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MG MGA - Air Filter Material

Steve Gyles and I today found that it was near impossible (very heavy) to blow (by mouth) through the air filter fitted to my 1800cc. motor. Looking at recent posts re air filters, I'm not sure that we have good filters - see attached picture.

Fuel consumption is very high despite leaning the carbs off as far as I dare. We have checked the electronic dizzy and it is at 10 deg. and responds correctly with advance etc. so have ruled that out.

Could these very thick/heavy filters cause excessive fuel consumption and a pop-pop-popping backfiring on a long down hill run?

What about K&N filters? Your comments please.


Barry Gannon

I am using the same type of filters, and mine are extremely breathable. From your picture it seems to me that it's time for you to replace those filters. They look very dirty indeed. As for K&N's they are the very best filters there is. I would certainly recommend them.

F. Camilleri

Frank, They have been in service for 12 months! Maybe they look dirtier than they really are.
Barry Gannon

Must have been quite an experience trying to blow through that thick wadge of matted 'stuff'....good way to pass time!
I attach an extract from the magical book 'Tuning etc ' by Vizard. The comment at the bottom is a good K & N . I have ....and they are good .

Neil Ferguson

Barry, just threw a pair of those away whilst having a clearout, they are rubbish! I had all sorts of problems with them on my car, lack of performance, oiled-up plugs to name but two. If yours are the same make as I had, I would throw them away and fit K&N elements. Look in the archive for "Plug colour" and you will see the trouble they caused me!
Lindsay Sampford

K&N are great for our cars with their carburetors. Clean and lightly oil often.
DO NOT use them on a car with a "Hot Wire" air flow meter type of fuel injection. The oil and dirt through a K&N will kill the air flow meter. The money spent on the trouble caused by K&N filters on modern cars is what I term "Stupid Tax"
R J Brown

You tried to blow through that? How many beers had you both had? MB
M Blencowe

Seeing as how you have Mr Gyles there, why don't the two of you rig up a water manometer across the filter element?
All you need to do is disconnect the breather to the filter, and hook up a piece of clear hose to the back of the air filter. About 4 feet of hose in a U shape, free end open, and some water and you can give us numbers. Add an extension so you can carry it in the car on the road for good numbers under full load.
I've seen those filters and they might make good winter boot soles.

FR Millmore

RJ, I've got K&N's and didn't realise that they needed oiling -is this recommended by them or just your practice?
J H Cole

Barry, I can also recommend K & Nís

R A Evans

Barry, I think the type of filter you show is a very poor reproduction design compared with the original. I've been looking on Ebay for years now for one to the original design and have refused to buy this sort.
Years ago I bought one advertised as original and I've attached a photo. You will see there are quite a few differences. First, the size of the concertina folds is much greater; this will increase the effective area and reduce the pressure drop. Second, the height of the steel mesh, top to bottom, is greater which again increases area and lastly and perhaps most importantly the felt does not cover the central part of the steel mesh on either side. I believe that if the mesh is covered with felt it will not only clog up comparitively quickly but when it is dirty you won't be able to wash out the dirt in the felt with paraffin so in effect it is a use once and throw away design.

If you look carefully at the original filter design there are in fact two layers of steel mesh and sandwiched between them is a layer of fabric gauze with a similar mesh size as the steel. I think this gauze is present to retain oil and to keep the steel wet with oil which would drain away in it's absence. I reckon the oily mesh would be similar to fly paper in effectiveness.

I don't know anyone who sells the original style of filter and have toyed with the idea of making up a few. Unfortunately as yet I've only been able to find a source for stainless steel mesh and it is rather expensive. I guess mild steel would have been used originally and would have been a lot cheaper.............................Mike

m.j. moore

They do need cleaning and oiling, not too often, but it's about a one hour chore using their special fluids. Check the K&M web site for for the instruction sheet.
Barney Gaylord

Good. Looks like we have found the culprit. I was suspicious the moment Barry described the systems to me. He fitted 'new' carbs and filter boxes about 12 months ago. He had never looked inside the canisters (did not see the need). The car actually goes surprisingly well. Sounds great with its straight through exhaust. Burbles and pops a lot on the overrun. It is just that fuel consumption is so dreadful and he is unable to lean it out correctly.

Is there a supplier of k&ns in Melbourne who is likely to keep the E3180 in stock?

I think that when he has the k&ns and stub stacks fitted he will have a totally different car.

Steve Gyles

Spelling error: for 'systems' read 'symptoms'

Phoning suppliers as I type. Looks like they will have to come from Sydney.

Steve Gyles

I have taken your advice and the K&N's are on the way. Thanks for your input.

We intend taking a run down to the Philip Island Classics on Sunday. I would like to discard the current filters and substitute with a stocking wrapped twice around the canisters, just to see if the fuel economy and engine performance improves. This is only a short term idea as the K&N's will take 10 days to arrive.

Is this wise? Are they likely to melt? Will they provide sufficient filtering? We will be on sealed roads, no dust.

Barry Gannon

Some guys use sweaty socks on the big air horns so provided you have a material that can take the under hood air temps it should be fine.
Did Steve bring a set of stacks in his bags for you to conjunction with the K&Ns you will be getting a load more air into the cylinders..I would believe 10 to 15 % ......a whole new world!
Neil Ferguson

Neil, I have stub stacks from UK on the way as well. I hope you are right about the improvements!
Barry Gannon

Barry..the reason I make the volume of air comment is that if you look at at the comparison chart I sent on a previous post the K&N allows about 6.5 cfm per in2 compared to about 4.5 for most of the inferiors( and your existing old folded felt blanket filter looks in the latter ). These are both measurements at 1.5in head loss. i.e. at the same head loss there would be 44% more air .... However the head loss will increase for the poorer filter unit as the car struggles to get the air in at a lower pressure less the benefit will be be less than the fig above. It may be also that the area of the filter is large enough to give nearly enough air with the poorer filter.
..but the benefit will still be significant I believe.
Good luck.
Neil Ferguson

just did some quick calcs and I make the total filter area (for two carbs) to be about 44in2 and the theoretical airflow pumped by the engine ( 1.6 lt) at 3500rpm to be about 49 ft3/min
This gives about 49/44 ft3 /min/in2 i.e. 1.1.
If you apply this to the Vizard chart I included on an earlier post then we seem to be at much lower veloc through the filter element and therefore head losses . The filters on an MGA look quite generous in size for the engine capacity..
In conclusion you will get a benefit with the K&N but not a huge one...
Neil Ferguson

NF, when I fitted K&N's there seemed a significant increase in the engine breathing judged by sound and my spark plugs quickly went white that I took to indicate an increased airflow and consequent more lean air/flow ratio. However the K&N's replaced modern filters exactly like MJ describes so my engine might have been slightly asthmatic to begin with.
J H Cole

Thanks for your input Gents! I have discarded the clogging felt filters and covered the wire cage with a double thickness of 30 denier panty hose! (OK you lot just behave yourselves!! They are surplus to requirements donated by my wife!)

I have the K&N's on order. So just to tide me over I have fitted the panty hose. We will see how they go on the run to the Island this weekend.

Gyles and I have just fitted the 'stub stacks' which arrived from Steve Ash today so we are looking for a substantial improvement in performance. Will report later.

Barry Gannon

Niel, -- 1600 cc engine is about 97 cu-in displacement and will pump half that much per revolution (remembering 4-stroke operation). That comes to 98 CFM at 3500 rpm or 196 CFM at 7000 rpm (of you have the heavy foot). If the filter area is 44 in2 for two filters, air velocity through the filter would be about 5.3 fps at 3500 rpm, and around 10 fps at top speed.

In terms of volume it is
2.23 cfm/in2 at 3500 rpm,
4.46 cfm/in2 at 7000 rpm.

At 7000 rpm this is just 2/3 of the capacity of the K&N filter(s), and still below the capacity of a thoroughly clogged K&N (according to the Vizzard chart). The specified 1.5" H2O allowable pressure drop across the filter element is exceedingly small, like 0.004 atmosphere. This air filter installed will have roughly the same effect on engine performance as open intake with no filter. If the engine makes 120 HP max with open air intake, then use of the K&N filters might drop about 0.5 hp at full chat (with a clogged filter).
Barney Gaylord

Mr Cole don't worry about oiling them now,they are ready to go right from the package.When you clean them get their kit which includes the oil.
gary starr

My engine does 4 strokes per rev........beat that!
Agree with your comments
Neil Ferguson

Here is K&N part# 99-5050 On their site:
This kit is to clean and re oil the filter.
R J Brown

Thanks for info RJ, I'll check out a UK supplier.
J H Cole

Just checked the cleaning/maintenance period for K&N filters. If I've got the right product K&N say between 30,000 and 50,000 km subject to a visual check -filter should not be black. No need to worry quite yet then.
J H Cole


Oh dear. Barry and I used black panty hose. Should we have used white?!

Actually, the car is going extremely well on it as Barry will report shortly. Maybe a marketing opportunity as a K & N alternative!

Steve Gyles

Wow! What a difference! The combination of stub stacks and no clogged felt filters certainly makes a difference.

Steve Gyles and I had a fast run down to the Phillip Island Classics, about 80 miles each way, and the car ran smoothly. Noticed a huge improvement (lowering) in fuel consumption, I expect much to do with the removal of the filters, and a marked improvement in throttle response due to the stub stacks.

Steve 'piloted' the 'A' on a run around the race track during the lunch break, caught the 'E-types' and a Carrera in the corners, had the engine up over 5000rpm. most of the time and had me hanging on for dear life!

The K&N's are ordered. Thanks to all for your comments.


Barry Gannon

This thread was discussed between 08/03/2012 and 12/03/2012

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