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MG MGB Technical - K&N pancake filters on MG B GT

Hello all,
I was wondering if anyone has fitted K&N pancake filters and stub stacks onto a MG B GT and if so did you have make any changes to the cards wrt new needles etc and if so what changes / adjustments were needed ?

Thx.
J.
Jon

Hi Jon

Yes I fitted a Set to both my midget and BGT, I would recommend you get some better needles to feel the benefits of the filters. Of course your not going to get super performance from this type of mod but it does help.

My Advice is change your needles to uprated versions and then adjust the fuel according to the engine, simple job

Cheers

Nathan
Nathan

I dont think the short flat K&Ns are much good. I have the deep K&Ns that would replace the elements in the original saucepan filters, and the MaxPower style ribbed alloy plate with MG on it over the open ends. (A bit bling really, plain circular ends would be easier to fit)

The original needles were ACD(1977), and I couldn't get it to run right, so it had to have AAA needles (recommended with K&N). I think they are a shade rich, as although it runs far better, it doesn't need a lot of choke first thing in the morning (It will pull away on fast idle as soon as it has oil pressure, it needed full choke before).

You might get away with ABD if you are already fitted with them, as they are only slightly leaner than the AAA.

Martin Layton

The short filters mess up the airflow. With a modified engine I have found that cutting a 2" square out of each of the stock air cleaner housings gives more air to the engine. The stock snorkels can short change the hi rpm air on a modified engine.
Barry
Barry Parkinson

I use the factory stacks on my HS4s and counter bore the two mounting holes so I can use socket head allen bolts and flush out the mounting bolts, then use a K&N universal cone filter, part# RU-4011, fits like a glove and has better flow that the pancake units.
Hap Waldrop

There are some tests results online involving a Mazda that show that the K&N flows better dirty than a dirty paper filter and a little bit better than the paper filter when both are clean.

The filter area with the stock 2 carb setup is quite generous. The type of filter or even lack of filter shouldn't make much difference in performance. The limiting factor is not the filters but the snorkels.

It would be interesting to put a sensitive pressure/vacuum guage inside the air filter cannister and see what happens to the air pressure at max throttle & rpm.

Cleaning up the air flow into the carb with stacks is one which has been shown to make a meaningful difference. A flat air cleaner without even the stock stacks is going to be less efficient.

Barry
Barry Parkinson

I was going off memory this morning on the K&N universal cone filter, the correct part number is
RU 4410. One of the things I never liked about the pancake filter is the fact you had two bolts or studs going through the middle of air filter disturbing the air flow. The cone filter and the counter bored fastners on the factory substack (base filter casing) atleast have less obstructions than the pancake style and because the cone filters are just held on by the hose clamps provided with the filters, it's a 5 second deal to get them off or on. David Vizard tested many different velocity stack designs in his book, for top end, no velocity stack out flowed a short radiused stack like the factory MGB base filter casing. It has been proven that the longer type bell shape units create more mid range and grunt. SCCA Midget racers for year have been using HS4s and the MGB stock substacks and even making custom units that resemble the MGB stock unit for the Spridgets in HP and GP that have to run twin HS2s. So I won't argue that a longer bell shape horn might give you slight performance gain on the street down low and in the middle, but if you already have the stock MGB stacks, a drill press, a counter bore tool, and $50 for the 2 cone K & N filter you can do this with a little money and very little labor, and it easier to mantain and remove than pancake or stock housings. If anyone would like to look at the set up, feel free to email me at hapwaldrop@acmespeedshop.com and I'll send you a photo of my 67 GT with this set up on it.
Hap Waldrop

Jon-
A pair of 6" Diameter x 3 1/4" deep K&N airfilters (APT Part# SD23-319) will permit increased airflow without sacrificing protection. In the smaller Original Equipment size these reusable cotton element filters have an air flow capacity of 6.5 Cubic Feet per Minute while some filtering elements made with paper have an air flow capacity as little as 3.2 Cubic Feet per Minute. With proper jet adjustment, when installed on an Original Equipment specification engine these larger aircleaners are worth about 3 HP on their own. When attempting to build a deeper-breathing engine, they are a prerequisite. The B Series engine with its Siamesed intake port design causes some very powerful shockwaves within the induction system. The volume and depth of this large filter dissipates these very effectively. Both the 5 7/8" Base Diameter x 3 1/2" Top Diameter x 2" Deep cone and the 6” Diameter x 1 3/4” Deep pancake type filters reflect these shockwaves back into the induction system, causing induction pulse problems that will increasingly disrupt air flow above 3,500 RPM and cause the pistons of the carburetors to move independently of air flow, interfering with their consistency in their metering of fuel. In order for the carburetors to help the engine develop its maximum power output, the fuel/air ratio may vary no more than 6% from the ideal. For this same reason, if you should elect to install ram pipes inside an aircleaner, never use one that has a mouth that is closer to the inside of the cover than the size of the bore of the carburetor (1 1/2” for the SU HS/HIF 4, 1 3/4” for the SU HS/HIF 6). Airhorns that have walls with an exponential curve can dampen these shockwaves to a limited degree, but should not be considered to be a substitute for an air filter assembly of adequate clearance and volume.
When installing these deeper aircleaners, one thing that I might suggest would be the fitting between the carburetors and these custom aircleaners of a pair of 1 1/2" deep velocity stacks with a 7° taper and a .250" radius (APT Part# RP-HS4). These are proven to boost airflow by 5.2% by means of drastically reducing the contraction of the airflow at the mouth of the carburetor. As a side benefit, this reduction in contraction will help to accelerate the velocity of the fuel/air charge, maintaining fuel suspension in the airflow and enhancing volumetric efficiency at high engine speeds. However, the carburetors will become more sensitive to the state of their synchronization. If you feel that you do not desire to include this modification, at the very least install a pair of Advanced Performance Technology's stub stacks (APT Part# SS51). This additional refinement won't create a perceptible increase in power (about a 2-3 HP increase), but they will make both the throttle response and the engine running characteristics slightly smoother by reducing turbulence at the mouth of the intake tract and contraction of the air flow, thus providing more efficient fuel atomization at the jet bridge and allowing the greater air flow potential of the larger airfilters to be fully exploited. They might even eventually pay for themselves by thus slightly improving fuel economy (maybe). The Original Equipment aircleaner boxes incorporate stubstacks into the airfilter housing design, so it is obvious that the engineers at the factory saw the value in them.
Steve S.

Steve
Hap's idea of using the stock stubstacks as the base for an aftermarket air cleaner is an elegant solution for both mounting and for cleaning up the air flow.

Looking at the catalog for K&N, the RU-1790 and the RU 2990 look like eligible choices. The RU-4410 is compact but could be marginal flow capacity for a modified engine. (air cleaners aren't always fresh and clean and extra capacity must be considered for a dirty filter).

There other choices as well in the catalog. I'm sure there are other mfg out there with similiar products.
Barry
Barry Parkinson

I fitted a pair of K&N "Bob" filters to my 73 MGB (HIF carbs) per the attached link http://www.cibolas7.net/12299.html - the original stubstackes are retained. The reduced air resistance (in part due to elimination of the OE Cooper cans resulted in a much weaker mixture which was addressed by a change to AAA needles from the original ABD.

The engine seemed to breathe easier and was more responsive after the change.

Barry
B.J. Quartermaine

The difference between Hap's approach and the Bob filters, appears to be the attachment.

Hap uses a filter with a rubber flange at the carb end and apparently uses a hose clamp to hold the filter in place. The long bolts are replaced with short allen bolts. It is necessary to drill out the stock stubstack to make the head of the bolt flush.

Either way, there is still the major issue of the engine breathing heated air. In cool weather this may be necessary to prevent carb icing. The rest of the time the hot air will reduce engine power output by several horsepower.

The real solution would be an air box with a duct gathering air in front of the radiator. There was a post a few years back from someone in Fla. that replaced the heater box and made it the engine inlet air source.

Barry
Barry Parkinson

You might want to read Roger Hotelling's account of his installation of the "Bob Filters" at http://www.hotelling.com/mgb7.htm .

His account is better than my own, and incorporates much of what both Steve S. and Hap suggest. There are, of course, refinements which both gentlemen have found beneficial to their requirements, but a simple benefit can be gained by the basic changeover and requires probably the least additional parts if you are simply driving for pleasure.
Bob Muenchausen

Also, the air box Barry mentions is offered by
TWM, http://www.twminduction.com/airbox.htm . Not the cheapest way to go, but Barry does have relevant point about the cold vs. heated air induction. As you may know, the MGA addressed this to some extent by simply using a piece of flex ducting which aimed cool outside air into the engine compartment apparently for both the air intake and to help move stagnant air out of the engine compartment.
Bob Muenchausen

Yes, a remote aircleaner and ducting to channel cool air to the carburetors is a possibility. For every 3° Centigrade (5.4° Fahrenheit) that the air ingested by the engine is lowered, power output is raised by 1%. Although wrapping the exhaust manifold in insulating tape (sometimes called “lagging”) may seem to be a good idea in principle, it is a very bad idea in practice. Why? The heat cannot escape from a wrapped cast iron exhaust manifold and both the cylinder head and the exhaust manifold will consequently run hotter. The heat will just build up and up, far beyond what the factory engineers designed it to handle, with the result that the exhaust manifold will warp. In addition, the heat is also transferred to the cylinder head, heating the walls of the intake ports and thus reducing the density of the incoming fuel/air charge. Peter Burgess mentions this problem in his book "How to Power Tune MGB 4-Cylinder Engines." Even worse, the coolant passages in the cylinder head were not designed to remove such an excessive amount of heat, thus preignition of the fuel/air charge can become a problem and valve seat life can be shortened. In extreme cases, due to the fact that the exhaust valves for the middle two cylinders share the same central exhaust port, the cylinder head can actually warp between #2 and #3 cylinders. In the case of tubular steel headers, the metal will become so hot that it will often spall and form flakes that will eventually disintegrate to form a hole in the area where the heat accumulation is greatest, usually at the junction of the pipes. The tape also becomes a moisture trap, accelerating the rusting process that can plague exhaust manifolds.
Instead of wrapping the exhaust manifold, get it Jet-Hot coated. Jet-Hot coating is a ceramic coating that can be applied to coat both the interior of the exhaust manifold as well as the exterior. The heat will have nowhere to go except out through the exhaust system, thus it will greatly reduce underhood temperatures. The biggest advantage of this is that the air being inhaled into the engine being denser, more fuel can be mixed with it to result in a more powerful fuel/air charge. Another benefit is that the setting of heat-sensitive SU HIF4 carburetors can remain more consistent. One word of warning to those considering Jet-Hot coating or any other type of ceramic coating: Be sure that the entire surface of the manifold, both the interior as well as the exterior of the manifold and that of the flanges is coated so that the heat of the exhaust gases will pass on through the system instead of being absorbed and trapped in the metal of the manifold, otherwise the manifold will create the same problems as in the case of wrapping the manifold with insulating wrap. Jet-Hot has a website that can be found at http://www.jet-hot.com/ . Should you decide to use a tubular exhaust manifold that is not Jet-Hot coated, be sure to use a rubber gasket (Moss Motors Part# 296-375) on the rear tappet chest cover as cork gaskets tend to fail under prolonged exposure to the extreme heat radiated by such headers. Use of the more warpage-resistant rear tappet chest cover from the 18V-883-AE-L, 18V-884-AE-L, 18V-890-AE-L and 18V-891-AE-L engines will assist in this as well.
Steve S.

Cold airboxes are failrly common on SCCA race cars. I was fortunate enough to drive a Huffaker built H-productionn SCCA racing Bugeye during the 2005 season.
This car had a custom carbon fiber airtight cold airbox. Huffaker picked up air from the left side headlight opening, at the headlight opening they had intalled a flat sheet of airfilter type foam. The air box as mentioned above was completely air tight at the carb and the float bowl vents were vented directly into the air box via tubes so to equalize the pressure between the carb and float bowl vents. On the Huffaker F-production cars they did not use cold air boxes but rather a K&N cone filter, pretty much like what I do on my street MGB and on 1275 race car, Joe Huffaker told me there was no gains on the 1275 engine with a cold airbox. I have a custom made plastic air box for the 1275, but have never used it. I don't know how much good a cold air box would do on street car, the whole idea of the cold air box requires air to be crammed into the airbox, on a race car, it is constantly in motion at a high rate of speed, but the street car spends a fair amount of it's time sitting in traffic, I have a notion in the case of the car sitting in traffic the flow to the carbs is worse for the carbs with a airbox than without it. I think the idea of a duct hose directed towards the carbs make better sense for me on a street car.
Hap Waldrop

I bought an electronic oven thermometer with remote readout for about $20 a year or two ago. I think I'll put the sensor on the air cleaner and see what temps are being experienced.

Air boxes in racing conditions can be used to produce a small positive pressure to the carbs - a slight supercharger effect - if you will.

Air boxes can also be used to bring cooler air into the carbs, which of course is more dense than hot air.

There is also the wintertime issue of carb icing. Any airbox system will need to be adjusted for cold weather. I had a DKW (3 cyl 2 cycle fwd car) it had a lever under the dash that you pulled in cold weather to bring hot air to the carb. I found I needed it to avoid icing in temps below 36 degrees f.

Barry
Barry Parkinson

This thread was discussed between 06/09/2006 and 11/09/2006

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