Warm air intake/ resonator removal
 

I have been thinking about redoing the intake on my wife's 2001 subaru outback. Currently it has a factory cold air intake with a resonator. I understand the role the resonator plays in the vehicle's performance, but I believe it is only effective with the CAI setup the car currently has. If I removed the resonator and replaced it with a non restrictive warm air intake, could I possibly see significant gains?

There's a lot of disagreement on this site about how effective a warm air intake is. Many people think that what happens is the warmer air creates a leaner air fuel ratio. But that's not the case. As warmer air comes in through the intake, there will be less oxygen and the engine computer will reduce the amount of fuel. But the real benefit to your fuel economy comes when in order to accomplish the same amount of power you depress the throttle further. by opening the throttle plate further, you reduce the restriction on the engine referred to generally as pumping losses. The reduction in pumping losses is in effect an increase in the efficiency of the engine. But saying that doesn't prove that installing a warm air intake will increase the fuel economy of your car.

What do you think about the resonator? I think that it only helps in the specific factory application on my car... I think that if I were to change things around I should remove it.

I vote for deleting the intake resonator, to remove the restrictions...

I also think you want to track your intake air temp before you change anything. Get a baseline of comparison between ambient temps and IAT readings. IAT will be higher than ambient even in a stock vehicle. You wanna know if you improve the delta from stock configuration as a basic way of knowing if your WAI design is doing anything. Temps in an engine compartment are always higher than ambient when the engine gets hot.

The warm air vaporizes the fuel better. And with a warmer mix you get faster combustion.

But the resonator (depending on which rpm it is tuned to provide benefit) makes the air jiggle about at a specific frequency and it can ram in to the engine providing more air.

Very true. And, as California98Civic says, you also have reduced pumping losses with a conventional automatic or manual. This will not be the case with a Subaru CVT, however, as reduced power will just cause it to rev higher. I could see this as being counterproductive.

Only way to know for sure is to test. I'd think running one in winter, at least, would be a good idea.

I'd almost bet your vehicle has no problems quickly building up the heat to run efficiently.
Once the vehicle is already warm there is nothing to gain with a wai. A lot of 4 cylinder/ stop start cars have problems maintaining temp, but large engine vehicles with no start stop heat up almost immediately and produce excess heat and any extra heat consumed is just bled off by running the cooling circuit more often.

Not necessarily. The temperature of air drawn into the cylinder does have an impact on combustion, regardless of how warm the engine is.

Hey in theory that is 100% true.