The fuel system under the hood needs changes to go from CIS to an EFI fuel setup. If your car already has a Digifant fuel system with EFI injectors, then you don’t need to do this!
I used 5/16″ fuel Injection lines for both feed and return lines. They fit the VW fuel rail – that’s what size VW runs OEM from the factory.
It is VERY important that you use Fuel Injection Lines and not just regular fuel lines. The regular lines can only handle about 20PSI, which is far less than the 45PSI required of EFI injectors, and not even close to the 70 PSI that a CIS fuel pump can send!
You also have the option of re-running new fuel hard lines all the way to the rear of your car. Make sure you use a good quality bender and flaring tool. This is a safety issue, do not cheap out on your fuel lines!!
CIS fuel pumps push a LOT of fuel to the engine. V8 Megasquirt converters use CIS fuel pumps on their cars. A CIS pump can do about 90 gallons of fuel per hour at 70 PSI. That’s quite a lot of fuel!
So that all means that you can keep your stock pump easily, and no matter what modifications you can come up with, you should only have to look into better fuel pumps when you are going for more than 500hp.
If you have an A2 car, or a Scirocco/Cabriolet made after 1984.5, then you will want to inspect your transfer fuel pump under the back seat and make sure it’s working ok. Check the filter screen and make sure it is flowing properly according to the procedures in the Bentley Manual.
In my Scirocco – the fuel filter is located in the engine bay. I use my current existing filter, tied it down to the frame rail, and used it in my new injection system. The Bosch fuel filter is huge, can handle very high pressures, and it has enough capacity for much larger engines. A2 chasis cars and Foxes are lucky enough to have the fuel filter mounted out of the way under the car.
I suggest you get a new fuel filter when you do a conversion however, it doesn’t cost much, and it’s cheap insurance for your new injectors. New filters even come with a little adapter thing you might be able to use.
Remember that it’s VERY important to use a “Fuel Injection” filter, and not a regular fuel filter. Regular ones are only designed to work with less than 20 psi or so, and fuel injection runs higher pressures (at least 43.5psi) than that. I will go further to say that if you are using a CIS fuel pump – you should also use a CIS fuel filter – because that fuel pump can push more than 70PSI – and in the event of a clog – you don’t want the fuel filter to burst!