Throwing sensibility to the...
Throwing sensibility to the wind, we ditched our air filters and hit the dyno.
A racer will do almost anything in search of an advantage over the competition, even if it means risking life, limb and machinery: Everything from removing mufflers and running dangerous gas blends to questionable oil additives and even secretly (against the rulebook) tuning a motor or skipping meals to reduce weight.
Another old trick in the racer’s book is to remove the air filter in hopes of cutting the inlet restriction, thus increasing power. A quick search of the ever resourceful Inter-web revealed that this old trick has stretched far beyond the track as many people are even ditching the filters on their streetbikes. Some claim they “felt” a sizeable increase in power while others noted little to no seat-of-the pants improvements.
Although running without an air filter on the street can be risky (more on that later), we decided it was time to put this old racing folklore to the test on the dyno. Was it worth a few more ponies?
On the dyno
To keep things as scientific as possible, all before-and-after runs were made on the same dyno no more than 5 minutes apart from one another. We also decided to test both a stock Ninja 1000 and a modified Hayabusa in the order of fairness since one bike might respond differently than the next. We’re not saying that all bikes will react the same as these two, but a lot can be gathered from the results.
We rolled the stock Ninja 1000 on the dyno first and made a few pulls with and without an air filter. The big Kawi gained roughly 1 HP from 7500 RPM to the limiter without the air filter in place. Changes in torque were negligible at less than 1 LB-FT.
Next up was a modded ’Busa fitted with an M4 full system. Oftentimes uncorking the inlet side of a bike that already has an open exhaust usually nets larger gains than if it had a stock exhaust. Think about inhaling air through a huge pipe and then having to exhale it through a straw–it’s a bottleneck. Considering that, a bike with an open exhaust was a nice alternative to the stock Ninja. After some before and after pulls the ’Busa netted roughly 2 HP from 6800 RPM to the limiter with a torque increase of less than 1 LB-FT.
Myth: Confirmed. Plausible. Busted
Both bikes did gain minor power without an air filter, but at a huge risk to severe engine damage. Beyond ingesting large road grit, it’s the small debris the human eye can’t easily see that will quickly destroy an engine. Instead of the air filter catching these contaminants they’re free to enter the motor where they will quickly destroy valve seats and even your cylinder bores and rings. Eventually, the motor will begin to leak compression and oil.
Although 2 horsepower for free might sound great, it’s really not free when you consider the cost of an inevitable motor rebuild. However, if you’re a racer in search of every last ounce and refresh your motor several times a season, why not? Otherwise, stick with your stock filter or look to a freer flowing (but still protective) aftermarket replacement.