Welcome to our resource for MG Car Information.



MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Air fliters

Hi folks, thanks for all your help with the electronic ignition question, lots of food for thought!
Another performance issue, keep old ugly filter housings or change to pancake or K&N filters, would I get better performance?

Cheers Jack.
Jack New Forest

Barely. Whilst they may flow better at higher throttle openings, they will also weaken the mixture, so you may need a 'richer' needle. It's not really worth the bother, and certainly not the expense, unless you are into 'bling'.
PaulH Solihull

air filterf it's performance that you're after, then pancake filters are a move in the opposite direction. The B Series engine with its Siamesed intake port design causes some very powerful sonic shockwaves within the fuel induction system. The volume and depth of the large K&N airfilter dissipates these very effectively by creating a plenum over the opening. Sonic shockwaves simply dissipate within the confines of the plenum. Air entering the airfilter from the outside is slowed, smoothed and straightened. The large airfilter then becomes an endless source of calm, clean air. Both the 5 7/8
Stephen Strange

I agree with Stephen, the original items may not be the best looking disign, but in terms of technical, airflowing design they are hard to improve.

That's why I installed K&N airfilters in the original housing; best of both world's.
Willem vd Veer

Thanks Guys, Stephen your explanation, (me not being an engineer)will take me some time to think through but loads of info, Willem your idea sounds good, I guessed when they made these strange looking filter holders they were designed like that for a reason, well done I'll think about your idea,
Thanks paul no I'm not into bling, and you are right don't change for the sake of change, I think i'll go with Willem's idea, keep the old casings and stick a couple of nice new K&N's in there.
Cheers lads lots of good info as usual.
Jack New Forest

Jack. Please be aware that the current K&N filters are being made in China, not the USA. The net result is that the filters are not as well made and the cotton material is weak/broken in spots where the bends are. The net result is that the more expensive K&N filters are not filtering as well as the older, paper types. Nor, is K&N honoring their warranty on these defective filters. A mechanic friend has identified five of these defective filters over the last two years (one on my truck) and K&N has refused to replace them. Anyone purchasing new K&N filters needs to examine them, quite carefully, before purchase and when in use. If you see the filtering material deteriorating at the angled sections, replace the expensive K&N with a good quality, paper air filter. Another formerly good company done in by their desire for cheap production costs.

Les Bengtson

Jack. I have done the exact opposite to what you intend. I have retained the original filter and removed the casing, putting an ally plate over the ends of the filters and using the original bolts and mounting plates. This does increase induction noise slightly but gets rid of the restricting inlets of the original casing. The PO had installed richer needles so was probably intending to fit K&Ns at some stage. I figure that the now unrestricted paper filters can flow a bit more air through.
Steve Church

Reduction of quality after a move to Chinese production is no surprise, and not always the Chinese at fault but the desire for reduced production costs and greater profits for the parent company!! However cotton filters will provide a smaller resistence to the inlet air, but unless more air can physically get through the inlet manifold, around the valves and through the cylinder head, and the exhaust can exit with minimum restriction, just changing the filters will make no appreciable difference to performance unless the old ones are clogged up of course!!
Allan Reeling

lots of good info here guys, thanks.

Jack New Forest

Nobody has said anything about these foam filters, I cannot recall the name, but are they a no no? The tecnology of foam has come a long way. Do they not filter as well as cotton or paper? And what about oil to help catch particles? Particularly with foam? Mike
J.M. Doust

The oil on the foam filters is there only for the purpose of making particles ahere to the surface of the foam. I don't know of a foam filter that both filters and flows as well as a K&N cotton filter. Do you know of a foam filter manufacturer that shows on a website what his filters can do?
Stephen Strange

Stephen I state this site with some trepidation, seeing they are an Australian manufacturer I think. They seem to have some following, and I was rather tempted. In the end I settled for the wife's best cotton kitchen tea towel wrapped around the intake! ( Joking really, nice to have a little laugh now and again.) Honestly though, I have an open pancake so to speak, with a two grade foam insert with oil, and as you recommended in the tuning the 1800 write up, a small radiused ram pipe (if that is the word) to create a better flow rather that the 90 degree edge directly into the Su throats. And do you know I can feel a difference, if it is not there. Mike
J.M. Doust

Hi All

For an MGB application. K&N filters flow the same as paper ones. Cut away the old metal casings which are restrictive and you get the same flow as K&Ns only very vulnerable to damage and less 'blingy'. the casings cause a pressure drop on the main jets, the needles are selected to match this. Remove the casings and the engine runs weak as the pressure drop on the main jet is reduced. Fitting the K&Ns or just keeping the paper elements and sorting the mixtures will add around 4 bhp at the wheels on a standard engine, with a standard chrome Bumper B making a paltry 58 at the wheels on our 'new' dyno, 4 extra bhp is surely most welcome?

With regard to foam filters, we worked on filtration on tank domkey engines some 25 years ago. We had to use a triple layer of different bubble size foam to trap particles. The area required was approx 2.5 times the area needed with paper or K&N pleated style filters. I seem to recall we used special dust from the USA as a 'standard' test medium, possibly from an Arizona desert? The foam also clogs fast and denatures fast.

P Burgess

Damn, Thanks Peter. I think the foam filter manufaturers imply, they do not actually tell you that you need to wash the filter often and re-oil if it is going to work at all! Ok, I had better get some K&N. I do like the look of them anyway. Another arrangement I had, and because it was my own invention, and every one knows if it is your own dream, it always works! Was a sort of forced air plenum. A box enclosed the air filters, in turn this lead to a wide corrugated tube (a kitchen overhead duct tube. oh, alright I took it out of the wifes' unit.) this then neatly fitted to the hole in the bulkhead that housed the heater which I removed in Oz ( too hot) Now air taken in from the front windscreen intake goes straight into the filter box. Must be worth something surely! Ram air? Mike
J.M. Doust

Hi Mike

Cold air is good....every 3 degrees centigrade reduction gains 1% bhp. No chance of ram until heading upwards of 200 mph, need very long downhill road :)

P Burgess

There is a lot written about the restricting effect of the K&N pancake filters.

I fitted them to my car, but with a modification to the rear plate to allow the use of the original baseplate outside the filter housing. So you get a good inlet shape and a bit more height.

104 RWHP on Peter's old rolling road so she can't be strangled that much!

Piper 285, +60 bore, I flowed the head.

D Balkwill

This thread was discussed between 22/08/2011 and 23/08/2011

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.