Independent Throttle Bodies
03-23-2004, 01:27 PM
#21
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Originally Posted by Kenku' date='Mar 23 2004, 11:06 AM
An interesting note though is something I saw at the SAE World Congress; Opel had one of their V8 touring car race motors there. It was using 1 throttle body per cylinder *AND* a plenum for each bank of 4. Best of both worlds?
J
03-23-2004, 02:10 PM
#22
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If you try and get a plenum to resonate at above 3000RPM then it becomes impractically small to get a good shot at the runners. Witness the fuel distribution problems many v8 manifolds have. Drag racing is often odd, because of the rules that you have to run. Dunno if that is why tunnel rams are popular as I've not yet seen evidence that they are good at high RPM.
Have a look at www.bgsoflex.com/auto.html and click on the intake resonance calculator. I've compared the results of this to dyno runs and the correlation is very good. This is on a 1.6litre 4 pot pumping out 208BHP at 8000RPM (that's flywheel BHP calculated from coast down tests on calibrated rollers, so about 220 dynojet wheel HP). Its a street car during the week.
Being pedantic, if you have a tuned volume before the butterflies, its an airbox, after the butterflies its a plenum.
I've looked at the theories and they all show that the resonances due to runner length are far stronger than those due to a helmholtz resonance in the airbox/plenum. Now I come from a county where IR is the norm for a performance application so am biased. I also think real cars should have the intake trumpets poking out the bonnet. An air box then can be used to fill in the low end and you have your cake and eat it
Bill
Have a look at www.bgsoflex.com/auto.html and click on the intake resonance calculator. I've compared the results of this to dyno runs and the correlation is very good. This is on a 1.6litre 4 pot pumping out 208BHP at 8000RPM (that's flywheel BHP calculated from coast down tests on calibrated rollers, so about 220 dynojet wheel HP). Its a street car during the week.
Being pedantic, if you have a tuned volume before the butterflies, its an airbox, after the butterflies its a plenum.
I've looked at the theories and they all show that the resonances due to runner length are far stronger than those due to a helmholtz resonance in the airbox/plenum. Now I come from a county where IR is the norm for a performance application so am biased. I also think real cars should have the intake trumpets poking out the bonnet. An air box then can be used to fill in the low end and you have your cake and eat it
Bill
03-23-2004, 03:49 PM
#23
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Originally Posted by DJ Rotor' date='Mar 23 2004, 11:27 AM
The Skyline GT-R engine is the same way. A big plenum feeding the ITBs. I believe the Pulsar GTi-R uses this system as well.
J
J
03-23-2004, 08:57 PM
#24
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Originally Posted by bill shurvinton' date='Mar 23 2004, 04:10 PM
I've looked at the theories and they all show that the resonances due to runner length are far stronger than those due to a helmholtz resonance in the airbox/plenum. Now I come from a county where IR is the norm for a performance application so am biased. I also think real cars should have the intake trumpets poking out the bonnet. An air box then can be used to fill in the low end and you have your cake and eat it
Bill
Bill
03-24-2004, 08:25 AM
#27
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I have to wonder how much good pulse tuning a rotary intake is going to do. Evidently it does work to some extent otherwise the 787B wouldn't have used the variable length runners. But since a rotary draws air all the time, as opposed to a boinger which only draws air about a third of the time at most, it will not get anywhere near as strong pulses in the intake as a boinger will.
03-24-2004, 09:12 AM
#28
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Not quite, you still get a pressure event from inlet open and inlet close. However compared to a piston engine you are tuning to different reflections. In piston circles you tune off the inlet closing, which then gives 450 or more degrees for the pulse to fly up and down the runner one or more times. The rotary does not allow this so you only have the 330 or so degrees that the inlet is open and cannot have multiple reflections (you can but they don't seem to help much).
So the resonances that you have to tune with are:
Relection caused by inlet opening (negative pulse heads up inlet, reflects at bellmouth to postive pulse and heads back) in same cycle
Above coming back in NEXT cycle
Helmholtz resonance due to runner/rotor combination
Exhaust scavenging pulse.
Some of these will help you, some will hinder, depending upon the set of compromises you are tuning fo
So the resonances that you have to tune with are:
Relection caused by inlet opening (negative pulse heads up inlet, reflects at bellmouth to postive pulse and heads back) in same cycle
Above coming back in NEXT cycle
Helmholtz resonance due to runner/rotor combination
Exhaust scavenging pulse.
Some of these will help you, some will hinder, depending upon the set of compromises you are tuning fo
03-24-2004, 09:58 AM
#29
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Originally Posted by DJ Rotor' date='Mar 24 2004, 10:25 AM
I have to wonder how much good pulse tuning a rotary intake is going to do. Evidently it does work to some extent otherwise the 787B wouldn't have used the variable length runners. But since a rotary draws air all the time, as opposed to a boinger which only draws air about a third of the time at most, it will not get anywhere near as strong pulses in the intake as a boinger will.