Intake Runner Length

[galahs]

I know I didn't make any alteration to or even add a belllmouth. I'm talkig possibilities, not actuals. Maybe a diagram of my thinking is required.

As for sahring a comon supply, that shouldn't be a problem as long as the supply entry is large enough.

[CirclesCenter]

Tuned manifolds are a black art.

DIY's fiddle with such an item and end up porking something.

[Rangerkyote]

Shorter runers give more top end HP.  Longer runners give more low end torque.  It goes back to whoever made the 5.0 reference.  On motorcycles, the carbs are almost on the head.  This is because they are tuned to operate in the 6000+ rpm range.  Notice a lot of your V-twins have a longer intake, partially because of design and partially they operate in a lower power band.  As far as putting trumpets in front of your butterflys... that's some voodoo science.  Same with runner length.  It's lots of experimenting on a dyno that produces results. 
Of course, me personally, I've done plenty of seat of the pants experiments on bikes and cars I've owned.  Stuff doesn't aways work.  Have fun, try stuff out but don't kill your budget.

[galahs]

I just think it could be worth experimenting with, and could be done fairly cheaply too.

I know on most race engines the entire air intake system is the 'black art' of making more horse power. Just think the GS500 could possibly benefit from a few R&D projects.

[GeeP]

Intake system design is no more a black art than cutting somebody open to transplant a heart.  Most people just don't understand it.

If you're truly interested in intake design I suggest reading "Scientific Design of Exhaust and Intake Systems" by Philip H. Smith and John C. Morrison.  Both the authors did years of research on the design of induction systems for racing applications.  Their reference papers are good too, but good luck finding them! 

Fluid flow aside, what you're trying to achieve is "organ pipe" tuning of the intake manifold.  The effect of carburetor throttle plates, runner length before the carb, trumpet, and the design of test gear are all discussed.

The problem for a street bike is designing a system that will both increase usable power in the cruising to full throttle area, but not sacrifice bottom end torque.  I suggest that you do some reading on the Bessel horn and it's application to music.  Musical instruments have evolved some interesting ways to alter the tuning of a long pipe that could be applied to a mechanical system. 

BTW:  The V&H exhaust system is textbook Morrison.  I got curious one afternoon in the shop and measured it.  It's specifications are right out of chapter 5.

[galahs]

Champion!

I' getting really interested in this sort of stuff.

Will have to chase this up for a read when I've got alittle more spare time 

[laranjatomate]

I am planning to convert my GS500 to electronic injection (and run it with ethanol). I need to have an estimate of the length of intake which is inside the cylinder head (my "blue mare" is in another city and I don´t know when I´ll be with it). Did somebody measure that?
I already know the carburettor length is around 95-100mm.

I´ll make some acoustic calculations in order to know I may put off the air filter box and use smaller sports conic air filters. I need space for put electronic injection and ignition modules (there is not enough space on the under rear seat toolbox area). As there will be no acoustic interaction between cylinders due to the plenum, it is need to recalculate some things ad maybe project my double throttle body with some connecting pipe.

[saxman]

I am planning to convert my GS500 to electronic injection (and run it with ethanol). I need to have an estimate of the length of intake which is inside the cylinder head (my "blue mare" is in another city and I don´t know when I´ll be with it). Did somebody measure that?
I already know the carburettor length is around 95-100mm.

I´ll make some acoustic calculations in order to know I may put off the air filter box and use smaller sports conic air filters. I need space for put electronic injection and ignition modules (there is not enough space on the under rear seat toolbox area). As there will be no acoustic interaction between cylinders due to the plenum, it is need to recalculate some things ad maybe project my double throttle body with some connecting pipe.

The distance from the center of the intake valve face where it meets the combustion chamber to the center of the intake valve port where the throttle body attaches is almost exactly 3".

Why are you measuring the carb length? If you're doing electronic injection, you're not going to be using the stock carbs in any shape or form... you're going to have to switch to a throttle body designed for this use(well, unless you're not planning on doing direct injection, but still doing this with the stock carbs would be way counter productive.

Why are you planning on running a plenum?

[laranjatomate]

Thanks for the 3" measurement.

I am fearous to build the throttle body with the same pipe length of the carburettor's one because I'll have no interaction between cylinders through the air filter box.
I still did not understand the phenomena [I have a book on intake and exhaust manifold acoustics, but it's complicated :{) ], but I know they exist and have strong influence on volumetric efficiency.
If I discover I need longer lengths, I accept even to design a corner and point part of the length downwards.
Once I want to have more than one ECU program (gasoline, ethanol economic and ethanol "nervous") I perhaps have attachable pipe parts for better torque in low or igh range. Maybe I do that.

I need do retire it because the programmable electronic ignition modules I'll use need this space and to be as nearest as possible the coils and spark cables.

[laranjatomate]

Design Techniques for Engine Manifolds: Wave Action methods for IC engines.
DE Winterbone; RJ Pearson.
ISBN 186058179X

Theoty of engine Manifold Design: Wave Action methods for IC engines.
DE Winterbone; RJ Pearson.
ISBN 1860582095

[noiseguy]

Textbooks? Here's a summary:

84000/RPM = intake length in inches from carb bell mouth to intake valve.

Where the carb sits between the ends (bell mouth to intake valve) affects how peaky the power comes on. Dead center = highly tuned to length. Off center = less so.

Bell mouth design affects this as well, with a straight cutoff being (again) the most peaky and a gradual taper less so.

Two stokes are 42000/RPM=intake in inches, between reeds and bell mouth, BTW.

[laranjatomate]

Where the carb sits between the ends...

So it means I need to choose carefully the lontigudinal position of the fuel injectors?

Yesterday I was looking for some drawing or photography of the crankshaft. It means the cranks are opposite. So, one cylinder realizes work through gas expansion, the other does so, and the next two strokes without any fuel explosion.
Meditating about it I concluded the plenum (air filter box) volume is not important for resonance, due to this asymetry. If there is any acoustic interaction when some wave comes out the bell mouth of some cylinder, which could affect the other one; the opposite would accour at different times and with different intensities, affecting the vacuum equalization fo the carburettor bodies.
Finally I can concentrate my calculations on the pipe length without think on connections among them im my throtle body design. :{)
The texbool I cited points 2 phenomena in its 2nd chapter: The "organ pipe" in which length and diameter of both cylinder and intake pipe are taken into account and the pressure/rarefaction waves which occour when intake valve opens or closes (because this I required the camshaft phasing in anither topic), which travels towards the intake pipe until its entrance (the bellmouth), retunrning in the opposite sense (rarefacion returns as pressure waves and vice versa), while it may also reflects in the same sense when it reaches the coldsed valve. There is the possibility of some of these waves reach the intake valve about to close. If a pressure wave reaches the "close-to-close" valve, there is a little more of air intook.
If I have LaTeX installed on my computer I would put the formulae exported to some figure format. :{)

[noiseguy]

Wow, you drug up a old post.

So it means I need to choose carefully the lontigudinal position of the fuel injectors?

I don't know about choose carefully, but the longitudinal position along the intake tract will affect things. This is usually a pretty easy thing to play with on the dyno or street... just get some diffferent length hoses.

Air box volume is as much about intake noise control as anything. It's easier to do the figuring on a straight pipe (which has easy acoustic equations) than a box, which is more like a helmholtz resonator.

I can tell you from experience with automotive tuning, that even now this is mostly done manually, cut and try, by OEMs. You basically start with the biggest volume box you can fit (bigger = quieter) and then play with it with heat tools / plastic welders until you get something that sounds and performs as you want it to. There's some analytical work (computer models) with the basics set by equations (what you're talking about) but at some point you'll just need to build it and run it and make changes to suit. That last bit is the "tuning" and it makes the difference between something that runs sweet vs. stubborn.