Quad Throttle Body Induction

The throttle bodies are based on a pair of stripped 40DHLA side draft Dellorto's. While 40's are probably a bit too small, I had them lying around and they weren't doing anything - hence I was able to make this setup reasonably cheaply.
All the jets, chokes, venturi's, etc have been removed. They have suitably sized alloy sleeves in them to block up the holes left over from when they were used as carbies. I have deliberately mounted them upside down on the manifold to bias smooth airflow to the roof of the port.

For the moment, the fuel injectors (SR20DET items) will be mounted in the air box, at the trumpet. This will be done for 2 reasons:

1) It is the easiest way to mount them without having to destroy the carbies;
2) This arrangement has given improved top end power on a friends car, when measured on a dyno.

We were orignially going to run FJ20DET injectors, but were unable to fit them due to the limited space in the airbox. The fuel rail would have had to run along the side of the box between the airbox wall and the strut tower - and there wasn't enough room. Instead we needed to find an injector which was fed fuel from the side. As it happens, this is exactly how the SR20DE/DET (except GTiR, apparently) are designed. It may beg the question as to why we considered running FJ injectors in the first place and the answer to that is that they were alot cheaper than SR injectors and there was much less fabrication involved to fit them (had there been enough room in the airbox).
We sourced a set of SR20DET injectors from a 180SX. These injectors fire a much finer (ie better atomised) spray of fuel than the FJ injectors. Had the injectors been mounted closer to the valve, this would have allowed greater fuel control, but being at the trumpet this advantage is negated.

Down the track we may go to a dual injector arrangement (one set of injectors at the trumpet and another set closer to the valve) for a better fuel control, and hopefully, improved torque. The problems with doing this are:

1) The carbies will need to be permanently modified to accept the second set of injectors, which is something we're trying to avoid for the time being;
2) It is reasonably expensive to enable the extra software on the engine management system to run the second set of injectors;
3)A second set of injectors needs to be purchased.

The throttle bodies have been mounted on a custom manifold which I had to make. Due to the lack of room under the bonnet, it was necessay to use a manifold which was as short as practicle. No aftermarket organisation could provide something like this for a reasonable price, hence I resorted to spending long, hard hours with a die grinder. More info in the following section here.

Using quad throttle bodies means it was always going to be easier to use a throttle position sensor (TPS) instead of a mass air pressure (MAP) sensor. Fortunately, the ECU was already configured to use a TPS.

Mounting the TPS was pretty easy. All that was needed was to bend up 2 pieces of alloy strip, clamp them to the manifold and then drill them at the appropriate height to mount the TPS. Finally they were welded in place.

The actuating lever for the TPS is off the original throttle body, which was on the old plenum chamber. It simply needed to be ground off the old throttle shaft and then shimmed and bolted to the new carbie throttle shaft.

This view gives a good indication of the transistion from round port (carbies) to oval port (SR20 head). Here you can also see the butterfly arrangement. Notice that the throttle shaft is not visible from this angle. This was cut down so as to improve flow, along with the replacement of the butterfly screws with smaller cap screws. Having done these mods it is ESSENTIAL to ensure the throttle bodies are adjusted properly, so as not to bend the shafts.