Quote:
Originally Posted by dmac257
I am trying to understand this as it applies to more than just the SOUL. You seem to be saying two different things:
1) If you modify the intake and exhaust to ALLOW more air flow this doesn't actually PULL more air does it? Air flow is a function of engine RPM right? Are the "flat spots of acceleration" due to air flow restriction?
2) After the mods will you be able to use less throttle at lower speeds also or does the increased AVAILABLE air flow only help when at higher RPM than most FE driving calls for??
Don
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It depends on the how/why the intake was designed. There are many different reasons why air intakes have ribs/ tubed chambers/ large chambers, etc. Sometimes its to mellow out the noise of the engine. Sometimes it is to provide better throttle response.
And yes modifying the intake will increase the amount of air the engine actually pulls. There are realistic limits as to how much air you can suck through a hole without generating more turbulence within the pipe. By opening up the smallest "diameter" of the intake and exhausts you can change physical amount of air that can be pulled by the motor. You can also effect this by length of the intake piping, number of turns, types of baffles, etc.
Think of it like a vacuum cleaner. Consider the motor of the vacuum to be a constant. If you hooked a dryer vent onto your normal household vacuum cleaner, how well would it pull up dirt from your carpet? not very well..
Now switch to something like a 1/2" radiator hose. You'll have a higher PSI vacuum on the 1/2" hose than the dryer vent, but It would also be very ineffective because the motor could be fighting itself to pull more air though the small 1/2" hose.
Now consider the regular hose. Neither the dryer vent or the 1/2" hose would work as well as the normal 1" or 1-1/4" vacuum tube your vacuum came with. There is a peak operating diameter for the hose to get the most pull/area without losing the vacuum like the dryer vent and restricting the motor with the 1/2" hose.
A car works the very same way...except that the motor has variable speeds (and thus volumes of air flow). So one type of air intake may work better for lower RPMS when you achieve the best fuel economy, while one style of give you the most power in the higher RPMS, which when you're ecomodding will
NOT help fuel economy!
Maybe that clears some of it up.
As for the "flat spots" have you ever been climbing a hill (in your car, on a paved road...) and notice that even with increase the throttle the car simple does not accelerate any more? Or in case of an automatic it simply down shifts to jumps to a higher rpm. Thats the flat spotting i'm referencing. If the Soul has flat spots in the acceleration it may benefit from an after market intake or exhaust. The flat spot is a key indication that the motor has been restricted by factory design. This may be to keep down noise, provide back pressure which effects valve train, sometimes there are restrictions just by fault of the design (Fault of design example: the 2.0L (first generation 85-88 Chevy Cavalier had a 4-1 header from factory, it was a straight bar that had a T shape, so by design it had a faulty flow, later corrected for a cast iron, true 4-1 design which provided an additional 5-10 hp to the 2.0L and 2.2L engines).
