotive hp engines. I doubt there is any significant difference in actual propshaft HP between the forward or rear engine. Cams are also not as radical and there is less scavenging affect.
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Old 01-07-2011, 03:45 AM
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With boat headers, water is not induced intot he exhaust until the very end of the tail pipes right before it goes through the transom.
I know, but exhaust collector it is submerged in water and pipe have more or less water temperature an it have much more cooling efect like if it is "submerged" in air by car collectors. Good car collectors are almost in red collor...

Good collector wxhaust must be long enough, but not to much, to help engine for good work. If you cooling collector pipes with water, you will have pipe temperature same like water temperature and exhaust gases will be cooled. It mean les volume of air - shorter collector.
I know that correct lenght it is wery important for long live of engine, good torque and lees fuel consumption.




PARALELE:
Car intercooler which cool compressed air with athmospheric air must be much bigger-longer like intercooler which cool compreesed air with cooling liquid from car cooling sistem.



I think that collector which have pipes cowered with water film must be shorter like car collector.

I am sure, that somebody there know how much is this and please tell me. We are "fight" with brother round of this and we would like to know who is winner.
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Old 01-07-2011, 07:20 AM
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Performance boats have the exhaust above the water. except for those downturn exhausts. It's inboard yachts that have the exhaust exit below the water. and the use a muffler the size of a 5 gal bucket or bigger with the intake of the muffler well above the water line.
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Old 01-07-2011, 08:18 AM
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o.k.
My trouble it is english, and I do not know how to ask, now will try in another way.



Engine xx? need 35 inch long collector pipes for race car.

What lenght must be collector pipes for same engine caracteristic for boat use?


-I know, that exhaust it is above waterline.
- I know that water come in the gases just before outlet.
- I do not know how much cooling effect have boat collector, which is water jacked. If you use logic it must be shorter becouse of cool water jacked, which cool gasses and they shrink.
Any idea round of this cooling effect or percentage in lenght diferent betwen boat/car collector?




bye
Saso
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