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.

And that's the thing. This debate about warm air intakes has always been like this. It's clear that they can work on some cars given the testing people have done and it's clear that they don't seem to work on some cars giving the test thing that other people have done. The key is to get a good baseline on how warm your intake air temperature usually is, try a modification, and track the data on intake air temperature and fuel economy carefully. Do a good ABA test and you might be able to see whether it's good bad or indifferent.

Sounds like I need to go buy some dryer hose lol

Go for it.

I used black PVC for my last version (not installed anymore).

Seems like it wouldn't hurt to keep the resonator (it will still keep the intake quiet), but I don't think it's really needed when air is being drawn in from inside the engine bay. Its not being forced into the intake tube like the factory setup is.

Doesn't torque have an IAT display? I can play around with that. I've been wanting to get a Bluetooth OBDII scanner for this kind of stuff

I had a wai intake on my intrepid, really it was just a cone filter on the end of the stock intake tube. Drawing engine bay air worked well and it was definitely warmer than original.

However; at highway speeds the temps will be very close to ambient if you don't specifically design for warm air. Grill blocking helps but could cause other heat issues.

Good luck!

That's true. I didn't even think of that. I'll have to plan on a good place in the engine compartment to move my intake so I don't end up with the same thing as before.

If your car has a cold air intake, close it off and rout hot air from the engine into the air intake.

In a way, the air filter, and resonator box is mounted under the hood, where the air is very hot already. So it'll all work towards creating warmer air.

I wouldn't delete the resonator box. It's specifically designed to make your car run better. Without it, you'd be driving at sub-optimal air-fuel ratios.
You may be much better off, taking your car to a dyno shop, and tune it for high MPG, or buy tools to read AF ratios from the OBD2 port and exhaust.