Plenums.... why bother?

[kingmick]

yes Takai, packaging is half the battle in most cases e.g bonnet bulges etc.Takai's setup is good setup for IP on atmo 1600 as it would give nice midrange and make it a much better car out of the corners.
Compromise is in everything automotive
Some great work here guys.

side note! what happened Takai? fuel hose or rail leak?

[takai]

Throttle jammed open at WOT, and then when i shut off the engine it must have died with both intake and exhaust valves open on cyl 3 which backfired and spat the fuel air mix out the intake and the supposedly non-flammable Unifilters caught on fire.

[Ben Wilson]

and then when you are designing the plenum you can calculate the Heimholtz resonations in order to see where the air is going.

Please explain, every time I try to work it out my brain starts to melt....

[kingmick]

That hurts takai,i hate fuel at those times.!
amazing how much fuel is outside the intake at times, I remmeber doing a non crossflow nissan egine on the dyno with SU's and smelling fuel eveywere after power runs and seeing the fuel mist back out of the intakes of the SU's with hot exhaust just below it and there i was with an airflow meter checking the carbies on the dyno! hahaha

[takai]

Ben: Yeah, my brain melts a lot when calculating Heimholtz resonations. However, thankfully the dual Xeon doesnt melt so much (although it tries). I use a combination of Solidworks and Ansys Workbench to do my flow analysis, including modelling reflections.

For giggles i set up a quick and dirty V8 manifold ("standard" crossed runners, 50mm throttles, 90mm before the throttle and about 150mm after) and told it to show the flow using just a simple plate across each port in the valve order, and model it from 1500rpm to 9000rpm. Then i went away on holidays. I came back two weeks later and it was only up to 2200rpm.
I just gave up.

Kingmick: yeah i had the "joy" of seeing a Jag V12 (oooold XJ) with Weber downdraughts on the dyno once. The haze which was coming off the trumpets was really very scary.
At the very least the plenum keeps the fuel mist in a nice controlled area.

[o_man_ra23]

damn I cant keep up with this thread.

But back to rivers question as to why doesnt the pressure wave cause air to flow out the throttle body:
to answer, we look at the MAP at the point when the pressure wave is coming back. Unless you are on boost or at WOT, then MAP will be a negative value (vacuum). This negative value integrated over the volume of the plenum will cause a volumetric vacuum great enough to absorb the volumetric pressure of the returning wave such that it cannot compete with the velocity of the incoming air.

Quite hard to explain, but there is the most comprehensive readable version I can think of just at the moment.

Oh, and as for pressure waves, theres a really complex subject. Took me until the third year into my degree to begin to understand wave theory, and there is so much that I still dont understand about it. water waves is the best way to begin to understand waves, as you can see that... see what happens when you drop a rock in a pond and put an object in the wave's path... can be quite interesting.

Cheers, Owen

[Ben Wilson]

That hurts takai,i hate fuel at those times.!
amazing how much fuel is outside the intake at times, I remmeber doing a non crossflow nissan egine on the dyno with SU's and smelling fuel eveywere after power runs and seeing the fuel mist back out of the intakes of the SU's with hot exhaust just below it and there i was with an airflow meter checking the carbies on the dyno! hahaha

There's a good article in the latest Race magazine about injector placement etc which covers a lot of this sort of stuff...

[takai]

There's a good article in the latest Race magazine about injector placement etc which covers a lot of this sort of stuff...

QFT. It is a very good article. Heck its a good magazine all round.

[jezza323]

But back to rivers question as to why doesnt the pressure wave cause air to flow out the throttle body:
to answer, we look at the MAP at the point when the pressure wave is coming back. Unless you are on boost or at WOT, then MAP will be a negative value (vacuum). This negative value integrated over the volume of the plenum will cause a volumetric vacuum great enough to absorb the volumetric pressure of the returning wave such that it cannot compete with the velocity of the incoming air.

extremely simple version

BIG vacuum in plenum, small higher than vacuum pressure wave trying to come out of plenum, not enough to overcome big vacuum

[kingmick]

There's a good article in the latest Race magazine about injector placement etc which covers a lot of this sort of stuff...

Race engineering?

[Ben Wilson]

Nah - It's an Australian magazine.

Go to www.performanceforums.com and look for a post in general by Nero about the latest issue.

[oldcorollas]

So i cant just say "intresting read" like most people i have to give information?
Things seem to be going fine,so i see no need to add any practical knowlege.
Yes i am very busy at the moment so dont have time to sit and write and essay on it.
I am sure you will never bring my kids into it again, I can tell you im showing restraint.

since when have you EVER used the term "internet knowledge" without seriously taking the piss..
ie "all those people on toymods just learn internet knowledge, and have no idea about the real world" (paraphrased). given your usual tone of posts, and your distinct disdain for the level of knowledge here, and the FI comment (eg, i like those cars with wheels and a steering wheel )
it seems you hardly ever have the time to add any practical knowledge? your practical knowledge would be very welcome, and i for one would love to see you make a more practical contribution about the theories discussed here, rather than your usual comment of "i know, but i won't tell" . your experience being involved and watching "race car prep" means you have knowledge of the practical application of the theories, and i am sure many people would like to hear your angle and interpretations.
heh heh, i can tell how pissed off you must be... your spelling and grammar are almost perfect
and yes, i was having a light hearted joke (as i usually do with you.. you know it's not serious)

" ridiculous oversimplification, but the concept is sound." that is the best way to explain it to young people as they learn.
No point jumping to most avanced point without learning the steps on the way.

ok.. so you think we are all young people, and that is the ultra basic way to explain it (althought i would have phrased it as, "when valve opens, a negative pressure (relative to average) goes up the runner, and is reflected as a positive pressure pulse, which you time to hit the open valve as it is closing, giving a final shove to the air going in)

i would LOVE to hear your advanced theories. i would highly appreciate if you would take the time, and type out a response bit by bit between taking care of kids (a handful i can only imagine ) and explain why the normal theories of reflection of pressure wave, combined with port velocity, are only a basic starting point. yes there is a lot of experimentation required in terms of shape and length of bellmouths etc to actually achieve the harmonics and the best compromise of port velocity, but why is the theory incorrect?


edit:
and for Race magazine, they are not always at stands, due to lowish circulation, but here is the thread
http://www.performanceforums.com/for...php?t=67207338
adn current cover (if you can view it? pdf link)
http://www.performanceforums.com/for...6&d=1158062652
not super detailed, but as a magazine, it is accessible and covers ground that is of interest to people with a technical slant, as opposed to bling

[Big rob]

^^^^^^^^^^^^^^^^^^^^ I agree, i didnt know if you were taking the piss, being serious or an asshole. So please enlighten us KM!

[kingmick]

For internet knowlege it was an intresting read as i said. Not much like it on the internet i wouldnt imagine so it is good internet knowledge.
I will add when i feel the need, i think it is going along nicely with some good inputs and as i said i am very busy at present, so when i get the time i will add if i think its needed, but as far as i can see its going along very well, just my opinion of course.
I always thought it was better to have some than none, but thats just me.

[Big rob]

Yeah this is true, but that is only the case with a reasonable argument behind it.
Anyway I agree there is very little information around on this topic, I personally have only started getting some understanding on it through 2nd year mech fluids class. At the moment I am looking at doing much more research through our SAE team. I've been playing around with this program called RICARDO, which esentially is an engine modeling/optomising program. Thinking about modeling our head and intake/exhast maniolds to increase thermal efficiency and provide better tourque for our application.

Anyway KM you race sports sedan so you must be doing something right ! Are you going to be racing down at Phillip Island in October?