Intake Design Exploration

[tervo rodriguez]

here is a look at my custom intake that positive pressure comes in at 2200k w/webbers dcoe 45 on 13psi boost at 3200k and puts out 322 to the wheels 360hp on my raceported 12A

Originally Posted by vex

Alright, I think understand what you're saying concerning the Plenum design. Shouldn't be too hard to do a digital mark up in a few. As for the velocity stacks I was already considering doing that.

My question however is for turbo charged applications does wave tuning do that much to begin with? I'm curious because if I'm understanding it correctly the positive pressure comes on (for me anyways--Turbo 6PI) around 2k RPM. If i'm getting positive pressure that quickly, no matter what wave I tune for with the intake runner lengths I'm going to end up with more pressure than the wave could shove in by itself (even when it's not during a compression wave).

If my thinking is correct then I could be able to have rather long runners and be fine power wise. My concern from this however is will throttle response be adversely affected by having abnormally long runners? As it stands right now I'm thinking about keeping the runner length the same as a stock NA (roughly 17" or so), but directed much differently so the air needs to only take one continuous turn once inside the manifold.

I think the best bet for me (and everyone else who follows this thread) right now would be to focus on one stage at a time. For now lets focus on Plenum design and worry about intake runners later:

If I'm understanding you correctly you are telling me that a diverging-converging
(Air-> TB:) nozzle design will work best for when the throttle body is placed on the longitudinal axis of the Plenum. Lets focus on this setup as it seems the easiest to manufacture and produce in ones garage.

As air inters the divergence portion of the plenum the air will slow down according to thermodynamics:

A/A*=1/M[(2/(k+1))(1+(k-1)/2*m^2)]^((k+1)/(2*(k-1)))

Since it's air, k=1.4 and M<=0.6 the formula will give you A/A* for the divergence. (Note: A- Area when gas inters, A* When gas is at M speed)

If the pressure drop is significant enough the temperature will drop, but flow speed will suffer as it drops down in mach number. Knowing what the temperature will drop to we can solve for velocity using

Ve=sqrt(k*R*Te)

Note: There is a conversion factor in here (and this will end up in metric units)

Now you mentioned something about a baffle or is that not needed in a rotary application? Do we even need a Divergence-Convergence Plenum, or is it just a simple matter of getting a big enough pipe and sticking a throttle body on the end of it?

Aside: Can anyone scan a lower intake gasket for a 6PI and take a single measurement for me? I wish to be accurate and start a digital construction of the intake system so when I have access to CFD I'll be able to accurately see where potential flow issues are. Thanks

[vex]

Originally Posted by tervo rodriguez

here is a look at my custom intake that positive pressure comes in at 2200k w/webbers dcoe 45 on 13psi boost at 3200k and puts out 322 to the wheels 360hp on my raceported 12A

Your plenum and intake are simple enough. Though I don't think your runners can readily be seen in the pictures you provided (since you're running a carb the runners would be underneath the carb).

Though I must say, I really like the way your plenum is set up. It looks somewhat similar to my first attempt to digitally model the intake, though I didn't place the blow off valve on the plenum. I like the thought of having the vac/boost lines coming off the plenum. Do you run into any issue with pressure sensing with a turbulent flow? I suppose you really wouldn't because stock does the same thing.


As for the code generation for calculating intake runner length and diameter I have some good news to report:


I've also included the code below for further investigation for users who wish to run it themselves and maybe even critique my math. I wrote it in matlab which allows easy 3d surface rendering accurately.

function []=runnerlength()
gamma=1.4;
R=287;%J/kgK
T=293.15;%K

a=sqrt(gamma*R*T);%M/S

redline=8000;%rpm redline
v=0.0013;%m^3
r=linspace(0.001,0.015,100);%m
A=@(x)pi().*x.^2;%m^2

rpm=linspace(3000,10000,100);
f=@(x,y)a.^2.*A(y)./(4.*(x./60).^2.*pi().^2.*v);
z=zeros(length(rpm),length(r));
for i=1:1:length(rpm)
    for j=1:1:length(r)
        z(i,j)=f(rpm(i),r(j));
    end
end

surfc(r,rpm,z)
colorbar
xlabel('Radius, r (m)')
ylabel('RPM')
zlabel('Length (m)')