K&N filters really improve fuel economy?

K&N filters really improve fuel economy?

No.
The only one argument I've ever heard of that comes close to making some sort of sense for the 'oily gauze pad' filter type is that they can statistically reduce landfill usage over paper/pvc filters.
It's a lame argument, since you have to flush K$N filters with water and re-oil them, but some wild-eyed ecologists have insisted in the past that even this downside places them above paper filters for the eco-chic set.

As far as their intended purpose (filtering air) they suck....pun almost unintended.
You either have to use enough oil to fod out your intake, or you have to let enough dirt pass through the filter to fod out your intake.
If you know what a Mass Air Flow Sensor is and how they work, you won't put one of these things anywhere near your car.
If you don't know what a MAF sensor is, then you'd better find out how to clean one if you're going to stick an expensive oily rag into your intake system in place of a proper air filter.

Gas mileage: Asked and answered above. If they made a measureable difference? They would be standard equipment and Toyota would include 'filter cleaning' in the maintenance schedule. Fortunately, even Toyota dealers aren't that greedy or dishonest.

BHP: See also - Gas Mileage. I don't remember what the Prius 'redline' is, but I remember that it's not very red. Something like 5,000 rpm, but if you're considering BHP why not use the same filters that the OEMs put into cars like the Hellcat, Z-06, GT500?
All of these are $50-60K cars, and I might be mistaken but I do not think that any of them use K$N filters.
It can't be cost - because even a 1-percent increase in a 707 BHP car would be worth it - especially since the OEM filters are probably almost as expensive. A 2-percent increase would turn a 707BHP car into a 720BHP car....which is actually something you could probably notice (if it were real.)
You know why I might be wrong about this?
Because K&N has been desperately trying for years to get OEMs to switch to their media type for their performance cars.
There's a REASON that the OEMS are hesitant to do so......THEY have to provide a warranty for the car.

For a Prius?
Gimme a break.

Nobody ever notices a BHP or an MPG change.
Usually they have to come up with something like "increased throttle response" to justify the $50 expenditure.
YMMV!

 

Well said.

I love K&N (motorcycle), but it's sole purpose is to maximize air flow to the engine but still offer a level of quality filtration. You can't install one on a bike without retuning your carburetors/remapping your ECU, and it offers little benefit without an improved exhaust system reducing restriction on the exhaust as well.

All of of this in the quest for more HP...which is irrelevant for the Prius unless you want to turn it into some kind of hybrid "sleeper" when flicked to PWR mode.

 

I wasn't going to go that deep into the weeds for a Prius forum, but you're right.
I have a high-performance air filter (AMSOIL's Ea) for my motorcycle, but I also remapped the ECU and uncorked the exhaust.

If the air-flow gains that a K$N filter allegedly provided were real, then you'd also have to uncork the Prius' exhaust otherwise it would be like running with a straw in your mouth and only removing the straw when you breathe in.

If this product were only ineffective as well as overly expensive, then it wouldn't be so bad but most of the people that buy this junk only keep their cars for 100,000 miles or less.
Then, some poor sap has to deal with a dirtier intake and increased engine wear becuase they bought a car and were not warned about the prior abuse.
K$N thoughtfully included a sticker in the filter package to warn people, but most of the people that buy this junk do not use the sticker for its intended purpose.