Answering your question about the 28/36 DCD. Yes, my Series 1V is fitted with one. The 1592 engine was originally fitted with the Solex Compound Twin Choke carb. Because the second choke was operated by vacuum depression created by the flow of air through the primary barrel, the secondary choke would only operate above 4000 rpm ish with your foot to the metal. This made it almost impossible to get the second choke working which meant in effect the engine was being throttled back.

To alleviate this problem throughout Rootes Light car range many carburettor suppliers offered the Weber 28/36 DCD jetted to suit your car.
Apart from the fact that the hole in the manifold wasn't quite the same size and shape as needed by the Weber carb it was a simple bolt on replacement fot the Solex.

The result is nothing short of a revelation, especially if you use the Weber insulator block as means of templating the cutout in the manifold.
To fit this carb on a 1725 you will need the 1592 4 branch water heated manifold.
Regards Eddie

A little more to explain what the Weber 28/36 DCD is. Quite simply it is a Compound Twin Choke Downdraught device that employs as it's name suggests 2 Barrels. The Primary barrel 28mm is the one that also has the accelerator pump jet. This barrel's butterfly is operated directly from the throttle lever and takes the job of providing an accurately metered fuel supply up to approximately 2/3rd's of throttle movement.
Any further depression of the throttle will result in the Secondary Barrels butterfly opening on a cam linkage so that when full throttle is reached both barrels are fully open. This larger barrel is the 36 mm one.

Together both barrels are capable of flowing 225 c.f.m ( I made a conservative error in my earlier post ) Each cylinder sees this joint flow capability with the result that it is more potent than 1 barrel of a 40 DCOE which can only flow 175 c.f.m Even a 45 DCOE barrel will only flow a bit more at 242 c.f.m

It is not only highly potent at producing power when required but it is capable of astounding economy at high speeds 70/80 m.p.h when only light pressure on the go pedal means that only the primary barrel is operating. It was the carb of choice for enthusiasts in the Seventies and was used to great effect by Ford on the Lotus Cortina.

Sadly they appear to be rarer than Rocking Horse poo now but David also recommends in his book the Weber 32/34 DMTL which may be available and might give similar results. As mentioned earlier the 1592 Series 3/4 manifold will be needed along with modifications to the manifold cut out to remove the bridging piece and open out the the orifice. You may find one through the club mag, or someone might just have an old unit in amongst stuff they're selling at the National. They will be highly sought after.
On my car it produces fuel consumption figures at motorway speeds of about 70/80 in the mid forties ( VW Golf stuff ) but when you jab the throttle by heck does it take off.
In the next post we'll discuss manifolds and their effect on power. Its contains a few surprises.
Regards Eddie

The strength of the 28/36 DCD is the way that the smaller primary barrel and the larger secondary barrel provide a progressive transition from idle and light throttle running up to full bore. The high velocity of air in the smaller primary barrel provides very finely emulsified droplets which produce better combustion and hence more power or better economy.
When the secondary barrel begins to open this process is repeated in the larger barrel as well since this is now accepting high air flow rates as well.

The effect on driveability is that the car has an amazing amount of low down grunt. It's hill climbing ability is awesome ( when I regain my leaded fuel ignition settings this will be considerably enhanced )

When the car is travelling at higher speeds, as the two chokes begin to combine there is a noticeable urge that builds relentlessly as more throttle is applied. At full bore the engine emits an urgent snarl and the rear squats down under the power, there is no tail off in power as the revs rise, clean hard pulling power all the way round to the red line.

And yet it can be driven around town in the most docile manner with a gently burbling exhaust and a smooth quiet tickover, whilst the gentle whine from the gearbox is more reminiscent of driving a Hillman Minx.
In effect the 28/36 DCD is such a good all rounder that it gives you 2 cars
A boulevard cruiser or a hustling road eater , the choice is yours.

Having driven Holbay engined cars in the past I know that whilst the top end can be quite thrilling, the loss of flexibility at the bottom end is too high a price for me to pay. I also like the sheer economy of the 28/36
Petrol station visits are very few and far between, even in out and out hustling mode.

The reliability of the thing is legendary too. I've only ever had to clean it out twice since 1975, after which it performs as new again.

Having said all that I know that the fact all the DCOE stuff is still available and the Webcon manifold is also available off the shelf it must be very enticing for an enthusiastic owner, because even I'll admit it looks marvellous. Seeking out a Weber 28/36 DCD could be a fruitless and thankless task, but at the end of the day the driving experience is worth the hassle in tracking one down.
If you do ever see one at an autojumble grab it, it's probably the only carb that could improve a Holbay, beyond recognition.

Of course the manifold it sits on is important too and this ticks all the right boxes bar one. It would be better if it was cast iron, however, but the weight saving does help our cause.
Next we'll investigate what makes a good manifold, and why it helps the 28/36 over the DCOE's.
Regards Eddie

No one spotted the deliberate mistake in my previous post

Quote:

Only if the manifold was designed to distribute the mixture from both carbs into all 4 cylinders equally would the Twin carb philosophy work. And no manufacturer does.

Of course this isn't actually true because the manifold that Rootes designed for the Series 1 did use the flow from both carbs into a common plenum chamber accessible to all 4 ports.

This manifold actually has very good properties for making power and is probably key to why the Series 1 and 2 were so sprightly in the road tests.
The fact that they were a lot smaller than the engines in the later series show just how good this manifold probably is. From our point of view this is quite important since the later Solex carb was mounted on a nearly identically designed manifold but with a central flange for the Compound Twin.

Of course the manifold and carb have to be considered together since the manifold's flow properties will be affected upstream by the carb and filtration system and downsream by the cylinder head itself but in general the carb will limit the flow into the manifold.

In exhaustive manifold tests it was found that ideally to make the most power the inlet tract from the carb to the port needed to be as straight as possible and about 6.5 inches long. This produced the highest hp figures all other things being equal. Bolting sidedraught carbs onto very short stubby manifolds killed all performance markedly. The reason for this is due to the loss of a very desirable property of a good manifold and that is inertial ramming.
More on that in the next post.
Regards Eddie

So what is inertial ramming and why is it important ? Since the whole point of performance tuning is to get more air and fuel into the cylinder lets consider what happens on the induction stroke.

As the piston starts it's downward stroke it creates a partial vacuum above it and air is drawn through the carb pulling finely atomised droplets of fuel with it. This air has mass and so does the heavier fuel droplets which as the piston accelerates imparts more pull into the manifold. The length of the path from the carb to the port gives the mixture time to swirl and acquire kinetic energy ( or inertia ). The charge is now nearing the port where it is squeezed into a smaller opening and produces high port velocity. This is a very good thing because as the piston slows near the bottom of it's stroke the charge carries on rushing into the cylinder even as the piston stops at the bottom.

In fact if we now hold the inlet valve open for a few more degrees as the crank rotates ( before the piston starts to rise on the compression stroke ) then the charge will still be rushing in and we will get more air.fuel and power from the resultant burn inside that cylinder.
Conversely if the distance from carb to port is significantly greater than 6.5 inches then the situation starts to reverse and power is lost.

Tests on short stubby manifolds resulted in huge losses of performance so to get good ramming we need that 6.5 inches.
Now we are coming to the crux. The Solex manifold has that parameter.
Against it is the fact that the flow has to change direction but at the critical phase it gets a good straight run into the port and arguably this is it's great strength.

Unfortunately getting that length on a Twin DCOE set up is not possible, so even if you have made your head flow better, the loss of inertial ramming is going to be significant in limiting the engines potential.
This is why I believe the Weber 28/36 DCD on the Solex manifold is so unbeatable. It is synergistic, it works, and beautifully.

If you want to know which carb your tuned engine might need there is a simple rule of thumb that David uses. It's generalistic but unarguably quite accurate.
That is for every single horse power your engine produces you will need 2 c.f.m through your carb.
This means that the 28/36 DCD is good for 112 h.p.
Twin 40 DCOE's will produce about ..............87.5 h.p.
Twin 45 DCOE's will produce about..............121 h.p.
Twin Dellorto 48 D.H.L,A. ...........................142 h.p.

So the 28/36 DCD is perfectly good for a Holbay in fact better than 40 DCOE's by quite a margin which is what I've been saying for a fair time but at least I've got the figures to back it up now.
Don't believe the absolute figures you get off a rolling road. They can be very useful for getting the best out of your set up but I doubt very much you'd get 124 h.p out of 40 DCOE's. The flow figures just don't add up.
Regards Eddie

Hello Eddie,

I have followed your posts about special tuning and fitting different carbs with interest. Your knowledge on the subject is very impresive !

My question is... unless you are into racing your classic car why change it from it's original spec?

A large number of cars in the Alpine club has been modified. Along with the different engines and carbs members put on non standard wheels and tyres and an endless list of modern upgrades, doubtless so that they can enjoy the car every day.

I have no objection to this, each to his own but my point is... most members are actually not driving a Sunbeam Alpine...they are driving a car that is the shape of a Sunbeam Alpine.

When I sit in my Alpine it looks like it did in 1964...It sounds like it did in 1964... and drives like it did in 1964. That is why I bought a 1964 car !

The SAOC as a club is quite unique in that it does not encourage members to keep their cars true to the marque. You will find more posts on here and articles in the Horn about modifiying Alpines than how to keep them period correct.

What is slowly happening is the Alpine marque is losing it's identity. The long term consequence will be the club will become smaller and fade away and the Sunbeam Alpine will become a rarity with very few cars to see.

John Boggis

I don't know whether it is true that the SAOC does not encourage originality - and if it is, whether it is unique. It seems to me that there are modified examples of most cars around.
I would say that if the Club has any policy, it is to encourage members to enjoy their Alpines - however they choose. For a few, this means scrupulous originality; for most, a few mods are OK - radial tyres, better shock absorbers, a hood on a GT, radio etc., and there is a tiny minority who enjoy the challenge of installing a Toyota V6 engine. If there seem to be more questions on the Forum about modifications, it is probably because staying original is easy - it's all well documented, whereas modifications require thought and enquiry. As Information Officer, I try to answer whatever questions are posed, trying (probably often failing) to keep my own views to myself.
It is undoubtedly true that there are things you can do to make driving an Alpine more enjoyable. Just look at the tremendous number of changes Rootes made through the Series to improve their design. A good example - and one you referred to - is the Solex carburettor. It was never very good when new, either for power or economy, and time has shown that it does not age well. Rootes themselves discarded it after less than two years. The alternative 28/36 DCD improves the car enormously, and it is a 'period' modification. You could contact V W Derrington in 1964 and buy the kit for the Alpine.
My observation is that most members' deviations from original are along these same lines - things which were or could have been done during the 60s and changes which don't spoil the character or appearance of the Alpine. I think that in making the Alpine more enjoyable and usable, we actually encourage their long-term future.
The world is not short of Sunbeam Alpines, and they are hardly artifacts of major historical significance - just a better-than-average effort at producing a well-balanced enjoyable sports tourer. What matters is that the owners enjoy them. I would hope they enjoy them by driving, but I respect those who prefer to preserve and polish.

Well Mr. ED, Isee you dont trust my figures from the rolling road! You just stick to your facts and figures from books, well if its in black and white it must be right. Or is it?
Lets take your dismissal of the 40s ram length, It is in fact exactly 6.5"" straight ram length from butterfly to valve stem(apex of curve before entering ported area before valve) afact used by Holbay. This has also been accomodated on their Pinto and lotus conversions. Mine has also had the ram pipes adjusted in length to give 13" overall to take max advantage of induction pulse waves on induction.
I dont know where you get your induction volume figures, But the 1725 engine dissplaces aswept volume of 91.497cf/m per cyl @ 6000rpm based on a grade A tolerance engine. Which is a volume both carbs can easily handle.
As for your quote
Only if the manifold was designed to distribute the mixture from both carbs into all 4 cylinders equally would the Twin carb philosophy work. And no manufacturer does. Im sorry but the 40s manifold does!

Alvin, I'm glad your following the topic even if you dont agree, Its good to have a bit of discussion on the site. I agree totaly with you. In an ideal world I'd have 2 x sIVs one standard and one to tinker with, just bcause Im an engineer & thats what we do!
I wouldn't like to say what a standard Alpine is because they were supplied in the most basic form possible to avoid Purchase tax, then "customised" from an almost endless list of options to suit personal taste & requirements. Including radical engine mods by Hartwell or Holbay. as in the case of the le mans cars & Harringtons, but yes, it is important to keep a section of cars standard as bought new.

Firstly I must say Chris's reply to Alvin's post was much better than anything I could have put together. We simply are doing what we've always enjoyed doing since the club started.

Both Chris and I wrote articles about converting GT's to roadsters.in those far off heady days. His conversion was a far better engineered one than mine, ( which involved unspeakable use of a junior hacksaw Alvin ). But it was up to the individual themselves to adopt their own approach. Hardly anyone has done it entirely the same way we did. That's what makes the world go round. How many standard MGB's do you think there are ? Judging by the thickness of the Moss Catalogue I've got, not many. Sports car owners tend to be like that.

Nothing's changed except we've got a bit less hair and more of it is grey.
When I give up trying to make my car go that little bit better I'll probably be in a box.
Best Regards
Eddie

Dave, looking at your figures from the rolling road, you say that you had 124 h.p at the rear wheels. Well Geoff Woolf, a number of years ago built a monstrous 1998 cc engine which he called the Marathon. This had twin DCOE's 40's ( probably would have been a screamer if it had 45's )Big valves, a hot camshaft, lightened and balanced flywheel, crank etc.
Yet even that was only able to produce 111 bhp at the rear wheels at 5000 rpm on a rolling road. Geoff estimated this to be 130 h.p at the flywheel, You lose 20 h.p through the transmission so what you are saying is your engine is making 144 h.p. at the flywheel. That stretches the bounds of credibility quite frankly. I'm not calling you a liar either.
I believe you may be being duped somewhat by your rolling road man. David Vizard ( that man again ) shows evidence that some ( not all) outfits find they get more customers when their figures are adjusted in an upward direction, since the truth is unacceptable to some people who then show a reluctance to pay the man.
As long as you don't take the figures too literally the whole point of a rolling road is to maximise your power, nothing more.
As an aside, I am interested to know more about induction wave pulsing since this is not covered in David's most extensive book, perhaps you can explain how it works.

Another point worth mentioning is that the distance 6.5 inches is most definitely to the port not the valve and that Holbay engines had to be tilted at an angle to get the manifold into a Hunter engine bay which is far roomier than an Alpine.
Best Regards
Eddie

No more about originality here! I want to question Dave Baldwin's figure of 91 cf/min. He is correct that this is the displacement per minute, but Eddie is talking about the volume of air sucked in. In the 4-stroke engine, air is only drawn in during alternate revs, so at 6000rpm, there are only 3000 induction strokes per minute and the volume (making the rash approximation that the air drawn in is the same as the piston displacement) is, for the 1725 engine or 105 cu in:

105/4 x 3000 /12/12/12 which equals 45 cf/m per cylinder. However, as the induction stroke only occupies 25% of the time, the carb has to be capable of supplying air at 4 times this figure or 180 cf/m. BUT if the induction system were perfectly efficient, a carb of this size would be OK for all cylinders as the 4 induction strokes happen sequentially. This is why twin 150CD carbs are as good - at least for the normal Holbay head - as the twin 40DCOEs. (The 150CD is 1.5" which is close to 40mm diameter)

Looking at the flow figures for the SU's would appear to back this up as well, since it's more than likely the 150 CD flows as well as, if not better than SU's. Strombergs were very popular on a wide range of sports cars too so their performance would have been expected to be good in this area.

The Twin DCOE's are not twin carburettors, as pointed out already they are literally a single carb for each cylinder, but as already explained if high air velocity isn't maintained ( and at low revs this condition will undoubtedly exist ) through the venturi then emulsification of the fuel will suffer along with low speed performance. It has already been widely documented that DCOE's are not that good at the bottom end. They do not excel at grunt. They are more suited to high revving cammy set ups where their undoubted strengths lie.

It is almost certain that putting DCOE's on an otherwise standard 1725 will kill performance, economy and driveability whilst putting your standard 150 CD Strombergs and manifold back on a Holbay engine will produce a very satisfying quantity of power, both grunt and sprint. And you will save a shedload of cash on the hardware, and running costs. The only mod that will be needed here is a couple of K&N filters to let them breathe a bit easier.
Another plus point is no one need ever know you're running a Holbay. Until they try to keep up with you on a run.
There are still a couple of tweaks for people running running Series 1-3 cars and one of those will undoubtedly interest Series 5 owners too.
Best Regards
Eddie

During some exhaustive tests of manifolds on the A series engines it was discovered that the manufacturers OE manifold with the exhaust casting joined to the inlet castng to form a hot spot killed performance to a large degree. In fact the manufacturers had done this to aid economy and allow the choke to be returned sooner.

The big downside is that the heat not only vaporises the fuel ( killing inertial ramming of the fuel droplets ) but causes a loss of density of the air charge too. This means that the engine suffers a marked loss of power.
Water heated manifolds suffered the same fault too.
This was estimated to be between 3 and 4 h.p. On an engine developing only 47 h.p. this will be quite noticeable.
Even on a more highly tuned Alpine engine 3 or 4 h.p. is not to be sniffed at. All these little gains accumulate and add pep to your motor.

I will investigate what happens when I disable the hot water jacket on my inlet manifold. This should be quite easy to do by plumbing in a washing machine type hot water tap in the front dogleg hose to the water pump.

Series 1 and 2 owners might like to try this out too.

If successful I will cap the outlet at the rear cylinder head and front elbow.
The water jacket will then be dry.
Next post will look at the induction system.
Regards Eddie