Intake design part 1: Pressure resonance in the plenum with forced induction???
07-10-2005, 05:33 PM
#31
Three Wheelin'
The larger the radius, the better it will be. Obviously, you begin to run into decreasing returns though. If you can make/buy/fit a bell with a full tube radius, that should work great. 1/2 tube radius is where the flow starts dropping off more significantly.
For the bellmouths, you MIGHT be able to buy some tubing donuts with an ID equal to your tubing ID, and cut them in half like they were a bagel...
You'd get two per donut. Or you could try just pressing your own, but that might be a huge PITA.
For the bellmouths, you MIGHT be able to buy some tubing donuts with an ID equal to your tubing ID, and cut them in half like they were a bagel...
You'd get two per donut. Or you could try just pressing your own, but that might be a huge PITA.
07-10-2005, 05:36 PM
#32
Three Wheelin'
Eh, scratch that tubing donut idea. The bell radius will likely be larger than the runner radius for those. Unless theres some huge selection of them out there.
07-10-2005, 05:44 PM
#33
Three Wheelin'
Click here, scroll most of the way down...
If someone has a full Autospeed subscription, can you find/quote the rest of that story for all of us? $1.84 (AUS) each is pretty darn cheap.
If someone has a full Autospeed subscription, can you find/quote the rest of that story for all of us? $1.84 (AUS) each is pretty darn cheap.
07-10-2005, 05:49 PM
#34
Three Wheelin'
One more link...
Much more expensive, but appears to be much higher quality. Possibly even weld-able to the rest of an all Aluminum manifold.
Too bad they'd be hidden inside the plenum. Although you could try to have a window built in, out of some lexan or something. That would be pretty sweet, until it got coated with oil/fuel vapors, or cracked/burst from the heat and pressure.
Much more expensive, but appears to be much higher quality. Possibly even weld-able to the rest of an all Aluminum manifold.
Too bad they'd be hidden inside the plenum. Although you could try to have a window built in, out of some lexan or something. That would be pretty sweet, until it got coated with oil/fuel vapors, or cracked/burst from the heat and pressure.
07-10-2005, 06:17 PM
#36
Rennlist Member
Have you looked at the plenum on the 928 GTS engine? It's dual length plenum creates an amazingly flat torque curve and doesn't do too bad on power either.
The 5 liter stock 928 GT put down 325 rwhp, the amazing part was the torque curve. Started at 275 ftlbs at 2000 rpm peaked at 298 ftlbs at 5600 rpm then ony dropped to 285 ftlbs at 6400 rpm red line. Not too bad for a naturally aspirated stock 3 liter.
You could use the rpm based output switch of one of the boost controllers to operate the flappy valve that changes the intake runner length. The change over is at around 4000 rpm.
Thought it would be interesting since it is two 944 engines slapped together at the crank.
The 5 liter stock 928 GT put down 325 rwhp, the amazing part was the torque curve. Started at 275 ftlbs at 2000 rpm peaked at 298 ftlbs at 5600 rpm then ony dropped to 285 ftlbs at 6400 rpm red line. Not too bad for a naturally aspirated stock 3 liter.
You could use the rpm based output switch of one of the boost controllers to operate the flappy valve that changes the intake runner length. The change over is at around 4000 rpm.
Thought it would be interesting since it is two 944 engines slapped together at the crank.
07-10-2005, 06:25 PM
#37
Race Director
Thread Starter
Rich, no I have not even seen one that I recall to be honest! Do you have pics handy? It would not be the cheapest option, but may be cool to use Porsche parts in the design, providing they allow the GT to fit under it.
07-11-2005, 04:43 AM
#38
Race Director
Thread Starter
Whoa these kicks *** for selection... v stacks.
http://www.velocity-of-sound.com/commerce/search/index.php3?merchant_id=2107&keywords=&search_type=ANY&custom_store_categ ory=8&by_category=+++GO!++
http://www.velocity-of-sound.com/commerce/search/index.php3?merchant_id=2107&keywords=&search_type=ANY&custom_store_categ ory=8&by_category=+++GO!++
07-11-2005, 02:59 PM
#39
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I posted my own topic related to this one and am still looking for answers.
If instead of dual runners, you had a dual plenum, as seen in the Audi Rally cars and offered for the new Audi cars, how well would this work?
Basically I am saying, you use some long runners, even the stock ones connected to velocity stacks inside a large plenum, this plenum joined to a smaller plenum. The Smaller plenum has the TB on it. The two are welded together. The connection between the two is a 30mm wide full length slit running the length of the two. The Smaller one would be tappered. Ideally if I you are doing your own runners, you could do an ever so slight tapper from the velocity stack to the Head.
Doesn't "Maximum Boost" suggests venturi-style runners?
For a better idea of what I am talking about on the dual plenum here:
http://www.bufkinengineering.com/intake%20manifolds.htm
I am talking about getting the pressure uniform over the runners in a boosted engine.
The Dual plenum works as a type of diffuser to equalize the pressure.
So I see a smaller plenum, ahead of the main one holding the entry for the runners with some nice length in runners. You could give up some runner length since its boosted. But I don’t believe you would have to, you could use something like a combo between a U and an S laying on its side. Runners come off the head and drop down then come up to larger plenum or something like stock runners connecting to a larger plenum, then stick a smaller plenum next to the larger (under runners, etc… where it will fit) both are joined.
Design a slit with consideration to turbulence > than the throttle body to avoid pressure drops across that segment and letting the TB still be the thing that controls the amount of air entering the main plenum.
Bbasically two plenums welded together One atop the other.
http://www.924board.org/viewtopic.ph...r=asc&start=15
I get some of this, but some of it is lost on me, I seek to understand and try something like this especially if I end up boosting my 924S. Of course some of this seems like it would help an NA as well.
If instead of dual runners, you had a dual plenum, as seen in the Audi Rally cars and offered for the new Audi cars, how well would this work?
Basically I am saying, you use some long runners, even the stock ones connected to velocity stacks inside a large plenum, this plenum joined to a smaller plenum. The Smaller plenum has the TB on it. The two are welded together. The connection between the two is a 30mm wide full length slit running the length of the two. The Smaller one would be tappered. Ideally if I you are doing your own runners, you could do an ever so slight tapper from the velocity stack to the Head.
Doesn't "Maximum Boost" suggests venturi-style runners?
For a better idea of what I am talking about on the dual plenum here:
http://www.bufkinengineering.com/intake%20manifolds.htm
I am talking about getting the pressure uniform over the runners in a boosted engine.
The Dual plenum works as a type of diffuser to equalize the pressure.
So I see a smaller plenum, ahead of the main one holding the entry for the runners with some nice length in runners. You could give up some runner length since its boosted. But I don’t believe you would have to, you could use something like a combo between a U and an S laying on its side. Runners come off the head and drop down then come up to larger plenum or something like stock runners connecting to a larger plenum, then stick a smaller plenum next to the larger (under runners, etc… where it will fit) both are joined.
Design a slit with consideration to turbulence > than the throttle body to avoid pressure drops across that segment and letting the TB still be the thing that controls the amount of air entering the main plenum.
Bbasically two plenums welded together One atop the other.
http://www.924board.org/viewtopic.ph...r=asc&start=15
I get some of this, but some of it is lost on me, I seek to understand and try something like this especially if I end up boosting my 924S. Of course some of this seems like it would help an NA as well.
07-11-2005, 03:27 PM
#40
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This is making me wonder about something else more pertinant to 16v engines. . .
Is it possible (or done) to slightly offset the opening & closing time & duration of the two intake valves in a 16v setup? By opening one valve slightly earlier and closing the other slightly later you'd dampen out some of the pulses caused by the air charge slamming into a closed valve, particularly at a constant RPM which would cause a harmonic (or could) pattern. . .
Just a thought. Dunno that much about the 16v setups but it seems like if you have two cams, there's really no reason they have to be identical - in fact it might be better if they're not.
Is it possible (or done) to slightly offset the opening & closing time & duration of the two intake valves in a 16v setup? By opening one valve slightly earlier and closing the other slightly later you'd dampen out some of the pulses caused by the air charge slamming into a closed valve, particularly at a constant RPM which would cause a harmonic (or could) pattern. . .
Just a thought. Dunno that much about the 16v setups but it seems like if you have two cams, there's really no reason they have to be identical - in fact it might be better if they're not.
07-11-2005, 04:21 PM
#42
Race Director
Thread Starter
As for the dual plenum, I think a properly designed and runner flow tested plenum will be fine, and MUCH less complicated to make.
Chris, do you have consensus with the plenum shape point? I.e. can be at an angle and wont effect pressure reflection waves?
Chris, do you have consensus with the plenum shape point? I.e. can be at an angle and wont effect pressure reflection waves?
07-11-2005, 04:35 PM
#43
Three Wheelin'
NZ, just to summarize all the stuff I posted yesterday...
Runner tuning is bounded by the runner to plenum sudden expansion (and the valve, at the other end). Sudden expansion is known as an "open" boundary condition in duct acoustics. The shape of the wall of the plenum opposite this opening has ZERO effect on whats going on here. Try not to think of whats happening as being analogous to billiard *****.. ie angle of incidence/refraction. We're talking about pressure waves, so the only geometry we care about is duct cross sectional area and length.
Runner tuning is bounded by the runner to plenum sudden expansion (and the valve, at the other end). Sudden expansion is known as an "open" boundary condition in duct acoustics. The shape of the wall of the plenum opposite this opening has ZERO effect on whats going on here. Try not to think of whats happening as being analogous to billiard *****.. ie angle of incidence/refraction. We're talking about pressure waves, so the only geometry we care about is duct cross sectional area and length.
07-11-2005, 04:40 PM
#44
Three Wheelin'
PS to that post above... the opposite wall on the plenum WILL begin to affect the runner acoustics if its too close. The minimum distance from the runner opening to the opposite wall should be approximately 2 times the diameter of the runner or more.
07-11-2005, 04:50 PM
#45
Race Director
Thread Starter
Originally Posted by DanG
PS to that post above... the opposite wall on the plenum WILL begin to affect the runner acoustics if its too close. The minimum distance from the runner opening to the opposite wall should be approximately 2 times the diameter of the runner or more.
Ok, I think I am getting the pressure thing better now... its good news really!