Messing With Factory Intake Setup?

[JT95]

I've got the bug to create a custom air filter/intake setup for my non-turbo Impreza. 99 model. I want to run a T-fitting off the throttle body and from each side run an aftermarket cone filter. I thought dual cones would look pretty sweet as well as let my engine suck in some more volume and hopefully gain at least 5hp. Assuming I customize it to keep my factory vaccum lines and my sensor as part of the intake housing, is it generally not that much of a difference in power and/or mileage when replacing factory air intake with a less restrictive system? Are there any common issues that I need to be aware of when trying this?

 

Am I just better off leaving the factory setup as-is? I thought about just buying a K&N element to fit my stock filter element box, but then there's another filter in the big box right there at the throttle inlet, correct? Wouldn't both have to be replaced with upper quality filters in order to actually do anything? Why two filters in the same flow path anyway?

 

I'll admit part of me wants the dual cone filters because it would look sweet, but there's no sense in investing the time and money if it runs just the same. Experienced input?

[Manarius]

It seems to me that if you aren't going to at least run the cones into the fender, there's no point in wasting your time. Having air intake from under the hood is a waste because the hot air provides worse HP than the stock intake resonator.

 

Also, it seems to me that the less restriction in the intake the better. But, the least restriction possible would be having only one pipe, not two. I mean, there's a reason that almost every intake system provides only 1 intake filter.

[subaru360]

You won't make much more power. WRX's use the same air filter and box and can make over 300 hp with it, it's a good setup.

 

But if you just want to make a little more noise and have some fun go for it.

[JT95]

Well, I have an OBS, so it has the hood scoop. I know it's only there for looks, but there is flow through it, although I have no idea if it amounts to anything. I don't know of a practical way to see if there's any real air movement through the thing. If so, it probably still wouldn't negate the engine heat, huh?

 

As far as the sound--does a different setup like that really change the tone of the car's sound, or do you have to do exhaust mods too to get any effect?

[thatswhatshesaid]

No, if you mess with the intake, you'll definitely get a nice, deep rumble out of it when you give it throttle - exhaust modification or not. I had part of my intake piping off the car for a few days to repair (glue) it, and it sounded awesome. But the power was markedly decreased (maybe it was my imagination, but I doubt it) due to the intake getting air from the uber-hot engine bay, instead of the cool atmosphere. I realized that the stock ram-air-type setup on my car kicks butt. I won't screw with just to sound cool (which it TOTALLY does).

[OB99W]

[...]But the power was markedly decreased (maybe it was my imagination, but I doubt it) due to the intake getting air from the uber-hot engine bay, instead of the cool atmosphere. I realized that the stock ram-air-type setup on my car kicks butt.[...]

I agree that it wasn't likely your imagination. The issue isn't directly temperature, but air density (which decreases with increased temperature, other things being equal). If you're looking for performance, more-dense (colder) air is what you want.

 

A ram arrangement helps, although obviously to a greater degree as speed increases. Of course, a turbo can assist as well.

[idosubaru]

the "engine bay temperature" theory isn't applicable to all vehicles. there have been people that have tried both and gotten better actual dyno numbers with the shorter intake hose in the engine bay. so whatever difference the hot air makes is offset by something else. a member on here even tried both, on an older generation vehicle to find the engine bay intake got better results, after everyone of course said it wouldnt.

 

and in a dyno set up i would imagine the "hot engine air" set up is hurt the most since the fans they blow in front of the car probably don't ventilate the engine bay as much as actual driving.

[thatswhatshesaid]

Good point, grossgary. As I inspect the area around the engine bay in my Outback, I realize that driving at highway speeds would force tons of fresh air into the engine compartment from every angle.

[newsoobdude]

Granted you have an Impreza and I have a Legacy but I found that going the e bay intake route to the stock airbox was the BEST mod I've done for sound and upper rmp gain. The intake was for an 01 RS and had to be modded (read shortened) to work with the stock airbox but well worth it. I also took the inner fender snorkus out and plugged the hole with an RS blockoff plate. While your modding everything and have your air intake off, you might want to go ahead and do the TB Bypass mod as well, it really made the throttle response crisper. Also gives a nice throaty growl with the intake and stock exhaust.

[subaru360]

On my wrx I have the stock airbox, but I got a GP moto silencer delete. It replaces the snorkus in the fender with an elbow.

 

You guys might want to try adding the big scoop above the radiator from a wrx, if it fits. I have datalogged my wrx and have data that proves that the scoop does work. As you go faster the IAT drops. My car came with a cobb short intake on it. That would not drop the IAT, it stayed the same or went up. I took the intake off and put the factory box back on with the silencer delete. I think this is the best setup.

[JT95]

Granted you have an Impreza and I have a Legacy but I found that going the e bay intake route to the stock airbox was the BEST mod I've done for sound and upper rmp gain. The intake was for an 01 RS and had to be modded (read shortened) to work with the stock airbox but well worth it. I also took the inner fender snorkus out and plugged the hole with an RS blockoff plate. While your modding everything and have your air intake off, you might want to go ahead and do the TB Bypass mod as well, it really made the throttle response crisper. Also gives a nice throaty growl with the intake and stock exhaust.

 

 

I like that setup you've got. I'm gonna try the dual filters off the backside of the engine first--mainly because I just want to see what it looks like and how it does out of curosity--and if I don't like it I will do a setup like the one you have here. Heck, I might run a Y-pipe off the throttle body and do the right side just like yours and do the left side to the back with a cone filter. I just want something that looks a little trick, is different, something I can say "Yeah, I made that", and at the same time either enhances or has no negative effect on throttle response. Otherwise, what's the fun in owning a 10 yr old car?

 

 

Just out of curosity, does anyone know if there's any info/data on the actual airflow that takes place through the factory Outback Sport hood scoops? I know some cars with non-functional scoops don't even have the thing vented--it's just an add-on on top of the hood, but the Impreza's has some flow, though I'm not sure what kind of air volume realistically passes through it.

[subaru360]

I like that setup you've got. I'm gonna try the dual filters off the backside of the engine first--mainly because I just want to see what it looks like and how it does out of curosity--and if I don't like it I will do a setup like the one you have here. Heck, I might run a Y-pipe off the throttle body and do the right side just like yours and do the left side to the back with a cone filter. I just want something that looks a little trick, is different, something I can say "Yeah, I made that", and at the same time either enhances or has no negative effect on throttle response. Otherwise, what's the fun in owning a 10 yr old car?

 

 

Just out of curosity, does anyone know if there's any info/data on the actual airflow that takes place through the factory Outback Sport hood scoops? I know some cars with non-functional scoops don't even have the thing vented--it's just an add-on on top of the hood, but the Impreza's has some flow, though I'm not sure what kind of air volume realistically passes through it.

 

The OBS scoop really works. It just has a block off plate under it. It is the same hoodscoop used on the older JDM WRX's. If you take off the block off plate, it will be functional.