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The K&N 57i (part number 57-0238) has gained wide acceptance in the MGF community as one of the best options for an after market filter. Independent rolling road tests have demonstrated an 8 BHP gain on standard 1.8i models, and an impressive 15 BHP on the VVC (click here for the power graphs). At a unit cost of approximately £100 including VAT and delivery within the UK, this represents excellent value for money, at up to 0.15 BHP per pound sterling. This compares favourably with less than 0.02 BHP per pound sterling for a typical new performance exhaust system.

The unique aspect of the K&N kit is the adoption of additional cooling ducts that run from under the car into the engine compartment, reducing the temperature of the air being drawn into the engine by up to six degrees Celsius. Cold air is denser, and there fore contains more oxygen. More oxygen means a more efficient burn of fuel, and more power.

A common feature of all the cone filters available are that they are attached almost directly to the inlet manifold (via the throttle body/ plenium chamber). This eliminates the somewhat tortuous route that air drawn into the engine has to take as standard (turning over 300 degrees in its 2 metre passage into the engine). This has advantages in terms of the 'ram air' characteristics of a normaly aspirated engine (further explaination, click here). Furthermore, these filters enable high airflow through their elements, have good filtering characteristics, and be washed and re-used almost indefinitely!

Is there any bad news? The majority of insurance companies do not raise premiums for fitment of these airfilters, although I’d advise you check first (for instance, General Accident do not allow for ANY modifications to your car). The issue of the Rover warrantee is a little unclear, but most MG dealerships appear to be very enthusiastic about these products, and have a quite liberal policy. Again, it is advisable to check with your dealer first. Of course, you could always uninstall the filter before you returned your car to the dealership for servicing... In fact, removal is so straight forward, it should enable you to fit a filter to a hire car too, although I wouldn’t necessarily recommend it!

The fitting instructions below apply to the K&N 57i kit specific for the MGF, although many of the points would be applicable to the other makes of filter.

Tools required: socket set or spanner (10mm), pair of pliers and a flat head screw driver.

Estimated time for completion: for the first attempt, budget approximately 60 minutes.

1. With the boot lid open, remove the engine grill. This is clipped in place along its front (towards front of car) edge. Gently pull the four clips from the rubber boot seal and lift the assembly clear of the car. View of engine bay, standing at rear of car, looking forward: right- oil filler and dip stick; centre: engine, and closer to you, the plenium chamber [also known as the throttle body]; left: airbox and flexible tube jubilee clipped to plenium chamber.

2. Remove engine cover from inside car. Here's how:

a. Erect hood. From inside the car, there are five clips visible at the base of the hood, under the rear screen. Release these, and raise the rear of the hood so that it is vertical. Take a piece of string, and tie the hood in this position by fastening the other end of the string to the front of the hood, around the fastening clip.

b. Remove carpet and sound deadening material from the rear deck. It will require a bit of tugging, but should come free reasonably easily. Exposed will be the engine bay cover: a dull-metal coloured plate, fixed in place by a number of hexagonal headed bolts. Go round each of these in turn, unscrewing them and putting the each in a safe place.

c. Put all of the hood-securing clips in the down position. Push the released engine cover plate towards the front of the car, lifting the free trailing edge upwards. Ensure that each of the hood clips are under the trailing edge of the engine cover plate. Once completed, pull the cover free from the car. You will now have a much clearer view of the engine bay.

A quick word of caution: there is a sharp edged piece of metal under the rear edge of the T-bar- this will easily graze unwary knuckles!

3. Undo the jubilee clip at the airbox, and the spring clip at the plenium chamber, holding the flexible air duct in place. Remove ducting.

4. Remove the black plastic screws (should be two, although often only one is to be found!) holding the airbox to its mounting bracket. Pull the airbox free. Now peer down into the engine bay, from inside the car looking towards the rear. On the right, near the bottom of the engine bay is a black plastic box. This is the resonance chamber. On its inner surface, there is a rigid elbowed plastic tube pointing upwards towards you, that once lead into the airbox that you have just removed. This needs to be removed to enable you to later thread through the 57i cool air induction tubing. It comes free will a non-too-gentle tug (it won’t damage anything).

5. Assemble the filter cone as described in the 57i kit [putting together the cone, a connecting piece and a length of induction tubing]. The induction tube is curved asymmetrically. Make sure the curvature is closest to the cone filter itself. Affix the assembly to the plenium chamber. Tighten the jubilee clips. It is tight enough when it is no longer possible to pull the induction tube off the plenium chamber when attempting to move the attached cone filter back and forth.Click here for the picture of the finished article.

6. Attach the cool air ducts. [UPDATED 4/5/99]

You will need two small cable ties, and SIX large cable ties. (You will need to purchase extra , as the kit only comes supplied with two or three large ties).

a. Extend the compressed cool air ducts (x2) to about 40 cm (approximately the distance between the boot catch and furthest boot corner, if you don't have a meter rule handy).

b. Take two large cable ties, and attach them together (via one of the ratchet eyes)- and do the same with the other two large ties. This is done so that the cable ties are large enough to comfortably go around both cool air ducts. Affix these cable ties at one end of the extended cool air ducts to bind them both together, leaving the other end free for the moment. Trim excess material from the ties.

c. Thread the ducts, free ends first, into the engine bay from the top so that the bottom of the ducts are under the car. Fix the top end of the ducts so that they are 4 inches (10 cm) from the K&N air filter. The best place on a 1.8i is probably a convenient point on the front fire wall; fix the ducts using the small cable tie tied around the composite large cable tie. (The 1.8i throttle body is in a slightly different position to the VVC's illustrated in the supplied K&N instructions). For VVC models, the tubes can be connected as described on the filter box mounting bracket.

7. Underneath the car, next to the near side rear wheel, draw the cool air ducts so that the lips of each duct underlie the rear subframe front crosss member by pulling/ extending both of the tubes down and forward. Bind the two ducts together with the two large cable ties. Thread the other two large cable ties together at one end. Scrabble under the car, and pass the tie over the top of the cross member and down again so it encircles the crossmember. Present the ends of the two cool air ducts towards the crossmember, and thread the crossmember tie around the cool air duct tie, and fix and tighten together. Trim the excess material. Click here to see what this should look like.

You do not need ramps to do any of this, so long as you do not mind getting a little dirty!

8. Replace the engine cover, in its correct orientation. Position the hood retaining clips to facilitate the process (as described in 2c above), and recover the clips above the engine cover plate to allow it to settle in position.

DO NOT OVER TIGHTEN THE RETAINING BOLTS: the screw threads are fragile, and the bolts will strip if tightened over enthusiastically.

9. Reposition the sound deadening material and carpet- pay particular attention to that sharp edge under the rear edge of the T-bar. Restore rear aspect of the hood to its original position, and clip back into place.

10. Replace the engine grill from inside the boot.

11. Now rev your engine, with a manic grin on your face! Enjoy!

Budget about 60 minutes for this process. It is quite straight forward, and the difference the filter makes to your car is staggering (but don't just take my words for it!). You will notice greater forward thrust through all the intermediate gears, smoother running, and some people have reported up to 10% increases in fuel economy (shamefully, not something I personally have been able to repeat!). The sound that the filter makes is pure induction noise. It is almost shocking when you hear it for the first time from inside the car. But the greatest plus is that this sound is almost inaudible at a constant cruise. You only get the roar when you want it: when you are putting your foot down!

I have had the 57i kit fitted from there introduction in the early half of 1998, and have not regretted it. I certainly could recommend this product. Happy motoring!

Thanks to Andrew Phillips for his help in installing the airfilter, and for many of the tips appearing above.

The ‘Big Four’ Filter manufacturers for the MGF, and where you can purchase them:

The Abingdon Trophy (1.8i & VVC) and Moss International Speed Chamionship Standard class allows the fitment of any after market filter and cold air induction system sold with that kit. Note that there appears to be some ambiguity regarding home made kits, but at present these do appear to be allowed.