Modified Air Intake
1990 928 S4

November 16, 2009

Before the 2009 Silver State ORR I wanted to update the intake for the
Vortech supercharger. I drew up a simple diagram for a new air box and
asked Tim Murphy if he could build one of these. Here is version 3 of the

After he and Todd checked it out and brainstormed for a while, they agreed
to build one for me. In the mean time I tried to find an air filter that would
work. My original drawings had a round air filter, but it was too small and
didn't provide enough surface area. So I went with an oval filter with a
"open" top. I found one at Summit Racing that would fit. Here is a photo
of the finished air box and air filter on a sheet of insulation:

I then made a card board pattern for the filter shroud, here is the base:

Then added the walls:

And finally the whole system:

Next it was on to the aluminum version. I got some sheet metal, outlined
the template and cut it out. I then pop riveted the sides into position:

I then lined the back side with the insulation and mounted the air filter. I
also modified the air dam (top of the radiator) that came with Tim's supercharger
kit. Here's the finished product along with a new C&R radiator from 928 International:

Oh, and I did move the hose from on top of the radiator to the front edge to
allow better air flow.

Update 11/29/2011

It's been a year with the new airbox. I was still measuring some high temps in the airbox
because of the gap between the radiator and the intake scoop.

So I added a divider, this drop the intake air temps by 20 degrees!

Another issue I found was at the dyno I was only able to get 12.5 psi of boost with this set up. I put a
vacuum gauge on the airbox and saw 3.5-5" of vacuum.

(The sensor on the right is an air temp sensor.)

Anyway, I added a 2" intake to the box and a hose around the radiator with a K&N filter:

This should get me back to 15 psi boost.

Update 03/05/2016

In an attempt to increase airflow through the radiator, I moved the top of the radiator forward about a 1/2", this gave more room between the back of the radiator and the front of the supercharger airbox. It also changed the amount of clearance between to hood and some of the other components in the engine compartment. I had to shorten the airdam on top of the radiator and remove the chrome ring on the air filter. I also took some photos of the filter shroud from inside (hood up/hood down) and noticed that there was an inch gap between the top of the shroud and the hood. So I added some aluminum sheet metal to the top of the shroud to fill in the gap.

This should stop more of the hot air from the engine compartment from getting into the engine.

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Copyright 2009, George A Suennen
written: 11/16/09
rev: 03/06/16