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MG MGB Technical - Sub Stacks for K&N Filters

I have fitted K&N filters to my MGB without Sub Stacks being fitted.
Can anyone tell me if there is a noticable difference
with Sub Stacks fitted? My car runs very well without them.
Robert
Robert Collier

For most MGBs, there really is no need to use aftermarket stub stacks if you simply use the OE cast aluminum backing plate supplied by the factory with the original Coopers air filter cans. The aluminum plate incorporates a "stub stack" or velocity stack into it (the bell shaped curved mouth of the casting) which tends to work well for most street driven and slightly modified cars using some sort of OE carbuation and cam.

As things get wilder ~ Weber DCOEs, hotter cams, flowed heads, etc, etc ~ then you might find some advantage to longer or differently shaped stacks designed for engines which produce their torque and HP at higher rpms than more or less standard tune engines. If yours is one of these, however, outfits like APT or TWM should be able to tell you specically what type to use for your specific combination of hopup parts.
Bob Muenchausen

Hi,

If you have fitted the pancake style filters rather than the deep ones that fit onto the original filter bases (as mentioned above) - you will have to fit stub stacks - otherwise you are retarding air flow.
Iwan Jones

Iwan is right about the pancake filters. However, they have other flow problems in my opinion, which are outweighed by the better characteristics of the deep filter units. This, of course, presupposes you have clearance for the deep filters for both carbs.

Unfortunately, the later cars with power brake boosters force a different choice and you are back to the really short stub stacks Iwan mentions.
Robert Muenchausen

You should check out David Vizard's book "Tuning th A-Series Engine." There is a section on stub stacks and velocity stacks that shows dyno results. Most stacks on the market actually proved to reduce airflow or make no difference at all. There are 16 pages about it!
The stock air cleaner base actually had the best airflow improvements at 5.8%. Anything without a large radiused or rolled edge reduced airflow. Anything with a rolled and radiused edge was either neutral or a slight improvement over nothing at all.
Jeff
Jeff Schlemmer

Actually, a person wanting to use Pancake filter housings from K&N could do as I did to those used on my 18GA engined MGA. I simply carved a hole in the back plate furnished by K&N big enough to accomodate the MGB rear filter plate casting and its rubber sealing ring. The two together worked just fine within the limitations of the Pancake filter's shortcomings.
Robert Muenchausen

This thread was discussed between 16/11/2005 and 18/11/2005

MG MGB Technical index

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