I am in the process of rebuilting s5 n/a with a mild street port in mind using stock airflow metre and ECU, custom long primery header collect at rear axle.



I wonder what will happen to the power/torqre band, if intake port open progressively? what about if the intake port open abruptly at once? I am aim to get good street power.



also how about port closing? same as intake opening?



thanks



Ben

 

from what i've read, i think you'd be better served having a progressive opening due to the afeect it has on airflow.

 

what kind of effect it has on airflow?

 

i'm still learning myself, so don't jus take my word for it. my best advice would be to look up Judge Ito threads and Rx7Carl threads on the subject of porting. that's where i've been piecing my information from ...



with that said, from what i've read the simple answer is that air prefers to flow with smooth transitions. sharp edges and sharp turns are not as desirable. granted it applies mostly to the closing of the port, but i would imagine that if it opens smoothly, too, then there should be less turbulence involved in the whole intake event.

 

On the FAQ section, Judge Ito did mention the effect of round and square closing on horse power, I am aware of that.



I like to inquire about intake opening here.



1) Air is an elastic medium, like a rubber band.

Would I get more air into the chamber by created a sudden vacuum from an abrupt intake opening, or would I get more air in by a progressive vacuum from progressive intake opening? This is the core reason I asked.



2) When you have a sudden vacuum, your shock wave generated is more intense, it might benefit my VDI designed in S5 N/A intake manifold. Does this give me benefit in higher rpm?



I know that I want turbulence in my intake, but not just anywhere.



Thanks for commenting

 

i also use the rubber band comparison when it comes to the behavior of air. now watch out, here comes a load of uneducated, wild guesses:

the main problem with an abrupt opening is the mentioned sudden vacuum. this "gap" has to be filled, either by atmospheric pressure or a turbo. but while this gap gets filled, the rotor still turns and this means: less time for the air to go into the chamber.

on the other side, the coliding shock waves in the intake can lead to an internal supercharge effect....so we have to separate between NA and FI engies AND where we want to have peak torque.

i better stop now

 

You basically need a super computer to support or disprove anyone's claims.

Anyone got a spare one handy?





-Ted

 

even then, modeling the dynamic flow of fluids is something best left to the real nerds....umm yeah

 

It's not actually that hard to model if you look at it from a travelling sound wave perspective. The confusing bit is deciding which of the resonant modes to use in your tuning.



If you are using stock S5 bits, then IIRC they were the first to have DEI. This uses the reversion pulse from the opening of the intake to help supercharge the closing event and the high pressure wave from inlet closing to create a second wave. With this in mind you actually want both the opening and closing to be as abrubt as possible to maximise these effects.



With a carb or any IRTB setup port opening is far more important to the tuning than closing.



Bill

 

^^^real nerd =)

thanks for that, i woudn't have thought to model it that way. Still beyond the scope of my expertise in fluids (minimal), but i get what you're saying at least.