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MG MGA - Carb stub stacks

Well, the results are in!

Place your bets gentlemen, negligible gain or noticeable improvement?

The car was dyno tested this afternoon a couple of runs without stacks and again with stacks.

Those were the only tests I did as my car was not in particularly good tune! It was running very weak at idle, rich at mid revs and slightly rich at higher revs and so the tester recommended changing needles before doing a complete re-tune.

Before I reveal the test results I would make some comments on the design as I believe there are some (minor I hasten to add, Steve) improvements that could be incorporated.

At the base of the retaining columns on the filter housing back plate there are small raised sections (that are spot welded to the back plate) to secure the columns. See picture. Providing clearance for these and a little more clearance for the columns would make the stacks a simple no modification fit.

These are 3/4" in diameter and 1/16" high so the recess on the bottom of the stack should be increased from 0.68x0.07 to 0.78x0.07minimum. I had to file the 0.5 pillar holes slightly to fit over the pillars so would recommend increasing to 0.52 to allow for pillar thickness and position.

N McGurk

Noticeable on the back plate are the marks left by the filters. The innermost marks were made by the original filters (removed over 20 years ago) and the outer rings by the K&N filter.

The stacks as made are ideal for the original filters, but if the outside diameter was increased from 3.5 to 4.5 then they would be perfectly matched to the K&N filters. Most people looking for improved efficiency and airflow would switch to K&N filters anyway?

N McGurk

Neil

I wait with baited breathe!!

Your face plate is better engineered than mine. I had uneven welds holding the tubes. Your collars look much better. Had I known I could have turned the reverse side of the stubs to fit. All part of the learning curve.

Not sure I could have turned 4.5 inches in my lathe. My chuck was at its limit on 3.5 inches.

Steve
Steve Gyles

In order to fit the stacks easily (without resorting to the grinder) I made up a couple of 1/16" thick cork gaskets.

N McGurk

These allowed the stacks to fit flush to the back plate. There was an added benefit in that my filter elements were no longer loose and I could finally get rid of that 50 year old felt!

N McGurk

Oh! I almost forgot, I think the inner radius on the stack could be increased from 0.25 to the full width 0.31. Not sure if that would make a lot of difference or not, but surely an improvement?

All the dimensions I refer to are taken from Barneys CAD drawing.
N McGurk

Neil

As it happens I am making another set at the moment and have increased the radius a bit. They look better. I will measure them to see if the radius is near to your your suggested 0.31. I am eye balling the shape and just running my fingers over the curve until they feel right. Remember that this design was drawn on the back of a fag packet using basic data from from FRM and Neil (Australia). If the concept works then improvements will follow.

The fact that you are offering improvement suggestions makes me think that they did work on the dyno. I vote for a significant improvement, but there again I am biased and have been running a set for a month!

Steve
Steve Gyles

"The fact that you are offering improvement suggestions makes me think that they did work on the dyno. I vote for a significant improvement, but there again I am biased and have been running a set for a month!"

Maybe, or maybe I think they might offer better results with some improvements?

Either way, that's one vote cast!
N McGurk

Neil,

I agree with Steve, improvement with stacks fitted
John Bray

I'll bite too Neil, I reckon you found an improvement as well.

My guess is something in the region of 3.5%.

Are you offering a prize for the nearest estimate?

Cant wait for the figures Neil.

Colyn
Colyn Firth

The torture, the suspense.....I can't digest my porridge oats until I know....!!
Neil Ferguson

Come on Neil, already past my bedtime.

Shane
Shanerj

My guess....1.5% improvement .
Neil Ferguson

I will break the news tomorrow, once our friends from across the pond have had chance to have a say...
N McGurk

Neil I'm intrigued by your design and must say that it looks beautifully made. I know that in theory there should be some increase so I will side with the yes crowd but say less than 2% but that would be around 1.5 bhp and that seems a lot. In any case with a properly tuned engine it could be more.

Andy
60 Coupe
Andy Preston

OK. We know that the open pipe flow improvement should be about +5.5% max, probably less on an assembled carb, possibly a bit more with the top plate in place. But, these are flow at WOT; expected change would diminish at lower throttle openings. These are things you would measure on a flow bench.

Power output is an entirely different matter, being dependent on correct AFR. At WOT, power should be proportional to flow capability, but it all goes off at lower flow, ie, normal driving. The aforementioned possible pressure variance across the balance ports, plus the change of turbulence in the airflow, could easily cause changes either up or down - or both, depending on where in the throttle/load range you measure. None of it means anything without AFR figures at each measuring point.

There seems to be a general experience that reducing intake restriction causes leaner mixtures at high flow, so power improvements could be expected if this is true at whatever point data is gathered, and the engine is running rich, as this one seems to be. (the combination of weak idle and rich above may indicate a vacuum leak being compensated by overly rich jet adjustment).

I am more interested in the perceived off/part throttle changes Steve reported, as these are the real world effects noticed in driving. I've often said I'll trade 5bhp where I rarely drive for 3 where I do. Unfortunately, part throttle and transitional throttle effects are very difficult or impossible to measure on the dyno. Peter Burgess' new one might be able to do it, as I think it can measure acceleration between rpm points. Coupled with a TPS, you might get some good info. Otherwise, it's timed runs between speeds with a fixed throttle stop to get any info.

Steve: if you make more or bigger ones, start with plate, drill the 4 holes, but Drill the pillar holes small and use countersunk screws to hold the blank on a face plate. Machine to shape, then finish drill the pillar holes. And, as I said before, leave a flat around the radius, stop your taper outboard of this by about .5-1x the radius dimension, and blend the taper, flat, and radius together to finish.

FRM
FR Millmore

FRM

I agree that using a plate would be easier. I found that parting-off from the round bar quite laborious and wasted a lot of metal. I have not done faceplate machining before so it will be an experience. I will investigate. Looking forward to reading all about Mark's results.

Steve
Steve Gyles

Good work in testing Neil. Bearing in mind Steve's initial testing , I would guess that the power gain is marginal only the smoother flow giving better response to the throttle - my bet is that it is probably nearer 1% improvement but hope Colyn's guess is right!
Cam Cunningham

My guess is "within the accuracy limits of the dyno". The tyres chew up a good portion of the power, so any variations there are significant.
Art Pearse

Art

As Neil did a before and after run on the dyno all the common factors cancel out resulting in an accurate analysis. I wonder when he is going to publish the figures. The wait is agonising.

Steve
Steve Gyles

OK here are the results:

Peak power increased from 88.03HP at 4,641rpm to 92.31HP at 4,601rpm and peak torque increase from 104.4ft-lb at 4,350rpm to 107.4ft-lb at 4,350rpm

There were a couple of runs on each (without, then with stacks) and these were the best of both. As soon as the second set started the tester said there was a definite difference.

It is possible to tell the difference on the road too. Definitely a more "lively" feel is how I would describe it.



N McGurk

Second chart

N McGurk

A superb result......thanks Neil it was worth the suspense....
Neil Ferguson

Neil

I am delighted. It validates my 'seat of the pants' feel. I must get my backside calibrated!

If my maths is correct that makes it a 4.87% increase on HP and 2.87% increase on torque.

Glad you noticed the additional 'lively' feel on the road. When I first tested mine I said "The car felt as though it was skipping and dancing on the throttle; very lively. It was so much more responsive on throttle opening."

Steve
Steve Gyles

Steve, congratulations with this result and Neil thanks for the test. The suspense was killing me, too!

Amazing what a good discussion on this BBS can result in. Will the next step be the 'flowing' of the internals of the SU carburettors? David Vizard wrote a chapter on this in his book 'Tuning the A-series engine'. With his modifications you can make any SU flow like the next larger size SU. Especially the sharp internal edges, the screws of the throttle disk and the shape of it's shaft cause a lot of flow robbing turbulence

I did most of the recommended mods on the single H2 fitted to my YA and was amazed by the increased livelyness, so I'm not really surprised by the dyno results.
Willem vd Veer

N McGurk, -- Can you send me a larger high resolution copy of the charts? I would like to post these on my web page.
Barney Gaylord -- barneymg@mgaguru.com
Barney Gaylord

Barney, Pdf files sent.
N McGurk

Many thanks to both Neils and FRM for all the help in producing a viable stub stack specific to the MGA. A true international project.

It's been a great adventure for me. I am a basic lathe user and have learnt a massive amount.

The drawing is there on Barney's site. Any one with a lathe can produce a couple in a week. Don't forget the magic BlancoPolish, great stuff.

Steve
Steve Gyles

Wow,an almost 5% increase! and I thought I was being conservative when I guessed at 3.5%

I think Steve is going to have to set up a production line to cope with demand for his stub stacks!

I have read in Steve Strange's amazing MGB engine tuning manual ( known as "the book" on the MGB forum ) that the stub stacks were worth an up to 5% improvement on the MGB engine. I must admit that I didnt think it would be so much, which just shows how little I know about the subject!

My car has the longer inlet Ram Pipes fitted with Piper sock type filters and I would love to find out what difference these make.
Looks like I need a run up to Neils rolling road dyno to get my car checked out.

Thanks again Steve and Neil, its been a really great thread.

Colyn
Colyn Firth

Neil -
Excellent! Now we know it does something, and a bit of what.

Could you also send me those charts? I cannot see and compare them side by side very well on here.

You will note that it did lean things out a bunch on top. So, anybody not starting out rich needs to pay attention here. Now to work on the expected idle vac leak, and then get the midrange sorted. As it stands, you should be well paid in high speed touring! A free mod after a couple of tanksful.

Is any one of you near to Mr Burgess? I would really like to see transient accel figures in the lower ranges.

Steve - It is great fun making faceplates too,and then you can really go nuts. Far more versatile than chucks, especially if you are pushing the limits of the lathe.

FRM
FR Millmore

Well done Steve, I thought you may get a slight improvement but nothing like your actual results.
Just goes to show its worth retesting well held assumptions.
J H Cole

This is getting better as it goes. Neil sent me high resolution images, and I have posted them here:
http://mgaguru.com/mgtech/power/pp104b.htm

I think I am going to try some additional image processing to equalize the horizontal and vertical scales, consolidate colors, then superimpose the images in a single view for direct comparison.
Barney Gaylord

Barney

You have got them the wrong way round!

Steve
Steve Gyles

Neil's tests were on a 3-bearing 1800 engine. It will be interesting in the fullness of time to see figures for the 1500 and 1600 engines. If there is any one down my way who wants to trial them I am happy to lend out my filter boxes, using their box for the initial run and mine as the after as I have the stacks firmly glued in!

Steve
Steve Gyles

Steve, I should hopefully have a mild tune 1600 in the spring to test these on, but of course anyone wishing to do another test can also use these stubs as they are not bonded in (yet)
N McGurk

Neil, what kind of dyno test was this?
engine, rolling road, axle hub, etc? it appears to be engine HP quoted.
Art Pearse

Neil,
Do know the make and model of the dyno?

Well done Steve.

Mike
Mike Ellsmore

Sorry about the image swap, just confused two file names, but fixed now.
Barney Gaylord

Art and Mike,

This is the where the tests were performed:
http://www.jdm-dyno.com/index.html

The dyno is a custom made rolling road with computer control and data logging. Graphs and figures are provided of the vehicle's performance using DYNO-MAX software from www.land-and-sea.com. Yes it shows flywheel Hp.

N McGurk

Steve , I was so impressed with your fabrications that I made the nearest copy that I could. Not having a lath or the skills to go with it I made a negative mould from the dims you provided out of chipboard and a rotating arm with the cardboard stub stack profile. Filled with polyfilla the arm rotates to give a passable negative mould for filling with glass reinforced epoxy filler. Sanded and sprayed black they are quite presentable and fitted to my car.

J H Cole

Brilliant -well done Steve - wouldn't have believed they gave such an improvement - thanks Neil for using your car as a guinea pig .
Cam Cunningham

finished items

J H Cole

Neil,
It would be interesting to see what improvement the proprietary K&N filter housings give? I can see you being our full time device evaluator!
Mike

Mike Ellsmore

John

I love your glass fibre stub stacks. That may be the way to go for mass production. Let us know if you notice any difference in performance.

On the issue of fuel consumption it may be early days as I have only done about half a tankful since fitting the stacks, but with everything else being equal my MPG has jumped suddenly showing a 2.46 mpg improvement (11% improvement on my recent average consumption). On a full tank this would probably equate to a 4mpg+ improvement. The last time my consumption was even close was on a 250 mile run 15 months ago and even then it was 1 mpg short of my current figure. Bear in mind also that this latest figure is based on generally shortish runs of 10 miles or less. I hope this is not a red herring and due to some other factor, so I will be monitoring and will report back at the next refill.

Steve
Steve Gyles

Good looking work, JH.

I will have to copy your idea.

I have a wood lathe, not a metal lathe. I was considering making them out of "plastic" lumber for my own use...but "casting" them in plastic might be a better solution.

Also, you now have a mold - you can go into business selling them to the rest of us...how much?

JIM in NH
AJ Mail

Mike

Were those filter boxes standard equipment on Australian assembled cars? I remember from other threads that some of you guys down under seem to get better fuel consumption than us. Just wondering if there is a link with the designed-in stub stack.........

Steve
Steve Gyles

Full time device evaluator!?

Not at £60.00 a pop!
N McGurk

Neil..you mention 60 quid..was this the cost of a single dyno run? It seems very reasonable . if not just how much is a single run. I for one am delighted with the tests and the results are of benefit to many of us not just your fine self so I would like to contribute ...pl advise. My email is neilferguson.nf@gmail.com if you can send details of an account I can credit.
For me as an engineer the results were extraordinary..I thought you would get a significant result but nearly 5% ..Yarrooo!!!!
On a technical basis the usual head loss calcs. were way way off and I think it may be because of the very high velocities and consequent gas momentum involved. The sharp edge and rounded corner loss calcs were probably derived at normal and much lowere pipe/tube velocities ( liquids 5 to 20 fps and gas 10 to 30 fps ).The throat veloc in the tests were about 4 times higher......
Neil Ferguson

I finally got around to taking a photo of the stub stacks I bought from Rimmer Brothers a few months ago.
(Part number 01FD23ALO1)
They measure 16mm thick, and 100mm diameter.
Going on what's been written so far, they may be a bit thick for ideal MGA application, but they seem to fit very nicely into the original MGA air filter housings, and inside the air filter elements. The rim at the base is 3mm thick, so presumably I could get them down to 13mm thickness with a bit of machining. I was intending to use them in conjunction with K & N filters, which I've also purchased.
Any comments or suggestions from the assembled experts?

T Aczel

AJ my mould material was using polyfilla that is not very durable. Epoxy would be better and it could be cleaned up after casting. A hardwood mould turned on a lath would of course be near perfect used with a releasing agent.
Steve, I cannot honestly say I noticed any significant improvement with the stacks BUT I already had some diy stacks fashioned out of spare carb spacers with rounded edges so I was not starting from the same base
as you. Only the dyno can give an impartial test!
J H Cole

Steve,
My K&N filter housings are an aftermarket addition (1800 3 Brg engine). Australian CKD cars had the standard Vokes housings as the UK cars.

Tom,
Your Rimmer Bros part look pretty good, do you have a part no and price? Maybe the key to Steve success is the navigator's Blanco or Miele stainless steel saucepan polish!
Mike

Mike
Mike Ellsmore

Mike, the part number's in my post above.
(The number 01FD23ALO1 is on the package along with a bar code, so I assume that's the part number.)

I think I paid about $70 (Aus) or so, but no longer recall if this included postage. Since then the exchange rate's improved in our favour anyway.
Incidentally, despite being aluminium, those Rimmer Bros. stub stacks are surprisingly weighty.
T Aczel

The Rimmer Bros part may work okay inside of the deeper MGB filter housings. For the shallower Volkes filters on MGA this part may work better if you shave the back side to reduce the thickness to about 8-mm (5/16-in). That may lose about 2/3 of the weight in the process. The extra thickness is obviously a hindrance. There is likely little or no benefit in the length of the cylindrical throat. Smaller OD and slight difference in ramp angle may be nearly insignificant. A sharp edge on the OD may be a good thing.
Barney Gaylord

A less expensive test than the 60 quid dyno may be to detect a change in the intake manifold pressure at WOT and say 4500 rpm. An increase in MAP should be directly related to airflow and therefore potential HP if the fuel supply matches. Being cheap, it would also allow for multiple runs with and without stubs, which would give an idea of experimental variability.
Incidentally, what is a typical MAP reading at full bore?
Art Pearse

Neil Furguson, many thanks for the kind offer!

My comment was more tongue in cheek and I am very happy to have done the testing! The cost was for the full session that took about an hour and a half including chatting and looking at different needles. It could easily have been done in half an hour.

I need to do a bit of work to sort out my car now. Unfortunately my own cars are always bottom of the priority list, so that will have to wait.
N McGurk

AP- what does WOP & Map stand for? Just been looking again at Neil's graphs. There's a hp curve & torque curve but what are the other 2 curves showing? I know its a 1800 engine but is anyone else surprised at how the max hp occurs at only 4350 revs. According to Clausanger my 1622 develops 90hp at 5500. This is the gross figure so it will be quite a bit less at the wheels but its the fact that it needs another 1000 rpm+ to develop the max hp that I found interesting.
J H Cole

JH - WOT means wide open throttle and MAP means manifold air pressure. Sorry for the jargon. One of the other curves is air/fuel ratio
Art Pearse

There are only 3 traces per graph. I think you are looking at a "pointer" line. I wonder how they calculate the engine HP from the road wheel measurement.

Art Pearse

Not trying to nit-pick Art but MAP actually stands for manifold absolute pressure.
Andy Bounsall

Thanks Andy. I was guessing"air" - it made sense.
So, what is a typical MAP at WOT?
Art Pearse

Neil,
I had a look at the dyno software site you mentioned above, www.land-and-sea.com , but also could not see how they got power at the flywheel rather than at the wheels. I suppose they could just use correction factors for tyre and gear losses, etc.
Mike
Mike Ellsmore

AP, how can a dyno calculate air/fuel ratio? are these values measured somehow or is it purely theoretical?
J H Cole

Measured with a probe up the exhaust
N McGurk

The air/fuel ratio is measured by a Lambda sensor in the exhaust.

Mick
M F Anderson

Mick

That reads much better than "....a probe up the exhaust". Sounded a bit painful!

Steve
Steve Gyles

So the mixture was richer in the 2nd run?

A/F ratio 12.3 compared with 14.3 - what effect would that have on power output?
Geoff E

Measuring O2 in the exhaust can only aproximately calculate the air/fuel ratio, since some of the O2 is retained as CO, and some might be in any ethanol in the gas. So, some assumptions have to be made. However at about 14.5 ratio, all the O2 should be burnt, and once you get down to that point I don't understand how a lower value, say 12 could be calculated, unless you also measure the unburnt fuel. Maybe this shop had a full exhaust analysis.
Art Pearse

A lambda sensor is not affected by the presence of carbon monoxide.
Exhaust gases contain oxygen as compounds in carbon monoxide, carbon dioxide, nitrous oxide and maybe a bit of sulphur dioxide.
However a lambda sensor measures free oxygen only, not oxygen present in chemical compounds that have totally different chemical and physical properties.

Mick
M F Anderson

Mick, exactly my point. Free O2 alone cannot tell you A/F ratio unless you make assumptions about fuel mix and CO and HC in the exhaust.
Art Pearse

The usual statement that the sensor is "measuring O2 in the exhaust" is incorrect and misleading.

The sensor is not comparing free O2 in the pipe to O2 outside, rather, it is comparing "hungriness" of the exhaust gases for O2 compared to free air at 21% O2. the O2- ions create a voltage as they migrate through the porous sensor trying to balance the partial pressures of O2 inside and out. Thus, a rich mixture is very hungry for O2, but plain air would not be, as the pp would be balanced.

You might consider the exhaust gas as an ionic vacuum, with rich conditions being "more vacuous". The deviation is all in the rich direction from air, so there is no zero crossover in the voltage, which you can see from the fact that the voltages are always positive and do not cross zero. The AFR do have a crossover as "lean to rich", but that is purely an artifact of convention.
This is a pretty good functional description. The sensor acts as a fuel cell, with the "combustion" being in the fuel rich pipe. The voltage is a measure of how hard it is pulling O2 through the sensor to attain balance.

It's just a matter of having picked the stoichiometric ratio of AFR=14.7 for gasoline in air as an arbitrary zero point for rich/lean, and it would be different for other fuels and/or oxidisers.

Basic:
http://www.nernst.de/lambda/lambda-sensor.htm

Real World:
http://www.innovatemotorsports.com/support/manual/LC-1_Manual.pdf
"Gasoline 14.7
LPG (Propane) 15.5
Methanol 6.4
Ethanol 9.0
CNG 17.2
Diesel 14.6
The measurement Lambda is the actual air fuel ratio over the stoichiometric ratio. A Lambda
measurement of “1” equates to the air fuel ratio of 14.7 (for gasoline engines). When Lambda is
less than 1 the engine runs “rich”, i.e., unburned fuel exists in the exhaust stream. If lambda is
greater than 1 the engine runs lean, i.e., free oxygen (02) is present in the exhaust."

FRM
FR Millmore

I used to just take out the plugs and look at the colour!

It was much simpler on my old racing 2 stroke engine, I used to increase the carb jet size until it was so rich it would gas-up. Then change the jets down a couple of sizes until the engine ran cleanly.

Unfortunately, there were only 3 or 4 jet sizes difference between gas-up and seize-up!

Maybe SUs are harder to mess up!

Colyn
Colyn Firth

Steve Gyles..
just to let you know that my engineer friend has finished making a couple of S/S's for me. They came out pretty well, and identical to yours. I will post a picture soon for all to see. Haven't tried them on the car yet, will keep you posted when I try them out.

Frank
F. Camilleri

Steve Gyles..
just to let you know that my engineer friend has finished making a couple of S/S's. They came out pretty well, and identical to yours. I will post a picture soon for all to see.

Frank
F. Camilleri

Frank

Hope they fit! Interested to hear your impressions. From Neil's graph most of the performance improvement seems to be at fairly high revs. My initial feeling was that throttle response seemed much better at the lower end of the revs range.

Steve
Steve Gyles

Steve, they seem to fit OK. As soon as I find time to fit them in place, I will be back with my comments on the result. As you know removal and fitting of the filters is a quite a PITA, so I need to find the time. Additionally, rain is forecast for this weekend, so I'll have to wait for dry weather to try the car on the road.

Frank
F. Camilleri

Steve Gyles,

Steve, sent you an email with a couple of pics attached. Was unable to upload the pics on this forum. I hope you don't mind. You may if you wish try and upload them here yourself. They are pics of my new stub stacks.

Frank
F. Camilleri

Fletcher, while you are giving us all these wonderful figures, maybe a guideline value for HC and CO would be nice to have as well (for an engine that isn't worn out!)
dominic clancy

Frank

Good effort. I like the good clearance on the back for clearing the welds.

I downsized the picture size and I hope you don't mind me showing them here for others to see.

Cheers

Steve

Steve Gyles

Dominic-
Not info I have, since I have managed to live in a place where I don't have to contend with it.
In theory, stoichiometric would give 0ppm HC, 0%CO, since that is the definition of complete combustion.
In practice. most and especially older engines just won't run at that, and need to be a bit rich. There's no good reason for any HC, as a little less fuel should turn it into CO, which is what you get when it hasn't all gone to CO2. I think the main reason to specify a small amount of HC & CO is to ensure that it is not too lean, which is bad for the engine and increases NOX, very bad for air.
There may be published limits for emissions for early engines, c1966-67, but those are tailpipe limits, not desirable conditions. I've heard a lot of reports of engines meeting the next generation of limits if well maintained and tuned, in some cases even without the specified air pumps etc. MGB specs are 68-71 4.5% CO, 72 3.5%CO, 73-74 2.5% CO - BUT all those have air pumps.

This might be a good question for Peter Burgess, as he actually measures this stuff.

FRM
FR Millmore

Steve,

sure I don't mind you posting the pic here. That's the idea for everyone here to see. I tried to upload the pics to display the images here but no go. I believe their file was too large. Steve can you explain to me how you down-sized the pics, that is if it's not too complicated.

Thanks
Frank
F. Camilleri

Frank

There are many packages for doing this. I think it was discussed in a recent thread. I use PhotoShop, but there are plenty of other options that I have not used.

I believe one of the simplest that you may already have loaded on your PC can be found in the Microsoft Office Suite - Microsoft Tools - Microsoft Picture Manager. (look in 'All Programs' by pressing the start button bottom left on your PC screen).

Your pictures were high resolution and measured about 50cm x 45cm. Simply resizing down by 50% to 70% on the side menu should make them suitable for uploading.

Steve
Steve Gyles

I think 1 MB is the limit, from my experience.
Art Pearse

Well folkes, I went for a run in my A this afternoon, with the stub stacks fitted inside the air filters. I'm so impressed and so so happy. Throttle response is indeed fantastic, but I really like the way the engine runs now. It seems to go much faster with the stacks than it did without them. It really made all the difference, even my wife noticed the difference in performance. My sincere thanks to Steve Gyles for giving me all the necessary details to be able to fabricate the stacks, which were made identical to his and as per his specs. They really work a treat.

Frank
F. Camilleri

Brilliant Frank. Well done. So pleased the seat of my pants is not telling me porkies.

Steve
Steve Gyles

Now a convert. Frank has hit the nail on the head with the throttle response. For my money it's drivalability that counts, not high H.P. figures. Is anyone able to arrange some " mass " production ? A previous thread suggested moulding. Well done Frank. Sean
S Sherry

Thanks Steve, I most certainly recommend the stacks to anyone. Sean thanks to you too pal. The throttle response is so noticeable that it gives you the feeling to keep pushing the gas pedal hard to the floor. If you can find an engineer with a lathe, it would be quiet easy for him to fabricate a pair from Steve's info. Also Barney's engineer's diagram, with all the dimensions specified is quite sufficient to go by. Good luck.

Frank
F. Camilleri

I thought I'd drag up this thread from the archives to add some independent info. Although there is nothing like testing a particular design, it is always nice to have some non-biased confirmation to support one's testing. I found this diagram of different designs on another forum I visit: Locostbuilders.co.uk. I'm not sure what the original source of info is from. From what I can tell, the design presented here matches design #11 and is just about as good as you can get.

Sorry for the bad picture. It is what it is.



Chuck Schaefer

Most interesting Chuck. That design (#11) which I machined and had tested thanks to Neil McGurk was due entirely to the considered opinions of Neil Ferguson and FRM. Good to see that quite independently we got it about right.

Steve
Steve Gyles

That pic is lifted straight from David Vizard's "Tuning BL's A Series Engine"; P57 in my original 1985 edition. It is one of the best real world compendia on tuning mods, claimed to be based on actual testing. I refer to it constantly, and I think I said so in the original discussion on the stub stacks. While much of the data can be found elsewhere, that requires lots of reading and the ability to filter BS well.
In this case, once you read the Vizard's background discussion of airflow, the proximity of the filter cover makes it pretty obvious that the design used is the only one that will work effectively.

FRM
FR Millmore

Interesting set of designs...would also seem to show two things...
....the fancy horns you see protruding from many carb. inlets do no extra over the simple rounded plate.
....5.8% extra air is consistent with the dyne tests by steve.

It can't be this easy to get 5% extra power?????...for 20 quid?
Neil Ferguson

FRM, I knew it was from some reference book. I have read that book but it was a loaned book and that was some 10+ years ago. I could not reference it. Thanks for giving Mr. Vizard his due credits. He is definitely THE GUY for series A engines. The same techniques seem to follow thru on the B series engines.
Chuck Schaefer

This thread was discussed between 12/10/2011 and 04/01/2012

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