anyone try a open air filter

Till you get a slug of sand in your engine. Then the MPG goes way up since you are running strickly on the battery.

 

I wonder if the OP isn't talking about getting rid of the airbox and going with a cold air type intake that has a filter on the end of a tube?

 

I doubt there would be any measurable benefit and there would be an increase in engine noise in a nice quiet car. Don't let me stop you though. My experience with motorbikes has been a reduction in performance without jetting richer.

 

Your links are missing.

You'll save more fuel by practicing good driving technique and keeping the tires inflated.

 

Unless you spend a lot of time at high engine loads, I doubt you will see much of an economy improvement by reducing the restriction of the intake.

The first thing to do would be to measure the restriction posed by the intake under various engine loads by using a manometer. It could be that the stock intake is already sufficient for the amount of air the engine sucks through the intake.

The air filter design on the Prius is fairly complex. It looks like Toyota went to great lengths to ensure smooth airflow through the mass airflow sensor. It would be pretty easy to mess this up and make it difficult for the ECU to maintain the proper air/fuel ratios.

 

My mistake. It is a reasonable question.

 

driving techniques will get you better millage on a Prius.. Open air (short ram) filters can improve mpg because of better use of air for proper burning (there are also Cold air intakes which have longer tubes and usually point down to the ground to get cooler air in the engine)... however Prius engines run on a different cycle... they are made strictly for economy...

I dont think anyone has tried this and made a detailed review about performance/gas consumption changes... Someone should

 

Again, an open air filter (short ram, cold air, doesn't matter) will not lead to "better use of air for proper burning" and improved mpg.

All modern cars strive for a specific air/fuel ratio to reduce emissions using feedback from multiple oxygen sensors in the exhaust. Because of this feedback loop, the air/fuel ratios will stay the same, except for in cases where the ECU is not monitoring the air/fuel ratio, but on the Prius, it appears to almost always operate in the feedback loop mode.

The only way an open air filter will improve economy is if the intake it's replacing is a significant restriction. The stock intake on the Prius (or any other car) is highly unlikely to be significantly restrictive given the engines measly output. But I haven't measured it using a manometer, so I am just guessing.

 

I put in a drop-in replacement K&N filter a while back and I didn't see a gain or loss in MPG. Anyway, In the air box, there's an additional permanent filter right after the replacement one (blue mesh plastic stuff). Does anybody know why another filter is necessary after the expendable filter?

 

Well, that middle sentence took some analysis. I think what you meant was:
"Taking air through the air filter takes energy, (so) an open air filter is easier for the engine to take air from." You seem to revel in using the wrong homonyms/misspellings and minimal grammar.

As for the content of the statement, you're not intending to increase airflow, but making it easier to supply the air. I've wondered how easy it is to get air thru these filters when I open one up and look at it, but apparently it works pretty well since all cars (that I've seen) use a pretty similar design. What is it that actively pulls the air in?

I remember driving in freezing rain on the interstate one time in a 1987 Nissan Sentra, and it started losing power. Turned out the radiator was entirely crusted over with ice, and apparently that's where the air intake was, as when I knocked off the ice, the car got its power back (this repeated a couple times until I drove out of the weather system). A dirty air filter supposedly reduces your mileage on the same principle, so I can believe changing the air filter could improve it, but since Toyota spent a lot of time tweaking things on the Prius for best mileage, like the thermos for storing coolant at engine temperature and using an Atkinson-cycle engine, I would think they wouldn't leave a simple thing like a restrictive air filter in place. OTOH, their tire pressure recommendations are definitely low.

 

What I wrote I wrote it the simplest way for people to understand...

Race drivers... (or retired amateur race drivers) work on everything that means better air intake together with proper fuel injection to generate more power in RPM ranges where power was lacking... There are other components that must be changed to get "good" gains... but its common sense that better or more air in a shorter period of time will mean less throttle use... because needed power will be available at lower RPM. Air temperature is also important depending on your setup and car... (for example you can get 10+hp on turbocharged vehicles when you lower intercooler temperature a few degrees)

Sensors play and important role in maintaining a balance but cars are not stuck at some air/fuel ratio established by "John Smith" at Toyota. Feedback is achieved through input.. that is.. if more air is inside more air needs to come out... No air should be "trapped"... unless you are using turbo where exhaust air is used to spin the turbine generating a suction to get more air inside the engine.. that is the reason turbo cars with big turbines lag... however better virtually lagfree turbines are available...

Again, no significant power gain or mpg change will be noticed unless other components are changed... ECU will control most of it (it can also slightly adapt to small changes)... reprogramming is possible, but with a car like a Prius... its risky... but someone should try