Quote:
Originally Posted by Ikendiken
That flap is certainly there to reduce noise.
As far as it being there to control back pressure, you may be right. I am no expert, but I don't know if that's as important in a FI engine.
The way that I understand it, in a NA engine you want to control the sudden release of exhaust gases so that you don't slow it down enough to interfere with the next cycle. If the volume of space the gases have to fill is too large the gas will slow down causing back pressure and a loss of power. This is more likely to occur under low RPM.
However, in a FI engine, the turbo results in a steadier stream of gases from the engine, and since the turbo uses the differential in pressure to produce boost the lower the back pressure the more efficiently the turbo can operate. Thus for a FI engine freer flowing is almost always better.
There was an interesting post here awhile back about this mod and its effect on performance. http://www.xbimmers.com/forums/showthread.php?t=341367 |
Thanks for your thoughts. I believe you are mistaken about how the internal combustion engine works in general and the difference between naturally aspirated and forced induction specifically.
There is no such thing as "steadier stream of gases" with the turbo. To simply put: the air comes in when the intake valve is opened, and after compression and combustion, the byproducts are exited through the exhaust. The only difference with a turbo engine is that the intake air is compressed (higher density) rather than being at atmospheric pressure. With that said, theoretically (from a thermodynamic standpoint) there is no difference between the two as far as how backpressure affects performance.
The problem I see with removing the flap and also other modifications done by casual operators with knowledge gained from internet boards are that the original design intent is not fully understood (even though this is rather minor).
To certain extent, I can empathize because even as a mechanical design engineer, I can't fully understand some features in legacy designs. However, I always give them (the OEM engineers) the benefit of the doubt initially.
This thread, however, appears like an aesthetic issue rather than performance because I don't see a performance nor economical benefit in "upgrading" to a 50i exhaust.