Intake design part 1: Pressure resonance in the plenum with forced induction???
07-09-2005, 05:19 PM
#1
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Intake design part 1: Pressure resonance in the plenum with forced induction???
This is part of the intake design project. For those that are unsure, pressure waves are created by the piston as it moves up and down. On the intake stroke, there is a negative pressure wave which travels back to the plenum and reflects off it making a positive wave. These waves may also come from the exhaust scavenging and from the intake valves closing. So, I can see perfectly how this would happen on an NA, as there is little pressure in the plenum to influence the resonance. But in a forced induction environment, it seems A) the waves may be (I guess) overcome by the incoming pressure from the turbo or B) the waves are huge! I am tending towards A as the force of the resonance would be less than the force from the turbo. The idea of this being when considering intake design, that the pressure waves may reverb x number of times at a given speed and arrive at the intake valve just before it closes, more air is rammed in. I have a forumla which is indicating a circa 9 inch runner length with a diameter of 1.9 inches. (based of pressure wave speed of 1250 ft/sec), 2.5 displacement, VE of 75%, 228 degrees of intake duration, desired rpm tune traget of 6,500rpm. And most importantly 5 reflective waves. This seems high, but any less (which would be more intense), and the runner length gets too big (potentially 11.5 inches at 4 reflective waves). A more angular runner may make 11.5 inches possible yet... I have not go the that stage yet.
So why ask this? Well, the JME and SFR intake design have an angled plenum, this would mean that the pressure waves would not reflect back to the intake valve, but rather skewed to either side (for the most part). Maybe a stator / diffuser would overcome this if the pressure wave theory holds true in a forced induction environment? Mostly I see plenumns with a rounded shape where the wave would reflect also... Giving the same effect as an angled plenum possibly would.
Ideas anyone?
So why ask this? Well, the JME and SFR intake design have an angled plenum, this would mean that the pressure waves would not reflect back to the intake valve, but rather skewed to either side (for the most part). Maybe a stator / diffuser would overcome this if the pressure wave theory holds true in a forced induction environment? Mostly I see plenumns with a rounded shape where the wave would reflect also... Giving the same effect as an angled plenum possibly would.
Ideas anyone?
07-09-2005, 06:33 PM
#3
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Originally Posted by special tool
NZ - below is a section draft of my preliminary plenum design. What do you think?
07-09-2005, 07:20 PM
#6
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Originally Posted by jimbo1111
That BLOW'S my Theory.
What was your theory Jimbo?
EDIT: Oh it was a joke. I didnt get it, its Sunday morning, my bad.
07-09-2005, 08:19 PM
#7
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I always assumed (for no good reason whatever now that I think about it), that SFR and JME had a tapered intake to even the flow between the runners. Those intakes are fed on one end like the stock intake. Lindsey, on the other hand, feeds the intake in its middle and has a symetrical shape. As I said, this may be off base... just wild speculation. There must be books and hard engineering geekery about this out there somewhere.
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07-09-2005, 08:26 PM
#8
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I need to learn CFD is program a simulator. Cant be that hard surely.
Keep in mind the JME intake is twin chamber... I want to keep this kind of design in mind. I emailed John to ask if he minded if I use the concept in my design, I didnt get a reply sadly. I believe this is best as the flow to the intake valves is as straight as possible, the radical angles in the LR design would make the number 1 and 4 flow a lot less than the 2 and 3. When tuning off a single collective O2 sensor, that means a couple of cylinders will be way out of tune.
Keep in mind the JME intake is twin chamber... I want to keep this kind of design in mind. I emailed John to ask if he minded if I use the concept in my design, I didnt get a reply sadly. I believe this is best as the flow to the intake valves is as straight as possible, the radical angles in the LR design would make the number 1 and 4 flow a lot less than the 2 and 3. When tuning off a single collective O2 sensor, that means a couple of cylinders will be way out of tune.
07-09-2005, 09:14 PM
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Originally Posted by special tool
NZ - below is a section draft of my preliminary plenum design. What do you think?
Design looks a little small. Is that actual size?
07-10-2005, 12:01 AM
#14
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Ah my thread is struggling of content here! lol
Testes, can you do me a favour? On the LR headlight duct thread I have a pic of my car with the cover on, which is taken further back so you can see the whole front, could you please recolour the cover to match the body colour so I can see wat it will look like? Its red at the moment... thats ho bag!
Testes, can you do me a favour? On the LR headlight duct thread I have a pic of my car with the cover on, which is taken further back so you can see the whole front, could you please recolour the cover to match the body colour so I can see wat it will look like? Its red at the moment... thats ho bag!