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Fitting K&N Air Filters

Fitting K&N filters is an easy upgrade to any car especially a classic, they will add approximately 5bhp to the engine output but because they are washable and can be re oiled they have a life time guarantee so you should never have to buy another air filter.

Paper Verses K&N

To meet minimum filtration standards, paper air filters must be thick or the fibers must be tightly compressed and dense. Therefore paper elements that provide very good filtration are more restrictive to air flow by design. As a paper filter becomes more and more clogged, the pressure inside the filter drops while the atmospheric air pressure (approximately 14.7 psia at sea level) outside the filter remains the same. An excessively high pressure differential created by a restricted filter can literally pull dirt particles through the paper medium. In other words, the performance of a paper filter, i.e. air flow through the filter and its ability to protect your engine, DECREASES near the end of its service interval.

The K&N air filter is somewhat more complex. The design features multiple layers of oiled cotton fabric which captures the airborne dirt particles. These dirt particles cling to the fibers of the filter and actually become part of the filtering media. This process, known as depth loading, allows the K&N air filter to retain significantly more dirt per square inch than a paper filter. The cotton fabric is sandwiched between pleated aluminum screen. Pleating increases surface area which in turn prolongs service intervals. Pleating exposes substantially more surface area compared to a flat element like foam.

The dirt particles collected on the surface of a K&N element have little effect on air flow during much of its service life because there are no small holes to clog. Particles are stopped by layers of crisscrossed cotton fibers and held in suspension by the oil. As the filter begins to collect debris, an additional form of filter action begins to take place because air must first pass through the dirt particles trapped on the surface.  That means a K&N air filter continues to exhibit high air flow throughout the life of the filter while it is accumulating dirt.  At the same time, the air flow for an average paper air filter can decrease dramatically as the paper element gets dirty.  So as dirt accumulates, the performance advantages of a K&N air filter can increase!  Tests performed by an independent laboratory commonly known as the Frazier Permeability Test have shown that the Medium used in K&N air filters flows more than 300% more air than paper air filter medium when compared on a square inch per square inch basis. You can be assured a K&N air filter will provide dramatically more air flow which can enhance engine performance!.

Fitting Guide K&N filters to an MGB

MGB original air filter set-up1. This how the original air filter set-up looked before we removed them ready for the new K&N set. There is nothing wrong with the original paper air filters apart from the fact that they need changing every year and are not as efficient as a K&N.



hoses2. This is what the kit looks like when it comes out of the box. This kit has two large K&N filters with a smart MG logoed plate that covers both elements. The original back plates from the filter boxes are used.



drive belt3. With the old filter boxes removed the carburetors were given a quick clean up with the engine switched off with carburetor cleaner. This was to remove any loose dirt and grime on the outside and the mouth of the carburetor. The engine was then run and allowed to get up to operating temperature. With the engine speed increased short bursts of carburetor cleaner were sprayed into the mouth of the carburetor (if you use too much it will stop the engine)



Original Back Plates 4. This is what the original back plates look like (after they have been cleaned up). I have been told that these items flow very well and are very good stub stacks in there own right and it is not necessary to fit any others.



Carb Balancing5. Before the new filters were installed we had to set up the carburetors correctly. For this we used a Gunsen Carb balancer which is basically a flow meter. You place one end on the mouth of the carburetor and adjust it so that you can get a steady reading of flow (make a note of it). Next (keeping the settings the same) the balancer is put on the other carburetor and then the idle screw adjusted so that the flow reading is the same as the first carburetor. This is repeated until both carburetors are flowing the same. The idle speed can then be adjusted turning each idle screw the same amount.


Final Assembly6. The new filters use the same bolts as the original filter boxes into the clamps at the back of each carburetor, these are just screwed in and tightened up with a spanner.




K&N filters fitted to an MGB7. All finished and now the best bit, the test drive.With the K&N filters fitted it certainly sounded good and felt more responsive.



After the K&N filters had been fitted it was obvious that the airflow through the filters was much increased so as we had balanced the carburetors during the installation of the filters I decided to tune the car using the vacuum gauge which made a huge difference, to find out how to do this click here