How about we put interesting stuff from the service manual in this thread.

Things I found so far (after 5 minutes of reading):

The funny looking "extra filter" in our airbox (the on in the top part of the box) is a charcoal filter that's meant to reduce evaporative emissions when the car is stopped. In other words it abosrbs unburnt fuel that oozes from the throttle body when you shut off the car. That's like 5hp right there...

Our muffler has a 2-way valve that opens up at higher RPM to help with peak hp. Not bad for an econocoupe...

 

There was only a one (1) HP gain (no change in Torque) from removing both of the filters vs. w/ the filters. I think the OEM filters are quite efficient.

 

Both filters as in charcoal and paper? Ran with no filter at all?

That strikes me as odd - cause the stock airfilter is the same as the one used on a much smaller 1ZZ engine. And there was still 1HP gain - 1HP is well into dyno error margin...

 

Could it be that the stock airbox is actually very restrictive? Did you try dynoing the car with the airbox completly removed?

 

Dyno'ing without the airbox wouldn't work because the airbox has the MAF sensor on it.. My celica wouldn't even start if i had the MAF sensor out of the airbox.

 

Ahh ok. Surely there is a way to remove MAF sensor from the airbox though?

 

Yea, it screws into the airbox with 2 screws so its real easy to pull out.. but all of your idle control is based on readings from that sensor so its definately got to be drawing air thru it either in the airbox or on an intake pipe (ie. cai) to keep your car running.

 

Our CAI has a built-in adapter to screw on the MAF sensor. We are currently prototyping and hope to have it out in the next month or so

Thanks,
Clift