Originally Posted by Hobbymanbill
Well it is kind of silly, its the throttle body. I mean really the limiting factor is the size of the throat feeding the intake manifold, be it a carb or whatever restriction there is.Ultimately of course it is simply the ability of the pump (engine) to inhale and exhale. The more air/fuel mixture you move through the pump, the more power you make. Anything that restricts throughput limits HP. That's the reason most 4 stroke engines don't show much gain when doing intake stuff, the ones that do have either very restrictive air cleaners or have had changes (cams, headers, etc) which require a better intake. Remember naturally aspirated means operating at 1 atmosphere so whatever gravity gives you is all you get. Thats why nitrous and turbo's and superchargers give such impressive gains because they are stuffing the pump!
Maybe this is what has me most confused - I'm not sure what the theory is (we're still debating whether intakes work or not, so I'm calling it a theory, but that doesn't mean I'm dismissing the concept - just finding an acceptable middle ground) - is the question that an intake will increase performance due to more throughput, or because it is re-routed to a position within the engine that receives cooler (therefore denser) air? Personally, I don't think that we could really squeeze much performance out of an XFire based solely on increasing the breathing of the engine; it is true that our intake's are somewhat cramped and restrictive - however, I believe that increasing the throughput would have the counter-action of increasing the ambient temperature near the engine (the increased oxygen levels would mean a hotter, purer fuel burn), meaning we'd be pulling in more air by volume, but the density of that air would be less because of the heat...of course, I'm not saying this is what WILL happen, just making a prediction based on my limited knowledge. My understanding of fluid dynamics tells me that if increasing the throughput of the engine would increase HP, then so would those spiral-max things; the "swirled" air would create pressure imbalances similar to the forces which create lift on an airplane wing, accelerating the air down from the spiral-max into the engine. However, from what I've been told, the effect of these SpiralMax devices is so minimal as to be negligible. I don't think that simply providing a bigger opening would provide more air than the spiral max thingie would, since the spiralmax dealie-o also has the added advantage of creating a miniature ram-air effect as previously un-impeded air is now being both sucked through what is basically a smaller opening (the SpiralMax sits in the intake path).
Having said I'll that, I'll be honest and admit I really don't know what I'm talking about
I could be forgetting (or not even aware of) some other variable, and it's always a possibility my understanding of fluid dynamics (which I think is mostly what this thread is about) is off.
There's my $0.02
P.S. - Bullseye, out of curiosity why would you prefer the RSX over the xfire? I certainly respect everyone's opinion, but I can't think of a single attribute about the RSX I like more than the XFire - looks, power, RWD, warranty, craftsmanship (I really like the Mercedes feel of the car)...just interested in hearing another view.