40 hp increase solely due to an air filter change? Holy cow!
If 40 brake HP could be gained by a aircleaner GM would be glad to slap one on
Same thing by taking off a stock X pipe and replacing with another type costing $300 plus ( mine built for $40) , as it is most X-pipes are in the wrong place and only help change the sound where
correct placement ( closest to engine) would allow better exhaust pulses to clean out cylinders for next firing of the cylinder
Game played is tune the PCM then claim the aircleaner was the cause and use bogus chassis dyno results.
Though I like those with "Seat of the pants" they swear to test results
How interesting the same aircleaner, stock CAI and X pipe are used for the supercharged Z06 but somehow same parts are restricting LT1 performance
Add custom tuning LT4 raises HP to close to 700 HP so stock parts are just fine.
OP should just go back to that dyno shop and have them redo the runs correctly with verify the dyno is calibrated and correct for weather and elevation using the correct tranny gear
and PCM set for sport/performance mode.
I teach a performance tuning class at a college, using $100,000 new Mustang load bearing dyno that can support up to 2,000 HP and very seldom can one student properly setup the dyno and correction values
