PatrickT

Thanks, I'm also very pleased with the results.

Like I mentioned before, at one point I didnt mainly go for resonance anymore but for good flow.
I just decided to make the runners that length so that it may help if still resonance occurs.
Now I'm going to work on the boost control to maybe level out the torque curve with lower boost in high rpm / higher boost at low rpm.
and to make boost easily adjustable while driving.

The expansion intake manifold Porsche is using is a interessting concept, but I'm still not sure if it will work with a high overlap BP, so I didnt wanna risk to much and went the conventional way.

PatrickT

I did some calculations with the ECU data I got from the dyno run.

The recorded data were channels like: rpm, map , lambda , injection time , fuel pressure etc
So I tried to calculate the volumetric efficiency by first calculating the injected fuel mass per cycle with:

"Fuel mass" = "Injection time" * ((fuel pressure - map)/3bar)^0,5 * "Injector flow at 3 bar" * "fuel density"
Injection time had to be divided by 2 , I think the haltech is injecting for 2 cycles in rotary mode.
Fuel pressure is droping in my setup with raising injector duty so I had to take this into account

Then by multiplying the fuel mass per cycle with the AFR I'll get the air mass per cycle.
Besides I calculated the theoretical 100% air mass in the camber for 654cc volume with 0,769g

So I get the volumetic efficiency (lambda a in german) with: lambda a = "air mass per cycle" / 0,769g / MAP






Here I cant take into account that air mass may evade during overlap.
And its also not 100% sure that in reality it isnt a little lower or tilted, but it shows little peaks that may hint to resonace effects.
I looked up my precalculations. It predicted simple resonance at 3500 ; 5200 and 6900 and cross resonace at 6750, so it looks good to me at least for the 6500-7000 area.

This is not 100% proof but looks like it kinda works out.

PS: I had the little step from 4700 to 4900 already with the stock manifold, gonna look into old data again....

-Patrick

PatrickT

I did just one more thing, I normalized the torque curve from the dyno with the boost.
So the torque curve gets more flat like in a NA engine, and 400Nm at 1bar boost becomes 200Nm at zero boost.
With the "lambda a" curve overlayed it looks like this:

You kinda see the increase in "lambda a" at 5000 and 6500 also in the normalized torque, while I think the torque curve from the dyno is smoothed.

You cant see the "lambda a" peak at 3000 in the torque, so this is maybe fresh air exiting the exhaust through the overlap, while at this point when boost first comes in
back pressure is low and thus delta pressure from intake to exhaust is highest , leading to the most "shortcut flow"

PatrickT

I just made a simplification of the formula for someone and I want to share with you all.

For turbo:
Runner length in m = 3500 / RPM
So for resonace at 7000 RPM you want a runner of 0,5 meter, which is about 20"

For NA:
Runner length in m = 3400 / RPM
This matches exactly the numbers of the 26B race engine.


FYI: these are 3rd order resonances for the intake stroke that comes once each revolution doesnt matter the port timing
and the difference between turbo and NA is because of different intake air temps which affects speed of sound

TeamRX8

iTrader: (2)

it doesn’t take into account that it’s both diameter and length that influence the resonance though.

the one thing I often see is people hogging things out rather than decreasing the length …
.

PatrickT

Yeah I never included the diameter in resonance calculations, nor does Mazda.
IMO the diameter is important for resonance due to air inertia (flow speed)

My formula only takes resonance due to sound into account.

I`d rather adapt the diameter to flow requirements for the desired power.
Also I'd doubt that a high overlap or PP engine inertia has a huge effect.
For me it worked out great, but basically everbody can do it as he likes ;-)

BLUE TII

iTrader: (9)

My understanding was that the intake runner diameter is also used for resonant tuning because you use half the diameter of the runner and add it to the runner length to calculate runner length.

Not a bIg deal if your runners are "about" so many inches long cause you are adding ~ 1".

PatrickT

Oh yeah I did this, but as you said it makes no huge difference, temperature and pressure of the air propably have a bigger effect.