Quote:
Originally Posted by iroc_g
OK, I showed my boss the replies, so I could better answer these issues.
The Heimholtz resistance is in no way relative when testing a forced induction intake manifold. I got a crash course in what Heimholtz resistance is and how it is determined. Not only is it not relative, but even if it were, would differ depending on the individuals COMPLETE setup.
As far as the restrictions further down the line. Yes, those would effect the efficieancy of each individual cylinder. However, each cylinder has 2 equally sized valves, equally sized ports, cumbustion chambers, into the exhaust manifold and finally meet in the turbo. So arguing that these restrictions would change the balance of the intake manifold is not correct.
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The Heimholtz resonance does not vary with the complete setup, it relies only on the taper of the runners, distance from the back wall of the intake manifold, speed of the air and the time the valve closes and reopens. It is true that it isn't as big of an issue in a boosted application, but it is still a factor. The only thing that will change the resonance is cam timing for a specific application like this. It is true that the resonance can only be tuned for specific RPM range.
For others: the heimholtz resonance is the shock wave that is reflected from the valve closing, bouncing off the back wall of the manifold and shooting back in to the head. If this is timed correctly it can force extra air into the cylinder.
Quote:
Originally Posted by iroc_g
And yes, a exhaust manifold that is uneven could easily impact the power and afr balance of each cylinder. If you are going to ask a imbalanced exhaust manifold to counteract a imbalanced intake, then you have far more problems with your setup than most either of these parts are going to help.
Simply put, the intake manifold is the first part that divides the engines air charge. If it is imbalanced, then the rest of the parts don't have a chance at staying balanced.
If the flowbench is showing a 10% difference when comparing runners, that 10% is going to carry wether it was at X amount of vaccum, or Y amount of boost. So, if at 400 cfm it is 40 cfm short (10%), then at 1200 CFM, it will be 120cfm short. The more boost you run, the worse it gets. The percentage stays the same, but the difference in the volume of air will grow.
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This is not exactly correct, especially the part about it flowing 10% at any volume of air. This does not take in to account the efficiency of the air going past a restriction. The valves have a choke point and the closer you get to the choke point, the more restriction the air has. The 10% greater volume of air is just a measurement of the forces that are acting. As the air further downstream becomes less efficient it will take greater and greater force to get the air through the restriction. This will mean the runner with less flow is more efficient than the runner with higher flow, thus helping to equalize the difference between cylinders.
Then there is all of the forces that happen during valve overlap, but I am too tired to get in to that
Quote:
Originally Posted by iroc_g
Looking at the "whole picture" like the real world has to is the problem that we have been dealing with. The real world (I assume you mean end users, us DSMers) isn't setup to test these either the way I have, or the way that you suggest. If they did, I doubt there would be such a discrepency in these parts. And this is the way the racing world and industrial world tests their parts.
Finally, to the comment that these results don't represent real life at all. That is flat out wrong. Simply put, The auto manufactures, race teams, and industrial research and development departments all use a flow bench for all of their airflow design needs. That is its purpose, and the industry accepted way to do things. I have been told by two intake manufactures featured in this test, that the reason they have not provided any flow information, or even done that sort of testing, is because they feel that the average user will not know what to do with the information. The reason that Beyond Redline sent me a manifold was they wanted to know for themselves how their part does, because they had not yet flow tested it.
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What I said is the extent of the cylinder variances is not going to be equal on the flow bench as compared to what is seen in a real engine. Will there still be a difference? Yes. Will it be the exact differences you have shown in the flow bench testing? No. I agree that it is optimal to have all of the cylinders equal, I just worry people are going to start changing their mixtures 11.7% for one cylinder because your testing showed that it flowed 11.7% more air on a flow bench when this will not be the case in their engine.
I know we have a few engineers on here that have studied heavily in fluid dynamics, I would like to hear their take on this (floppy head and Jakey specifically) as well as anyone else that is well versed on the subject.