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1974 450 SEL Champagne Beige Metallic(Sold); 1986 560 SEL Champagne Metallic
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Discussion Starter #1
Hi All,

I am curious, and not being an automotive engineer, have wondered why certain exhaust ports are paired together in the Tri-Y manifolds. I am guessing it is due to some sympatheic pressures and flows related to firing order.
From my years in HVAC I fully understand allowing the engine to "breath" as easily as possible to increase horsepower, and attempting to get ever larger tubing out the back of the car as pipes come together to preserve velocity and low pressures with the added volumes of gases. These same theories are proven in air ducts all the time: the better the design at a certain static pressure, the better the performance of the entire system.

Give me your input please

Cheers,

Ron
 

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a device that is designed or used to transport people or cargo.
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wouldn't slightly smaller tubes towards the end preserve velocity as the gases cool?

making them larger after the final combination would decrease velocity, right?

Hi All,

I am curious, and not being an automotive engineer, have wondered why certain exhaust ports are paired together in the Tri-Y manifolds. I am guessing it is due to some sympatheic pressures and flows related to firing order.
From my years in HVAC I fully understand allowing the engine to "breath" as easily as possible to increase horsepower, and attempting to get ever larger tubing out the back of the car as pipes come together to preserve velocity and low pressures with the added volumes of gases. These same theories are proven in air ducts all the time: the better the design at a certain static pressure, the better the performance of the entire system.

Give me your input please

Cheers,

Ron
 

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Premium Member
560SEC, 190E, Frontier, 240Z
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1,329 Posts
I was told:
What he said was that as one jug fires, the next one to fire is siamesed after it so the initial pressure wave passes and there is a low pressure that follows... just as that next siamesed cylinder if firing thereby helping to suck out the goodness in a theoretical perpetual fashion.

EVERY word of that may have been BS.
But is sounded pretty good to me.
Same would apply to any other engine.
 

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1974 450 SEL Champagne Beige Metallic(Sold); 1986 560 SEL Champagne Metallic
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181 Posts
Discussion Starter #4
EuroSpec you are correct, but what I was referring to was the preservation of the low back pressure to assist rearward flow out of the system with each of the eight (or whatever) cylinders adding their respective contents to the final flow. Similar to what you see on American headers where the downpipes merge into a smooth designed collector pipe before going into the cat or mufflers.
For example, a usual compromise would be 1" down pipes from each cylinder merging into a cloverleaf 4" collector, but the leaving pipe would be about 3" diameter. I would not want to see those 6" holes similar to what the kids have on their "rice-burners" today!
T: I agree with the scavenging of gases and a counter wave or frequency to help balance the overall exit of gases rather than the pulsing you experience on a single cylinder exhaust. A lot of manufacturers use the infamous crossover pipe to help accomplish this "smoothing of the flow" as it were.
Some good points so far.

Cheers
 
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