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MG MGB Technical - K&N Air Filters - User Input/Results Req

Hello ALl -

I have crawled around in the archives for the last three days reading about air filters and the changes in mixture that result from the modification. I am getting ready to buy two of the K&N filters - the filters (K&N Part # E 2400) that serve as direct replacement for the standard filters (I currently have the Crosland Filters - Part 833- installed on the car).

In addition to the two K&N filters, I am going to buy the longer APT (Advanced Performance Technology) stacks.

My decision is based on an excellent archived post by Steve in VA.

What Steve recommends for certain applications is the addition of the 1 1/2" deep velocity stacks with a 7° taper and a .250" radius (this is called a "Ram Pipe for H4 SU" on the APT website - APT Part# RP-HS4).

Steve says "these are proven to boost airflow by 5.2% by 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."

My only question - and here it is - sorry for the long intro......

Has anyone opted for the larger K&N filter - the 6 inch round filter of 3 1/4 depth (K&N Part Number SD 23-319) rather than the standard replacement size - which I see as being a filter which measures 4 3/4 round by 3 5/8 deep. The larger filter is an assembly - and cost a little bit more. Any thoughts?
Thanks.
J Delk

I'd use the larger filters due to their higher flow capacity. I had a set of them on my previous engine (Peter Burgess Fast Road head + Piper 270 camshaft) and they worked quite well.
Steve S.

Thanks Steve - do those larger filters come with the bottom plates and top plates? Thats what it looks like from the APT site. Did you just buy two assemblies and then install the ram pipes

Jeff
J Delk

Hi Jeff

If you mean the type of filter which replaces the standard filter and fits in the original filter housings...you do not need a change of needle as the paper and K&N filter flow about the same amount of air.
If you mean the type of filter which is open to the elements....you will need a richer than standard needle. This is needed as the standard filter casings restrict air flow enough to create a pressure drop downstream of the filters...this pressure drop lifts more fuel from the main jet. remove the restriction and you get less fuel...hence the need to introduce more fuel into the carburettor.

Peter
peter burgess

Hello Peter -

Thanks for the reminder on the change of needle. I am planning on going to the ABD initially and then to the AAA if needed --this with the larger 6 inch filter assemblies. I will not go with the standard cannisters and the K&N inserts that replace the standard filter size. Thanks for that nudge.

Let me also take this opportunity to tell you how much I have appreciated your SpeedPro book.

I have learned a great deal from it and appreciate your attention to detail and your well written approach.
J Delk

Jeff-
You can get them either way, just a filter, or a filter with the needed plates. I ordered the whole set up, including the stacks, as a kit from APT in order to save on shipping.
Steve S.

Thanks Steve I am going to call them tomorrow. The B is running great now - but I still want to make this change. The dreaded miss is gone - I think it was that sliding points plate and the worn peg that located it. Also running it without the filters for about a month was causing the lean mixture.

Had a several fun runs in it today - revs great with the new standard cam and actually pulls when I step on the gas
J Delk

The sliding points plate is supposed to have a ground wire connecting it to the body of the distributor to give it a good ground. This is a very flexible braided tinsel wire, which does eventually fray and fail. When it does so you *will* get misfiring, especially when operating the throttle which changes the vacuum which moves the plate.

Some Fords were designed that way, a Scimitar GTE giving me near heart-failure as it staggered into the middle of a junction and stalled more than once. Fitting a ground wire to that cured the problem.

Late model North American cars with the 45DM4 distributor (remote module) didn't have it either as the electronic trigger had two connections to the module, it didn't use the distributor ground like points or the earlier 45DE4 (attached module). If you retro-fit points or an after-market trigger like the pertronix to the 45DM4 you have to fit a ground wire as well.
Paul Hunt 2

Thanks Paul - mine is a 71 so it already has the ground wire- I made sure it was in good shape.
J Delk

This thread was discussed between 01/10/2006 and 04/10/2006

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