Haha

"415s30 W123TSXWaggoIIIIIIo ( •_•))°)" (415s30) 02/23/2015 at 16:26 • Filed to: Supra, Z

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GhostZ > 415s30 W123TSXWaggoIIIIIIo ( •_•))°) 02/23/2015 at 16:37

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I have a hard time getting past the dual exhaust.

4muddyfeet - bare knuckle with an EZ30 > GhostZ 02/23/2015 at 16:56

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Wot?

GhostZ > 4muddyfeet - bare knuckle with an EZ30 02/23/2015 at 17:00

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Okay, that is cool, but I wonder what the point was. Is there some performance or speed, maybe balance advantage to be gained with splitting the single runner into two pipes? I was always under the impression that splitting the runner dropped performance.

4muddyfeet - bare knuckle with an EZ30 > GhostZ 02/23/2015 at 17:09

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According to this parts photo, the BRE never had a single runner, just two pipes straight off the exhaust manifold. (Or so it looks)

415s30 W123TSXWaggoIIIIIIo ( •_•))°) > GhostZ 02/23/2015 at 17:15

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Yeah the fart cans are dumb.

415s30 W123TSXWaggoIIIIIIo ( •_•))°) > GhostZ 02/23/2015 at 17:17

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Not sure, I know they were like 3 and 3, half for each pipe. Must be better. I want to get the center dual pipes someday with a really nice header that is proven to be better, waaaaay down the list though!

GhostZ > 415s30 W123TSXWaggoIIIIIIo ( •_•))°) 02/23/2015 at 17:20

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Yeah, after thinking about it, it does make sense. In a 4-stroke cycle you wouldn't have simultaneous exhaust firings on just 3 cylinders, so 3 and 3 might flow better than a single exhaust depending on cam timing and stuff. I'm not sure though.

Maybe there's also a weight centering advantage by keeping the exhaust low and centered vs off to the side too.

bryan40oop > 415s30 W123TSXWaggoIIIIIIo ( •_•))°) 02/23/2015 at 17:34

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Am I the only one who thinks the supra looks more feminine? I'm sure the datsun was feminine in it's hay day but still. Both beautiful cars however!

DrJohannVegas > GhostZ 02/23/2015 at 17:52

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With the likely-long duration of the exhaust valve opening, longer exhaust primaries (and secondaries) are necessary. Graham Bell's books on four-stroke tuning (and exhaust length for given exhaust duration and RPM targets) explains it much better, but the intuition is that the pipe acts in the same way as an organ's pipe does, so the length of the pipe and its diameter dictate the resonant frequency of the air inside. Big pipe, low resonant frequency.

The 6-2 layout here takes the secondary pipe length and extends it to the full length of the exhaust system. So, ignoring the first collection of three pipes into one (where three exhaust pulses meet at 240 degree-of-crankshaft-rotation intervals), the pipe for that cylinder is very long, and resonates at a lower frequency. 6 exhaust pipes would be another option, although from a packaging standpoint, that is less than ideal.

The interaction between the pressure wave in the pipe and the mass of air in the cylinder, moderated by the opening of the exhaust valve, is complicated. The timing of the valve opening affects when the pressure inside the cylinder is introduced into the pipe, and when the reflected wave returns to the valve. Where things get fun is when multiple pipes converge. Then, pulses out of one pipe induce pressure variations in other pipes. Again, tuning gets complicated. When you converge two pipes, the two interact. When the pressure wave gets to the end of a single pipe, where the two (or more) pipes meet, the pressure wave travels back up the other pipe, to some extent. So, connected tubes share pressure pulses (and negative pressure pulses). If you join two or three or four pipes together, the number of pulses in each pipe increases, almost as if you had halved the length of the pipe (or divided it by three or four...I am getting to the limits of my knowledge here, so real engineers feel free to drop the wisdom on me.) relative to the single cylinder example.

So, why dual exhausts? It's a good balance between long pipes (necessary because of tuning) and packaging (necessary because six pipes are heavy and bulky). Big duration cams need long pipes, even when tuned for high-RPM torque (and thus power) peaks. In other words: because racecar.

Edit: Oops. In my haste, I replied to the wrong thread. This belongs in the other part of the reply chat...derp.