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ed_ma61
Forums Junkie

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Lost in the K hole
Registered:
May 2002

Re: Help needed with designing...	Mon, 10 May 2004 08:26

ahhh, intake design research continues... just thought id post it all here on bell mouths: "The following facts are based on empirical knowledge, direct observation and published data. After the intake port opens, a low pressure pulse is produced. This pulse propagates along the intake runner until it reaches the end (the end being the point where the diameter of the runner increases significantly) where it inverts and returns as a high pressure pulse. It has been demonstrated that the characteristics of this pulse (amplitude, duration, slope) are proportional to the air requirements of the engine at that throttle setting and RPM. The runner length should be set so that the returning pressure pulse coincides with the closing of the intake port. For proper wave reflection the runner must terminate in a full radius bell mouth (Radius >25% ID for >90 degrees). The absence of the bell mouth will result in a vena contracta significantly smaller than the runner ID and attendant flow losses." CHRYSLER 300 ram theory: http://www.chrysler300club.com/uniq/allaboutrams/r amtheory.htm Commentry as above ram theory: "Ideal intake tract length is huge, somewhere on the order of 35-40 inches. So, you have to tune for the resonant pulse. Chrysler did a bunch of research on this. When they developed their ram air system 40 years ago, they found that most calculations, no matter how many variables were applied, were unreliable, They ended up using a variable length intake runner and changing its length under operating conditions to find an ideal legth. As a result of this research, it is generally accepted in making these calculations, in order to approximate an ideal length, that the sixth pulse is used to effectively shorten runner length. The sixth pulse makes the runner length accceptable while maintaining the lions share of the pulses strength The frequency of the pulse is a function of port velocity, runner length, cfm, reynolds number, cam timing, etc. These are fluid dynamics calculations that make even the best of engineers weak in the kness. Its kind of funny, while we look at this type of thing to make more power, Buell(and every single auto manufacuterer) has taken it one step further. There helmholz resonator uses these theories to not only make more power, but also to reduce noise to satify uncle sam. I have some formulae that can help with some of this, but honestly, it becomes very subjective. Each and every application will be different. If you are interested, let me know and I can provide with links to the information I have found. dodgy harmonic calculator: http://www.bgsoflex.com/intakeln.html [Updated on: Mon, 10 May 2004 09:11] [Report message to a moderator]

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