I think that any hp gain is marginal. You might not think that your air filter would get dirtier quicker since the air box lid has a wide open scoop anyway... but it does. And a dirty air filter would take away any hp gain. There are other ways to get more air flow... The filter itself... If you look at the cage inside, you'll see how restrictive it is. A UNI filter is not much $$ and flows more air than stock. Or, you can open up the stock cage a bit to allow more air... enlarge as many holes as you can with a drill... But make sure you don't weaken the cage too much.