Flow over an open hole

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BOOT
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Flow over an open hole

Post by BOOT » Wed Nov 28, 2018 1:42 am

How does flow over an open hole hurt cfm? I have a TB that has some vac cut-outs that I am not gonna use and am debating on filling them in, largest are bout .3/8"x3/8". I got all winter to mess with it.
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Re: Flow over an open hole

Post by mag2555 » Wed Nov 28, 2018 6:43 am

For certain it would not harm airflow levels to fill them, so have at it !

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Re: Flow over an open hole

Post by Olds455 » Wed Nov 28, 2018 2:42 pm

Think about a straw when you blow through it after cutting a small hole out of the tube. Air through the tube doesn't exit the hole. It actually creates a vacuum that pulls air into the hole. Ever seen that trick where you cut a hole in a straw and blow through it near a piece of paper? It sucks the paper to the hole. I'd expect similar results in this instance...that it wouldn't be losing cfm through that hole if it's open to atmosphere. I'm not physicist so I could be wrong but that's how I would approach it initially. If it works as previously explained, you'd be drawing in unmetered air, for whatever that is worth. Basically just a huge vac leak?


What kind of TB? What's it off of?

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Re: Flow over an open hole

Post by BOOT » Wed Nov 28, 2018 3:02 pm

It's no longer sucking cause the ports are sealed off. TB is irrelevant, people always want unnecessary details then go off subject on something else and others just dismiss it because they don't like that platform or w/e.
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Re: Flow over an open hole

Post by Rick360 » Wed Nov 28, 2018 11:10 pm

SB2 heads have a head bolt hole right in the fastest part of the SSR. When you flow it without clay in the hole it can make a loud high-pitched whistle but it doesn't seem to affect the flow.

If you have a dead hole in a straight pipe it won't hurt flow.

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Re: Flow over an open hole

Post by modok » Wed Nov 28, 2018 11:21 pm

If they go nowhere it won't hurt flow, it's down in the boundary layer.
If they go somewhere, where stuff is actually flowing in and out, maybe.
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Re: Flow over an open hole

Post by BOOT » Thu Nov 29, 2018 2:46 am

I know small round holes don't affect perforated tubes at high flow but figured a larger non circle hole may have some neg effect.

I also know most don't bother to fill in the stud bolt hole on an intake runner but that is a wet flow area.
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Re: Flow over an open hole

Post by Olds455 » Thu Nov 29, 2018 5:36 am

I'm not those people so you shouldn't expect that sort of pettyness from everyone at this forum. It does matter. I was asking to get an idea of what the tb looked like. Size. Shape. Etc... Sorry this place has turned simple questions into this. But I'm not part of that crowd.

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Re: Flow over an open hole

Post by GerryP » Thu Nov 29, 2018 7:08 am

Rick360 wrote:
Wed Nov 28, 2018 11:10 pm
...When you flow it without clay in the hole it can make a loud high-pitched whistle but it doesn't seem to affect the flow.
...
Helmholtz resonance. You're right; no affect on airflow.

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Re: Flow over an open hole

Post by gruntguru » Thu Nov 29, 2018 7:27 pm

Everything has an effect. When the hole diameter << main bore diameter the effect is negligible. At larger hole diameters the effect becomes measurable. The effect would also be reduced at the low velocities seen in a TB feeding a plenum. Holes or similar irregularities would be of more concern in a port or runner where peak velocities are much higher.

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