Mass air meter worth 11rwhp on stock 5.0??

[FivepointOH]

I was always under the impression that changing the stock mass air meter for a bigger one didn't pick up that much hp on a stock 5.0. However in the new 5.0 they put a C&L 76mm mass air meter on a 90lx that had only pullies and a K&N. They gained 11hp and 16lb ft to the rear wheels! I wondered why my friends car with only mass air and pullies and mufflers ran so strong. Anyone else see that big of a jump from just a mass air or is this car just an exception?

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92 AOD GT, K&N, ram air, pulleys, 2 ch. flowmasters, 4:10's, shift kit, 1 5/8 mac longtubes and offroad hpipe 14.249 @ 97.34 mph before the headers and hpipe