Quote:
Originally Posted by Christ
I just agreed with you about bernoulli.
What exactly is the "mistake" I made? If you're referring to bernoulli and the flow equation, read the first line again.
PS - I'm doing my work while chatting with you. It's a nicety for me.
Keep in mind, that you can increase the pressure driving a gas through a pipe by simply allowing it's expansion to drive the increase in pressure.
Like I said, there's more to it than simple pressure and velocity. Since the flow is compressible, and is not adiabatic (it loses heat and expands), keeping a lower pipe diameter will increase the flow's velocity due to expansion until the expansion is complete. If the pipe is longer than what is necessary to exhaust the flow after complete expansion, the flow will stack and pressure will build behind it. The larger the pipe diameter, the faster the exhaust gasses will expand to fill the pipe, and the lower it's velocity, since more expansion is perpendicular to flow, and less is parallel. Lower velocity has less potential energy, and thus, will create less pressure drop across the valve.
If you have some piece of information that refutes this, please post it for review.
|
Sure, it's called the ideal gas law: pV=nRT. If temp drops or volume increases, then pressure must drop. Thus you are refuted by the laws of thermodynamics.
Quote:
Originally Posted by Christ
To keep things clear, I have never suggested that a smaller pipe is universally the answer. I have been suggesting this whole time that pipe diameter should be based on mass of flow, and that larger is not universally better for a given application.
It appears that you're arguing from a performance standpoint primarily, which is likely why you're refusing to see my stance on the subject. When one isn't looking for more potential power than is actually necessary to do the work required, it changes many of the variables in determining the proper size of pipe required for maximum efficiency.
For the third time, there is alot more to the model than force (pressure) and velocity.
So before you start thinking that I'm arguing with you simply to argue, It needs to be mentioned that I'm not saying that you're wrong at all. I just don't agree that the method you've used for determining what works best in your situation necessarily applies to what is necessary for the best BSFC at lower RPM.
To take your suggestion to extremes, the best possible configuration is always the larger diameter pipe, which can quickly get out of hand. Ask anyone who's ever over-ported a head.
|
Head ports have nothing to do with cylindrical pipe flow - their shape is too complex to be directly comparable. However, just for S&G's, I'll point out that the typical gen I smallblock had 170cc intake ports and 67cc exhaust ports. The LS1 had 200cc intakes and 70cc exhausts. Now the LS3 has 257cc intakes and 86cc exhausts, gets better mileage, makes more power, and produces less pollution (12% less hydrocarbons and 40% less NOx) than the LS1.
Oh, and if we take YOUR suggestion to the extreme, since we seem to be going to extremes, when the exhaust hits the essentially infinite diameter at the end of the tailpipe, it should just stop and stack up, since it will expand and cool waaaaay more than it will in a larger pipe.