When I put a blower on my LS2 it didn't perform as expected, but I gained 34hp switching from a stock air box with a Wix paper filter to a Lingenfelter intake with a Green Filter. Sometimes the simple things make a big difference.

 

That's surprising and disappointed. Based on this data, I had hoped Wix was one of the better ones for performance.

https://www.project200.com.au/dm-iso5011/

 

There is a yawning difference between paper filters and cloth or oiled cloth filters when it comes to air flow. That said, I don't like K&N, they flow well but let way too much dirt through. Green Filters are the same concept and actually flow better than K&N but stop a LOT more dirt.

Also, surface area plays a factor. A panel filter in the stock air box has a lot less surface area than the double cone Green Filter I changed to.

The GTO air box is pretty decent for stock or a few bolt ons, but by adding a blower we overwhelmed the possible capacity of the air box design. The stock air box could have been much more effective with a K&N or Green Filter flat panel filter in it, but I decided to replace the whole setup and the blower was much happier for it.

Another interesting tidbit, when we dynoed it the 2nd time with the improved intake and filter, we also tested it with open headers and through the full exhaust. It actually LOST 2hp with open headers. But of course it wasn't specifically tuned with open headers in the mix, but even if it had been the difference between open headers and full exhaust would have been minimal. Car has a Magnaflow 2.5-inch catback in my instance but does also have Kooks high flow cats. I really thought the cats would have been a choke point but I guess they were not. My system does NOT have the Kooks green cats, but their regular catted mids. Green cats are supposed to flow even better but this test seems to indicate that the standard cats are more than enough in my particular instance.