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MG MGB Technical - Air Filters

I recently bought a 1973 B-GT. I am looking to replace the standard airfilters. Mainly for a bit more poke, not expecting dramatic changes just bit more willingness.

She already has a full stainless steel exhaust, which sounds pretty sweet so I thought this is the next obvious step. (No?)

As far as I can tell I have three options normal K&N, Pancake K&N with Stub Stacks or SU Performance jobbies.

I imagine there is no straight this is best answer but I was just wondering if all you good good people out there could let me know what the relative merits of each are.

Technical fact and bias baseless opinion both welcome !!!

Cheers
Simon Crozier

Any of these will help, but K&N are re-cleanable with a good tested performance at dust particle removal down to a critical level.
However, to get the real benefits, you need to change the needles in the SU's.
Next step would also be a ported head and extractor manifold to get all the benefits of the better breathing.
Martin

I swapped out the stock filter elements and replaced them with K&N's, retaining the stock canisters. I did not change needles, but the car's eagerness to rev was strongly (and positively) affected.

Perhaps I could tweak the response by playing with the needles, but it seems to work just fine. I believe that the rule of thumb about K&N's and changing the carbs applies more to the pancake, full flow modification, since the potential for increased flow is so much greater.
John Z

Hi.

I looked at the K&N website, and I think that the E2400 is the right size to fit in the original canisters, can anyone confirm this please ?.

They cost around £25 each, BTW.

Don
Don

Simon,

I installed a pair of K&N pancake style filters on my 74 1/2 "B". I had to enlarge and bezel the hole in the base plate of the filter so that it was properly contoured to the original stub stack. Took a lot of time, but runs well.

Cheers, Doug
Doug Keene

Simon-
A pair of 3 1/4" deep K&N airfilters will permit increased airflow without sacrificing protection. The B Series engine with its Siamesed 5-port design causes some very powerful shockwaves within the induction system. The volume and depth of this large filter dissipates these very effectively. Both cone and shallow pancake type filters reflect these shockwaves back into the induction system, causing induction pulse problems which will increasingly disrupt airflow above 3,500 RPM. One thing that I might suggest would be the fitting of a pair of APT stub stacks between the carburetors and the aircleaner. This additional
refinement won't create a perceptible increase in power (about 2 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. They might even eventually pay for themselves by thus slightly improving fuel economy (maybe). The stock aircleaner boxes incorporate stubstacks into the airfilter housing design, so it's obvious that the
engineers at the factory saw the value in them.
Steve S.

Don,
E2400 is correct. I just installed a pair and I'm looking at the box as I type this. Moss list them under their part number 372-395.

HTH!
Rob
Rob Edwards

In the US you can order the K & N E2400 filters through Auto Zone (lowest cost) or Advance Auto Stores.
FWIW, Clifton
Clifton Gordon

Just put the SU stub stacks inside the pancake air cleaner, the K&N base does not need to be enlarged.
John
John Simmers

Rob

Thanks for the confirmation.

Did you need to change the needles ?.

I cut the elbows (which I assume were to take warm air from the exhaust manifold) off my (late) air filter cannisters, and am planning to pipe in cold air from the side of the rad. I will deliberately make it leaky so that ram effect doesn't change the mixture according to road speed.
Has anyone else tried this ?.

Don
Don

Don,
My car has been driven very little since I put in the K&Ns -- I've had it down to implant an o/d gearbox, and the weather has been less than cooperative. So I just plopped them in and bolted the filter cans back on. I expect I will at least need to twiddle the mixture a bit to get it dialed in, but so far, with no mixture changes whatsoever, it seems to run well. (That suggests to me I probably didn't gain much by installing the K&Ns...)

I've got a home-built manometer with which I thought I might experiment a little, just to see what kind of depression there is in the cans, and thus get an idea how restrictive they are...

HTH!
Rob Edwards

Well,

That was great guys cheers.

Went out today and got a pair of K&Ns - everyone seemed to think these were at least as good as anything else. Got the ones what looked same size and shape as original ones not the pancake.

They came with a blinding little plate/plaque affair for the top with a big olde "MG" sign across it which brightened things up well nicely.

Haven’t had a proper test run yet but they certainly sound like they are a right little number down there.

Thanks again.
Simon

Simon, if you haven't already, take a look at this site http://www.hotelling.com/mgb7.htm Roger has a very good account of doing the project outlined by Steve S. at this site.

In a recent issue of Grassroots Motor Sports, they did some Dyno testing which included comparisons with K&Ns vs. stock, and K&Ns used in and out of the stock air filter cans. The dyno's conclusion was that K&Ns were definitely worth a gain, and removing them from the stock cans was ALSO worth an additional gain in HP.
Bob Muenchausen

Bob Filters ? :-)
Dauntless

Dauntless:
They were "fancy cast aluminum end plates" for $XX at Moss, etc, long before they were "Bob Filters". Bob filters are essentially "do the same job for cheap filters"
;-)
Bob Muenchausen

I went to the hardware store & purchased the said covers(the don't put a hole in the wall with the door knob thingies)& if my order from Moss ever gets here, then I too will be running Bob Filters
Dauntless

Don, All,

Just reporting back -- today was a perfect top-down day (70 deg!) so I took the B to work. It ran a little rough so I checked the mixture when I got home. As people have pointed out here before, the filter elements made it too lean by about two flats....

Cheers!
Rob

Rob Edwards

Thanks Rob

I guess this proves that the new filters are flowing better than the old ones.

I suspect that the next restriction to look at is the inlet pipes, which are of the same diameter as the carbs, but both ends of the pipes would benefit from some 'flowing' attention. David Vizard's 'A' series book gives some general guidance on this.

Don
Don

This thread was discussed between 29/01/2003 and 04/02/2003

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