Re: K&N X Stream Air Cleaner Toppers?
Any testing of any "minor" (or low buck, bolt-on, whatever you want to call it) engine modification such as a spacer of any type or height or something like this "extra" filter area done by any of the more reputable publications almost always explains, either in a table or chart or text, exactly how much tuning had to be done and how power/torque output was affected by a given modification.
I did not intend the link to Super Chevy testing the Xtreme lid to be anything remotely definitive... Just to illustrate what you can find with some simple googling.
You can't just throw some simple bolt on at an engine and see significant gains without tuning. Now in the case of something like a plastic spacer, maybe some gains can be seen just because of the spacer's insulation properties (increasing the density of the fuel/air charge, curing a "problem" the user did not know he or she had). But again, most all different bolt-ons get tested by reputable publications and/or websites, and information is out there to find and review.
I have an old drag racing buddy who was great at this. someone he knew would buy some new bolt-on like a carb, or lifters, or headers, just plop stuff on their car, and go slower. He'd buy the parts that didn't "work" cheap, and because he understood how to tune, he'd be out on the track soon after, and things worked.
So, as Dennis pointed out, just because somebody with a Chevelle saw some power gain with that Xtreme lid doesn't mean everybody will.
I personally would not run one. I don't like the look, and intuitively I feel that much filter area and letting air in from sides AND top would affect air velocity and fuel atomization. Clearly you could try to tune/change components to make it work. But...
69 'vert project big block/TKO 600 RR
68 'vert driver RS clone -- gone!