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MG MGB Technical - K & N Filters

Does fitting K&N air filters to a 69 MGB improve performance or just increase the induction noise?
Michael Beswick

They do both! I've not tested this against the stopwatch, but subjectively the performance of my '73 BGT seems to have been improved by the K&Ns. But I've got 2 caveats, one from experience.
The garage that fitted mine insisted that there was no need to change the needles in the carb when fitting them. After 2 trips back to them,when they couldn't get both the correct mixture at idle and at cruising speed, I took the matter into my own hands and fitted the needles recommended by the MGOC myself. They looked no different, but the car now accelerates and cruises better, and even the MPG has improved!
I have the larger type of K&N which includes filters for both carbs, however I understand the type which just replaces the filter on each SU individually also requires you to buy the correct stub stacks to maintain the airway. If you don't do this the benefits of the K&N are negated again.
I recommend the K&Ns - even if you don't use the performance the noise is better and they need less maintenance - go for it!
Ian

Thanks for the info -seems like a possibility. I was put off by a previous
experience with a 1500 midget -the K&Ns supplied didn't physically quite fit
- the 1500 has a strengthening rail that means there is less clearance betwen
engine and the inside of the wheel arch -and when I tried them the
performance (with original needles) was awful. I was then advised to change
springs in the dashpots -no better -so I gave up and sent the K&Ns back

Do you recall the needle number for your B and does your setup keep the original
backplates. I assume your twin filter is the one with two filters and an
oblong plate on the front

Thanks again

MB
Michael Beswick

Ian

What needles did MGOC recommend? I have just fitted K&N's using the "Bob filter" arrangement. I think my current needles are ABD.

Thanks,

BarryQ
73B
B.J. Quartermaine

If the MGOC have a listing for alternate SU needles for K&Ns, it might not hurt to replicate it here for those who aren't in the MGOC, but could benefit anyway. Not everyone doing this conversion uses the same HIF-4 carbs as the 73s. Just a suggestion.
Bob Muenchausen

Bob & Ian,
Where can I locate the MGOC list of carburetor needles?
Also, I have the K & N replacement for the original filters and want to run them without the original filter housing.
Are the stub stacks absolutely necessary?
Thanks.
Regards, Graham
Graham Ayers

Moss Europe in their Performance manual(sales@moss-europe.co.uk) Show suggested needles for HS4 Fixed, HS4 Biased, HIF4, HS6 Fixed, HS6 Biased, HIF6 with various setups from standard to modified head & camshaft.
Michael Beswick

I spoke to Roger Parker at the MGOC about the needle types. He recommended no.6 needles for the earlier type of HS4s (non-biased) and AAAs for the later type (biased).I believe the change in carbs came in the late '60s in the UK. If your car is tuned or worn your needs might differ however... Despite my car being a '73 it had the earlier type of carbs so I fitted the no.6s. Even though I'm a poor mechanic it was a 5 minute job and really worth it! I've got the twin filter type of K&N with the oblong front piece, which retains the original backplates - according to what I've read the single K&Ns don't use this so they need the stub stacks to maintain performance.

I don't think the MGOC publish a needle chart (or if they do I've not seen it), but the one that Michael recommends in the Moss Performance manual looks a good starter. I've bought a copy since the needle fix and it has provided plenty of inspiration for when I win the lottery!

Ian
Ian

Hi all...

I haven't tried K&N's, but I have tried something that has reduced the tendency of the engine to pink (ping) or run on.....

I sawed the elbows off the standard (late) air filter boxes, and ducted in cold air from the front of the car.

Has anyone else tried this ?.

Don
Don

I've always thought the aftermarket air cleaners with their 360 degree opening was a step backwards. Pulling all that low density hot air off the exhaust manifold and heated by the radiator is an excellent way to reduce horsepower. Getting dense cool air to the engine is critical. All of your new cars have an air inlet that is outside the engine bay to collect unheated air.

I've read a couple of postings which claim the oiled fabric filters such as K&N are very poor for very fine dust and that hi quality paper air filters are better protection for the engine.

One of the technologies developed for tanks in desert warfare in ww 2 was engine air filtering. A small snorkel - with a venturi end - as small as you could get it without losing much power is important because the air speeds up as it enters the snorkel and the heavy dust particles don't accelerate and don't enter the engine. The MGB has those snorkels as part of the air filter system. If you install high compression pistons, a modified cam or other flow/hp increasers, those snorkels are probably too small. getting more air and cool air to the engine intake is the key. With a stock engine just cooler air would help. In chilly old England carb icing on a foggy morning was a bigger worry than getting cold air to the carbs on a warm day.

Bigger carb size is only meaningful over 4500 rpm. Compared to a 4 barrel carb on a v8, the engine has very large carburators. The vacuum piston, variable venturi design of the SUs permits a large carb and still have a driveable car. Look at some of the old posts and you will see people extolling the late model single carb combined with change of cam, hi compression pistons, freeer exhaust, etc. Probably the difference in power below 4000 rpm is insignificant, with or without dual carbs.
Given these circumstances a hi flow air cleaner on a stock engine is mainly a pyschological improvement.
Barry
Barry Parkinson

Barry's comments have put me right off K & N filters.

Sounds as though the originals with a length of tubing running from the front grill area will be better.
Fred

Pretty interesting post. Would like to know more details from Don. Also, makes me wonder further about air collection and impact of altitude here at 5,000 feet and up on needles and car set-up. Our air's thin to start with.

JTB
J.T. Bamford

According to Roger Parker its the 360 degree intake of the radius filter (with fitted end plate) that helps give a 3% or something increase in power over standard straight through feed filters on the SU carbs. Add that to claim of nearly 5% improvement of a K&N and there should be some feeling of improvement when this is fitted to an MGB.

Oil filled air filters should offer some improvement over fine dust protection than paper because the oil fills the fine pores between the paper fibres. K&N's are not the only make around however and pipercross are another good make which rivals K&N. I have not heard a definitive answer either way, although i believe K&N to have been around longer and therefore are usually most mentioned.

Would have thought the faster the air, the more likely the larger particles of dust/grit are to be picked up. Of course this still may not be sufficient to carry them up the snorkel.

I have had a few conversations with Roger about cold air feeds to the engine bay of a B. A tube from the front would most likely suffice. Direct feeds into the carbs can lead to venturi problems i believe and also icing.... Certainly driving in france last summer i noticed a slight drop in power when in higher rev range - heat being up to about 40 degrees i suppose, no idea what under bonnet templs were, but hotter than that i shoud imagine!

~PHIL
Phil

Barry-
The air filtration system use on tanks during the desert warfare of World War II utilized a wire mesh in an oil bath. Incoming air passed through the oil in a manner not unlike a water pipe. The "acceleration theory" was disproven in the late 1940s when it was realized that the higher the velocity of a mass, the greater its inertia. If dust is light enough to be suspended in the air, it's light enough to be accelerated along with it.

A pair of properly oiled K&N airfilters will do a far better job of filtering out fine dust particles than paper filters. I know this because long ago I worked in a refractory operation where microdust was literaly everywhere. Microdust is so fine that a handfull of it can be tossed into the air and it will simply remain suspended in the air in the form of a cloud, not sinking to the floor. Virtually all of the internal combustion engines used in the forklifts were protected by oiled cotton filters. Yes, they were made by K&N.
Steve S.

It's probably also worth noting that in general a K&N will filter better as it gets dirty, as the dirty actually become additional filter media. K&N's own tests show this....
Rob Edwards

Hi all...

My cold air intake is still under development, here is what it looks like so far....

A cold air duct of slightly larger internal diameter than the filter box inlet tube was obtained from the breaker's yard. I don't recall the car model it originated from, but I do remember it was a small hatchback.

It comprises a length of tube made of some sort of closely woven fabric terminated in a plastic mounting flange with two fixing holes. It is sufficiently flexible to absorb engine movement.

A hole of suitable diameter was cut in the panel which supports the radiator, and the duct's flange bolted to it. The other end of the duct (which had to be slightly shortened) is simply slipped over the sawn off filter box intake tube.

I have not attempted to deliver cold air to the rear filter box intake, I am hoping that ram effect will provide sufficient pressure to ensure that both carbs get air from the front of the car via the duct. I have plans to put some sort of flap valve on the rear filter box, so that ram aided air can flow straight through the system and OUT of the rear filter box intake tube, but when ram effect is absent air will not be drawn in through the rear box intake.

This arrangement is poor from a flow point of view, but it does seem to have reduced pinking significantly, which is more important to me that 0 to 60 time.

I am considering fitting E2400 filters at some point in the future.

HTH... Don
Don

Some points:

If you wanted cooler air, why not use a plenum which has cooler outside air ducted to it from ahead of the radiator baffle? If you have the money to buy one, TWM induction have one that will fill the bill and take chunk out of your wallet.

Yes, you will get more hot air from around the engine compartment when you take off the air cleaners, but little more than you would with the stock air cleaner housing. Consider that on a typical air cannister the rear snorkel pulls in air from near the firewall, and the forward snorkel pulls in air from below the "air inlet" hole in the radiator baffle. For whatever effect the "balance tube" might have on incoming air temp (probably none, I doubt seriously that is why there is one on the air filter housings) I doubt it has any more effect than no housing at all. I suspect that the fallout of dirt and dust within the housing is probably great within the housing, but I would like to see a weighing and sizing of the collected grit on indentical K&Ns in both the wide open and the OE housing situations over maybe 3000 miles of actual use. It would seem to me that the particles collected by the filter elements themselves would be the real test, not how much accumulated in the bottoms of the housings.

Anyone wanting an a bit of empirical "data" about the effectiveness of an Open K&N setup can take a look at a photo of the mouth of an HS-4 on my GT, taken immediately after removing one of my filters after having gone over a year since the filter's last cleaning. You can judge for yourself.

If cooler air to the carbs is really worth the effort and will show up on the dyno, then call up the good boys at TWM ~ they have an air box just for you!
Bob Muenchausen

Sorry, forgot to include the link to the photo of the "Empirical data" mentioned above. Here you go, for anyone interested: http://hometown.aol.com/idbritcars/MiscPage.html
Bob Muenchausen

Bob

Have you a link to TWM ;->

just curious....

~PHIL
Phil

Boy, you guys have got me sold on the idea! I'm taking off the snorkel on my M-4E4 and my M-24 as soon as I can get down in the basement! I put in a call to K&N to see if they have the right size to fit and they said they might have to special build a pair for me. I hope it doesn't increase the induction noise too much. (I would hate to disturb the neighbors)
In the mean time, I have figured the increase in horse power on the two cadillac engines will be about 11 horse each, for a total net gain of 22 more horses. That's going to come in handy when pulling around 20 tons.
On the other hand, the M-4E4 has a Ford 500 hp V8, so I am looking at around 25 hp increase, but it is closer to 35 tons. Talk about 0-60!!!
Talk about pulling in air from the firewall, this M-4E4 is equiped with a flame thrower. We may put it on the dyno and check the power with and without a burst.
Microdust? We like to call them post lock-on targets!
Rip

Just thought I would throw this in the mix. Anyone looking for a good cheap way to improve air flow and increase filter life could do what I did. Cut around the tops of the original air filter cans, using just the tops with original paper filters (this makes it run too lean). Then add foam filters like those used in a canister vacuum cleaner. The one I found you cut in ½ and it fits both air cleaners. It did not require a change in jetting, works much better than stock. The foam filters are cleanable and the stock filters never seem to get dirty. Looks pretty good and cost about $3.00. I would like to get more cold air there, but this worked so well I never got around to doing any more.
Dennis Hill

Hiya

We have found....

K&N filters work better than foam for keeping fine particles out...especially RV comp use.

Foam filters require 2.5 times the surface area of paper or cotton/gauze filters to flow the same amount of air, they also damage very easily and look scruffy quickly.

A change in air flow characteristics through the carbs will require a change in needle from standard, especially part throttle conditions, unless the standard set up is running too rich due to wear of needles and/or jets.

K&N filters on a 1500 Midget work very well if much richer needles are fitted.

A cold air supply is fine...1% more bhp for every 3 degrees C drop in temperature. One has to ask oneself why didn't the manufacturers do this? Answer: the carbs may ice up in cooler/damp conditions, viz - September to May UK !!!! Best use for Race applications only.

I have had an SD1 V8 exhibit icing up...2500 rpm idle till the engine bay got nice and hot. The worse case I had was a Kawasaki 900R motorcycle, which was recalled for factory mods after a few nasty
'happenings' to quite a few riders!!

Peter
Peter Burgess

Dennis,
I'm a bit of a preservationist, so the idea of cutting up original housings is a bit disagreeable to me. To my mind, better to sell the parts to someone who needs originals rather than destroy them. I have heard of people having good luck making end plates with materials found at home centers, such as the round plates used to protect walls from doorknobs. Bob Muenchausen has discussed this before -- plenty of info in the archives.

Bob, I just looked at your website and couldn't air filter info. Didn't you have a page covering it, or is my memory faulty?

Cheers!
Rob
Rob Edwards

I am new in this field but the PO has spend a lot of money to fit a 2" SU to my B instead of the single Zenith but has fitted the original airfilter housing right back on the SU.
As far I have found out now this can not be right and I want to change to K&N. Does any of you know if this will deliver anything in power in addition to the 2" SU?
C. J. Gaasbeek

Can anyone say what the correct K & N filter is for the twin SU.

I understand there is very little clearance once these are fitted to an RB car, so the part number for the individual paired units would be appreciated.
Jack

Here is the web site describing Bob M's filter project - it is hosted by another MG enthusiast, Roger Hotelling:

http://www.hotelling.com/mgb6.htm

The K&N replacement filter that matches the origical for the twin SU's is E-2400.

I have just done the mod and am pleased with the appearance. I think I need a richer needle now and am looking for a pair of AAA to replace the current ABD.

Regards,

BarryQ
73B
B.J. Quartermaine

Rob,
go back to the page I linked above. The photo of the clean SU carb throat (after over a year with a K&N filter in front of it) is down near the bottom of that page on the LH side. You may be thinking of Roger's webpage on this project. Go to the link above that Barry gave.
Bob Muenchausen

Don, I had a chat with Roger Parker (MGOC) who mentioned the principle of reducing air intake temp to produce more bhp and also the problem of icing. My B is a highdays and holidays car -it doesn't go out in the winter/cold. I intend to build (in plywood to begin with ) an over size air box incorporating the two original back plates inserts (for the stub stack effect). The intake will be from the hole in the rad side shroud but I think the input pipe needs to be about 3 ins diameter.The box will be over size to allow the air to rattle round to get to the back carb. It would seem that K&Ns will keep the dust out best but the above might help reduce to air input temp. If it seems to work I will make it in steel or glass fibre. To avoid icing in cold weather the pipe could be removable to allow repositioning towards the exhaust manifold. I saw an MG C over the weekend that had what I guesss is an original air box of a design similar to the above
Michael
Michael Beswick

Hi Michael.

Your ideas sound good to me...

Another possible route, if you have the workshop facilities, is to make up a box without filters to feed air into the carbs, and fit a single (large)filter in the feed to that box.. I recall this being used in a twin carb Triumph saloon as standard, but can't remember which model.

Tony Vizard's book on tuning the 'A' series engine is well worth a read for it's general comments on airflow.

Don
Don

....

Make that DAVID Vizard..
Don

I've tried both K & N and Pipercross filters on my V8.....the K & N made more induction noise and eventually the rubber sealing ring snapped, I think the Pipercross flows better as I think I can detect an increase in performance. I had the engine tuned after fitting the Pipercross there was an improvement in fuel consumption ......in fairness both of these improvements may have been due to re-tuning.

The Pipercross filter was recommended by the local rally shop who also sell K & N. I don't think he had any axe to grind as they were both about the same price.

Mike
Michael barnfather

I did mention it on my web page, but when I went to the K&Ns, I did not need to change any needles (twin HS4s). There was enough adjustment left to work just fine. Throttle response is great, the car runs great and the plug color is spot-on. That was my experience.
Roger Hotelling
'69 Rdstr.
Roger Hotelling

Rip, you need to eat less sugar...
Val

Back in the 1960's while I was in school I bought a DKW Sonderklass. It looked sort like a VW, but had frontwheel drive 3 cylinder 2 cycle engine. The car ran great but on cool (less than 50 f) damp/foggy days it would start losing power. Finally I found a pull rod under the dash which helped greatly. It re-directed the carb air across the exhaust manifold which stopped the icing condition. If you ran the engine with the rod pulled in ordinary conditions there was an obvious reduction in power.
Before I discovered the solution I pulled the air cleaner to see the problem and the venturi area was nearly clogged with snow like ice crystals. There is a major pressure drop as the air flows past the venturi and creates the vacuum the pulls the gasoline into the airflow. This low pressure also causes a substantial localized cooling condition right at the venturi. It would seem to me that a variable venturi carb such as the SU would not be as vulnerable to icing. In light throttle conditions it would ice, but as it iced you would give it more throttle which would open the venturi and allow more air to flow. There would be some power loss but not the almost total power loss that can be experienced with icing of a conventional venturi. Modern fuel injection cars have the throttle body heated by hot water from the engine cooling system to avoid icing. A quick performance fix is to cut off the hot water supply to the throttle body.
Set up your cold air intake with summer & winter options
Barry
Barry Parkinson

ps
the centrifugal air cleaners are standard fare to this day on industrial earth moving equipment, etc. At the end of the day you remove the can at the bottom of the filter and empty out the big stuff. You still need filtration for the small stuff. Snorkel intakes(small venturi shaped intake openings) centrifugal, filter media and oil bath, are all used together for extreme conditions. And even then you need chrome rings and frequent oil changes for engine longevity. I'd like to see the air intake system for the Bradely fighting vehicles recently used in Iraq.
Barry
Barry Parkinson

This thread was discussed between 14/05/2003 and 23/05/2003

MG MGB Technical index

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