Depending on your budget converting an engine to individual throttle bodies can be relatively straightforward if you're prepared to pay for a complete kit. There are any number of suppliers, but they come at a price usually in the £2-3k range by the time it's finished. On the other hand, if you're prepared to take some time, overcome a few technical challenges, and be a bit more innovative, it's possible to fit individual throttle bodies together with a fully programmable ECU and have it running efficiently for £600-700. This article covers how I achieved the latter on the 2 litre Zetec engine in my Westfield. The article is in two parts; the first covers the fuel tank, swirl pot and pump mods; the second part (link at the bottom of this page) covers the fitment of the throttle bodies and the fuel pressure relief valve. There's a separate article, directly accessible from the Westfield page, that covers the ECU and engine tuning.
Part One - Fuel tank, swirl pot and pump mods:
Carburettors have a float chamber which is effectively a small fuel reserve, so if you corner or brake hard it doesn't really matter if the fuel in the tank sloshes away from the outlet to the fuel pump and starves it, and consequently the carbs themselves, for a few moments. The fuel in the float chamber will keep the engine running until the g-force subsides and the fuel moves back to cover the outlet to the fuel pump, at which point the float chambers are topped up by the pump once again. However, fuel injection is different; there is no inherent fuel reserve in the components so if you starve the pump of fuel the engine stops, which isn't an especially desirable feature. The required modification is the inclusion of a "swirl pot" in the fuel system which will ensure there is always fuel available to the high-pressure fuel pump irrespective of the cornering or braking forces. There are several ways of tackling this issue. Firstly, depending on the original specification of the car, it's possible there's already an intrinsic swirl pot fabricated in the tank. If so, thank your blessings and move on. If not there are really three available solutions.
The first is to remove the fuel tank and have an intrinsic swirl pot fabricated into the tank. The usual way is to weld a small extension underneath the tank fed through a 30-50mm diameter hole in the bottom of the original tank so it fills up from the main tank by gravity but when there are high cornering or braking forces the fuel can't escape back into the main tank. There are some good photos on the WSCC forums of typical examples. The benefit of this approach is that the system can feed directly to a high pressure fuel pump, it takes less space than the alternatives and the plumbing is relatively simple. The downside is that the bottom of the additional tank sits quite low in the car as does the high pressure pump (most of which will not "suck" very efficiently), and there's the cost of getting the fabrication carried out.
Now I'm going to digress a little bit but please read this section. If you are doing any work on the fuel system, especially the tank, do not underestimate the essential safety precautions. We all know that fuel is flammable, and a little goes a long way, so when you first start and drain the system make sure you are away from any sources of sparks or heat, the battery is disconnected, there are no lights, heaters, etc nearby, the area is extremely well ventilated and surplus fuel is efficently drained into a recognised fuel container. With the fuel drained you will have reduced the fire risk but substantially increased the risk of explosion as the fuel tank now contains an air/fuel mixture. The next step is to thoroughly clean out the tank. A friend of mine who is a fabricator by profession puts the jet of a pressure washer in the tank and just leaves it to flush through for 15 to 20 minutes. Personally I like to take my steam wall paper stripper and put the outlet hose into the tank for 30 minutes and steam the fuel out.
Back to the tank/swirl pot options; the remaining two options leave the tank more-or-less as standard, with the exception of an additional return fitting, and retain the low pressure pump to feed an external swirl pot/high pressure pump of one form or another. The first alternative is to use the combined swirl pot, high pressure fuel pump and filter from a Digifant injection system as fitted on early VW Golf GTI's. I know of a couple of Westfield installations that use this successfully, and although it's a bit bulky it is neat in terms of minimising plumbing and good units are usually available on ebay for around £30-40.
The other option, and the one I pursued, is to take the outlet from the original low pressure pump into a separate swirl pot, which in turn feeds a high pressure pump. The advantages are that it minimises fabrication, the fuel tank doesn't have to be removed, and there's a lot of flexibility to where each of the individual bits are fitted. The downside is that there is quite a lot of plumbing and joints to be made.
Looking at this in more detail, here's the swirl pot. This was made by my aforementioned fabricator friend to my own design, but they are available from most motorsport catalogues. The swirl pot works by the supply from the low pressure fuel pump, and the return from the engine entering on the periphery of the container causing the fuel within to "swirl". Any entrapped air, and the surplus fuel, exits via the centralised top exit and returns to the tank. The supply to the high pressure fuel pump is taken from the bottom of the "pot". So, if the low pressure pump is starved of fuel during cornering or braking there is around three-quarters of a litre held in the swirl pot to ensure a continuous supply to the high pressure pump.
There's one trick here I'm going to pass on. The delivery flow rate (and hence the rate of the ticking noise) from the low pressure pump is regulated by the back pressure it has to pump against. In the normal course of events when it's feeding a carburettor or two and the float chamber needle valves close, the back pressure increases and the pump stops ticking away. In the system I've described where all the LP pump does is keep the swirl pot topped up there's very little back pressure so the pump ticks away like mad. The trick is to fit a small orifice, around 1.0 - 1.2mm in the return line from the swirl pot to the tank, to limit the flow. This will slow the LP pump down to a not-too-intrusive ticking rate.
While we're discussing the return to the tank, this will require an additional fitting somewhere in or near the tank. Some people cobble a fitting into the fuel filler neck, and indeed it works just fine. I chose to install a hose fitting just under the sender gauge, as this is about the only place you can readily reach.
The high pressure (HP pump) needs to be fitted below the level of the swirl pot, as the external HP Bosch type pumps don't suck particularly efficiently. In choosing one, and mine was a tenner off ebay, the critical factors are the end fittings, the pressure rating and the flow rate. The end fittings really want to be hose fittings, otherwise you'll need to look for some more specialised adaptors. The operating pressure rating is usually 3 bar or 42 psi. Flow rate depends on the engine spec, injector spec, system pressure you plan to run etc, and you need to ensure the pump can deliver more than the maximum flow rate the injectors will ever see. There is a simple double check, and that is to make sure the pump you choose is normally fitted to a car with similar or more power than you plan for your engine.
When it comes to plumbing the whole lot together I chose to use 8mm copper fuel pipe, from Car Builder Solutions, and minimised the hose lengths. Note that there are specially designed jubilee type clips for fuel hoses that make a more even contact than the normal jubilee clip. Also the hose needs to be correctly specified for unleaded fuel and rated at more than the planned system pressure. Somewhere in all the plumbing you'll also need some filters. The usual setup is a low pressure filter after the LP pump (there is usually a strainer over the outlet in the tank to provide some initial protection for the LP pump but without restricting flow very much). Then a high pressure filter after the HP pump to protect the injectors.
This photo shows the complete package installed in the rear of the Westfield. The LP pump is just out of shot to the left but this shows the swirl pot, and just below it the HP pump.
The supply and return to the injectors passes through the two copper pipes running inside the transmission tunnel, neatly clipped out of the way so there's no danger of contact with any of the moving parts. This is particularly important on a live axle car like mine where there is more propshaft movement than there would be with an independent rear-ended car.
The link below moves onto part two of this article which covers all the stuff at the engine end of the car.
Part 2: Throttle bodies and pressure regulator.