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MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGA - Improved Airflow Stubstacks

The latest MG Owners Club magazine (Enjoying MG) carries a new product called an Improved Airflow Stubstack. It claims that fitting the small air rams within the pancake air filters, the airflow into the carburettors is greatly improved, resulting in improved performance.

The advert is also shown on-line as a PDF download: http://www.mgocspares.com/pdfs/hotline.pdf

Any comments? Anyone tried them or something similar?

Steve
Steve Gyles

Steve..I fitted similar stubs inside the filter housings about 3 years ago after reading an article about them on Barneys site. The needed a bit of polishing and fitting to ensure a clean entry to the carb. but seemed to marginally improve performance for almost zero cost. Recommend... as every little bit helps on an MGA.....
Neil Ferguson

Steve,

Yes I've had stubstacks installed in my Volks pancake filter for several years. A slight improvement of throttle response was experienced. I can't say whether this was an indication of increased horsepower. I purchased my stubstacks from Advanced Performance Technology in Riverside CA. Seeing the stacks illustrated on the page address you've provided - they appear to be more cheaply made than the ones I purchased as the radius edge shape contributing the the smoothing of the air flow seems too abrupt. The ones I purchased were shaped from aluminum billet, be wary if these are cast. Also it took some minor modifications, I can't recall what I did (post 60's memory - my age not the 60's decade although the decade may have contributed to my post 60's memory) using the drill press to allow them to fit my H4 SUs. -Martin Straka
Martin Straka

Steve,

The MGB had some sort of aluminium bell-mouth fitted inside the filter housing as standard fitment. I use a pair of these in my filters although I'm not sure how much difference they make
John Bray

The MG factory introduced them on the mga twin cam during production.

See image.



Mick


M F Anderson

Another view.




Mick


M F Anderson

Improving the flow is always a good thing.

K&N supply a similar (the same?) item: http://www.knfilters.com/search/product.aspx?Prod=85-5039

The much smoother APT-items Martin has are top of the bill, and almost a shame to hide in an airfilter.
http://www.aptfast.com/UserData/Images/Large/101221.jpg and http://www.aptfast.com/ListItems/SubCategory/SU%20Carburetors/Stub%20Stacks%20and%20Ram%20Pipes.aspx

The standard MGB airfilter is a very good design that will flow better than a K&N without stub stacks.
Willem vd Veer

I used the K&H units and they are poorly made and as rough as old boots when they arrived and required a load of mechanical buffing and polishing to get to a reasonable smooth contoured surface and to match the bores. The APT units shown in William's pic. look beautifuly finished and well contoured and if I was not fitting a supercharger later this year I would take out the basic K&N and replace.
Neil Ferguson

I have the ones from APT for my '74 midget. When I saw the increase in flow numbers they produced (in a book by David Vizard) I felt they were a very worthwhile investment for such a small price. Rim shape and polish is critical--hence the need for the good ones from APT.
JM Morris

When wet behind the ears as an engineer I specialised ( for as short a time as possible ) as a gas engineer and when doing calculations for pressure head loss in piping systems I used the following factors...
For a sharp entry to a pipe ( as per standard pancake filter entry to carbs ).....about 0.4
For a well shaped bellmouth entry ( probably better than ram entries but similar)....0.1
So whatever flow restriction pressure loss is present in the basic set up is at least reduced by about 3 times ( possibly 4)..this means more air will flow for the same overall suction pressure from the engine cylinders. The APT units are a great simple addition without any downside effects...and much easier than grinding, contouring and polishing top end engine passages...
Neil Ferguson

These are the type to get...http://www.aptfast.com/showitem.aspx?id=101220&name=H2%2FHS2%20(1-1%2F4%22)%20Billet%20Stub%20Stack&
Don't bother with the cheaper ones. They look like the K&N type.
Neil Ferguson

All very interesting. I had not realised these were available. Incidentally Neil, the link you posted is for a 1 1/4" H2. This is the one, I think, for our carb:

http://tinyurl.com/http-www-aptfast-com-ShowIte

Steve
Steve Gyles

Steve..you are right.....a thousand apologies!
Neil Ferguson

Steve

How about buying a few sets of the APT's and save on the shipping costs to the UK? They look very good.

John
John Francis

There are these on ebay, I have no idea how good they are and no connection with the seller.

http://www.ebay.co.uk/itm/CARB-AIR-FILTER-STUB-STACK-SPITFIRE-MGB-MINI-HS4-/230654941073?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item35b41b1791
John Bray

I tried my car without filter inserts on the run to Upton House today and the car didn't feel quite as crisp as usual, also the noise of air going through the filter and carburetors was a lot louder without the inserts.

As stated above, mine are from the MGB and I believe they were standard fitting on earlier cars.


John Bray

Mick,
after study David Vizards book about carbs and intake manifolds I cut the much to long vents inside the after market air cleaners of the Twin Cam and had a pair made quite close as shown in John Brays post.
Siggi
Siggi

John

Sounds a decent idea. Anyone else in the UK for a bulk order?

Steve
Steve Gyles

I've had the K&N ones in my carbs behind the K&N filters for a few years now. I'm not sure that I can definitely say how much better it runs, but it sounds nice !
Dan Smithers

Steve, I'd be interested if someone wants to organise it. Start a new thread solely to gauge interest?
Lindsay Sampford

Steve

The APT ones look very nice but you would need to check that they fit into the MGA filter housing.

In particular if you look at the picture it looks as though the stub-stack is bolted to the carb which I don't think is possible with the MGA filter housing.

You would need to ensure the fixing holes in the stub-stack are bored to a diameter which is large enough to slide over the threaded tubes in the MGA filter.

This would mean another method of securing the stub-stack would then be required possibly by use of a distance tube which could slide over the threaded tube once the stub-stack is in place which would be held in place by the outer filter case.

Sometimes a picture is worth a 1000 words but I don't have one available!

Regards...John
John Bray

John,

Regarding your post, yes I now remember drilling them out to slide over the fixing tubes (my earlier post.) All I did to hold them secure to the pancake filter base was to use the brown permatex rigid gasket adhesive. They've remained firmly attached for years. -Martin Straka
Martin Straka

re Martins comment above on fitting the APT smooth profile units. I had a similar problem fitting the K& N rough ones into the foiter and onto the carb. You fit them over the two filter top tubes...but what holds them in position ...I used two pop rivets through the bottom of the filter housing ( and made sure they were outside the carb gasket area. ). The arrangement inside the twin cam filters above looks terrible for gas flow dynamics. Top of bellmouth is much too close to the top plate retainer.Keep as large a clear plenum above the bellmouth ( ie keep latter short) as possible to stop pressure loss due to eddies.
Neil Ferguson

Found this pic I took when I installed them..see how far out the pop rivets had to go...and contrary to what I said above I fitted them around the tubes. Use the APT units...shorter, better finished and profiled.


Neil Ferguson

Hey John,
I have a set of MGB filters kicking around with the inserts. Have you fitted yours within the factory MGA filters?

Ron
R emgeeaa

I am wondering if I could manufacture a set in my lathe. Can anyone supply some dimensions/diagram?

Steve
Steve Gyles

Steve..your idea is excellent. The units available on the market are not great and need bastardising to fit anyway. I would suggest you could make a cardboard template of the bottom of the housing ,get some 5 mm thick aluminium plate, cut and shape ...and most importantly round the well matched borehole with as big and smooth a transit contour as possible. Above would give all the advantages of a large plenum for even flow plus massively reduced deltaP( factor of 4). It is not rocket science ( or lightning science ) ..
Neil Ferguson

I had some spare carb spacers-about 10 mm thick and fitted them onto the ends of the studs after sanding a smooth radius on the outer edge. I could also adjust the diameter so that it exactly matched the carb diameter without any ridges. Cheap option for smoothing the airflow. Can't say if there was any improvement in engine performance but of course in your head you sense there is. This does not extend the throat of the carb very much and not sure if that's the object.
J H Cole

Hi Ron,

Yes I have fitted the MGB ones in my MGA filter housing.

They are a straight (but tight) fit over the MGA captive tubes, you can either leave them as they are or fix them in place in which ever way you think is best.

Regards...John
John Bray

Interesting. I have just removed my filters to study the issue in greater detail. First, I measured the hole in the canister (Volkes). It was 1.42" diameter. I thought that was undersize as we use the H4 1.5" carbs. So I then measured the carburettor inlet hole and it was 1.389" diameter.

Do I have a problem? Or is it the carb to manifold hole that is 1.5" diameter?

Steve
Steve Gyles

I bought a set of sub stacks from Rimmer Brothers a couple of months ago, a few months after I first saw them publicised. I intend to fit them when I refurbish my original air filter housings (the car came with "Ram Flo" foam/mesh air filters), for which I've also bought K & N filter elements. The Rimmer Bros sub stacks are nicely finished, though surprisingly heavy. It looks like the sub stacks , K & N filters and the original Vokes filter housings should all fit together well, albeit with some internal modifications.
While you can't believe all you read, I've seen claims that the MGB items, on the MGB were credited with the engine producing an additional 3-4 Hp by the factory. Elsewhere I read that that the benefit translates to about one HP at the rear wheels. I'm not sure that's a benefit you can sense by the seat of your pants, but at the very least it appears that they MIGHT be helpful.
T Aczel

After I posed my last question I spoke with Bob West. My assumption was correct. It is the hole on the manifold side that is 1.5". The inlet hole from the filter box is smaller as I discovered.

Steve
Steve Gyles

A while back I computed the pressure drop at the entrance (K=0.5 velocity heads). This was .047 psi. My assumption for airflow was 5500 rpm x the standard displacement of 1622 cc. this may be off quite a bit, I have no experience, but it does give a ball park figure for what can be gained IF you can reduce the loss to zero. A good rounded entrance stub could, but what I see in the pics are nowhere near the shape that would give zero loss. Also, seems they cut down the bore a bit, so might actually lose some. Maybe the S/C boys can estimate the bhp change for .047 psi boost. My flowrate was estimated at 4460 L/m, so if anyone has a more realistic figure, just apply the flow^2 rule.
Art Pearse

Art....if they reduce the bore then they will be useless. You do not want a Venturi,velocity increase , or restriction.The ones I have seen do not and it is important to match the bores of the stack and the carbs. Cannot comment on your head loss calc ..but as a one time specialist engineer in gas flow and as stated previously just getting away from a sharp edge entry reduces the loss a lot and a reasonable rounding and tailoring should get the loss down by a factor of 3 to 4. it is also important NOT to take up too much space in the housing or any tortuous airflow paths into the bell mouth . It will assist engine air intake , is easy and cheap..but the gains will be small..only 1 to 3 % ...but .......

Neil Ferguson

My car produces more intake noise without the bell-mouth inserts than it does when they are in place.

I presumed this was because the air flow is smoother with less turbulance which to me indicates a greater intake efficency.

Steve, many years ago we tried fitting a pair of smaller (1 1/4")carbs to a MGA to see what would happen.

It appeared to produce a lot more low down torque with the expexted fall off in power at higher rpm although not as much as expected,


John
John Bray

I have got hold of some 3.5" diameter aluminium round bar that I am going to play around with in my lathe. I have drawn up something from the pictures above and that will be a tailor fit for my Volkes filter cases with K&N filters.

The attached photo shows what I have in mind. I have drawn the stub thickness at 12mm. Is this ok or thicker/thinner? I have also put a 7 degree slope on the throat. Again any comments? Does the throat lip need to be more rounded than shown, thereby reducing the overall thickness?

I will probably attach the unit to the case with glue. I think this should be sufficient as the unit will be a tight fit over the internal filter box attachment posts.

Steve



Steve Gyles

Steve.. My suggestions...
... trim down thickness to 5 or 6mm so that plenum vol in filter housing is as large as possible minimising turbulence above entry.
...feather bottom of taper/carb bore interface slightly so smooth intersection and matched bores.
...Increase top internal radius to max poss. within the restraints of the smaller holes .Looks like 5mm poss. ( in which case the taper is not needed if you reduce thickness ).
...shape outside edge of boss to eliminate sharp changes in air direction coming through filter.

Above is vernier detail stuff. At one time in my career I designed valves and tools located at the bottom of high pressure gas wells and every PSI mattered... As proposed without my bumf above the idea looks good and much better than my K& N units. Good luck!
Neil Ferguson

Neil

Thanks for your thoughts. I agree about tapering down and smoothing the circumference edge of the disc. I am surprised that as little as 5mm thickness is required. I had visions of a deeper venturi throat. I will have to see how good my machining is. If it works I will have to start taking orders!

Steve
Steve Gyles

Steve..the last thing you want is a venturi effect . This generates an increase in velocity through a narrow throat and reduction in total press....and a bigger deltaP . As you know from your "Lightning" fast days the venturi effect was often used to measure flow ( as well as pitot tubes). I believe you should be after as smooth a flow from filter plenum into throat and as short a throat as possible..Air flowing in a pipe( ie down into the carb.) is at a much higher velocity, has steel friction and losing pressure head much more quickly than in the low veloc.filter plenum..so max the air path in the latter and minimise the former ( ie plate thin enough to take a good smooth entry mouth) , Good luck....
Neil Ferguson

Thanks again Neil for a lesson in everything I have long forgotten about airflows!

The only thing that firmly remains in my mind was in my very early flying days when, on a flight check , the instructor asked me why the static vent slots on a pitot tube are staggered in 2 rows round the circumference of the tube (see diagram).

After a long deliberation I had to admit that I did not know, whereupon he advised me that if the were all in one row the tip would fall off!

Steve


Steve Gyles

Steve.. A few thoughts ..and harking back to my days as a gas design and process engineer in North Holland. The stack most of us have images of is the bright shiny well rounded and inlet tapered tube stuck on the carb..and without filter. These suck air ( plus contaminants,dust etc ) from an unfiltered large plenum...the under bonnet. Once you come to design a unit to go inside the the shallow filter housing then the design premises are different. You need a well contoured radius shaped into as thin a surround as possible ..latter to allow as much plenum space in the pancake housing. Any stck protrusion into the filter would lead to increased air turbulence and hence loss of head. I have convinced my self after the application of the grey cells that the APT design shown in one of the pics on this thread looks great and my K&N units ( and the twin cam units also shown )are as useless as tits on a...... plus any increased noise from the filter means more turbulence and more head loss.....over and out.
Neil Ferguson

Per Vizard's flow measurements, a nice 1/4" radius will be very near the best you can do. It should run out into a flat or radiused tangent if the radius is less than 180 degrees. Normally this just means that you drill a big hole in a 1/4" or thicker plate and radius the hole edge. Bigger than 1/4" gives you very little, a runout into an elliptical curve gains very small amounts over the plain radius.

FRM
FR Millmore

Steve,

I have measured the MGB plates that I use and dimensions are:

Thickness of plate = 15 mm
Overall diameter of plate = 100 mm
Bore on side facing the carburetor = 36 mm
Bore on side facing the incoming air = 48 mm

My apologies for not creating a drawing and for not having an imperial vernier available.

Rgds...John
John Bray

Thanks John. The carb bore tallies with mine, so that's fine. It will be interesting to see what Neil says about the 15 mm thickness. The 100 mm diameter disc would just fit my front Volkes canister without modification to avoid the breather pipe.

I have done a couple of drawings using Neil's and FRM's criteria. Limiting the thickness to 6 mm I found that a 1/4" radius edge created what looked like a venturi orifice (top diagram). Using 9 mm (just under 3/8") thickness seemed to get round that issue and looks a reasonable compromise.

Any thoughts? Hope to start machining tomorrow.

Steve


Steve Gyles

Steve,

MGB filter housing is deeper than the MGA Volks unit therefore the aluminum plate that I use will fill a greater percentage of the housing volume. However as Neil suggests the fact that it appears quieter with the plate in also indicates that it is reducing turbulence and increasing air speed which is what we want.

If you look at the picture of the MGB plate you will see that in addition to the bell-mouth the edge of the plate is also contoured which will assist in smoothing air flow as well.
John Bray

Sorry,

Forgot to include a picture of the MGB plate


John Bray

Steve...both look very good . I like the taper down on the outside.I do not see a Venturi ...which Is reduction in diameter and then an increase. I would plump for the thinner one but it is a judgment feeling..I think both will perform well...and be silent. Happy machining....count your fingers before and after!
Neil Ferguson

Neil

My Myford will do me proud. I have been looking for jobs to do on it. I am not into steam engines which seem to be the favourite for most Myford lovers.

Incidently, the company went bust a month ago. Myford has turned its last cog. Another 100 year old plus company gone to the wall thanks to the global turmoil.

Steve
Steve Gyles

Well I'm not sure I would call them a new product - although a sales magazine might.

Ram Pipes aka Stubstacks etc have been around pretty much as long as carburettors. I think the BMC part number C-AHH 7209 was for those suitable for SU 1-1/2" carburettors as fitted to MGA and probably earlier cars.

It's way too long since I did any such flow calculations, but I'm sure Neil and Frank have the practicalities summed up.

Have fun with the turning.

Jim
J N Gibson

Very good Steve,
1/4" radius is sufficient if a full radius, and the outside taper is excellent when drawing from an open volume. An elliptical flare would give very slight improvement over what you show. Plain radius about +5%, flare about +5.8% by Vizard, taper + radius somewhere between. From Vizard's drawings, the TC stubs may well be - 2 to -5%, even without considering the excessive proximity of the filter top plate. Blend any edges of intersection.
In the MGB application, the filter element effectively blocks airflow over the outer corner. If this is used inside an A filter or other open volume, the outer edge should then be tapered or given the same 1/4" radius as a minimum.

FRM
FR Millmore

I have to stop reading this blog, it always cost me money. Just fitted a pair of stubstacks to my MGA (1800B) motor and I am impressed with the difference in running and smoothness they give. I chose the ones that John Bray pointed out from EBAY which are the design being made up by Steve. Anyway I enjoy this site and gain a lot from your vast knowledge and expertise - thanks to all.
Go Well
Frank
F Watson

Steve et al..Greatly enjoyed this thread and the discussion and exchange of ideas. Irrespective of the fact I am going to fit a judson later this year if I could get my hands on my car right now ( but I am Italy) I would tear out the crappy K&N units and install units shown by Steve....thinner one. Keep us abreast of deveopments, steve!!
Neil Ferguson

Neil

I will photograph the progress of my efforts - when the aluminium arrives, should have been today.

Steve
Steve Gyles

Steve...way back in the early to mid 60s I did a Student apprenticeship for my engineering degree ( sponsored by BP) and spent a load of time in workshops.4 years of a 50/50 mix of practical exposure to manufacturing and lecture/lab time at university.The format disappeared a long time ago ( academia did not like,I believe )but I was an ace on the tools..even a respectable welder. Need some static time to get back on top again. Envy you your workshop ..good luck...
Neil Ferguson

Steve -
(click in metric calculator brain cell)
Hard to form a full 6mm radius on 6mm stock, without leaving a sharp edge or enlarging the hole inadvertently, so increase thickness to 8mm or so.
Since you are cutting bar stick rather than working with plate:
Leave about 6-8mm flat on top outboard of the radius, start your taper cut outside this. Then blend the intersections of these cuts to form the quasi-ellipse. (I do it with a file in the lathe).
As it is, you can envision the air flowing up the taper and jumping out over the radius, which is the same effect you are trying to eliminate at the bore, and just as detrimental.

Neil - good point on degrees, summed up in my assertion "Nobody should ever be allowed to design anything they haven't got field experience in making/fixing."

FRM
FR Millmore

FRM

Thanks. I understand what you are saying.

Steve
Steve Gyles

"Nobody should ever be allowed to design anything they haven't got field experience in making/fixing."

Ah yes, I have had my experience of the fresh graduates who know all the theory but know little that you can actually do anything with....

All trainings here involve a LOT of hands-on work, part of the reason that Swiss quality is exactly what it says on the tin
dominic clancy

Interesting practical advice Dominic. Where does copying rather than designing come into the equation. For my part I have practical experience in metal turning. Makes for an interesting project.

Experience is only gained by practice and having a go.

Steve
Steve Gyles

May be of interest

http://www.youtube.com/watch?v=ueTNtwvczNY&feature=player_embedded
John Bray

JB interesting video- I couldn't get any any commentary, is there any?
J H Cole

John..that horn arrangement in a restricted area looks worse than nothing for airflow...terrible turbulence would be created . I mentioned earlier that I have a fairly crappy K&N stub in my filter ...the right type for Su according to their site but I also note on their site that for other carbs ( holleys) they have designed rounded transitions on the same general lines as the one Steve is busily machining. from a 1 ton ingot. see below... Note that in the text they caution about the distance from the top of unit to top of housing.
http://www.knfilters.com/Racing/stubstacks.htm
Neil Ferguson

I don't think there is any sound with the video, but if you look at the legend it suggests that there is an increase in air pressure with the ram pipe before the air gets into the carb which is what we are after.

Neil, I did notice the price of Aluminum has increased dramatically this week courtsey of Mr Gyles!
John Bray

John.....Compressible gas flow and momentum mean that (a)when the air hits the side of the extended stub stack shown and tries to flow up it creates eddies/turbulence (b)it then hits the underside of the filter top and has to turn through more than a right angle (c) it then passes through the decreasing annulus and then switches through another sudden right angle .During each stage of above the gas velocity will slow and the pressure increase( a square law) and less air will flow through the total system. The reason for the latter is that the filter housing is part of the total restriction and if the pressure goes up inside the housing then less air will get into it. However probably would create a great sucking sound--like a pint of bitter going rapidly down !!! The same stack without the filter would perform well.
Not a good design and the short K&N will have a similar ..but much less pronounced... effect.
Ye Gods..I hate the units in my filters!!!..should have thought it through as above before putting them in.
Neil Ferguson

Neil, I think the longer stacks work better with a forced cold air supply typically from an air-box rather than a filter housing which is collecting warm air locally.
John Bray

John..agree. also I note that the sketches compare apples and oranges. The housing around the stack is totally different and deeper/larger...a luxury we don't have.
Neil Ferguson

For what it's worth, I fitted the APT stubstacks with K&N filters to my MGA carbs a few years ago. The stubstacks are well made, easy to fit, and seemed to improve response slightly (although that could be my imagination). Before purchsing them, I contacted John Twist of University Motors to see what he thought of them. John recommended stubstacks and said they could add a few horses to a standard engine.

M.D.
'57 coupe
M. D.

John, if I understand correctly, I would need to bore out the holes in the MGB units in order for them to fit over the bolt tubes within the mga housings?
And then hold them in position with silicone, etc so that they don't rattle around?

Ron
R emgeeaa

Hi Ron,

The MGB units will go on as they are but they are a tight fit.

My suggestion would be to try them and see how they align, in particular do they provide an uninterupted flow without any misalignment of edges.

Mine are not held in position with any adhesive as the fit appears strong enough just by pushing them in place. However if you decide to enlarge the holes then they will rattle unless fixed.

Regards...John

John Bray

My first one is coming along. Busy polishing, almost there, then part off to the required thickness and drill the holes. Followed by final polishing.

Steve


Steve Gyles

This is the profile. It's 7.5mm thick; 1/4 inch radius throat; and 20 degree sloping face.

Steve


Steve Gyles

Not bad! I'd have put more of a flat outboard of the entry radius, with a more gradual transition to the taper.

How are you holding the bar in the lathe, and how much overhang do you have? Parting tools give me the willies on such a setup. You can do serious damage to a small lathe spindle if the tool grabs, not to mention broken tools and ruined parts. All the more likely with a deep cut and a lot of tool extension.
I do most of the cut with a live center in the tailstock, make a centering plug for the bore if necessary. Better yet, leave the bore well undersized, use a center while you make the parting cut to depth, and finish the bore to complete the parting. Or the quickest and least nerve rattling way: start the parting cut to guide a hacksaw, cut off with the saw, flip the part over and finish face the backside.

FRM
FR Millmore

FRM

I have plenty of bar to experiment with, so might change the design as I go along.

I have not parted this diameter before, so making it up as I go along. It's that 'experience' word that Dominic was referring to earlier. All part of the learning process.

In the set-up in the photo above I was running the parting tool level centre and it was tending to bite chunks of metal, rather than spirals. So I read my book of words and it suggests having the parting tool just below centre so it is less inclined to dig in (grab). More likely the tool will flex downwards. I will try that method tomorrow. The hacksaw method had also crossed my mind.

I am running the 3.5 inch bar in my 3-jaw 4 inch chuck with the jaws reversed. Not ideal, but it's all I have. The lathe has a 7 inch bed. My larger 4-jaw chuck has gone to the scrap yard. I am probably getting away with the set-up as it's aluminium and cuts without too much lateral pressure.

Steve.
Steve Gyles

Yes Dominic, experience we earn. Definition .
A series of mistakes we make that we remember not to make again ! Sean
S Sherry

Steve
Check yr email before shop time.

FRM
FR Millmore

First stub stack machined, parted off and interim polish. Just got to ruin it now when I drill the 4 holes! It will require very precise setting up in the lathe vertical slide for that task.

Many thanks to FRM for some sound advice that he emailed me, such as holding the aluminium block more steady with the tailstock and finishing off the parting with a hacksaw - far more controlled way of doing it and no damage.

Steve


Steve Gyles

Drilled the 4 holes successfully. Question: Should I leave the the 2 air pressure balancing holes to the carb pistons sharp edged or should I flare the edges?

My thoughts for static air vents is that they should be sharp edged, but I will bow down to superior aerodynamic knowledge.

Steve
Steve Gyles

Brilliant stuff Steve - I never mastered the lathe so I am in awe at your skill.
Cam Cunningham

Pretty!
I agree about the vents, except that the sharp edges will scramble airflow across them, So, I'd leave the outer edges fairly sharp (deburr only), but put a good blend radius on the side toward the main bore.

FRM
FR Millmore

Cam

Don't kid yourself. I used a lathe for 3 years at school from 1959 and then started again only about 3 years ago. Self taught mainly and listening the the good advice from the likes of FRM.

My first rule in any project has always been to develop a plan. I often think about the issues and methods for days or often weeks on end before doing any practical work.

Steve
Steve Gyles

Steve, the MGB vent holes are flush with no flare

Regards...John
John Bray

It fits and all the holes line up!

Just a bit of recessing required at the back so that it sits around the spots welds on the 2 shafts.

Steve


Steve Gyles

OK - now make about 100 more so we can all start placing orders.

I will take two, please.

JIM in NH
AJ Mail

Send two to me as well. Very nicly made.
David Lake

I'll have a pair Steve if reasonably priced. Remember I have to pay for the postage to Malta as well. Tks

Frank
F. Camilleri

Steve...a lovely piece of tailored work.....
Neil Ferguson

As much as I would love to accommodate all those orders, it's not that easy to mass produce on a small amateur lathe (Myford Super 7).

The basic machining is very straight forward which anyone with a lathe can achieve quite easily. The time consuming teeth gritting part, which I think FRM will back me up on, is the parting off. It took me hours to cut it off from the main aluminium block. I am sure professional machine shops invest in equipment for just this purpose.

The issue is that the parting-off tool has a tendency to dig into the work, partly because it has to be long and thin and has a tendency to flex, also causing inaccuracies in the cut surface. When I finally parted it, I had to turn the stub stack round in the jaws and square off the reverse side. I was surprised how much metal I had to trim - as much as 1mm near to the centre.

Steve

PS. I now have a carrier bag full of swarf, and that's just from the first stub stack. I am beginning to understand the importance of recycling in professional production.
Steve Gyles

Steve, you could probably have parted it off the lathe with a 10" chop saw and a carbide blade. But that hindsight.
Art Pearse

Art

Nothing hindsight here, still got another to do! Excuse my ignorance, but what's a chop saw?

Spent a few hours fettling and polishing. I got banned from using the wife's stainless steel cleaner which was doing a brilliant job! It is now cemented in place (photo).

Next one starts tomorrow.


Steve Gyles

It looks great! "The biggest factor relating to how well a ram pipe works is the radius on the end of the ram pipe. Anything with a radius over about 1/8 inch is in with a 99% chance of working. Where a radius is not totally formed, i.e. it doesn't roll back completely on itself, then so long as it turns out at least 60 degrees, it will work." Quoted from John Vizard's book "Tuning BL's A Series Engine". Eleven different configurations of ram pipe were shown and the one producing the greatest increase in flow (5.8%) was the one that looks like the APT offering.
JM Morris

Nice job Steve.
A chop saw is slang here for a mitre saw (see Wikipedia!) they come either simple pivot or sliding.
Used to make square, mitred or compound mitres in lumber. So you would clamp the 3" bar to the table and make a 90 deg square cut.
How can you live without one?
Art Pearse

It looks to be a superb job Steve and you should be proud of it.

My dad was also a Myford lathe owner and he was a superb engineer making ( surprise surprise ) many working model steam engines. My older brother became an engineer too and so naturally, he got the lathe and my dad left me a wood turning lathe!(and a couple of his steam engines)

So I could probably make up a similar pair of sub-stacks in mahogany or similar and I expect they would also look great and work well, that is, until they become petrol soaked and burst into flame!

So maybe I should have argued for the Myford!

On the other hand maybe it is just as well he didnt let me loose on his lathe.

I remember an unfortunate incident at school when I was in the metal working shop setting up my lathe.
I had just set up to turn a piece of round bar, tightened up the chuck with the chuck key and switched the motor on to begin turning.

I heard a swish as as I turned the motor on and a muffled thud from some distance behind me.
When I turned around I found our engineering teacher sitting dazed on the workshop floor.

We all ran over to see if he was ok and he was quite embarrassed and convinced that he had walked into one of the many girders that were suspended around the shop.

Maybe I should have removed the chuck key from the chuck before starting the lathe!

I never did tell him!

Colyn

PS does anyone have any info on the advantages (if any ) of having the long rampipes fitted as on my car. 1950 cc MGB engine Thanks


Colyn Firth

Steve, its a great pity that the end product is hidden within the filter body. Transparent covers from Plexiglas next?
Art Pearse

Art. I could not agree more. Last peek before the cover goes on.

Colyn. The chuck key was the first golden rule I was taught. It's all too easy to forget. I make a point of checking all round the chuck, the cutting tool etc every time before I switch on.

Steve




Steve Gyles

Beautiful! Will you make another?
If you go into production, it is a good deal easier to make them from plate.
Now you need to research slimming/fairing in the pillars, as they create major flow disruptions.

Regarding chop saws and such, use of a carbide woodcutting blade can have disastrous effects; the positive rake teeth will dig in to the aluminum and raise havoc. Metal cutting blades have zero to negative rake to prevent this. I rebuilt my 28' aluminum dump trailer using a circular saw to carve out all the dead parts and welds - very effective, sometimes surprising and dangerous as the saw would grab and try to break my arm, and carbide teeth flying all over are not fun - lost a garage window and the rear window of my pickup which was about 20 feet away. But the blades were cheap and I finally learned to modify the teeth.

FRM
FR Millmore

FRM

I've got to make the second - twin carbs! Thanks for all your advice, it's been a great learning curve. Second stack ready for parting.

BlancoPolish was responsible for the shine. I thoroughly recommend it for polishing aluminium. It is marketed for cleaning stainless steel sinks.

Steve
Steve Gyles

Excellent piece of engineering Steve. I would love to get my hands on a couple for my A. Can you not task an engineering firm to produce a bundle for you. Professional engineers use modern CAD lathes nowadays, I'm sure they can manufacture your patent design in a matter of minutes.

Frank
F. Camilleri

If you were going to make 100 or more of these parts, the part may be least expensive to produce as a die casting (with very little machining).
Barney Gaylord

I totally agree with Barney.
F. Camilleri

Hear hear Barney, making 2 on my lathe is all I can manage in the short term. Commercially produced the way I have done it would be quite time consuming and not all that cheap when you think of the labour cost; the cost of the aluminium stock (most of which is cut away); the cost of the cutting tools - and regrinding; electricity; lathe lubricant; polishing sundries; and general wear and tear.

That all said, for me as an amateur making do with what I have in the garage (except for the aluminium) the production cost has not been too bad. The metal cost me $5 a stack and may be I used a couple of dollars of electricity. The rest of the stuff just gets absorbed in the enjoyment of a hobby.

I think others have mentioned above about having to fettle the stub stacks to fit. This will be the case with my type, mainly due to the inconsistent shaped welding blobs that attach the 2 posts to the casing. I had to grind some of the welding away to get it all to fit.

Steve
Steve Gyles

Counterbores on the back side of the new parts could allow for clearance around the post base welds.
Barney Gaylord

Barney

I went down that route but had to stop before I bored through to the front surface. The welds were as thick, if not thicker, in places than the tapered face of the stub stack. e.g. the tapered plate is about 4mm thick at the posts.

Steve
Steve Gyles

Wow, what a difference! and that was with only one stub stack fitted. Very noticeable difference in engine response. Can't wait to get the other one finished and fitted. About to drill the 4 holes.

Steve
Steve Gyles

Just thought you might like to see how easily BlancoPolish changed a 400 grit finish to a nice shine in just 4 minutes. Not finished as you can see, just the first buff. Brilliant stuff.

Might put it back in the lathe to make more throat; not totally happy with the profile yet.

Steve


Steve Gyles

The increased performance produced by the stub stacks highlights the importance of the airflow. Polishing the inlet & exhaust ports & matching them to the manifolds will also give a noticeable improvement in engine response.
I Hazeldine

Second one finished and a good fit. Unfortunately away for a week so it will be 10 days before I can test the car.

Steve


Steve Gyles

Having watched this long-running thread with some interest, are there any twin-cam owners out there who have any comment re the situation as applied to a twin-cam? What are the standard Vokes filters like and is some similar work needed there?
Bruce
Bruce Mayo

Steve, looking at your last image of the second stub stack, I was wondering if you'd be so kind as to give me the: 1. overall outside diameter
2. Diameter of the two large holes
3. Diameter of the two smaller holes
4. Material thickness of the large centre hole
5. Material thickness of the outer
circumference
I am assuming that the side on which it is standing is completey flat.
I have a very good friend of mine who runs an engineering shop, who is quite willing to fabricate a couple for me. The above are the measurements he wanted. Thanks in advance.

Frank
F. Camilleri

I believe 'stub-stacks' is hardly the right term for these units.....better to have something like 'Entry Profiles'..any ideas?
Neil Ferguson


ram pipe?
Siggi

Steve, have you a copy of the B series engine tuning BOOK by Steve Strange? It is a fascinating read and has a whole section on the subject on stubstacks and air filters and discusses harmonic shockwaves exiting from the inlet manifolds into the air filters. Check out page 207.
Let me know if you would like to forward you a copy but be warned that you will probably spend the next few months reading it!

Colyn

Colyn Firth

Colin, what is the title of the book by Steve Strange?
Mike
Mike Ellsmore

For Steve Gyles,
Steve, I refer you to my very last post before this one. I do not wish to impose on you or anyone else for that matter, but do I wait a bit longer for your answers or am I to forget it.?

Frank
F. Camilleri

Frank, please read carefully Steve's last post.

Richard
R A Evans

Tks Richard, silly me, I missed that completely. I'm getting old.

Frank
F. Camilleri

Mike, "The Book" as it is known in the MGB world is an amazing article that Steve Strange in California I believe, has compiled over many years on the subject of tuning the B Series MGB engine.
It is incredibly detailed and Steve has forwarded copies to anyone who asks for one.

The copy he sent to me is only a few months old and is probably an up to date version but if you check out the MGB forum archives you will probably be able to find his email details.

If you have any problem I am sure he wouldnt mind me forwarding you a copy.

Be warned though that it is really addictive!

Colyn


Colyn Firth

Thanks Colin, I have located a copy - note sure if it is current but will contact Steve Strange to get latest.
Regards
Mike
Mike Ellsmore

Frank

Just signed on in hotel in France. I will give you chapter and verse at the weekend.

Steve
Steve Gyles

Steve, I'm sorry pal I had not read your post where you said you will be away for ten days. I'm in no particular rush, always at your convenience. Have a nice time in France. My wife and I will be in France sometime late November, my daughter-in-law is expecting her second child, a boy. They live in Leoville, south of France.

Frank
F. Camilleri

Frank

The answers to your questions are as follows:

1. Outside diameter is 3.5 inches (9cm).

2. Internal hole is 1.39 inches (3.5cm). This matches the carb inlet hole diameter. Probably worth checking yours and get your machinist to match your measurements.

3. The 2 large holes are 0.5 inches (12.5mm) to make a comfortable fit, but you may have to do a bit of easing depending how accurately they were welded up. Mine were not quite parallel so I had to do a bit of filing. Again, worth checking the diameter of your tubes.

4. The 2 small holes are 0.315 inches (8mm).

5. The sloping face is 15 degrees, resulting in a maximum thickness of 0.315 inches (8mm), depending on how much you radius the throat. I aimed for a 0.25 inch (7mm) radius throat.

I used the gasket laid out on the back of the stack to get the positions for the hole centres. Worked fine.

You will have to enlarge the back of the large holes to get clearance around the welds holding the 2 tubes (see attached picture of reverse side of mine). You will also probably have to grind the welds down.

Steve


Steve Gyles

Steve, thank you very very much. Those are all the measurements I was asked to get. If my engineer friend asks for any other measurement/s, I might come back to you if I may. One other question which comes to mind right now Steve is this; How do you intend to attach the s/stacks to the filter box? will you bolt them on or will you use some other method?

Frank
F. Camilleri

Frank

They were a very tight fit in the tubes and I could have got away without any fixings. However, I just used an ordinary 2-pack adhesive on the contact surfaces.

I have just fitted the second stub stack and been for a test drive. I was very, very impressed. The car felt as though it was skipping and dancing on the throttle; very lively. It was so much more responsive on throttle opening. I have to admit that I felt a little nervous once or twice with the handling until I got used to it. You get used to driving your car in a routine sort of way on your local roads, then do a mod like this and it requires a slightly altered driving style.

In summary, a big tick for throttle response. Choke needed for less time. Engine pick-up on the still cold engine (without choke) very much improved. Love it.

Steve
Steve Gyles

Steve,

Thanks again, I did think that you might have used adhesive to keep them in place, but I wanted to ask to be sure. Now that I read your report on the difference they make to the engine response, etc., I cannot wait to have a pair fitted on my A. I will also be replacing the distributor vacuum advance unit with one from British Vacuum Units of USA. After I tested the one I have, using a vacuum gauge, it resulted that it wasn't working as it should. As you probably know, the unit should start to open at 7 lbs and continue to open until it reaches 14 lbs of vacuum. Mine was starting to open at around 5 lbs and stopped moving at 9/10 lbs. A good working unit should also make an appreciable difference in engine response. My conclusion is that with a pair of s/stacks fitted and a new vac unit the car should be much more pleasureable to drive. I will report back when the time comes.

Frank
F. Camilleri

Frank

On the subject of distributors I fitted one those Chinese copies a couple of years ago. Excellent performance and it only cost about £50.

Steve
Steve Gyles

Excellent Steve - who would have thought that it would make such a noticeable difference.
Cam Cunningham

That's fantastic that you can feel such a noticeable improvement! Sounds like a very cheap and simple bolt on performance mod!

I wonder if you can feel the difference more on the 1800 engine than the 1500, 1600 and 1622? Just thinking aloud, but maybe there is more "wasted" power to be released?

So going back to the start, how do these http://is.gd/PrfNCy compare to the ones you made? - Before I press the "Buy it now" button.......
N McGurk

That's interesting Neil - look very similar to Steve's homemade one's - are you going to be the one to test them out?
Cam Cunningham

Neil

Lot of posts to read on this thread, but in the early discussions FRM and the other Neil suggested that a good thickness of the stubs in our Volkes canisters should be in the order of 5mm to 8mm thick. The one in your link is 13mm thick. Obviously, I have not tried them so cannot make a comment.

May be I should get another couple of canisters and make up 2 more stubs to that configuration and make some comparisons. I have enough aluminium left.

Steve
Steve Gyles

Problem is interference of the top plate on the flow. I've seen reference that the minimum clearance to the top plate should be around 1.5x the bore. You don't have that here, so minimum thickness to develop the radius is best. And note that the importance of the radius becomes greater as the top clearance decreases, since more of the air must come from the side.
I think Steve's dimensions are about as good as you can get within the stock cans. I'd still improve the blend from taper to radius a bit, and I was not kidding about slimming/streamlining the pillars and holes above - they disrupt airflow a bunch. Best way is to fasten the "smoothers" to the carb body with CS screws, and move the fastening for the filter tops to the outer periphery, or better yet, outside the elements. It is very useful to think of yourself as an air molecule, traveling at high speed to get down the bore; what slows you down?

FRM
FR Millmore

Steve,

I'm not that keen on Chinese stuff. I have an original MGA distributor which I had bought as a rebuilt unit from Jeff Schlemmer of Advanced Distributors in USA, and now I think I'll buy a new vac unit newly built by BVU also in USA. The cost of the unit is around 83 Euros, and that is inclusive of postage to Malta. That's not too bad. To have my own unit rebuilt to specs in the UK, I was quoted a price of £70 incl. postage. The difference there is that from BVU I get a brand new unit and there is not much difference in price.

Frank
F. Camilleri

Ye gods and small fishes....I go away for a decade on holiday in Greece ( still there) and when I return the same thread is booming on...but a good subject.
Great to hear your performance results ,Steve.You obviously have got pretty close to getting the sharp entry loss coefficient down by 4 with the smoothing and rounding. From your throttle response comments it sounds like you got much more than a few percent improvement...and improved your machining skills.
Re FRM's latest comments...I totally agree and all the plate insert should try to achieve is to support a rounded entry and otherwise get out of the way of the airflow in as smooth/rounded a profile as possible.It should take up as small a volume in the restricted filter housing as possible. Steve's does this and thicker plates can only be detrimental ..but possibly only slightly. His comment re the housing and the columns inside is good. Getting rid of them will help stop turbulence and consequently head loss..
Neil Ferguson

Steve, sorry to be a nuisance. But I may not have understood a small detail, not that technically minded. You say the sloping face is 15 degrees resulting in a maximum thickness of 8 mm. I have not discussed your measurements with the engineer yet, I am assuming that the 8mm thickness is at the outside perimeter. What would be the thickness of the centre hole, from top to bottom? Maybe this is a stupid question, but please excuse my ignorance.

Frank
P.S. The thickness indicated in red on the attached picture


F. Camilleri

Steve, that last picture of yours is a work of art, have you thought of putting it on display in the Tate.
J H Cole

Frank

Your red arrow marks are the 8mm maximum thickness! It's all quite thin. Some of my photos made it look thicker than it actually is.

John. The shine is all down to BlancoPolish on a 400 grit finish. I have been amazed by it. I only polished for about 30 minutes, with a very small amount of the paste on a finger-tip cloth using a predominantly circular motion. Others with alloy rocker covers might want to try it.

Steve
Steve Gyles

Re: how close to allow between the stub entrance and the filter front plate - if you think of the air flow entering via a cylindrical space between the plate and the entrance, if you make that cylindrical area at least equal to the bore area, then there will be no unnecessary increase in the air velocity. That means you could go as close as D/2 to the plate, D being the entrance bore. Steve, maybe even polish the inside of the cover!
Art Pearse

Art-
It is not that simple. The air is coming in from the sides, and going in the wrong direction, namely, radially inward along the diameter. Opposing air streams collide, stopping flow entirely, after which the air has to be accelerated in the correct axial direction. The closer the top plate to the bore, the faster the incoming air, and the worse the collision.

Consequentially, there is all sorts of turbulence and loss of flow. In an SU, the situation is made worse by the fact that flow through the carb is not concentric, but heavily biased toward the bottom under less than WOT. At small throttle openings, the critical flow is adjacent to the bottom of the bore, ie, close to a sidewall. Any turbulence can be expected to have maximum effect here, as opposed to near the bore center. This would greatly affect the signals at the jet/bridge area. I expect this has a lot to do with Steve's rather surprising perceived result. I had questioned whether Steve would notice any effect short of near WOT; I expected improvement there, but that is not a very useful thing on a road car.

In theory, your D/2 (R?!) would be minimally restrictive IF you could figure out how to turn the airstream without turbulence. The Bristol engine, as fitted to AC, has very shallow filters (near D/2), due to bonnet clearance issues. Since Bristol know a bit about aerodynamics, they formed a curved cone in the top plate to turn the air in the space available. I unfortunately no longer have my AC Bristol, but as I recall, the Solex carbs incorporate most of the throat radius that Steve has created. This should be done on any relatively shallow filter housing, and in fact, many engines with big carbs and shallow filters do just this. See virtually any OEM 4 barrel filter. The fact that you don't see these features on most aftermarket filters is a good sign that the manufacturers and customers don't know or care WTF they are doing. Deep filters, like the OE MGB ones, don't have the problem, at depth around +2x bore size.

BTW, I was pretty appalled at the pics of the OE Twin Cam filters - horrid!

FRM
FR Millmore

for those like me who were not aware WOT=wide open throttle!
Mike
Mike Ellsmore

Thanks again Steve, much clearer now. I spoke to my engineer this morning, he is more than willing to fabricate the S/S as per your dimensions. But I'll have to wait a couple of weeks or so as he is rather busy right now.
F. Camilleri

I have just fabricated a pair of these as shown in this thread. I can not say I have noticed an improvement in performance / running and would be very disappointed if I had paid for some to be made.
Maybe it was running so sweet before I fitted them that I can not notice the change!!
A J Dee

FRM's comment about the non-concentric path within the SU makes me ask why there is a square profile on the piston? Why not round it slightly to enable the air to flow more smoothly at this point?
M Wellard

AJ

Most interesting. My car was also running very well before. I was wondering over the weekend if I was over-egging the improved performance I felt - it was raining quite hard at the time. However, I have just been out for another run in dry but windy conditions (remnants of the recent USA hurricane) and definitely felt the improved performance. The throttle pick-up was very pronounced and it was as if I had several more BHP. Not dissimilar to when I changed over from the 1500 to 1800 engine.

Steve
Steve Gyles

Steve
I obviously missed the fact that you have an 1800. Maybe they respond better to this mod. I have a stock 1600 all be it with a B head.
Andy
A J Dee

Steve:

Did you rebalance and adjust the mixture on the carbs after installing the stub-stacks? If not, you may partly be feeling the effects of a leaner mixture from the increased air flow. It would be fun to get your car on a dyno and test it both with and without the stacks, with properly set-up carbs each time, to get the true measure of the improvement.

M.D.
'57 Coupe with stub stacks
M. D.

MD

Not yet. I well check them out. Good call.

Steve
Steve Gyles

To M Wellard, Queensland, Australia,

Try to get hold of a copy of Vizards 'Tuning the A-series engine' there's a whole chapter about 'flowing' the SU carburettor; a very interesting read.
Willem vd Veer

I have summarised my efforts on my website: http://tinyurl.com/6ec2owh

Steve
Steve Gyles

This thread was discussed between 06/08/2011 and 13/09/2011

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