New mods for my Gen II / 2008 Touring

Keep an eye on the cleanliness of your engine oil with the K&N. I used one on the truck for a while but it sure seemed like the engine oil was getting dirty faster. I've also heard of the oil in the K&N getting onto the MAF sensor and causing problems. Nothing but OEM-style air filters for me now.

 

"I've also heard of the oil in the K&N getting onto the MAF sensor and causing problems."
This is more of an issue with Classic, since with that car the engine air filter sits directly on top of the throttle body, making it is easy for excess filter oil to drip down onto the MAF sensor. With the 2G air filter housing, the air filter is shifted to the side.

 

How much did you pay for the K&N and where at, if you dont mind me asking?

 

Did you know "our automotive OE (original equipment) replacement air filters generally add 1-4 horsepower?" LINK

Did your "improvement" in MPG occur under the same driving conditions, as performed with the previous filter?

• Traffic conditions.
• Road conditions (smooth, rough, dirt, gravel).
• Ambient air temperature.
• Tire pressure.
• Tire condition (tread).
• Alignment.
• Vehicle load (passengers and junk in the trunk).

Over how many tanks of gas was this increase observed? Unless your using a dyno and performing a controlled test, like the EPA, too much subjectivity.

Look at the controlled testing and objective findings, for 9 air filters posted on a Nissan/Infinity forum. LINK

"However, if a filter is using “better airflow” as their marketing tool, remember this….Does it flow better? At very high airflow volumes, probably. BUT, our engines CAN’T flow that much air unless super-modified, so what is the point? The stock filter will flow MORE THAN ENOUGH AIR to give you ALL THE HORSEPOWER the engine has to give. And this remains true until the filter is dirty enough to be recognizeable. At that point performance will decline somewhat. Replace the filter and get on with it."​

The factory engine is a balanced system (a compromise of performance, reliability, and efficiency). Air filter all the way to the exhaust, don't forget the ECU programming. Add a K&N filter, the system is unbalanced. To maximize the potential, additional air flow increase K&N can offer, one would have to change out many other parts; exhaust system for sure, as the stock exhaust is very restrictive compared to a "performance/racing" exhaust systems.

We are driving a Prius. Not a sexy car, nor a fast car, but sexy MPG.

If you did not read the nicoclub link above, here's a graphic teaser:
Filter Efficiency (How well does the filter captures debris.)


Accumulative Gain (Total amount of dirt that passed through the filter.)

So much for the oil theory.

These two graphs speak volumes. If you logically think about K&N's premise: increase Horse Power by increasing air flow. The less restrictive the air filter, the greater the air flow. Unfortunately, more debris will be passing through the air filter (as shown above), into the intake manifold, then into the cylinders. Even if no cars are ever damaged running K&N air filters, is the cost of the filter, filter oil, filter cleaner, and required maintenance of these filters require, worth K&N's claim of 1-4 Horse Power increase?

Most of us are probably changing the air filter prematurely. An interesting report by the EPA on clogged air filters and the impact on MPG, concluded

"Closed-loop control in modern fuel injected vehicle applications is sophisticated enough to keep a clogged air filter from affecting the vehicle fuel economy."​

LINK to the EPA study (2-2009).

The next time you see the K&N reps, show them Arlen Spicer's study and the results that were posted on the Nissan Infinity user group. Would love to hear what they have to say.

Your car, your money. Knowledge is power, and these are some hard facts K&N would need to refute.

 

That would be a good test to perform.

Consider starting the trip w/ full tank of gas, check tire pressure, cleaning throttle and MAF sensor, and use K&N on the "to" leg.
Prior to returning, another full tank of gas, check tire pressure, clean throttle and MAF sensor, and use Stock filter on this"return" leg.
Assuming same roads/freeways will be taken to and from, with same passengers and luggage.
Hopefully driving can be done at same time of day for each leg.
Full tank of gas each way to minimize starting weight differences.
Note mpg upon arrival at destination (ie lodging). Moleage would need to be the same for each leg. Don't include in town destination driving for this MPG determination. You'll have to note if traffic was more or less the same for each leg.

This will be as "controlled," as can be, w/o access to expensive equipment. Do report your findings.

Good luck and drive safely.

 

Too bad it isnt flat both ways. You'll see that same big hill going to Vegas. "To" leg will be short climb up then long descent. Return will be reversed. Not ideal, but the best you can do, unless you know you will be going to LV, again and soon.

You could also try using K&N for one or two months at home, then switch to stock filter for same duration. Hopefully overall mileage used w/ each filter will be as close as possible. Cleaning throttle body and MAF, before beginning test w/ each filter. Also, check air pressure and oil level, regularly, while this test is performed.

Not discounting your feelings of throttle response, but it's subjective, and might be the placebo effect. If two identical Prius (same color and brand new off the assembly line) were in front of you, and the only difference is the air filter (K&N vs OEM air filter), do you think you would be able to tell which Prius has the K&N?

Btw, may you win big, if you gamble.