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Old 01-30-2008, 12:40 AM   #1
williaty
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Default Flexible 3" Tubing That Won't Collapse Under Idle Vacuum?

OK, so I've been horsing around with intakes and have found something surprising, interesting, and possibly harmful enough to the engine that you all need to know about it. However, because of that last part, I want to be DAMNED sure I have tested every possibly configuration and isolated the problem down to one specific part. To do this, I'm going to need to mock-up different designs of intakes for short periods of testing. By short periods, I mean being on the car for less than 15 minutes and 100-500 yards.

Obviously, a real R&D facility could weld up solid metal mock-ups for each design. I can't. Second best would be using something like the Specrte modular system, but I can't afford that. So I need something with a 3" ID that's flexible but won't collapse under the ~12-13psi of vacuum the engine pulls at idle when used to fudge the fit between two pieces that don't quite line up, etc.

Basically, it needs to be flexible enough to bend around corners or "jog" to join two pieces that are offset slightly, but not so soft that it will suck flat.

Any ideas?
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Old 01-30-2008, 01:25 AM   #2
rougeben83
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flexible exhaust piping.
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Old 01-30-2008, 01:26 AM   #3
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What now?
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Old 01-30-2008, 01:46 AM   #4
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I think he means the dryer exhaust tubing. Not exactly "smooth" on the inside...
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Old 01-30-2008, 03:59 AM   #5
rougeben83
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ugh no, go to the exhaust tip/pipe section at a local autozone, you'll see "flexible exhaust pipe" which is like thick sheetmetal rolled up into a coil so that it can be relatively flexible.

It's used to for minor bends and stuff in exhaust for DIY work.
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Old 01-30-2008, 04:24 AM   #6
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Yeah, flexible exhaust tubing exists and would work, but I can't say I've ever seen the stuff in 3" diameter at a local auto parts place. Usually it's in 2" or 2-1/4", since that's what most OEM exhausts are. However, a quick search for "flexible exhaust tubing" did find it in 3" at JC Whitney.

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Old 01-30-2008, 07:07 AM   #7
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Try mcmaster.com, page 204 item number 55125K19.

I'm using naca ducting on both of our cars. It's very durable and doesn't convolute much inside when making bends. Good stuff.....

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Old 01-30-2008, 05:21 PM   #8
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Silicone hose
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Old 01-30-2008, 05:47 PM   #9
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i would say dryer vent hose
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Old 01-30-2008, 07:32 PM   #10
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you could get some 3" Scat ducting used on aircraft but its kinda pricy. 3" is $6.40 a foot and they say not recommended for negative pressure applications but its pretty darn sturdy. Im an AP mechanic and i would think this stuff would be tough enough for for short term experimenting til you find a design you like. You could go with the heavier stuff thats lined both inside and out and its $9.40 a foot and should have no problem with the vacuum pulled at idle. Id even be comfortable using it as a final design since its so tough. Anyway, heres the link to the page... http://www.aircraftspruce.com/menus/ap/ducting.html
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Old 01-30-2008, 08:15 PM   #11
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FYI there is only vacuum after the throttle body inside the intake manifold not before it so you don't need to worry about collapsing
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Old 01-31-2008, 02:02 AM   #12
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novacivic has a point. There is no way that decent 3" intake piping (silicone, heater duct, etc) can collapse unless your motor is consuming an extreme amount of air or you have an air filter on the end of the piping that is clogged. While there is negative pressure in any intake system, it is only significant inside the manifold. If you are just messing with intake designs and not the throttle body or manifold, then don't worry too much unless you are using paper maché.
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Old 01-31-2008, 02:09 AM   #13
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Interesting...

I can understand why the vacuum would "stop" at the TB if the TB is mostly closed (idle). Does this hold true if th TB is wide open?

BTW, I collected data on 4 different intake designs today (stock, snorkus delete, full SRI, and a "hybrid" intake). The results are startling to say the least. I think it'll shake up the MAF-based NA Subies a bit when I can get it all worked up into a post. The one main problem is that for the full SRI and the hybrid, I can tell that the MAF scaling needs altering in open loop, which I can't do because I don't have a WBO2. I can't decide if I should post what I have so far and say "look, that dip there? It's fake, imagine it was a plateau." or if I should hold off posting anything until I can afford a WBO2, rescale the MAF, and post without caveats.
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Old 01-31-2008, 02:19 AM   #14
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If the TB is fully open, the overall vacuum is reduced (like sucking air through a big straw versus a small one). However, the vacuum will always be the least at the very beginning of the intake piping because of the friction generated along the "suction's" path from the heads, through the manifold, TB, and all the intake piping. Think of sucking on a 50ft garden hose- You may aspirate really hard, but at the opposite end, there is relatively little vacuum, because of energy loss along the length of the hose. Don't hesitate to go out and try it... really
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Old 01-31-2008, 04:54 AM   #15
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Should we call 911 now, or wait until morning?
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Old 01-31-2008, 11:06 AM   #16
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I'm interested to see what's been learned, too... I've got a feeling my snorkus delete might actually have hurt me.
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