2008 Hyundai Accent Base model from North America - Comments

No air filter can change the ratio between road speed and rpm's. The match between the engine speed and the gear ratio doesn't change regardless of how much or how little air the engine is getting. I wish it were that simple.

My dealership advised me to switch to a K&N air filter to IMPROVE fuel mileage. I've done that on all my vehicles and found a very tiny improvement in power and a very tiny improvement in fuel mileage. Also, after market suppliers are now coming out with tube fittings that allow most cars (I'm not sure about Hyundai) to have cold-air induction systems very easily fabricated for them. I fabricated a short-throw intake system for my 4-cylinder Grand Am and the improvement in performance was amazing. It felt like an additional 15 horsepower. The whole setup cost me less than $50.

My Mustang has an expensive bolt-on system that gave nowhere NEAR the power of the fabricated system. The secret is using a VERY short intake tube and shielding the filter from the engine's heat (use sheet metal and put a sliced-open 1/4" rubber hose around the edges to keep it from cutting you accidentally and to help seal it to the hood padding).

I'd like to see what the actual difference is between stock air filter and the K&N, but the difference seems so minimal that it's impossible in actual driving conditions to have any, 'constant' basis for a test. Too many variables; temperature changes the tire pressure, which affects mileage because of resistance... outside of a constant, controlled environment there's no way to gauge it accurately. This is all really picky, I know, over what might be a mile per gallon (or even less), but I'd like to know if the K&N actually helps or hurts the mpg. There is no question about the gain in power.

I take mileage very seriously and have kept track of the mileage before and after with all my vehicles since I started using K&N filters. At one point my wife and I both owned identical vehicles and it was really easy to see with those. My wife DIDN'T have a K&N filter on hers and I did. In general there was only at best 1/2 mpg difference. I also later added a Flowmaster muffler to mine. This did nothing really noticeable for the mileage, but appeared to give me a tiny edge in power. On hilly areas near our home my wife's required downshifting to maintain the 40mph speed limit while mine could remain in 5th gear (both were 5-speeds).

I do recommend the K&N filters simply because they last forever. That alone can save you the cost of replacing paper filters and offset the higher cost of the K&N. I no longer use Flowmaster mufflers because of the annoying, incessant drone at cruising speed on the highway. There are newer high-performance mufflers that really do boost power, give a great sound taking off and don't deafen you while traveling.