Air Intake Improvement
This modification was submitted to this site by Robin XR from the XR Owners Club. He has a MK3 XR3i (pic in the Gallery) that I have driven and it certainly seems sprightly enough. His car is an '83 model and so has the earlier airfilter box so this modification might not be applicable to your particular car. If you find you have the later airbox fitted, then go to the bottom of the screen for the alternative to this modification.
I'll let him take it from here.
Hi Smiler, Thought you might want to include this mod if you can find a space for it on the site. It's my air intake mod, not sure if I showed it to you or not. Very basic mod but it's all I've done to the engine! Text might go like this...
Most engine mods improve the airflow, on the principle that more air allows more fuel to be burnt, hence producing more power. Removing any unnecessary restrictions in the airflow is often the cheapest and simplest improvement.
On the right of each of the pictures below is the original mk3 MFI air intake tube, facing forward and feeding air upwards into the bottom of the air box. Remove the tube by lifting up the fuel distributor (6 screws to undo), pressing in the tabs on the top of the tube and pulling it down. Cut off the forward facing narrowed section of tube, and replace it with a larger diameter, as shown on the left.
The larger diameter tubing is 3" drain pipe (cheap!), this is heated at the end until soft, and pressed onto a flowerpot to give the flare at the outer end, and pressed onto the intake tube to fit at the inner end. Pop-rivets secure it. The other side effect of this modification is a slight increase in "induction roar" - noise reduction is normally the reason for the restriction in the first place. The engine sounds throatier as a result of removing it.
Now, if you have the later type of airbox as fited to the MK4, then the equivilant mod is a bit simpler. This air box receives it's air direct from the front panel via an internaly trumpeted hole. The simple way of getting increased airflow is to drill more holes in it! Go for a small number of large holes as opposed to a large number of small holes. Also restrict the holes to the front panel only or you could end up with either warm air being sucked into the engine or the air being sucked back out of the air box by the oncoming airflow as the car is driven.
See the picture below.
One of the popular Ford magazines carried out a comparrison test with various different 'induction kits' and this particular style of modification. There wasn't that great an improvement in performance and some of the induction kits actualy reduced performance but the drilled airbox came out with the same results as the best performer.
I have since been advised of another alternative to this mod by a moderator from the SeriesOneTurbo forum by the name of Scott R. He suggests that instead of drilling the extra holes in the front of the airbox you should remove the internal trumpet. Then affix a length of suitable diameter flexible tubing to the trumpets mounting collar on the airbox and route the free end forward to a fresh cod air supply. Use as straight and short a route as possibe. Aparently this modification was carried out to the early MFi race cars to good efect on the track.