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Old 05-29-2018, 08:47 PM   #1 (permalink)
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Potato power

"Spherical back pressure oscillation" he calls it. I would post this in the lounge or the unicorn corral but he has it on a dyno, so it must be science!



I looked it up in the Google without much success. Something called the Helmholtz effect comes up, but it seems unrelated.

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Old 05-30-2018, 02:02 AM   #2 (permalink)
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That was mighty fun. And funny.

It's likely that the straight pipe is a bit too big, and adding the potato increases the exhaust velocity at the tip, allowing for quicker exhaust flow.

But the rest of the results, 49.9 to 51.6 kw is not a big difference, and without A-B-A testing, it could simply be an old motor shaking the cobwebs out on successive runs... especially if the previous owner never really revved it out.
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Old 05-30-2018, 05:06 AM   #3 (permalink)
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Before looking for this place, know that there are not any buildings this large in Windslow:

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Old 06-01-2018, 08:16 AM   #4 (permalink)
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Will I make more power with a cannon on my car?
That'll be a rocket car.
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Old 06-03-2018, 03:04 AM   #5 (permalink)
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One run per modification is a small sample size.

They should've tried the potato half-in and half-out of the tail pipe. Or in a bellmouth.
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Old 06-03-2018, 11:09 AM   #6 (permalink)
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Totally, freebeard. In a way, their potato test might prove tha their methods are not reliable more than anything about "spherical oscillation" or whatever. In general their approach to testing needs more thought about sample size, mods, and what sorts of gains "count". I like some of their stuff a lot, but if it is not a giant gain from a single mod, Moog in particular seems unable to see the point.
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See my car's mod & maintenance thread and my electric bicycle's thread for ongoing projects. I will rebuild Black and Green over decades as parts die, until it becomes a different car of roughly the same shape and color. My minimum fuel economy goal is 55 mpg while averaging posted speed limits. I generally top 60 mpg. See also my Honda manual transmission specs thread.



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Old 06-03-2018, 11:49 AM   #7 (permalink)
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Yeah. I would've expected at least three runs, then a final "back to stock" set at the end to check.

You can get a variance of one or two kW in successive runs with nothing done to the motor in between.
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Old 06-05-2018, 06:02 PM   #8 (permalink)
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LOL I sold truck parts to potato farms for a decade. What a moving obstruction does is alter the effective length of the pipe. The timing of the reflected exhaust pulse can be used to tune the scavenging. So the trick is to move the reflection point to match the instantaneous RPM. A stainless steel potato and a linear motor.. oh bother.
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Old 06-05-2018, 11:10 PM   #9 (permalink)
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If you used a mild steel potato it would weather to a nice Russet brown.
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Old 06-22-2018, 02:28 AM   #10 (permalink)
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Fascinating stuff though.

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