Plumbing (Air)

The pipe work for the air system is made up of 2" DIA Aluminium Tube and various bits of silicone hose.

Essentially with all forced induction systems there are two ways of plumbing the supercharger in; before the throttle (Downstream Throttle)  or after the throttle (Upstream Throttle). 

By far and away the most common configuration for Centrifugal supercharger installations is Downstream throttle, the main reason being the ease of installation.  You can leave the throttle as is without having to move or modify it.  But this does require the use of a Bypass (Anti-surge/Relief) valve to relieve the pressure between the closed throttle and the still pumping supercharger by pushing it back round to the supercharger intake.  This can be controlled in a number of ways but most commonly is controlled from the inlet manifold vacuum.

I chose to take the conventional route as this was the easiest and most cost effective.  So the throttle body remains as standard downstream from the supercharger.  Because the engine is an EFI it utilises an air flow meter (Air Mass metre) this can be positioned upstream or downstream of the supercharger, there are pros and cons for each, however once again I decided to go with the generally accepted best option and have he flow metre upstream of the supercharger.  i.e. not under boost.  This has the benefit of not passing compressed and therefore heated air through the flow metre, but does mean that the re-circulating bypass halve needs to return to the system after the airflow metre but before the supercharger.  If you did not do this and just dumped the excess to atmosphere the airflow metre would actually read excessive airflow under partial throttle conditions and therefore provide a very rich incorrect fuel air mixture.

The final air flow diagram looks like this in pictorial form:

These photos shows all of the components in place.

here you can see the K & N Air filter on the left that is then connected directly to the Air Flow Meter.  This then connects to a large diameter Aluminium tube that has a 1" DIA tube welded to the side of it, this is the air return from the re-circulating bypass valve.  This then connects directly to the Supercharger intake.
From the supercharger outlet there is a 90 Deg silicone hose that then connects to a custom fabricated 2" DIA Aluminium tube section.  This also incorporates a 1" DIA takeoff for the Re-circulating bypass valve.  Its the light blue 2" DIA pot shaped item on the right.  You can see the small vacuum hose going to the top of it which actuates from the inlet manifold vacuum.  The light blue tube coming from the bottom is the air return pipe which goes back to the supercharger intake.

The final components in the air circuit are two silicone hose sections, a step up section and a 90 Deg bend to attached the aluminium section to the throttle body on the side of the plenum chamber.  The whole lot is all connected using stainless steel jubilee clips, with Aluminium "p" Clips mounting the aluminium section to the top of the front grille panel.

There was quite a lot of time and effort that went into arriving at this configuration. below there are some pictures showing some abandoned ideas and also some of the ideas actually used in the early stages.

1st Attempt

These shots show the first attempt at plumbing the air circuit. The tube section is actually made of stainless steel.  The company that made the exhaust system also produced supercharger systems, so I asked them to make a section to connect the supercharger up.  However it was far from satisfactory mainly because of a poor fit, the bypass valve takeoff was right next to the supercharger and not near the throttle (it is best practice to have the bypass valve as close to the throttle body as possible).  The position of the takeoff actually fouled one of the crank case breathers so that it could not be connected up.  Also the weight of the thing was horrendous it probably weighs 5 times as much as the Aluminium section I ended up with even though it is half the size.

2nd Attempt

Here you can see my first pass at the aluminium tube section.
note: here the old 5AM Airflow meter is in place but I have not yet any provision for the Re-circulating bypass valve return into the supercharger inlet.  Also you can see that the initial idea was to use an aluminium section to provide the step-up and 90 deg. bend to connect to the throttle body.  It also housed a 9th injector to provide additional fuelling.  I later found out after talking to Mark Adams that this was not necessary.  As if the ECU is chipped correctly the standard injectors are easily capable of producing in excess of 300BHP.

It was at this point that I was having serious problems getting the engine to run correctly.  It was seriously rich, with black smoke bellowing out of the the exhaust.  I suspected the airflow meter.  I thought that I would need to change the standard unit to allow for the increase in expected airflow, so decided to replace it with the Lucas 20AM.  I was not sure where to position it in the circuit at this time and the pictures below show some tests with bits and pieces I had at the time.  These trying the Airflow meter connected to the throttle body.

3rd Attempt

Here I have the ali Tube with takeoff in place for the return back to the supercharger intake.  The silicone tube sections onto the throttle body are there too.  Also you can see the 20AM flow meter in line behind the Supercharger.  Whilst this looks a neat install it was rejected due to the air filter being located directly above the offside exhaust manifold.  Exactly what you don't want on a forced induction system.  The air gets hot enough due to the increase in pressure, without being pre-heated by the exhaust.

and Finally

All of the pieces in place, including the bypass hose from the valve to the supercharger intake.  Also you can see the airflow meter and Air filter relocated by using a silicone bend to get away from the exhaust.