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MG MGA - Short carb Stub inside Vokes filter

I decided to uprate the original Vokes air filter ( better called a coarse strainer as per a kitchen sink) and bought the K&N filter kit to adapt the Vokes and whilst researching read the article ( mgaguru.com )on using a short stub inside the filter housing so bought K & N stubs.
Opened up the Vokes and found the bolt pillars are
welded so could not fit the stubs without doing some serious destruction. In the end turned them through 90 deg,trimmed them to clear the pillars and the carb holes, put gasket gunk underneath and pop riveted them onto housing as per photo...not too pretty ( especially with paint job ) but hidden .Don't suppose I will ever know if get the 1hp benefit mentioned.....but hopefully a small step in the right direction. Anybody else fitted these?


n ferguson

Interesting claim. I figured out the pressure loss of an intake hole without stub as 0.2 psi
(theoretical 115 L/min at 5500 rpm). The stubs illustrated are nothing like enough to reduce this loss to zero. So how much HP does a .2 psi boost create ? At lower rpm the effect drops right off.
Art Pearse

Art...you may well be right ..when i look at the set up/depth etc of the stub it can't reduce loss very much and probably will be swamped by the beneficial effect of the improved filters. I was referencing the note PP 104 on Barney Gaylord's site by Carl Heidman re 1hp gain.
It all revolves around the delta p difference between a sudden sharp entry ( ie no stub ) against a longer but smoother profile of the stub. I used to do these calcs for equipment /pipelines etc in my engineering days so will try and find my slide rule.
...in any case i had better get a mirror finish on the entry and venturi !!!
n ferguson

Well Art, that sounds exactly right to me. 0.2 psi is 1.36% of atmospheric pressure.
0.2/14.7 x 72hp = 0.98hp
That looks like 1-hp gain to me. When people think power gain is worth about $100 per HP, this sounds like a cheap power boost.

The real gain is not from the 1" long tube, it is from removing the 90 degree sharp corner from the entrance to the carb throat (and it might be a little better than 1-hp gain).
Barney Gaylord

sounds like I need to round off the front outside edge of the stubs ( the K&N stub was quite rough finish and sharp eged ) as well as polish the throat..
Neil
n ferguson

Just for general interest I have attached an image of the stub that was factory fitted to the mga twin cam.


Mick


M F Anderson

Thanks....looks a very crowded air intake area,very low clearance between top of stub and top of housing and a tinny sharp edge on the stub.....does( or did ) it do any good?
Neil
n ferguson

The MG factory thought that it was worthwhile, but never published any figures. I don't know of anyone who has done a comparison. People are talking of 1 BHP. You would be lucky to get enough consistency even on an engine Dyno to confirm that. A wheel Dyno would be useless, my experience with them it that there is so much vibration that you are lucky to get any accurate readings.
The air cleaner housing cannot be made any larger, it is already almost touching the body of the car.


Mick
M F Anderson

I don't know how good my assumptions were about engine air flow. I used the theoretical displacement per stroke, but maybe it is not as good as that, due to lower manifold pressure that atmospheric at full bore, or valve overlap, higher temperature etc. Anyone know the conversion ? My real point was that these stubs do not look anything like what I would call a zero loss profile. Should resemble the end of a trumpet.
Art Pearse

Neil,
I agree with Art - these don't look much like the Ram Pipe set in the Moss Catalogue (page A27 Fall/Winter 2008)- maybe it is the black paint creating an illusion!
I assume it wasn't possible to have the ram flange on the outside of the canister (flush with carby flange) - then slide the cannister over the ram trumpet end. The way you have it set up looks like it has blocked off the hole that provides atmospheric pressure air to the under side of the piston in the suction chamber.
My $0.02 worth.
Mike
Mike Ellsmore

mike
The ones in my filter housings are only 13mm long ..the short ones shown in the moss catalogue are 32mm long. Mine are made by K&N ,the air filter manufacturers ( and hopefully air delta p specialists?)and since i was pulling the Vokes off and putting new K&N filters inside the old housings I decided to go the whole hog. I considered a few options for installing the stubs..
1) between the filter housing bottom plate and carb inlet ( as you mention ) but I would have needed to cut a much larger hole in the Vokes plate and also did not think I would get a reasonable seal surface between the plate and stub top surface.
2) overbore the stub bolt holes and run unit down the Vokes screw columns and then pop rivet
3) Install as i did by turning stub 90 deg and trimming stub flange to clear both balance holes.
But I dont expect that this has added wild power to my 1600...not sure I would bother in hindsight ( the stubs cast $44 each ..a wee bit excessive!!)
neil

n ferguson

Neil,

The factory fitted MGA Twin Cam stubs are 37mm long, but it is not known if this was consdered the optimum length or it is all that would fit. As things were a bit crowded inside the air cleaner it must be assumed that they did not want them any shorter.


Mick
M F Anderson

This thread was discussed between 26/04/2009 and 28/04/2009

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