nick n

The stock air box is under (during boost) pressure.

I believe that the spring loaded door accounts (alot) for this. It's not mechanical. It just uses a heavily wound spring. I think this is what I used to 'feel' slam shut on quick throttle lifts.

AFA pressure goes I'll assume that at 1/2 throttle the door is open 1/2 way. There must be some sort vaccum going on down there that may be affiliated with low end torque, somehow.

How is low end torque affected w/o the door, or is it at all? I think that there is an extremly marginal low end loss but mid to high end gain over the powerband.

FYI: I just performed the air box mod (did everything but cut the inlet cone on the MAF - thx clark).

I drove the car for about 10 minutes varying speeds. Does the ecm need more road time for recalibration or would this my imagination? I think I'm running 2 psi more to get moving throughout the low gears.

Status: Zero problems. No $ spent. Nice low volume tone (its really is low), a more audiable bypass valve, and, I just may have shaved .2 - .5 seconds somewhere in the topend.

MusaML

Or there is still small turbo-lag ?

WClark

First off the airbox isnt under pressure (e.g. above atmospheric pressure). It is below atmosphere. How much depends on several things including how much air the engine needs to draw and the resistance at the airbox inlets and across the filter. The secondary inlet is sprung to permit an alternate source of air when needed (when the vacuum in the box exceeds the pressure of the spring on that round damper). Pulling off the damper simply improves low end engine air feed as there will be less pressure drop in the box below engine loads that would not open the damper.

The engine should not really need any adaptation since all the mods occur before any sensors (unlike some inlet mods that change the air path after the MAF). That said though, I could swear my car did adapt over a couple days and performance improved.

xr4tic

The stock air box is under vacuum. The reason is because of restriction.
Under idle and part throttle conditions, the box will draw enough air.
Under WOT, the turbo is drawing more air than the box can supply, so it has to pull the air through the small opening, creating a vacuum, which opens the flapper door. If you measure the duct going to the box, you will see it has the smallest inlet area of the system. This is the restriction in the system. My 97 does not have a flapper door, so I have to cut holes in the box.
The amount of air needed is dependant on RPM and boost pressure, but I would guess the door probably starts to open around 4k at full boost. Chipping makes the problem worse by raising the boost and increasing the amount of air needed.

Getting rid of the restriction provides faster spool up. It also changes the pressure ratio of the turbo, making it more efficient (or should I say less inefficient) so the air is heated less.

nick n

On my morning commute (30 min/59 F/nrml operating temps) I took advantage of some highway passing/lane changing opportunities. After some throttle rolling into WOT I noticed a very strong pull after 3.5k in 4th gear. It's now even more easy to approach 125mph from 100. The needle on the right really moves - more so than w/ a 'stock' box.

On the street: In first gear I threw it at about 2.5k then easied it into 2nd. At about 2k I floored it and lauched. Zero bog or lag. This was noticable.

There is a very subtle grumble that lets the driver know what's going on. Speed from 2nd to 3rd gear + accumulates more quickly - certainly.

The removal of the two screens and the foam relocation was worth the back pain.

nick n

I makes sense expecially at low end. More air flow, less lag.

Something must've adapted b/c yesterday it seemed to need 1 - 2 pounds more air to get going!

KenHuglr

you should try to cutting the inlet pipe too.

nick n

I had a couple of screens and the door. Interesing to know if this has been changed throughout the model years.

xr4tic

Just some drain holes. All I did was drill the drain holes bigger. I plan on doing more later. I have some pics on my website. Look under Mods.<ul><li><a href="http://www.geocities.com/xr4tic/">http://www.geocities.com/xr4tic/</a></li></ul>

xr4tic

Not to get into an argument - but I wouldn't. The longer pipe smooths air flow, and the funnel shape helps air enter more quickly. Air flows better through some sort of transition - ramp, funnel, etc than through a 90 degree turn.
If you think there is still a restriction with the air horn, measure the pressure loss in the intake to the turbo. No loss means no restriction.