ITB Runner length calculation?

[Steven320]

Hi Ther,

i'M looking for a proper formula or calculator to calculate my runner length.

I find this page but, what i calculate was far from close to the spec what i got from engine analyzer pro 3.9. so i dont really understand it anymore.

http://honda-tech.com/showthread.php?t=1963201

they length what i calculate was around 680mm with the above link.
and the ideal runner length with e.a.p was 265mm+69mm intake length.

so plz help me out im add the point to start with the runner.

Steven

[reggid]

3rd harmonic is gonna be somewhere around 10-12" manifold runner (i.e bellmouth to gasket) dependent on specs and what you are trying to achieve. EAPro agrees with what pipemax says pretty closely. best thing to do is start a bit longer than what it says and have a bit of adjustability.

2nd and 1st harmonic are going to be alot longer.

[Steven320]

so E.A.P is pretty right with ther length.

10-12''(250mm-300mm)
E.A.P 265mm.

oke now i know wich length i have to make, but i still dont know ho w to proper calculate the length. just in case but maby it is also intresting for the rest of the forum.

(ty reggid)

Steven

[reggid]

how can EAPro be right? it doesn't tell you what length to use....you simulate various combos and you decide the power band you want. use it to to establish trends and why something works or not. inputs need to be pretty good to get useful info. if you cant correlate EAPro to a stock engine then it wont be much use simulating a modded engine of the same type

quick and dirty approximations

L=84000/rpm

where L=manifold runner length in inches intake gasket to bellmouth

or from Blair himself

L= 1100 x S / N

where N= rpm, S = crank degrees after BDC that inlet valve closes upto a max of 75*, L= total inlet length inches valve-bellmouth

or use this chart where length in this case valve to bellmouth

get it close to these numbers and fine tune it so build it with adjustability

[Steven320]

your right, but its gives you a roughly idea how its gonna react on the changes. im awear that the power specs what i if got from EAP are just a theory.

but thanks alot for your advise and help.

Steven

[Rav335uk]

What ITB's are you going to run?

[Steven320]

ad the moment 34.5 mm itb's from a bmw k100 motorcycle.
on a M20b23

Steven