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MG MGA - Stub Stacks on the market....

Steves..I came across this advert when on the sniff for parts. http://www.ebay.com.au/itm/CARB-AIR-FILTER-STUB-STACKS-TRIUMPH-MINI-MG-HIF6-HIF44-/230770501929?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item35bafe6929#ht_590wt_1106
Neil Ferguson

Neil

Yes, they look very similar. The only comment I would make is that they are described as 13mm thick which is getting on for twice our thickness. If you recall I made our prototype based on your advice and measurements and those of FRM. I wonder if 13mm is too thick for our slim filter casing?

Steve
Steve Gyles

Hi Steve,
I don't suppose you have any of your stub stacks left? If you do I would like to buy a pair.

Cheers ,
Phil
p parmenter

Neil, they don't fit in our new air filters.
dominic clancy

Dominic..I bought one from APT which does..not as good as the mga committee designed ones ..too fat....but will do a reasonable job..about $30. I may get half the thickness machined off if I can work out a way to get it held in position as currently it is held on bolts sitting on shoulders inside the holes.

Neil Ferguson

Hi folks
I'm also in the process to add a Judson to my MGA. I'm wondering if a stub stack in combination with the Judson can make any difference. I would assume that the the Judson incl. manifold with all the sharp edges doesn't help to get a good flow. I rather would increase the pressure and make sure to get a smooth airflow after the charger.

Cheers
Beat
Hofmann

I agree Beat, I don't think the stub stacks will add very much with an open filter. They certainly do reduce the considerable losses in the factory canister configuration though. On the other hand they will not do any harm!
N McGurk

Beat..
With the Judson set up you basically have an air pump( the Judson ) feeding the suction of another air pump ( the engine ) and anything that reduces the flow energy losses will increase airflow. More particularly the Judson suction manifold operates at a vacuum formed by the energy losses throughout the filter, the carb . and the manifold itself. Energy losses are reduced if the velocity of the air is reduced in the manifold and sharp edges, bends and orifices are smoothed ...but if the velocity downstream of the carb is reduced too much then fuel may come out of entrainment in the manifold. The simplest way is to reduce the losses through the filter and carb.. The filter provided with the holley set up looks undersized to me but has a big central bore ( 2 1/2 inch) reducing via a well tapered reducer to 1 3/4in before passing through the twin butterfly valves in the Holley. The big bore inlet and taper look excellent for minimising air energy losses so if you are using the Holley I would look at the filter size ( and its small external slits) to see if they are large enough. the Holley discs look like they could be much better flow profiled as well. A stub stack is not required .....
If you change to a SU 1 3/4 carb with a new filter then the picture is drastically different ...
Neil Ferguson

Beat

I am almost finished installing Eric's Judson, and will then install the SU on mine (after the trip this weekend). Do you want a drawing of the manifold?

Dominic
dominic clancy

My take on all of this is that the pressure drop of the square inlet (as I calculate) is quite negligible and the success of the stacks is due to the driveability factor, which is probably due to the smoother airflow through the carb. In that case, logically there should be a driveability improvement with the supercharger as well!
Art Pearse

This thread was discussed between 16/04/2012 and 17/04/2012

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