u should get about the same hp gains, in a mac or other name brand one ur payin for the name
straight from that link:The name of the company is the main difference. Another difference is the size of the filter itself. Ebay auctions come with a smaller filter than MAC does. Price is also another big factor. eBay auctions sell CAI systems for 50-70 dollars, where as the name brand CAI’s sell it for much, much more.
The smaller filter on eBay CAI auctions will perform just as well as the larger one. Example: If a car uses 650 CFM’s of air to run at peak efficiency, then why would you want an air filter that would filter 2000CFM’s?