S13 Silvia Tuning

One thing that many people attempt to build for their cars is a cold air induction system. Even otherwise stock cars can be seen with a dodgy bit of pipe hanging off the bottom of the front bumper in the hope to deliver fresh air ro the engine. This setup however is aimed at being about the best you could possibly do on a sensible budget, considering aesthetics, flow, cooling and reliabilty. It should look good and be very effective. For a cold air setup to be truly effective, many considerations must be made if it is to be truly effective. Doing this before you start to make the system is highly recommended.

Air Pickup Point

This is always a compromise between airflow and quality of air being picked up. Usually the best place for a pickup is also one where the opening will be subjected to heaps of water, rocks, bugs and other crap. A good example of this is seen in those that place the end of a tube leading to the air box hanging down underneath the bumper, only a few centimetres from the road. Imagine the steady supply of trash that is forced up into filter region.

The opposite approach is that taken by factory by putting the pickup in a position that will not allow dangerous particles into the intake, with the trade off of very little flow. Positioning the pickup behind a shut line or headlight is the norm here.

Therefore a compromise must be sought, in a pickup that receives good airflow but is is not in too lower spot as to ingest foreign debris. This is generally the case with a setup designed to create some sort of positive pressure, better known as a 'ram air' system.

Some pickups however, aim not to force air in but to simply suck it. These are commonly found inside the wheel arch of similar, not in a direct path of the oncoming airflow that the front of the car receives.

Air Pickup Shape

This seems to be something that is given very little thought, with most just leaving a tube hanging waywardly in the belief that it will magically attract plenty of fresh air. Obviously there are better things than simply a round tube for collecting air.

For a non ram air system this is not so critical, the placement is more important. However, a bell mouth is a mandatory requirement as they have been proven time and time again to outflow an open tube.

For ram air setups the shape of the pickup becomes more critical as the aim is to trap oncoming air and then translate its flow inside ducting towards the air filter. One must remember that air will always take the easiest path it is presented with, so having an opening in the front bumper with a tube places in the middle of it will probably result in most of the air travelling around the tube and into the larger volume area behind the opening. It would make sense then to trap all air entering that bumper opening into travelling down the tube, therefore giving it a much higher flow potential.

Factory bumper openings are a good place to source a pickup from, as they have been designed aerodynamically by the factory engineers to provide air to the various cooling systems of the engine and therefore should be quite efficient in collecting air. Because of tis thought must be given as to what the hole was placed there for in the first place, as robbing all of its airflow could have dire consequences on whatever is was feeding.

Ducting

Most cold air induction setups have some sort of ducting from the air pickup point to the air filter itself. Probably one of the least important areas as this piping is external to the actual induction system of the car (post air filter), and therfore is not critical in its volumetrics. The same priciples still apply however, in that minimal restriction should be introduced. Bends, small diameter piping and internal protusions are all restrictions that will hinder the available airflow to the filter.

In this situation volume of air is all that is important, so ignore any 'high air speed through a smaler diamter pipe' theories and go for the biggest ducting you can. Needless to say optimum is piping with no curves but realisticly this is very hard to achieve, so simply go for piping with as little bends as possible. Many choose to use convoluted ducting as used in air conditioning and this probably works quite well. The internal ribbing is not ideal but I doubt you would ever notice any difference when switching to nearly smooth plumbers PVC piping.

Whether this is simply a partitioned section of the engine bay or a sealed box the volume of this area must be as large as possible. Many have implemented a cold air system that simply sheilded hot air from the engine bay and have found the volume of the area left was not large enough and power fell accordingly. Its no good only having cold air if there is not enough of it.

This is particularly important in a non ram air situation, where suction is the only means possible for the air to enter the filter, where alternately any shortcomings would be compensated with the forced air flow. Either way the larger the volume the better, the aim to try and recreate the filter being placed external to the car where there is zero restriction.

Sealing is also important, as the suction of the filter is not intelligent and will draw any hot air leaking in from the engine bay. The better the sealing of the cold air to the engine bay the better it will work.

For any ram air system there is a possibility of water entering the area around the filter. Idealy it would be great if when the vehicle is stopped foreign particles could travel out of the system by simply using gravity. The availabilty of this option is determined by the shape of the inlet tract, and if a direct path is not available then perhaps it would be neccessary to place holes in the bottom of the chamber to allow drainage. This clashes heavily with the above principal of sealing. For larger objects, simply falling out would probably not happen. Therefore access to the chamber is important for regular cleaning and maintenance.

So far we have assumed that a sealed airbox is in use (whether the factory item or a larger box with a POD filter inside it), in cases where a simple partition is in place, the area will not be fully sealed and you will probably not have a problem.

My system as a basis uses a POD filter. I am no great believer in the fantastic power gains they are said to produce, as I don't mind a well setup factory airbox. My reason is that I already have the POD filter and it probably does have more ptential than an airbox in terms of flow. Around the POD I plan to build a two half custom airbox, with the pipe inbetween the POD and the air flow meter laying exactly on the part line of the box. The box will be as large as the space available allows, and will be fed by ducting from the underside, with all walls curving towards this for drainage. The most logical way for me to make this is by vacuum forming plastic. To do this I will make a foam model that fits into the available space, and use this to mold from. This will become clearer when I document the process.

The air pickup will be utilising the opening in the factory front bar designed for the factory intercooler, with all air travelling through the opening being collected and travelling into a PVC pipe elbow that leads to the botom of the airbox.

As described above I am using the opening in the factory front bumper that the factory intercooler used to use. If the factory designed this hole to feed such an important item as an intercooler then I'm sure the available air to it will be sufficient.

The basis for the pickup is a PVC storm water drain component, picked up at the local hardware store for $15. It starts as a large rectangular opening which tapers in to a 100mm round collecter. Unfortunately the piece was a little too big to fit behind the bar with the new shiny piping for the front mount so I had to trim it down a little. A copromise yes but still much better than a bit of small pipe dangling waywardly in the bumper opening.

As can be seen the unit is a snug fit indeed and will catch everybit of air entering the old intercooler feed and channel it towards the round feed, perfect for attaching ducting towards the airbox.

If your car still has inner guards you need not worry about this stage, as it will be very well protected. In my case the car came sans many items such as these, so I needed to fabricate something simple. I used 0.6mm polypropylene sheet as it is very tough, and gives crisp folds once scored.

This is the next step which is waiting on the purchase of a good quality holesaw. Coming soon...

	Shown here is the location of the fuse box in question. The shiny pipe on the left is the air filter adaptor, for the POD which has been removed to free up working space. The optimum result would be to run deucting from the bumper to the filter alongside the intercooler piping, but the fuse boc is in the way. The wiring attached to it has very little free length, so the box can't just be moved elsewhere. I finally came up with solution which doesn't require a single wire to be cut, that frees up the space completely. This is how to do it.
	Firstly unclip the lid of the box and then remove all of the relays from within. These have a simple clip on a single side that push in to allow removal.
	Now slide off the section of plastic on the side that the three big plugs are held by. There are two clips to be pushed to achieve this. This allows access to the remaining clips needed to be undone to remove the base of the box. Take this off next.
	Near where the box sits you'll notice this rubber boot that seals a factory designed passage into the area between the guard and the engine bay. Pull this out and then slice from the centre to one side as shown.
	Now push the fuse box through the vacated hole into the area between the guard and the engine bay. Orientate the box so that therelays will be facing towards the tyre when they are plugged back in.
	Reassemble the box with the base, relays and the top cover. Do not slide back on the plastic holding the three clips, this should still be in the engine bay.
	Use cable ties to secure the three clips and their plastic holder to the side of the engine bay out of harm's way. Reinstall that rubber boot with the cut facing upwards. This will protect the fuse box wiring from the hole in the side of the engine bay.
	Now it can be seen the space is cleared and everything is out of the way.
	With the air filter reinstalled it is obvious where he cut would go to run the cold air feed piping to the filter.

	Firstly Use a piece of paper to form a rough idea of how you want the shield to go. Cut away bit by bit until it fits fairly well. Lay this out over the plastic and use a sharp knife to cut out the shape.
	After some further trimming this is how my shield looked. You can refine it as you go to best fit the space.
	I secured it using five screws, Two of which were already on the car holding the piece of trim to the guard. Two others go into the lid of the fuse box and the last goes underneath the edge of the guard, pulling the shield tight around the box and away from the tyre which comes quite close if not done properly. A very strong, durable and lightweight solution. To access the fusebox the shield is simply undone and access is quite easy.