Dust extraction - sizing

[nova_robotics]

Pressure waves can be very important to the performance of highly tuned engines. I pointed out that the suggestion to evaluate this on a flow bench would have problems due to the need to emulate very high exhaust temperatures, because the wave velocity various with temperature.

I was mostly thinking for intake tuning. That's usually where people go after resonance. Variable intake runners and whatnot. Then you don't have to mess with any of that pesky hot exhaust.

But for the exhaust, if you made a closed(ish) loop system and ran 1/3 air, 2/3 helium you could pretty closely approximate hot exhaust at room temperature. That would get you your resonance tuning. A bottle of helium is cheap. I don't know how many tests you'd get out of it though.

[nova_robotics]

You are trying to modulate the flow and see where the intake or exhaust manifold is at resonance ?

Yup. Intake and airbox tuning is super important on engines. You can even achieve a light supercharging effect (I think about 5 or 6 PSI) by getting the high pressure reflections to hit the intake valves just right. A lot of effort has gone into tuning the airbox and intake of the car or truck you drive right now. It's pretty neat stuff. The problem is you only get resonances at one or two RPMs, and the rest of the RPM band doesn't benefit. I had an old '85 Porsche 944 with a weird flapper thingy that would open and close off chambers on the intake specifically for changing the resonant frequency of the intake as the RPMs changed. So by changing the internal volume of the intake they could selectively create a whole bunch of different resonant frequencies. My Porsche 928 has a V8 where the intake runners are static, but grouped in pairs. To smooth out the powerband each pair is a different length and tuned for a different RPM. So (for example, not sure if the cylinder numbers are correct but you get the idea) as you increase in RPMs, cylinders 1 and 5 do most of the work, then cylinders 2 and 6, then cylinders 3 and 7, then cylinder 4 and 8 as you wind it out. You have no idea how much I hate this, but I understand why they did it. Just to smooth out the powerband so you don't get one big punch at a certain RPM, and flat spots everywhere else. It's all very interesting, but I'm only an armchair expert. Never actually done it myself. A big part of the Wikipedia page on intakes is devoted to variable length intake manifolds and Helmholtz resonance.

https://en.wikipedia.org/wiki/Inlet_manifold

[mwmkravchenko]

Yup. Intake and airbox tuning is super important on engines. You can even achieve a light supercharging effect (I think about 5 or 6 PSI) by getting the high pressure reflections to hit the intake valves just right. A lot of effort has gone into tuning the airbox and intake of the car or truck you drive right now. It's pretty neat stuff. The problem is you only get resonances at one or two RPMs, and the rest of the RPM band doesn't benefit. I had an old '85 Porsche 944 with a weird flapper thingy that would open and close off chambers on the intake specifically for changing the resonant frequency of the intake as the RPMs changed. So by changing the internal volume of the intake they could selectively create a whole bunch of different resonant frequencies. My Porsche 928 has a V8 where the intake runners are static, but grouped in pairs. To smooth out the powerband each pair is a different length and tuned for a different RPM. So (for example, not sure if the cylinder numbers are correct but you get the idea) as you increase in RPMs, cylinders 1 and 5 do most of the work, then cylinders 2 and 6, then cylinders 3 and 7, then cylinder 4 and 8 as you wind it out. You have no idea how much I hate this, but I understand why they did it. Just to smooth out the powerband so you don't get one big punch at a certain RPM, and flat spots everywhere else. It's all very interesting, but I'm only an armchair expert. Never actually done it myself. A big part of the Wikipedia page on intakes is devoted to variable length intake manifolds and Helmholtz resonance.

https://en.wikipedia.org/wiki/Inlet_manifold

I have some new things to learn then. Funny thing I started cluing in on most of what you were saying here from your last post.

I have done similar work with distributed resonances in subwoofer enclosures. Same idea. The world is not as big and mysterious as many would have us believe. You just need to be able to connect the dots. Physics is physics no matter what the application.

[nova_robotics]

I have some new things to learn then. Funny thing I started cluing in on most of what you were saying here from your last post.

I have done similar work with distributed resonances in subwoofer enclosures. Same idea. The world is not as big and mysterious as many would have us believe. You just need to be able to connect the dots. Physics is physics no matter what the application.

So you probably know more than me then. I've never done any of it, and I only know from what I've read. It's all the same stuff, just different application.

It's funny because as a teenager I used to rip all that stuff off my engines, thinking I was reducing restrictions. Oh dear...

[mwmkravchenko]

So you probably know more than me then. I've never done any of it, and I only know from what I've read. It's all the same stuff, just different application.

It's funny because as a teenager I used to rip all that stuff off my engines, thinking I was reducing restrictions. Oh dear...

No I don't know more.

I don't know more than Tony either. I just have done similar work. Which means I can understand the ideas and the goals. Just not exactly what you have to do to get it accomplished. I hang around on this forum because there are quite a few intelligent people. And I constantly learn things. Some new, some old. But I learn new and intriguing applications. It get me thinking and I appreciate this a lot.

[nova_robotics]

And I constantly learn things. Some new, some old. But I learn new and intriguing applications. It get me thinking and I appreciate this a lot.

Same same. How gray the world would be if we couldn't explore new ideas. I think if I ever get into such a rut where I was just slogging the same thing over and over without learning anything new I'd probably drive my car off a cliff.

[marksbug]

I have a good few hundreds or more hours on our old super flo flow bench.I have missed it dearly the past 12 years. I was going to make one hear at the house for my own stuff but...Im trying to down size and not doing much more engine& head work these days.it's too much like work to tear car or toy appart to do it. I dont really need flow bench any more, but it sure is nice to have and test with. theres lots of hidden hp in cylinder heads. especialy older ones. I would love to pul the ehad of my new cars and do them up, but..again too much like work.and I nolonger race. but what gets e is...Ive never messed with those heads....so I dont know exzactly what they may or may not need without having one in my hands. if I ever need to remove one Ill know what to do when I see it.probably wont be a lot.or it may be a lot, you just never know...untill you do.