Head flow question

dwightp · 03-25-2004, 10:17 AM

I see and hear so much interest in steady state flows and I can see were this could be used as a good metric. However, the motor does not operate under steady state conditions. The air mass is going through numerous accelerations (open & closing of valves, various suction levels, etc.) It seems like an intake or exhaust chamber could be further optimized (especially at a certain conditions) with this in mind optimizing the momentum and energy at certain frequencies. Kind of like a Helmholtz resonator with flow through. Anyone ever tested or tuned like this?

I remember doing muffler analysis in the acoustics lab. The results are suprising! Bigger is not always better. Baffle placement is also important. We were able to increase flow at target rpms by adjusting some parameters. The acoustic wave literally reducing pressure at the exhaust chamber, increasing outward flow. Seems like a person could tune for increasing pressure at the intake or (in the case of the head flow consideration here) the intake valve face. Just seems like one could squeeze out a few more HP at a target rpm range. Those builders for the "24 hours" or high end F1 teams probably know about this.

garibaldi · 03-25-2004, 11:17 AM

Have you ever seen a flowbench or a dyno win a race? When all is said and done, the performance of the engine is what matters. I see so many people put their faith into these testing tools, when what really matters is the way it performs when in its natural environment. I agree, and am jsut putting in two cents.

To further expand on your statement, a flow bench in this instance also does not take into consideration piston velocity, intake manifold, exhaust manifold, valve speed, operating temperature, scavenging effects, etc. All it does is test in a controlled and static state. Not to say that they are not useful to some extent, but there is a huge difference between hooking up a shop vac to your head and holding a valve at a particular lift and recording the number, and measuring the flow comparisons at operating RPM, in its installed environment. I have seen head that have given great numbers on a flow bench lose power on the engine and some of the rattiest looking castings make power improvements. So it jsut goes to show you that you should not be fooled into thinking that we have all of this figured out- we dont.

jluetjen · jluetjen's Garage

...And now something from the department of redundancy department:

Quote:

Have you ever seen a flowbench or a dyno win a race? When all is said and done,...

garibaldi · 03-25-2004, 01:11 PM

And now for the sake of redundancy.........................

What are you getting all bent out of shape for? No one is bashing or "Nay saying" your thread. So relax. Like I said, good info. I will definetely question its valvidity though- all of this testing is done in a controlled environment in a room, on a flow bench and if you are going to argue that all of that doesnt change once that same head is on a motor and operating, then go ahead. I question how valid the numbers that your flow bench will yield once you are in operation? My expereince is that it doesnt matter much. I am not trying to discourage you from experimenting and trying to learn, by all means! But the reality is that at the end of the day, the head is going to be functioning on an engine, with manifolds, and a cam, at operating speed, and with temperautre, with varying throttle positions, and varying loads, with varying injection cycles and methods and so on , and so on, all of which do not get considered, and all of which WILL have an effect on the "flow" numbers in and out of a given head. It was stated earlier in the thread- what was the flow difference when a bead of clay was applied to the perimeter of the port opening? That was a strip of clay, what happens when you put the motor together and run it- how does that effect flow? A bench cannot tell you that. Thats all I am saying- again, its not bad in my opinion, I just put my faith in another number.

snowman · 08:20 PM

The head flow matters, a LOT. It represents the max flow you can obtain with all the other things youlall mentioned optimized, They are independant. If you do all the right things, on a real engine, the one that has the best head flow will win, period.

What youall are talking about is related to the fourier series, Do any of you know what this means? An engine is a PULSED SYSTEM. Do you know that your can calculate the proper cam rise time from the fourier transform of the impulses of the engine? Do you know that you can also do a very mathematical analysis that will allow you to spread the performance increases due to intake and exhaust tuning over a wider rpm range? But only with the help of ONE or TWO people in the whole WORLD? Its all in the math. Do you know what Ribblets are? The F1, INDY, and Nascar people do.

And all these people do head flows.

dwightp · 03-25-2004, 11:31 PM

"Have you ever seen a flowbench or a dyno win a race? When all is said and done, the performance of the engine is what matters. I see so many people put their faith into these testing tools, when what really matters is the way it performs when in its natural environment."

Indeed! But hopefully we all find tools that help us reach our goals. Screw driver, flow bench, dyno or fuzzy dice. Ok, maybe not fuzzy dice.

"If you do all the right things, on a real engine, the one that has the best head flow will win, period."

Hmm. That's an interesting claim. I'm not quite convinced yet that's the case. Perhaps I will over time. That's one of the things I'm trying to determine and sort out here. I've heard conflicting claims from engine builders supposedly substantiated with dyno runs. I may be missing the details of the stories. I found it difficult to digest, but am digging for the technical feesabilty of the claims before I claim foul. In my mind, considering attention to "pulsed" (as you say) or periodic scenarios, it might be possible for a design giving lower dc flow might make up losses considering wave/acoustic theory. Its a mass of air in a chamber with certain characteristics. Just trying to understand it in the domain of heads and porting. I'm already convinced that in the manifolds, it can be a significant contributor if done right.

I heard a similar claim regarding inertia values of engine components. I'm convinced that it's not necessarily the inertia (mass) values that matter but how it's considered between rotating vs. oscillating components (inertia tensor - moments and products of inertia) i.e. if given a choice between the 2, would an engine be better off with lighter weight rods (oscillating portions) or lighter crank or flywheel (rotating)? There is a difference when considering the higher order effects.

And another claim with static vs. dynamic balancing of components. The list goes on... Probably best for another thread.

"What youall are talking about is related to the fourier series, Do any of you know what this means?"

Ah, yeah, I know a little about FFT, fourier transforms and series. LOL

"An engine is a PULSED SYSTEM"

Which would lend it to having periodic behavior and flow? Yes? Much work has and still occurs with aerodynamic performance, back pressure, alternating acoustic flow superimposed on steady flow. Nordam and others try to master it in practice for noise reduction in jet engines. Others for reciprocating engine muffler design. Current ram jet, pulse jet design (and others) margins much from wave and acoustic theory and tools.

"Do you know that your can calculate the proper cam rise time from the fourier transform of the impulses of the engine?"

I guess that makes some sense. Probably could calculate many optimized cam characteristics in addition to "rise time". Hmmm. I haven't really considered that since custom cam lobs have been well beyond my desire to design.

"Do you know that you can also do a very mathematical analysis that will allow you to spread the performance increases due to intake and exhaust tuning over a wider rpm range?"

Sure. Not only analysis, but in practice. Perhaps related to the "Q" of a system.

"But only with the help of ONE or TWO people in the whole WORLD?"

Doubtful that it's limited to only 2 in the world. Related concepts taught in colleges (mechanical, acoustic, aerodymanic). Similar analysis took place in musical instrument design (winds) years ago, only slightly different objectives. I believe engine designers began heavy work on this technology during WWII. I also believe Porsche margined some of that technology in it's Varioram. Work continues, products being produced.

"Do you know what Ribblets are?"

Perhaps more commonly known as "riblets"? Drag reduction technique? Work out of Nasa Langley? Some fish have them, select ships and aircraft use them, Conner used the technology to help "Stars and Strips" wins in the late 80's. "Hairy plane" proposal? I know nothing about the technology.

Not clear on the relation of riblets to periodic flow and pressure nodes. Unless "ribblets" are the ac consideration of "riblets". Hmmmm.

Thanks for the input,

dwightp
(forever a student in the world)

jluetjen · jluetjen's Garage

That's what I like about this BBS, I don't usually have to search to hard to find people smarter then me!

snowman · 10:17 PM

The only reason that its ONE or Two people in the world, is related to how many people are willing to dedicate their entire LIFE to this topic, not how many are capable of doing it.

Its not as simple as the Q value. for a similar kind of analysis that has a great deal of published information see works by Ralph Levy, in IEEE proceedings of Mircrowave Theory and Technology, related to broadband microwave structures. May not sound like the same thing but it is.

Ribblets are one reason NASCAR engines are making more power than thought possible.

dwightp · 03-27-2004, 02:10 PM

"The only reason that its ONE or Two people in the world, is related to how many people are willing to dedicate their entire LIFE to this topic, not how many are capable of doing it."

I guess I misinterpreted your earlier comment that only 1 or 2 can do the mathmatical calculations.

Sure, it's not only the "Q" value, but I believe the value of the mechanical "Q" is a valid metric for comparison.

Why go to E&M domain? Work has been done, documented and applied in the mechanical/acoustic domain which is more applicable to engines.

dwightp · 03-27-2004, 02:15 PM

You sure it's "ribblets" and not "riblets"? I'll do a little research and see if there is a difference beyond the spelling. I'm guessing we're talking the same technology...different applications.

snowman · 06:31 PM

Thats correct, same tech, differen't applications. Ie same as a sharks skin or the 3M developed skin for the americas cup boat. I am a very sloppy speller, and the spell check dosen't work with Mozilla, so I gave up trying. If I remember correctly it may be Henry Riblet, but I wouldn't bet more than a cup of coffie on it. I have not been able to find a great deal of literature on the specifics of applying this idea to anything especially engines. No one is forthcoming or willing to discuss it. I have contacted 3M, some NASCAR people. NO one is talking. But I have seen the inside of a NASCAR intake with the things in it.

I am more familiar with the EM applications than the mechanical ones. I suspect that the broadbanding techniques are much more developed in the EM applications than the mechanical ones, mostly due to the development of broadband microwave filter technology. Q can be very misleading, but I guess something called Fanos limit would still apply. In any case microwave waveguide filters deal with periodic functiions and the sonic tuning of a periodic pulsed system, like an internal combustion engine should be almost identical, at least in terms of theory.