[darkpuppet]

NOS2Go4Me,May 30 2008, 08:55 AM Wrote:The Cosworth CAI (if you can get it) modifies the overall inside diameter of the MAF housing which in turn changes the amount of air flowing into the engine vs. what the MAF "thinks" is going into the engine. The main reason I went with the FocusSport CAI is because it uses the factory MAF housing tube. The Cosworth relies on a baffle to slow down the air so that the volume being seen by the MAF is roughly what it sees when stock.

I had also heard that the inside diameter of the FIPK from K+N was different than the stock housing, but that's not proven by me nor did I do enough research into it at the time.
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CAI's from AEM and others also do this... because it gets you some horsepower without tuning the engine.

At part throttle, the engine learns out the differences in the tube diameters so the engine runs alright, but at WOT, you hit airflow numbers that the engine hasn't compensated for, and your mixture leans out a tad, which results in a little extra power up high... that's why CAIs that use their own MAF tubes tend to see more HP gains than those that don't.

If you tune for the new MAF diameter, you'll undo most of that difference. However, in the end, a larger diameter tube will make more air available to the engine (intake diameter matched to throttle body diameter would provide the greatest gains).