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Originally Posted by TTopJohn  Folks are fond of saying that the throttle is the only restriction that matters, so a freer flowing filter or a less restrictive air intake won't add power or efficiency. But I don't think this is true. |
You are correct. Whoever says that the throttle is the only restriction that matters is an idiot. However, at less than wide throttle, you are leaving power on the table by not having the throttle plate wide open. At nearly every other throttle position (where 99.99999% of driving is done, but not 0-60 or 1/4 mile runs or dyno testing) the throttle is the most restrictive part of the intake. That is the point of the throttle. If it didn't restrict air, your engine would continue to rev uncontollably (the throttle is the control). So, in the overwhelming majority of cases, the air filter is not the most restrictive part of the intake. If you can free up air flow past the throttle body, you can make the engine run more efficient, get more hp and better fuel mileage (and you won't use as much throttle because more air will move for the equivalent throttle position). This happens due to reduced pumping losses. If the engine can move air with less effort, less of the energy from the burned fuel is used pushing pistons and more is sent down the crank shaft.