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## RE: large runner 1500 (single ZS) manifold needed (longish)

 To: Group44TR7@aol.com, ryoung@navcomtech.com RE: large runner 1500 (single ZS) manifold needed (longish) Bill Babcock Mon, 6 Dec 2004 14:36:08 -0800
 ```You're not really missing anything. It's a mental picture issue. We view these systems as having smooth flows when in reality everything that's going on in an engine is violent and fast. Our mental pictures (and for that matter, anyone's flow equations) don't describe this kind of flow, it's way too complex. For that matter, even in a very simple system there's no way to predict turbulent flow effects except in very approximate simulations. I know people think physics is very predictive, and something as simple as the onset of turbulence in a smooth pipe of known diameter with a homogeneous fluid at known temperature, pressure, viscosity and any other parameter you choose to add should be predictable. NOT. All anyone is trying to do with a flow bench is create a relative improvement with something that we can measure--in this case a differential pressure across the part we're testing. Turbulent flow, laminar flow, and all that other stuff isn't relevant in any way, because these aren't simple pipes with simple flows. At 7000 RPM in a four stroke engine flow is starting and stopping dead in a single intake tract 8 times a second. The instant pressure in the short distance of a typical intake varies hugely, from substantial vacuum to several times atmospheric even in an unsupercharged engine because of inertia at the intake valve and sonic effects. The exhaust pulse is an explosion (literally) of extremely hot gas that cools incredibly quickly as it travels down the pipe, also dropping in pressure from about 100 PSI when the exhaust valve opens to atmospheric pressure a few feet down the pipe. All that happens eight times a second also. Laminar or turbulent? Huh? It's really worthwhile to read Ricardo, even if you don't get the math. He was directly measuring all this stuff 70 years ago. The tools have changed but the complexity of the problems haven't. These systems are highly chaotic, and simple descriptions are about as accurate and useful as a second grade teacher telling kids that Columbus discovered America because he was the first to believe that the earth was round. One sentence and three major factual errors. Par for the course. Bill Babcock Babcock & Jenkins _____ From: Group44TR7@aol.com [mailto:Group44TR7@aol.com] Sent: Monday, December 06, 2004 1:35 PM To: Bill Babcock; ryoung@navcomtech.com Cc: fot@Autox.Team.Net Subject: Re: large runner 1500 (single ZS) manifold needed (longish) In a message dated 12/6/2004 7:51:22 AM Pacific Standard Time, BillB@bnj.com writes: But isn't the whole idea to develop laminar flow, not turbulent? At the point where it changes, there should be a fairly big discontinuity in flow rate, no? Avoiding turbulence is the whole reason we try to keep passages straight, smooth changes in cross-section, etc. Its been along time since I open a chemical engineering book. However, I seem to recall that the fundamental reason for keeping piping straight and rounded was to minimize the resistance to any type of flow. I can understand that would be very important to the passages leading to the combustion chamber be straight and smooth. But I would think that we would want some substantial mixing (turbulence) created as the fluid/gases entry in into the combustion chamber itself. Thereafter we would want to remove the gases as easily as possible, meaning as straight and smooth as possible. Seems I am missing something. ```
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