exhaust pulses cause vacuum
11-08-08, 01:21 PM
#1
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exhaust pulses cause vacuum
i was curious the other day and put my hand up to my exhaust to see the spacing of the exhaust pulses at idle. i noticed that in between each pulse my hand would be lightly sucked into the exhaust. i had my friend put his hand on theother side (dual exhaust) and it did the same thing.
Is this a problem? or should i not worry?
My exhaust is 3" from the downpipe to a high flow cat and then back to 2 megan racing mufflers with a 4.5" exit.
my engine is also streetported.
Is this a problem? or should i not worry?
My exhaust is 3" from the downpipe to a high flow cat and then back to 2 megan racing mufflers with a 4.5" exit.
my engine is also streetported.
uhhh, sucks?
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11-08-08, 07:19 PM
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According to the Mazda manual, there is some sort of overlap of the intake/exhaust, and maybe that is what your feeling. I don't KNOW that to be the case. I just noticed this page in the manual the other day. Just a guess and nothing more.
11-08-08, 10:55 PM
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hmmm. maybe so. i thought the overlap worked a bit differently. in a piston engie i could understand, but arent the intake and exhaust gasses constantly seperated? thats what i originally thought, but then ruled out.
either ay i would REALLY like to know the cause of this.
either ay i would REALLY like to know the cause of this.
11-09-08, 01:56 AM
#10
Here, I found this article from 1932 for you since you're so interested in why this might be happening, hah. http://blog.makezine.com/archive/200..._to_vacuu.html
This is how I see it: since you have dual exhaust, when you cover one side, the gases will be redirected towards the unrestricted muffler. When this happens, this flow will cause a slight vacuum on the restricted side, as the prefered path will be towards the other muffler. That's how the vacuum works in the article; the hose is a very restricted path, so the gas will flow out of the muffler tip in greater volume, which will cause a pressure gradient.
This is how I see it: since you have dual exhaust, when you cover one side, the gases will be redirected towards the unrestricted muffler. When this happens, this flow will cause a slight vacuum on the restricted side, as the prefered path will be towards the other muffler. That's how the vacuum works in the article; the hose is a very restricted path, so the gas will flow out of the muffler tip in greater volume, which will cause a pressure gradient.
11-09-08, 08:17 AM
#11
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but arent the intake and exhaust gasses constantly seperated?**************************************** *************************
The page out of the Mazda manual is right.
That said, what Rocket88 wrote makes a lot more sense as to why your experiencing what you wrote about. Still, what I pasted out of the manual is something worth knowing.
The page out of the Mazda manual is right.
That said, what Rocket88 wrote makes a lot more sense as to why your experiencing what you wrote about. Still, what I pasted out of the manual is something worth knowing.
11-09-08, 09:19 AM
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i agreeabout the dual exhaust thing, thats why i had my friend hold his hand near the other tip so both were equally (more or less) restricted. the same thing happened still. there was a slight vacuum from each tip.
and hailers, how does the intake inertia effect affect the exhaust? its happening in a seperate "chamber".
and hailers, how does the intake inertia effect affect the exhaust? its happening in a seperate "chamber".
11-09-08, 10:34 AM
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If you have dual exhaust you are fine. This is normal and more noticeable with larger diameter exhaust pipes. If you have a single tip exhaust than this means you have a massive hole up stream. Fist sized.
11-09-08, 01:25 PM
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and hailers, how does the intake inertia effect affect the exhaust? its happening in a seperate "chamber".
************************************************** ************************************************** *****************************
I just took 'em at their word, that just as the intake port is being uncovered, the exhaust port is still uncovered, and it's the exhaust gas that causes the *compression wave* that rushes into the intake port.
Like I said, I agree that this is not what is causing the suction at the tail pipes. I've already surrendered on that in my last post. No mas. Google for Roberto Duran for what *no mas* means.
************************************************** ************************************************** *****************************
I just took 'em at their word, that just as the intake port is being uncovered, the exhaust port is still uncovered, and it's the exhaust gas that causes the *compression wave* that rushes into the intake port.
Like I said, I agree that this is not what is causing the suction at the tail pipes. I've already surrendered on that in my last post. No mas. Google for Roberto Duran for what *no mas* means.
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