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IMPROVING THE AIRFLOW OF THE B21FT AIRBOX
by Jon Glommen

The B21FT used the same airbox throughout it's 6 year lifecycle:
1981 through 1985. The airbox sits beneath the fuel distributor and quietly supplies filtered air to the metering valve en route to the turbo compressor. The oval filter is comparatively large; at 50 square centimeters of surface area it is able to supply over 1980 cfm or air --enough for over 400 hp.

Air enters the box through a diverter valve switching between two air sources:

  • the fresh air snorkel behind the radiator grille
  • from the thermostatic tubing off the exhaust manifold.

The design of the snorkel helps silent the "whistling" and "whooshing" of in-coming air. The snorkel and the diverter valve both impose severe restrictions to the in-coming air. Therefore, the purpose of this project is to eliminate them and replace the fresh air tract with larger pipe.

 

 

Materials

  • 7" of 2.75ID PVC Pipe
  • 2.75ID PVC Elbow
  • #4 sheet metal screws

Disassembly Procedure:

  1. Remove front grille and right headlamp garnish.
  2. Disassemble intake snorkel and attached air tract bellows leading to airbox.
  3. From the engine compartment, remove hot air tubing leading from exhaust manifold.
  4. Unlatch top of airbox and drape fuel distributor over right fender exposing lower assembly and filter.

  5. Remove filter and set aside for later.
  6. From under the car, unbolt air box lower housing.
  7. Pull the airbox out of the car along with attached diverter valve. 8. Remove diverter valve from airbox.

Assembly Procedure:
It is necessary to trial fit the new air intake tract in the car to mark the housing for the sheet metal screws.

  1. Fit the elbow and 7" PVC piece to the lower housing.
  2. Place this assembly back in the engine compartment and fit to the 3" opening through the radiator support.
  3. Mark the inside of the elbow for the sheet metal screws. Use the existing holes in the airbox as guides
  4. Remove the assembly and drill out the elbow for the sheet metal screws.
  5. Once again, place the airbox and elbow assembly back into the engine compartment and securely fasten together using the sheet metal screws.
  6. From underneath the car fasten the lower airbox assembly to the engine compartment using the three mouting points.
  7. Replace the air filter and fasten the fuel distributor back onto the lower airbox --check for leaks!!.
  8. Replace the headlamp garnish and front grille.

This project cost me $3.00. And about 2 hours to complete.

 

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