re:exhaust systems

[JamesWolak]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by MalcolmG:
I give this 5 stars for comedy value </div></BLOCKQUOTE>

I have been doing that for months with these post. Helps me filter them out.

[RANeff]

dude bro-dog-man-ski. i could totally, like, answer, like, the question here but bro- that would be way to sweet dude.


dude


broski

[Drew Price]

Let me see how much of this I remember (I was the suspension guy), since I don't get to use my engineering school words very much at work these days (because no one speaks enough English).

Venkatesh:

In this instance 'effective' does not mean 'correct method,' it means 'equivalent' in the sense that it makes the computation easier. Think of it as meaning 'representative.'

For example, the exhaust flow restriction (or turbulence, or acoustic transmission, etc.) through a louvred muffler core is not the same as the flow restriction (or whatever) through a piece of similar diameter pipe with the same length, but it IS similar to a length of pipe the same diameter that is *longer*, so that longer length is your 'effective' length.

Usually 'effective length' would only be used for rough hand calculations or approximations - if you're doing reasonably complex computational analysis this should be taken into account already (although if you're asking this question, you may not have a handle on how to model a turbulent, pulsed, transient system. But I could be wrong....)

To simplify acoustical computations you make some assumptions, and you can approximate how the exhaust system as a whole MIGHT be similar to a length of straight pipe in terms of flow restriction or something like that.

For header primary design for maximum pressure reflection you approximate the length of the tube as being the length from the exhaust valve to the first *drastic* change in cross section, usually a collector, or muffler entrance. You don't use the end of the exhaust pipe, because by the time you go through the muffler or down that much tubing the first order effect has already dissipated, and the 2nd and 3rd order effects are close to negligible (for an FSAE car &lt;--- opinion, I think there are much more important things to be worried about with the car, unless you're doing it for your PhD dissertation or course credit or something, but that's a whole other buttload of problems.)


Best,
Drew

[barba_p]

really nice answer Drew Price
well done
+++

[samphlett]

Don't forget the end correction: 0.85r for a flanged pipe, 0.6r for an open pipe.

[PatClarke]

Samphlett, those figures are only good if they dont run a megaphone or stepped pipe, or if they have twin outlets. Chromed tips will reduce the efficiency and so shouldn't be used despite losing the bling factor

Pat

[Wesley]

Pat, do you mean the angle-cut chrome tips? or the slip on tips? Or any of the above that might impede flow or acoustic propagation?

Because I do know chrome doesn't hurt fluid flow. Right?

[Superfast Matt McCoy]

Effective Exhaust Length:


Ineffective Exhaust Length:

[Drew Price]

The chrome will facilitate increased optical diffraction, and will therefore aid heat dissipation (as well as blingification, and awesomesaucemulation).

Obviously Pat is trying to blind you from the truth.




Best,
Drew