High-flo B4 Airbox workshop starts...
I will only be doing a B4 box however most, if not all of the same rules will aplly to all similar airboxes of the era.
The goal is to have the highest flowing induction tract while retaining the stock airbox and OEM air filter.
Design goals:
1. Retain airbox stock mounting location so MAF outlet location & orientation remains unchanged.
2. A 100% "sealed system" utilizing stock/modified B4 headlight compartment backing plate so that high-pressure area between back of headlight and headlight backing plate is the retained and 100% of cold air intake charge comes from within the headlight high pressure compartment and NO heated air from engine bay.
3. A 186% larger air inlet than stock utilizing a 4" ID Velocity Stack with a 6" radiused-inlet OD.
I now have about 3 hours in the velocity stack getting it prepped and smoothed out as it was terribly rough with an undulated surface from it's flared inlet all the way to its outlet. I've also given it a more radiused inlet ID/OD as it was a bit "square-edged" on it's inlet ID/OD from the factory.
The headlight backing plate as mentioned above will have to be modified to accept the VS inlet diameter. Then some provision as yet undetermined for sealing it to the backing plate.
The VS will to be attached and sealed to the airbox permanently while the inlet side will allow it to be removed from the car via the headlight backing plate. Expandable urethane foam will be used for bonding the VS to airbox as once cured it's strong as nails, lasts forever and allows sanding, shaping and contouring so that once done it will appear as if the airbox/velocity stack came out of a casting facility and manufactured as a one-piece integrated system. Once sanded/shaped the uretahne foam can then be sealed and painted. I will probably also opt for a spray-on type bed liner product like "DuraLiner" or "Rhino-Liner" commercially applied to the outside of the airbox body, lid, VS and headlight backing plate to further everything appearing as if it all came out of a factory somewhere as a production unit and add additional structural rigidity. That will also act as both heat insulation on the airbox warding off heat and I "may" opt to also use a heat-shield of aluminum that via stand-off bolts also creates a dead air space between the airbox and heatshield. The insultaion will also mitigate some of the decibel level increases associated with induction sounds that these airbox modifications are certain to cause.
Very little is carved in stone as of today but all the details will be worked out as the workshop progresses.
Pic above shows velocity stack, airbox, 4" hole saw and B4 headlight backing plate.