a trip down Stromberg memory lane

[Pete Lewis]

I received this from  Brian   a local herts and beds member makes interesting read and will in the future be a 

page in the Courier 

Pete here is my Neighbour Bill's  life with Strombergs 

  Thanks to you Pete in the first instance, for tackling the difficult job of salvaging the carbs which as you well know, were in a terrible state and for attending to the fuel pump

I pushed the old girl out of the garage the other day and attempted to start her - it was about 6 weeks ago since I fired her up - but for some reason the fuel pump was not priming, I may have had an airlock, so took adjoining pipes off to get a flow of petrol and will have another go at starting the car in the next few days.

 

Battery is on charge at the moment and the weather doesn't look too good.

 

Hope to see you all once these restrictions lift. The car is insured, 'taxed' and nearly ready to go.

 

Best wishes,

Brian

 

 

A Step Down Memory Lane

My neighbour, Brian Copeland, who owns a GT6 Mark One, which had been in storage for 30 years, one day recently proudly pushed it out of the garage and announced a refurbishment was about to take place.
Opening the bonnet showed a straight six engine complete with mice nests and cobwebs etc and lo and behold two Stromberger carburettors under the dust. Trust me to open my big mouth by claiming I developed the first application of the Stromberg on the TR4 engine in around 1961/62.
The problem with memories then started !
Having helped Brian he invited me to the 2019 Triumph club meeting at Duxford and while there I met with John Davies, the ‘damper man ‘. We had an interesting conversation about torsional vibrations and his demonstration of the effect on defect dampers. I am sure John will not object about being called a damper man , he is far from that . Anyway our conversation lead to my experience and John suggested my story should be told so after all these years here goes .
At this point I should point out that this was before this use of computers and digital electronics which revolutionised fuel injection and some of the dates may be wrong .
Now let’s go back to 1961 , at that time Triumph were using SU carburettors for all the sports cars , however SU were part of the BMC group which manufactured amongst others Austin ,Morris , and various sports cars in competition to Triumph, this of course in view of the supply of the SU carburettor resulted in Triumph having to release details of new models to the BMC group which was not an ideal situation.
The SU carburettor was a constant vacuum variable choke device so it was decided between Triumph  and Zenith carburettor company to design a similar version but different in construction to the SU. The end result was the Stromberg CD carburettor,  ,  as I understand designed by Dennis Barbit of Triumph and Harry Cartwright of Zenith.
This article does not cover the design or construction of the carburettor, it talks about the experience of the first testing and development by me at a company called ERA of Dunstable. At the time I was employed by ERA as an engine tester and development engineer (the pre-war English racing automobile ) . The work involved testing new carburettors of fixed choke designs for various development engines of car manufacturers and jet settings etc .
I guess the testing of engines in those days is very different from today so I will briefly describe the work that was undertaken to arrive at suitable carburettor settings. Each engine was tested in a separate test cell using a dynamometer to load the engines. The test cells had suitable cooling systems , heat exchangers and a test bed exhaust system, although in some cases the car exhaust was used. Fuel flow and exhaust gas analysis was also available . To achieve suitable settings for the carburettor the engines were tested at various conditions of full load ,3/4 , 1/2 , 1/4 and road load conditions. To evaluate the settings the engine was operated in 250 RPM steps working up to the engine maximum. As well as working on the carburettors, ignition settings were also varied to optimise conditions . It will be appreciated that many hours of testing were undertaken to arrive at a good setting to give acceptable performance of power output ,fuel consumption and above all drivability.
I used to find it amusing that people could re-jet or change ignition settings and apparently achieve remarkable improvements in car  performance but generally this was at the expense fuel consumption or power output ,the manufacturer having put so much time and expense to achieve an overall acceptable condition. For example a 2% reduction in power output can result in a 6% fuel saving, and how  often do we drive at full load ,full powers on the roads. Possibly we try to all the time ! Of course with the latest technology and the ability to measure all aspects of the engine this method is I guess out of date now .
At this time the TR3 was in production using a four-cylinder engine of 1995 cc rating. The next step was to increase the engine size 2198cc with a maximum output of around 105BHP for the forthcoming TR4 possibly using the Stromberg CD carburettor. An up - rated engine was supplied to ERA by Triumph  and fitted to the test bed using the normal chasse exhaust system and two SU carburettors. I assumed the settings of these carburettors have been carried out by Triumph. Remember the object was to replace the SU with the CD . So to evaluate fully the engine was run with the SU carburettors at all conditions too so that the parameters were set to try to match with the CDs.
The CDs were fitted, accelerator dampers removed and dimension scales fitted to give the valve position so this could be related to the neddle position in the main jet.

Testing then started running first at full load, 250 rpm intervals , adjusting the jet position relative to the needle to give a match of fuel flow versus power output. Gradually working through the complete RPM range the needles could then be removed the diameter was adjusted and with the jet set at 1 1/2 turns (around the normal setting)  repeat testing was carried out , eventually arriving at a suitable needle profile .
Anyway things did not run as planned and the fun started, the first engine failure occurred. With the engine running at full load 5500RPM and me bending over the carburettors, an exhaust valve failed dropping into the cylinder with the piston disintegrating bursting the wet liner and the engine suddenly stopping .Being on the chassis exhaust the noise level ,as you can appreciate was extremely high and suddenly silence. Just the gurgle of water and oil from the breathers . My heart keep going ; just !
The engines were sent back to Triumph  repaired returned and testing continued. Running at 5250 RPM , suddenly “bang” , no power available , removal of the engine showed the crankshaft to have sheared adjacent to the flywheel . This was repaired again by Triumph but I had two further crankshaft failures when running at this speed . I thought I was becoming an engine destroyer , or perhaps the management thought so! . It was clearly a torsional vibration problem and hence the interest with John Davis .
Eventually a needle profile was reached and the CDs gave similar performance if not better than the SU . It is a long time ago and with a fading memory probably I would claim this.

The time had now come for road testing , the engine was fitted to a TR3 and taken on road test by a Zenith engineer, who returned saying that some conditions it was far too rich. This was a surprise as in general test bed settings were sometimes too weak for road conditions. The chief engineer of Zenith doubted the findings of the test engineer so off they went for a further road test. It would appear that the rich cut out of the engine occurred round a very tight bend with the test engineer saying to the chief engineer did you see that black smoke from the exhaust,’ upon which the chief engineer who was crouching below the dashboard replied ‘surely nobody would take a bend at that speed ‘ !!
The problem was traced to the venting of the fuel chamber. The initial design had two horizontal holes leading from the air inlet to four vertical holes into the fuel chamber. It was found that due to ‘G’ force  when cornering, fuel was being thrown out along the vents and sucked straight back into the air intake giving this extremely rich condition. The problem was overcome by just having one horizontal hole and one vertical vent to the rear of the float chamber with no fuel surge occurring from the vents. Out of interest, it will be noticed on some later CDs the casting still retains the original venting system but not drilled.
This article hopefully outlines the first application of the Stromberg CD to the TR4. Following this the CD was used on many cars in place of the SU and since that time many changes have been made to them to suit the ever changing environmental requirements, until carburettors disappeared and replaced by todays digital fuel injection systems .
Incidentally test bed conditions are much more arduous than on the road and in those days top overhauls were carried out after some 20/ 25 hours test bed running , so all of you with TR4s don’t worry just keep these wonderful cars on the road .
Back to Brian’s car !!!

[PeteH]

Whilst, not exactly a "Meaning of Life" issue. Having been around cars since a very early age, I have long been curious about the Origins of the Stromborg, especially when bearing in mind the (pre) existance of the SU. So it was good to have an insight into the thinking behind it`s development.👍 The comments about "moding" and Re-jetting are still valid. Physics are, as far as I am aware still the same. And it`s still the case that you can never get more out than goes in. You can only alter management of the energy.

Pete

[daverclasper]

Cheers for that Pete. I love Strom CD's. Very simple, easy to set up, Seem solidly made. One of my favourite bits of the car, An art form?!.

Great to hear the history. Thanks.

Dave