BD Intake

[TrickNipple]

Hi everyone, I am new to posting here, I have been reading for a while but decided to join and start adding to conversations. Here is my question, I have a 97 Legacy L and I was wondering about a part of the intake system. I have the air filter by the passenger fender and then it goes through the MAF and then right before it goes to the engine there is a big black box. I cant figure out what the box is, its looks like the filter box on newer Legacy's but I looked at it today and doesnt look like I can open it up. Does anyone know what it is? Or is it just part of the system to quiet my car?

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[ooberdoob]

i'm an idiot and patrick noticed it

[TrickNipple]

I know about the snorkus in the fender and I am planning on taking it out later this week. I was just checking under the hood today and saw it would be easy to remove the middle piece with the big messed up looking silencer piece on it. It looks like it would be easy to removethe part in the back and put an elbow there but it looks like I would need a 90 and a 45 due to the angle. Is there any problems associated with removing the PVC piece that goes from the headlight to the fender, it looks like it helps divert air to the snorkus.

[ooberdoob]

nah, piece of cake. just remember to get the lil plug or its a hontard hot air intake.

[Patrick Olsen]

ooberdoob, he's not talking about the intake silencer, he's talking about the big black box right on the throttle body.

What's it for? To be honest, I don't think anybody on the forum knows for certain. Some have claimed it's a "torque box" to provide a reservoir of air for when the throttle is cracked open. On some cars it is a filter box. Someone needs to take a field trip over to Tokyo to ask the Subaru engineers what's up with that piece.

Meanwhile, you can either purchase or fab an intake to get rid of it.

Pat Olsen
'97 Legacy 2.5GT sedan

[Huffer]

On the Impreza's (99/2001) that box holds the air filter. I know that when people have removed that box and replaced the whole intake with a J-pipe, they've lost some low-end torque. They did gain a higher top end though.

On the Legacies, I think it's some kind of air reservoir, because when a car opens the throttle, the volume of air sucked in is usually less than the air needed. It could also be a resonator chamber.

Guess we really wouldn't know unless someone was to do a flow-test on it...

[subysouth]

Originally Posted by Huffer

On the Impreza's (99/2001) that box holds the air filter. I know that when people have removed that box and replaced the whole intake with a J-pipe, they've lost some low-end torque. They did gain a higher top end though.

On the Legacies, I think it's some kind of air reservoir, because when a car opens the throttle, the volume of air sucked in is usually less than the air needed. It could also be a resonator chamber.

Guess we really wouldn't know unless someone was to do a flow-test on it...

I think its actually called a torque box(or someone called it that) and I believe it is for exactly what you said, a reserve of air right as the throttle is opened.

ss

[TrickNipple]

So I got the snorkus out and while I was working on it I realized a problem with removing the stock piping to the throttle body. There are two smaller tubes that branch off of the main air line before it hits the throttle body, would there be any negative effects if these are not connected because of putting a CAI in? Or does the CAI have places to hook these up? I dont think I have enough posts to put up pictures yet, there is one in the middle piece and one in on the left side of the torque box. Anyone have some knowledge they can share on these air lines?

[fastenova]

Originally Posted by NickLippert

There are two smaller tubes that branch off of the main air line before it hits the throttle body, would there be any negative effects if these are not connected because of putting a CAI in? Or does the CAI have places to hook these up?

A good CAI will have nipples welded on and supply you with some silicone hose to run to these three (four) places. Two are crankcase ventilation lines from the right and left valve covers, these are teed from the factory and connect to the torque box. Another is the PCV valve line that feeds back to the intake. Basically these provide a way for fuel that doesn't get burned up completely to recirculate and have a second chance at getting combusted.

The other one is the Idle Air Bypass line, which supplies air to the engine when the butterfly is closed. Since these all feed into/from the intake, you can tee these off however you want. However, I believe it could be bad to tee the line coming from the PCV and the IAB line... Can anyone verify?

My friend, who is a mechanical engineer and design enthusiast, and I have been talking about the torque box. We came up with this: since the intake runners are so long on subies because of the engine layout (Please excuse my beautiful ascii representations, and ignore the periods):

H4:

......(TB)
O===X===O
O===X===O H4

vs. Inline 4:

X=X=X=X=(TB)
O..O.O..O

So since the runners are so long, the plenum isn't nearly big enough for how fast the air is sucked into the engine, we think because of space restrictions and/or TB placement in design. So, they basically put the plenum before the throttle body instead of after it in the intake system.

Theoretically, if you could use that air box and have straight piping from that to a CAI, you'd not lose your low end torque and still have excellent high end pull. I am in the middle of sourcing someone to bend me a new piece of intake pipe so I can throw the torque box on and see what happens.

There have been some people making intakes out of PVC. I did the same a couple of summers ago, it was fun to mess around with but after a while the PVC started to deform from the heat, particularly around the clamps and joints, so I'd recommend having some aluminum tubing bent.

For the record, I've got a short ram intake now with conical filter in the engine bay right next to the fender. If anyone is interested, I may be able to have more made with the right bends and stuff. I'm hoping this is the best alternative for us Legacy owners who want an intake but don't want to have to roll into the throttle.

I have let a couple of other people drive my car since I've had the intake, and they get confused and scared by the fact that the car seems to die if you romp on the throttle from a stop. That's reason enough to design a new intake manifold... I think we may get one in the works in the next couple of months...

[Huffer]

Originally Posted by NickLippert

So I got the snorkus out and while I was working on it I realized a problem with removing the stock piping to the throttle body. There are two smaller tubes that branch off of the main air line before it hits the throttle body, would there be any negative effects if these are not connected because of putting a CAI in? Or does the CAI have places to hook these up? I dont think I have enough posts to put up pictures yet, there is one in the middle piece and one in on the left side of the torque box. Anyone have some knowledge they can share on these air lines?

The hoses you mention are vacuum lines, and forgetting to use them could make the car idle rough or have insufficient vacuum to run properly.

So yes, there are negative effects.

fastenova - have you considered simply installing an air box between your cone filter and the end of the throttle body? ie. cut a section of pipe and install a volumetric box where the removed section was?

[fastenova]

Huffer-

Yes and no: before I go about designing a box with good flow characteristics or whatever, I figured it'd be easy to get a piece of pipe bent to use the stock torque box. I also wanted to try moving the filter into the fender so I'd want a longer piece of pipe, with different bends.

Also, as I'm just a computer nerd, designing something that's just big enough to provide the air necessary without affecting flow too much is something by buddy is better at, being a ME.

Plus I have my stock torque box sitting in my garage and I figured I'd use it.

-Aaron

[Huffer]

Do you mean something like a Ganzflow intake?

[fastenova]

If the Ganzflow uses the stock torque box, then yes. I just have a GPMoto intake from Rallitek, and have been mostly happy with it, but don't want the loss of low-end torque.

-Aaron

[Huffer]

Like this?

[Patrick Olsen]

Originally Posted by fastenova

Theoretically, if you could use that air box and have straight piping from that to a CAI, you'd not lose your low end torque and still have excellent high end pull.

I have no torque box, and I have seen (on a dyno) zero change in low end. Torque is up throughout the RPM band, end of story. My dyno results aren't the only ones that show this, either. The whole "torque box" idea is something someone came up with but there is no data to support it.

Originally Posted by fastenova

I have let a couple of other people drive my car since I've had the intake, and they get confused and scared by the fact that the car seems to die if you romp on the throttle from a stop. That's reason enough to design a new intake manifold... I think we may get one in the works in the next couple of months...

There's something wrong with your car if there's that much of a noticeable loss of low end. It just shouldn't happen.

As for designing a new intake manifold, that would be great. I'm sure there are better options out there than the OEM setup.

Pat

[Huffer]

Pat - would you post your dyno graph? Do you have a stock vs. aftermarket as comparison?

[subysouth]

I had thought making an intake that widened out horizontally in that same area as the stock torque box but maintained the rounded inner transitions for better flow. You would need to make it out of plastic or a fiber product.

ss

[fastenova]

Pat - I have heard other people mention the same problem with aftermarket intakes - in that from a stop, if you push the accelerator all the way to the floor (quickly) instead of rolling into the throttle, the car hesitates quite a bit. I swear I'm not making this up!

And my engine is running very well, besides an oil leak, so I don't think it's related to that at all.

When I said "low end torque" I should have worded that as "launch from a stop" because with a stock intake setup, you could hammer the gas all day long from a stop, no big deal. The day I put this intake on, I started having problems with it. If you roll into the throttle, no issues whatsoever.

Maybe my intake just sucks. I honestly don't know. Also, I have an AT, so there's some loss there, perhaps coupled with this particular intake it's just a bed setup. But does that make sense about the lack of air because of a small plenum? Does anyone else have an intake like mine on an AT that they can verify this issue?

ss - I like that idea. Maybe like those bullet mufflers that looks like the tube just swelled up right before the throttle body... I will see. My buddy was talking about making an intake out of carbon fiber, and that would work very well for this application. Maybe we'll buy a roll and see what damage we can do in a weekend.

-Aaron

[Patrick Olsen]

Originally Posted by Huffer

Pat - would you post your dyno graph? Do you have a stock vs. aftermarket as comparison?

Unfortunately, that's the one graph I don't have. I have graphs from my other trips to the dyno, but my last trip got lost.

I swear I'm telling the truth, though.

Pat

[LetItSnow]

Originally Posted by Patrick Olsen

I have no torque box, and I have seen (on a dyno) zero change in low end. Torque is up throughout the RPM band, end of story. My dyno results aren't the only ones that show this, either. The whole "torque box" idea is something someone came up with but there is no data to support it.

+1, except for the dyno bit. I'm just familiar with my own car and plenty of miles with and without the box. I think it's just an opportunity to put a good-sized, flat filter in there.

I would like to see any evidence that it's there for a "gulp of air", either dyno'd or proven in physics. It's not as if you're stretching the flow limits of the stock intake at 700RPM.

[Gil]

I have one of those $15 eBay specials and my only problem with bogging is when the engine is cold. once it's warmed up, i really haven't noticed anything.

EDIT: I'm running MRT headers and midpipe.

[subysouth]

Originally Posted by fastenova

ss - I like that idea. Maybe like those bullet mufflers that looks like the tube just swelled up right before the throttle body... I will see. My buddy was talking about making an intake out of carbon fiber, and that would work very well for this application. Maybe we'll buy a roll and see what damage we can do in a weekend.

-Aaron

Thats pretty much it. Keep the inside transitions to that fattened area nice and smooth.

ss

[Dan Cech]

I'm with Pat on this one, just installed a '98 RS injen CAI last weekend and didn't notice any drop-off in low end torque. I did however see noticeable gains in the top end.

Disclaimer: I am running Borla headers and a 2.25" catback, which probably made the top-end gains more noticeable than they would have been with a stock exhaust.

[Jonathan]

Originally Posted by Dan Cech

I'm with Pat on this one, just installed a '98 RS injen CAI last weekend and didn't notice any drop-off in low end torque. I did however see noticeable gains in the top end.

Disclaimer: I am running Borla headers and a 2.25" catback, which probably made the top-end gains more noticeable than they would have been with a stock exhaust.

Yeah, and Pat is also running an injen CAI along with Cobb Cams & heads, running headers with a high-flow cat and an exhaust. Pehaps running an intake with out these other mods creates the low-end problems that arent evident with headers ?

Also the injen setup seems much better in the low-end, where the Weapon-R set-ups are perhaps more prone to these problems.

[fastenova]

Originally Posted by Jonathan

Yeah, and Pat is also running an injen CAI along with Cobb Cams & heads, running headers with a high-flow cat and an exhaust. Pehaps running an intake with out these other mods creates the low-end problems that arent evident with headers ?

Also the injen setup seems much better in the low-end, where the Weapon-R set-ups are perhaps more prone to these problems.

Agreed. In either case, my intake sucks. (but don't they all...?)