Air Box

[MBT]

Hi.

This one question has been bothering me for some time.

As you know our stock air boxes have 2 air inlets

- from the front of the car

- from the exhaust header

The second is used for the first ~5 minutes of car's operation (or till a certain temp is reached)

The first is used the rest of the time.

Today while inspecting my vacuum hoses I removed the airbox and asked myself this question: how is the inlet controlled?

I see that there is a spring that controls a plastic cover that can cover either of the 2 inlets, but I can't figure out how.

Also, how do you know that it is working properly? By default it is set to use the hot air from the exhaust header, so how can you check that it has switched to the cold air?

Thanks,

Mike

[merlin390]

Mike find a turbo air box base (bottom) and snatch that hot air intake OFF!! the turbo air box will hook up to the snorkle tube just fine and the air going in the engine will be worlds cooler.

[MBT]

Well, that is 1 way to go about it.

That still does not answer my question though.

Also, since spending money on this (unless it really IS broken) is low priority, I'd be much better off taping that gate shut (open toward the cold air).

by the way, I'm not saying that mine does not work, I just want to know how to check.

Mike

[merlin390]

open the elbow up and remove the door thing it is a HUGE flow restrictor!!!

[rodrigo]

can you elaborate?

[merlin390]

yeah, grab your air box and pull it out and look in the elbow that goes into the housing. that Darn flapper is covering 80% of the elbow.

this is the end result of swapping out the turbo air box ( dont have pics of my other elbow)

[rodrigo]

i did't notice that flapper. when i was messing aroung with the airbox during the tune-up, i just pulled out the snorkel that goes to the front to the rad support, and the bottom of the airbox was all empty. the flapper is on the inside of the box, or on the air inlet?

[EMDII]

The flapper works on a principle Ferdinand Porsche and the Swedes implemented during WWII for air-cooled engines. The spring is heat-sensistive (probably has a bi-metallic component). When heated, the spring responds by shortening, and the flap closes. The flap is allowing ambient air, heated by the exhaust, to warm the air going into the airbox until the engine warms up fully.

Go look at any pre-90s air-cooled Porsche, including the 911, 930, and 914. Mystery solved.

Pull the airbox out and check it with any LARGE air dryer (g/f or wife has the right tool).

VOILA!

[msestina]

The flapper works on a principle Ferdinand Porsce and the Swedes implewmented during WWIi for air-cooled engines. The spring is heat-sensistive (probably has a bi-metallic component). When heated, the spring responds by shortening, and the flap closes. The flap is allowing ambient air, heated by the exhaust, to warm the air going into the airbox until the engine warms up fully.

Go look at any pre-90s air-cooled Porsche, including the 911, 939, and 914. Mystery solved.

Pull the airbox out and check it with any LARGE air dryer (g/f or wife has the right tool).

VOILA!

←

On mine th ethermostatic control was stuck to alwys allow heated air.

Thats not good for the MAF. so I removed the thermo and pinned the

flap closed w/ a sheet metal screw to allow cool ambient air only.

that was 1000s of miles ago and car warms up and runs fine

[EMDII]

On mine the thermostatic control was stuck to alwys allow heated air. 

Thats not good for the MAF.  so I removed the thermo and pinned the

flap closed w/ a sheet metal screw to allow cool ambient air only.

that was 1000s of miles ago and car warms up and runs fine

←

It doesn't hurt the engine per se, just makes it run rich longer. I don't think 'stuck' hurts the MAF, only that the MAF and temperature sensors don't get the correct ambient air T to adjust the injection density.

"Fixing" it is quite OK, I'm sure!

[crimsonghost]

Is there much of a performance benefit to be gained by this "Mod"? I have an S70 N/A and anything I can do, I will, if it makes sense and is relatively easy. I installed a K&N Panel filter a few weeks back and immediately noticed an improvement in throttle response. Maybe ill try to remove the "Flapper", & if I dont see any benefit ill replace it.

[Bay13]

To test the thermostat/spring. use a hair dryer. If you are in a cold climate, I wouldn't take it out.

Like mentioned if you wire it open, you could cause problems for your MAF.

[rodrigo]

i think i will leave mine alone...the flapper for the air entry. in the winter, here in NY, it can get pretty darn cold, so it will allow the car to run on warm air sooner, as intended.

[MBT]

So, let me get this straight.

The car starts - the flap is open to accept hot air

Then the metal part gets to a certain temp and the spring compresses

The flap is now open to accept cold air

Then what? The spring cools down the the whole process is repeated?

I mean, whouldn't it be cooled down almost immediately by the incoming cold air?

Or am I mis-understanding how this whole thing works?

Mike

[rodrigo]

So, let me get this straight.

The car starts - the flap is open to accept hot air

Then the metal part gets to a certain temp and the spring compresses

The flap is now open to accept cold air

Then what? The spring cools down the the whole process is repeated?

I mean, whouldn't it be cooled down almost immediately by the incoming cold air?

Or am I mis-understanding how this whole thing works?

Mike

←

mmmmm ... thats a good point.

i'm just going out on a limb here, but what is the temperature the flap is set to close? if it is set to open at, say under 60 F, then it would be open just to get the to operating temp quickly, then switches to outside air. would't the air coming in be warmed from where the air inlet is anyway...it passes right by the radiator.