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Location:
Finland
Registered:
November 2002
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Help needed with designing...
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Mon, 15 September 2003 15:35
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...inlet trumpets/air horns or what ever you call them.
I had years ago a book from library that was about dellortos, webers, etc. and it had instructions for calculating correct sized/desingned inlet trumpets. The book itself is nomore in library (sold as a old book?). Anyway I'm making quad TB's and now I need desing inlet trumpets. My search from internet didnt help me. So does any-one know any good sites/calculators or anything about topic.
I'm not willing to pay a cent for those because I can make my own and often what you see for sale are very ascetic. 40¤ for 3cm stump of tin tube isnt cool  . I can either turn those in lathe or machine a mould and press them.
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I supported Toymods
Location:
melbourne
Registered:
June 2002
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Re: Help needed with designing...
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Mon, 15 September 2003 23:24
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i'm planning to do this eventually, a will make them by metal spinning, which is the easiest and cheapest way to make such items.
some info on metal spinning
http://aardvark.co.nz/pjet/spinning1.shtml
as for the design, i was going to turn the mandrel in a wood lathe, the ones where you can follow a pattern onto whatever you are turning, the pattern would be a parabola made in matlab or some mathematics program (or from a french curve or something) just made by eye to fit into the plenum i make basically. this would go from "flat" at the opening to "cylindrical" near the port inlet.
good luck with it
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Location:
Adelaide
Registered:
June 2003
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Re: Help needed with designing...
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Tue, 16 September 2003 04:48
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Bill Sherwood's site has a graph which tells you what intake length is needed for the desired rev range, have a look at the to tell how long to make the induction rams.
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Location:
Lost in the K hole
Registered:
May 2002
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Re: Help needed with designing...
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Tue, 16 September 2003 06:12
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| Steve M wrote on Tue, 16 September 2003 14:48 |
Bill Sherwood's site has a graph which tells you what intake length is needed for the desired rev range, have a look at the to tell how long to make the induction rams.
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intake length, i thought, was caculated from the butterfly of the t/b to the valve face. did not have anything to do with the bellmouth design/length etc... bellmouths are a whole other thing
for bellmouth design, ive got a few links, i just have to dig them up 
cheers
ed
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Re: Help needed with designing...
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Tue, 16 September 2003 11:07
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depends man,
when throttle is open, the entire tract from free air to valve is a resonating tube. true, bellmouths are for guiding air in, but if they have any amount of length (like the red ones in the pic) then you have to take them into account.... i don't think the unpainted one would have much effect tho....
hmm, so when throttle is half closed or less, only distance between throttle and valve resonates? or is there some weird stuff that happens around the throttle butterfly??
get them links 
Cya, Stewart
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Location:
Lost in the K hole
Registered:
May 2002
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Re: Help needed with designing...
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Tue, 16 September 2003 11:12
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| oldcorollas wrote on Tue, 16 September 2003 21:07 |
when throttle is open, the entire tract from free air to valve is a resonating tube.
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good point, but it would only stand for long bellmouths (like the red). the taper of the belmouth would have weired effects on the resonance too.
plus, being an open end, rather than a wall, means youre dealing with a switch from fixed boundary harmonics, to open pipe harmonics - and that sucks! where is the transition?
but yeah, my original comment was direct at small height bellmouths with a rapid exponential curve.
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Location:
Finland
Registered:
November 2002
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Re: Help needed with designing...
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Tue, 16 September 2003 13:15
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I have more than 10 years ago studied ALOT about air flow on air intake and wing dynamics due to my RC-airplane hobby and common interest to airplanes. I have forgotten most of it now because cars are far more interesting now. My own humble theories are that bellmouth side of butterfly there is over pressure and valve side there is under pressure and there are turbulence on both side but far more on less pressured side. This is valid at fully or nearly open butterfly but at idle engine generates heaps more under pressure(suck) than air flow can generate in collision to butterfly. I wanna add that I KNOW that there aint under pressure, only vacuum and pressure. Some smart-arse was going to correct me  . Anyway, I would do as long as I could from bellmouths with even mild narrowing for accelerating air flow and slightly compressing it. Also parallel it. Mouth itself would have desing like pic2 but bit more (round) edge on inside "lip". Have a look to jet airplane air intake and you know what I mean.
These are some of my theories and propably nowhere near truth. This why I would like to have some help. Feel free to correct me.
Engjish?
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Re: Help needed with designing...
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Tue, 16 September 2003 13:56
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Ed, man that sounds like it's gonna get very difficult to model really quickly  , it's over my head......
Jayem, good point man, why not steal the research of aero companies who spend literally billions working out the best angles for the intaks . granted we are talking different velocities, but the theory still stands (until we get to mach speeds).
Cya, Stewart
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Location:
Lost in the K hole
Registered:
May 2002
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Re: Help needed with designing...
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Tue, 16 September 2003 15:41
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What is the best Air horn ( / Trumpet / Stack / Bellmouth )?
The air horn serves three main purposes; 1) To convert the pressure difference between bore and mouth into air speed with the minimum of energy loss. 2) To act as the interface between the induction system and the atmosphere, i.e. the point at which pressure waves change sign and direction. 3) To complete the system to the required overal length.
For ease of description the air horn may be considered in two parts; the 'flare' and the 'tube'.
The main job of the flare is to spread the low pressure zone over the largest possible area - to reduce local pressure reduction - whilst guiding incoming air into the tube with minimum disruption or induced vortices. The flare should be shaped to encourage air to enter from the sides, but not from the rear, of the mouth. This is acheved by either finishing the mouth with a sharp edge when the arc is a little beyond 90 degrees from the air horn axis or by folding material back, parallel to the axis, when the arc is at, or just below, 90 degrees to the axis.
The main job of the tube is to accelerate the airflow smoothly and progressively. This is best achieved by an exponential shape - i.e. one where the radius of curvature is increasing constantly until the angle of the sides matches the next part of the system, usually the throttle body. At the intake end this should blend smoothly with the flare.
It should be noted that the requirements for fuel injection and carburation do not always coincide and the best horns for one may not suit the other.
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Location:
Lost in the K hole
Registered:
May 2002
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Location:
Lost in the K hole
Registered:
May 2002
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Re: Help needed with designing...
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Mon, 10 May 2004 08:26
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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]
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Location:
Adelaide
Registered:
May 2003
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Re: Help needed with designing...
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Mon, 10 May 2004 08:38
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But the thing is what would then happen if you were to then enclose the quad bells/trumpets in an enclosure and pump that full of +ve pressure (ram air/cai). I assume that would change these calculations greatly.
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Location:
On your mum!
Registered:
May 2002
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Re: Help needed with designing...
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Mon, 10 May 2004 08:46
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Perhaps it would. I thought down this track somewhat and I understand that the reflected wave travels at the speed of sound. Now the speed of sound will change when subjected to variations in air pressure and humidity, but by how much? I think that this at least gives something (better than nothing) to start working with.
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Location:
Lost in the K hole
Registered:
May 2002
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Re: Help needed with designing...
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Mon, 10 May 2004 09:15
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| takai wrote on Mon, 10 May 2004 18:38 |
But the thing is what would then happen if you were to then enclose the quad bells/trumpets in an enclosure and pump that full of +ve pressure (ram air/cai). I assume that would change these calculations greatly.
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takai...
i dont think the act of 'enclosing' would make any difference to the calculations whatsoever, as theyre only concerned with open pipe harmonics, thus, beyond the end of the bellmouth nothing more is considered.
as jase suggested, perhaps the role of altered pressure and the resulting changes in harmonic velocities could muck things up, but certainly not 'greatly'
as ive read many times, maths only seems to get you so far in designing these things, but its atleast a place to start
jase - got your email, and am waiting on a zip file of 400 odd relevant links, ill pass it on when i get it
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