This installation was performed on my 1990 NA.  I purchased theK&N kit from Stillen. The intake filter upgrade is one of the fundemental'stage' upgrades to make. Here's what's included in the filtercharger kit(1.):

1. K&N Cone Filter
2. Adapter Ring (shown already attached to the filter)
3. Ring clamp (holds filter on adapter ring)
4. Bolts and washers
5. E.O.  sticker
6. "Equipped with K&N Filtercharger" sticker!

Special Tools Needed:

Either a stubby phillips or a 18" phillips
2 plastic sandwich bags & rubberbands or 2 shop rags
Masking tape

Installation:

1. All of the air intake components (that we will be dealing with anyway)are located behind the front panel. This is the panel between the headlights.(Shown here hi-lighted in yellow. 2.) For the stock 300ZX panels,there are four bolts (4 x 10mm) across the top. For the Stillen louveredpanel (shown) there are only two (2 x 10mm). Once the bolts are removed,pull the panel towards the back of the car. They tend to be a little trickyto pull out but with some (gentle) wiggling it will come loose. Once thepanel is off, I like to tape the screws to the inside of it with some maskingtape ensuring that they don't get mixed up with anything else. Also, Iwrap the panel in a soft towel so it doesn't get scratched while it's off.

2. Once the panel is off, there are a couple parts to work with; theT-hose (shown hi-lighted in red at the top 3.), the air flow meter,and the airbox (shown in yellow 3.).  Remove the T-hose first.To do this, remove 3 ring clamps at the three ends of the T-hose. One ofclamps is attached to the air flow meter and the other two are attachedto the intake hoses that carry the air to the engine. Once the clamps areoff, get a good grip and bend and wiggle the T-hose to get it out. Be carefulnot to put any stress on the connector and cable that are coming out ofthe air flow meter. Also, do not use anything to pry the T-hose off ofthe air flow meter there is a delicate screen protecting the sensor insideit. Place the plastic bags and rubber bands over the two intake pipes goingto the engine or stuff shop rags into them to prevent any debris from gettingin there while working up front.

3. There are four bolts that hold the air flow meter to the stock airbox.  These are in a square pattern. Use an extension to reach thembut they're not too tricky.  Remove all four of these. There shouldbe enough slack to just set the meter out of the way without removing theconnector from the side.

4. Remove the cover and filters from the airbox. There are 4 clampsthat you pry up with a screwdriver. The cover then comes off and exposesthe two filters. Set these aside.  There are 4 bolts & 2 screwsholding the stock airbox to the car, two bolts (2 x 10mm) at the top cornersand two (2 x 10mm) at the bottom.  The two phillips screws are inthe front of the air box and hold the black plastic splashguard onto theairbox (in the area of the two red circles 3.). They can be blindlyremoved with the 18" phillips, leaving the driver's handle outside thecar & away from the airbox, using the stubby, the driver will haveto be leaned over to make room for the handle & fingers, which willhave to be against the airbox. The bottom two bolts (also in the area ofthe two red circles 3.) take a lot of the time to remove. They areunder the two rails that run along the sides of the airbox and the headsof the bolts face the back of the car.  I had to use an open-end wrenchand only turn a few degrees each time. Be very patient. The final two boltsare on the rails at the top rear of the airbox.

5. Remove the lower half of the airbox. I masking-taped the rear edgeof the front bumper in front of the airbox to keep from scratching thepaint on it while removing the airbox. Go about 4" deep with it. Removalcan be done without mutilating it. The going rate for stock airboxes islow, so destroying it might be the easiest way to get it out. Otherwisegently bend the metal part in the middle until the box can be wiggled free.Once again, be very patient.

6. Replace the T-hose. Put the clamps loosely around the top two endsof the T-hose. Take off the plastic sandwich bags or remove the rags andput the two top ends of the T-hose on first. Don't tighten the clamps downyet.

7. Bolt the air flow meter to the adapter ring provided with the kit.Use the four bolts also provided with the kit.

8. Slip the remaining ring clamp around the bottom end of the T-hoseand attach the air flow meter to the hose. Do not tighten the clamp yet.

9. Push the screw provided with the kit through the hole in the topof the filter.  The head of the screw should be inside the filter.Dry fit the filter to the adapter ring and mark approximately where thescrew you just pushed through touches the plastic flap below the filter.In the 3rd ripple from the top is the common placement. Pierce a hole inthe flap with a phillips screwdriver or an awl and push the screw through. Tighten a nylock nut (provided) down onto the screw so that the filteris now attached to the plastic flap.  This will keep the flap frombouncing around and protects your filter from water. Now put the filterring clamp around the filter and fit it over the adapter ring.

10. Make sure everything is straight and that all ends of the T-hoseare connected fully and cleanly. We can't have any air leaks! When allis set, then tighten all of the hose clamps. Make sure that the screw headsfor tightening are easily accessible for next time. Replace the front paneland go enjoy the ride even more with your newest upgrade!