What is the "mystery mod" I hear about?
The infamous mystery mod was first introduced by syncivic on acura-cl.com on 8/21/2001.
He did not say what the mod actually was, much to the dismay of the forum readers, but did leak the following information:
It is made by syncivic in Florida.
You can find a dyno of it on a TL here. Scroll down the page a bit.
It will cost about $299
It gives about 10 hp.
It adds about 15 ft lbs of torque.
It can be added in addition to an Intake and headers
It can be installed in 5 minutes with no special tools.
It is NOT an ECU or software upgrade.
It should not affect your warranty.
It should have CARB approval when it comes out.
It will "Look trick"
At the SEMA show, it was revealed to be an upper intake manifold cover that increases the mass volume and resonance to create an increased intake charge.
Since then, the following was known:

It does fit under the stock hood, although they smashed a few hoods during prototype testing.
It's offical name is RES (short for Resonance Enhancement System), although it is still sometimes referred to as the MM (Mystery Mod)
It will be polished aluminum, although it may be in color if demand dictates.
There are 3 separate patents for the RES.
It makes no additional noise.
It does not affect fuel economy.
However, it is not yet availiable to be ordered.

For a picture of the Mystery Mod, Click here
To see the cover it replaces, (circled in red), Click here .

Came from this site

 

from like a billion years ago a few people had it i think....or so ive read