Nice analogy. One thing to remember is that the baloon is a closed basically air-tight system. Now while air flows into the intake its really a closed system all the way to the backside of the valves. It will take some time, but 5lb in the charge pipe is basically 5lb in the intake plenum..and when the valves open it tries to fill the chamber with 5lb. Sjs was right on that you have to take efficiency into effect..obviously 5.00lb in the charge pipe does NOT mean there is 5.00lb in the combustion chamber..but i think everyone gets the picture. Here is my current idea for sjs's problem...5psi in the intake 'circuit' while none is flowing to the map...when you let off the throttle, the throttle plate closes causeing air to stop flowing.(never replied weather you had a bov or not) If it does blow off, it effectivily blows the pressure out of the current intake loop (including map line)...so the selenoid re-opens...when you mash the throttle, the 5PSI is already there and rushes the air in back in the manifold..the second it takes your selenoid to switch again you already have boost in your manifold ->lean... i think that's my best guess now. hrm.
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Basch SC dyno question
- Thread starter Khuang
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Nice analogy. One thing to remember is that the baloon is a closed basically air-tight system. Now while air flows into the intake its really a closed system all the way to the backside of the valves. It will take some time, but 5lb in the charge pipe is basically 5lb in the intake plenum..and when the valves open it tries to fill the chamber with 5lb. Sjs was right on that you have to take efficiency into effect..obviously 5.00lb in the charge pipe does NOT mean there is 5.00lb in the combustion chamber..but i think everyone gets the picture. Here is my current idea for sjs's problem...5psi in the intake 'circuit' while none is flowing to the map...when you let off the throttle, the throttle plate closes causeing air to stop flowing.(never replied weather you had a bov or not) If it does blow off, it effectivily blows the pressure out of the current intake loop (including map line)...so the selenoid re-opens...when you mash the throttle, the 5PSI is already there and rushes the air in back in the manifold..the second it takes your selenoid to switch again you already have boost in your manifold ->lean... i think that's my best guess now. hrm.
That was a good explanation of what my early vague assumptions were about the problems but improved on in terms of built up pressure in the system between shifts. The bov, such that it is, probably is not serving the purpose as described. It is a rather crude spring loaded device hanging about where you would expect, but I was told would not come into play under normal circumstances. Good thing, because it seems to like to freeze up. On these Aerodynes the boost is adjusted at the turbo, changing the amount of pitch on the variable vane turbos. (I think) For that reason, and since their maximum capacity on this car is only around 8psi, the bov is not expected to do much if anything. However, the question of what happens in that split second after the throttle plate closes and before the turbos relax is a good one. (I can almost here them popping and the flames spewing from the exhaust of tubos during an IMSA enduro and night) I’m a bit ashamed to say that I haven’t put enough time and effort into this to reason it all out. The days just seem to get shorter all the time.
Ooops, didn’t mean to hijack another thread.
[This message has been edited by sjs (edited 26 March 2002).]
Closing in on it.
If you ask a good turbo tuner what an X psi of boost increase will give you, they will tell you the question is meaningless. CFM (really mass) is what matters. The amount of mass of air you are moving into a motor determines the hp you can produce. If the intake system is operating efficiently, you may be moving more CFM of air than is indicated by a straight ratio of psi to psi (pressure delta). You can move all sorts of different amounts of air through a given volume and have a wide range of pressures, depending on how effeciently it is moving through that volume.
Last night I saw two 1.8L cars with the same engine management, both running 18 psi of boost and both witth the same A/F ratios. There was a 25-30 hp difference at the wheels because one had a better intake and valve train than the other. Same boost. Different CFM (volume of air) being used.
How do we make hp? Volume! Volume! Volume!
I think the blower is moving more air, more efficiently than the psi delta indicates. If the NSX intake system is well designed, this is not at all unlikely.
If you ask a good turbo tuner what an X psi of boost increase will give you, they will tell you the question is meaningless. CFM (really mass) is what matters. The amount of mass of air you are moving into a motor determines the hp you can produce. If the intake system is operating efficiently, you may be moving more CFM of air than is indicated by a straight ratio of psi to psi (pressure delta). You can move all sorts of different amounts of air through a given volume and have a wide range of pressures, depending on how effeciently it is moving through that volume.
Last night I saw two 1.8L cars with the same engine management, both running 18 psi of boost and both witth the same A/F ratios. There was a 25-30 hp difference at the wheels because one had a better intake and valve train than the other. Same boost. Different CFM (volume of air) being used.
How do we make hp? Volume! Volume! Volume!
I think the blower is moving more air, more efficiently than the psi delta indicates. If the NSX intake system is well designed, this is not at all unlikely.
A more effecient compessor wheel will do this as well. Larger Turbo's throw more lbs per min that smaller ones!
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