Well...I manage a smog test & repair shop here in CA. The high flow cat, like Magnflows (the brand of cats we use) will get you thru smog at least once. The specs are higher on our MKIIIs than newer cars. The high flow cats are just that, and many times the openess does not allow the cat to get hot enough to do its job.

I installed the 2 1/2" cat and piping all the way back. It seems to work fine. I am only 225 hp, though. My smog #s are very good.

Be sure to get a new O2 every few years. Cheap insurance for better fuel mixture ratio.

As for cold air intake, I've read lots on the net, magazines, and forums. With the AFM like our n/a has, you'll end up putting a K&N (or similar) either directly onto the AFM (mine), or on the 3" pipe you'll use to run out front somewhere (behind the headlight?).

I ducted air with galvanized sheet metal up from the front grill to the opening for original airbox, behind headlight.

Then I made a plastic box to seal off the heat from under the hood from getting into the K&N.

You DO NOT want hot air going into the air cleaner, it cause HP loss !!!

cool thanks for the info

I have a question, does anyone have a before/after dyno sheet pic of a stock N/A before and after mods? I was thinking about buying a header and getting the whole exhasut done, but i dont want the car to be loud so I duno if its worth the HP gains/noise

could someone point me in the direction of an exhaust that is quiet but doesnt restrict power too much. i would really like one that doesnt have any sound (as close to that as you can get). oh...i have an 86.5 N/A.

Put a 24 inch glass pack inline, And get a factory muffler from any car at an autoparts place. There like 25$ each.

what elese could i use to make a heat shield other than a plastic box?

You could use sheet metal, but it does not insulate as well as plastic.
By box, I meant I boxed it in. I actually used a household trash can. I cut 2 pieces out of it, one for the top, and one for the side that is toward the radiator.

The bottom is already there, as is the fender side.
The back is best left open, as the AFM blocks enough off, and you need it open in the back to allow the outside air to flow better over the filter.

great info nick. i to live in CA and deal with smoging. I'd like to clean up the intake like you have, but what about changing the original equip. when it comes time to smog? What does the state require?

Ca. smog testing
 

You must have the original equipment in place and working properly. Aftermarket stuff must be C.A.R.B. legal.

-Cat convertor
-EGR system
-Timing set to spec
-No check light on (except when they test for a good bulb)
-Evaporation canister & system
-Vacuum lines in place and routed properly
-No BIG holes in the exhaust or muffler
-No fuel leaks
-No BIG liquid leaks (oils, coolant, etc)
-No obvious signs of tampering (like disconnected stuff)
-Good gas cap (new ones cost $6)


Also, make sure its running good, and won't overheat during the test. Make sure the brakes work.