This thread will discuss what is happening on an ever increasing scale within the club, namely the habit of fitting Twin Weber DCOE's along with the ubitiquous Holbay rocker cover ( and precious little else )

The owner is usually either far too embarassed to admit that actually the car doesn't go that well or he/she bought it like that and hasn't got a clue why it isn't running properly and eating petrol at a rate only Alistair Darling would be pleased with.

The last time I saw this state of affairs the club was only a year or two old and most Alpines were at the banger stage. Why does this mechanical outrage seem to be returning?

Eddie

If you have got this far then we can assume you are interested in the subject If so then I implore you to get hold of the following book.

Tuning the A Series Engine by David Vizard 3rd Edition.

It's available from Amazon for the bargain price of £13=99. Reduced from £20. It's a large hardback which contains everything about this subject that has any relevance to squeezing more bhp out of a 4 cylinder petrol engine.
David is a veteran of the Mini Racing world and has built and tested more engines than we've had hot dinners. He has his own Flowbench and Dynamometer and backs all his findings on the track with hard graphical evidence showing what modifications make power and those that don't.

There are many companies out there making parts and accessories that purport to add power to your engine but fail to deliver. It is not the place for the unwary. He also makes the following observations about his fellow racers.

Many people invariably overestimate the amount of bhp their engine produces and if they can find the biggest carburettor that will fit they assume that it will make more power.

There in a nutshell is why I think the Twin DCOE set up is so popular in this club at the moment. That could have been written for us. He goes on to show why the humble SU and Weber 28/36 DCD ( his favourite carbs ) outperforms the Twin DCOE's in nearly every instance.

This actually backs up my experiences over the years as well. I have found in all but one case ( and then only marginally ) the Twin DCOE's are inferior to the 28/36
and actually produce pretty poor results. David shows with flow figures why the Weber 28/36 is such an amazing piece of equipment.

Interested now ? Get the book, it's the best fourteen quid you'll ever spend especially if you thought that polishing the ports made power

More later if you are interested now.
Eddie

With regards to fitting a Holbay engine, wouldnt you think this would have been the natural progression for a series 6 Alpine, given that the engine was available (Hillman Hunter London to Sydney rally car) and Holbay had been involved with Rootes for a number of years. Harring ton had been using sidedraught Webbers for quite a while. Sometimes it's not all about Brute Power, Just the sound of the Induction as you "give it some" when you see a stretch of road is music to your ears and sends a shiver down your spine!!! Hell I think I'll take it out right now (the car)!

A Holbay engine is a lot more than just sticking a pair of sidedraught Webers on and IMHO having a bit of induction noise does not mean you are getting any more power than you can get a whole lot easier with a downdraught 28/36 DCD. Power is just that, Brute power is a lot more of the same thing. I'm not talking about Brute power , I'm talking about an unquestioning mindset that seems to be growing in our club that the Holbay set up is the only route to more FUN. David's book explores this mindset that you have shown is out there. We've actually got to the point where people don't even consider why they are doing this ?

Interestingly Twin carburettors are shown to be a complete misnomer and are rarely any better than a single compound carb and quite often a whole lot worse. Think about it , each cylinder draws it's mixture as a separate event in the 4 stroke cycle. 1 and 2 will draw through carb 1, while 3 and 4 will draw through carb 2. 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. With all the aggro balancing the two carbs and the thrott;e linkage it's no wonder the results are less than perfect. Racers ( sucessful ones ) rarely use twin carbs for this reason.

So why fit twin carbs ? Because manufacturers found it sold cars.
" Ooh it's got twin carbs, must go like stink "
Rootes did try to get away from this silliness when they introduced the Solex B.32 P.A.I.A Compound carburettor. They were acting on the right idea, but unfortunately they chose the wrong carb.
It doesn't deliver at all, never did, never will.
But if they'd fitted the Weber 28/36 DCD, it is arguable that the development team ( the set 'em alight boys ) would have never found the need to fit the twin Stromberg 150 CD's.
It was a case of "if you can't beat 'em, join 'em.
Regards Eddie

Of course there is another danger developing as well, and that is that as people try to get hold of 28/36's the difficulty of finding a good secondhand unit increases. In the Surrey group alone I've seen 2 cars already fitted with Weber Twin choke downdraughts that are not 28/36's but look like it at a cursory glance. 32/34 and 34/34.

The engines run probably OK but don't think for one minute that the potential for making power is anything even remotely like the real thing properly jetted and set up as per McGovern's book.

These are unquestionably the right jets for our engine.
Add to that a 10.5 to 1 Compression Ratio, some Tetra Boost additive in your tank, about 15 Deg BTDC static timing and you'll have a ball.
Regards Eddie

I think you'll find tha t cotrary to what you are saying about twin carbs having to feed two cylinders, 40 DCOE acts as a single carb for each cylinder, with each barrel feeding vitually in a straight line to each cylinder. Why other than this being the best way would numerouse manufactors go down this route.eg Hartwell, ford (GT40) Ferari, Lotus, Jaguar. In fact with most performance tuning multiple straight through carb set ups are the best option. Nice discussion though.

It's a long time ago mow, but when I was a spotty Rootes apprentice, the accepted wisdom in the factory was that the twin Webers on the H120 and GLS were there to please the Marketing dept - and the Holbay went just as well (but with less induction roar) on twin CD150s. Remember that this engine was only putting out about 110bhp - less than my daughter's Mk1 1.8 Focus. Now if you want to go faster still, the 'one carb per cylinder' philosophy is probably correct - and most successful racers followed this route until injection came along.
So I agree with Eddie (again!). But not on his view of Strombergs. As long as you keep the dashpots full, I have found these excellent. Easy to set up, flexible and economical. Just don't keep fiddling with them!

OK Dave, you've taken my bait now, You are exactly correct in your assumption that with Twin DCOE's you have I single carb for each cylinder.
So in effect you have only the flow rate of a single barrel available to each cylinder. Of course each cylinder will be slightly different in requirements to the next so you probably have at least 1 possibly 2 barrels not properly calibrated out of the 4. This is not going to help our cause much.
Now do a flow rate test on a single 40 DCOE barrel and the result is a figure of 175 cubic feet per minute ( c.f.m ) Each cylinder can only get that much flow.

Do the same flow test on a 28/36 DCD and the result is 215 c.f.m. an improvement of approximately 23%. And each cylinder will see that improvement in flow with no imbalances or poor calibration. These figures are from this book, and accurately obtained on a flow bench.

Don't get me wrong, I'm not pouring rain on your parade, just illustrating why this book is so interesting, but maybe now you can see why everybody ( except David Vizard and people who've read his book ) think like you do. Everybody does it so it must be right. Wrong.
Think out of the box.

Best Regards
Eddie

After Chris's post I remembered something from way back. At that time my experience of Stromberg 150 CD's was confined to my Dad's Viva HC which was more or less new at the time. He had some poor running that produced a nasty flat spot. My mum called it Kangeroo petrol which was a good description. We read the handbook and sure enough as Chris said the oil in the dashpot was non existent. My Dad went along to the dealer and they gave him a small bottle of special Stromberg dashpot oil. It was a red colour not unlike Redex ( but wasn't ).
With that dashpot topped up the car drove beautifully for quite a while.
At the first hiccup a drop more oil and all was well again.
When the diaphragm went a couple of years later that too was easily replaced. It wasn't a bad carb, but it did need TLC and with two, double the TLC.
Then my brother in law bought an Alpine Series 5 but the carbs were in a bad state. I spent a long time fettling them and was really pleased with the smooth performance I eventually got from them.
A week later he drove my car ( with the 28/36 DCD ) and came back gutted. He couldn't quite understand how my car could outperform his by such a margin. He thought I'd messed up his carbs.
In the end we fitted the 1592 manifold and bought a new 28/36 DCD from Maryland Carburettors in Maida Vale.

It was a vast improvement, in fact the best 1725 I have ever driven.
Sparkling performance but with refinement as well, very impressive.
And the carb never needed touching again. It's probably out there now, we sprayed it Alfa Romeo Plum which was my sister's idea and it was hideous. Originally it was a Polar White colour. So that's the story of your car if you wondered where the Strombies went.

So I'm not saying that Strombergs are a bad carb, they are very good IF you know how to look after them.
And by now I should think Chris is pretty much the oracle on how to do just that.

Regards Eddie

Heres a quote from Weber


THE DCOE SERIES

With a Grand Prix Racing heritage, the venerable DCOE is Weber's premier Carburetor, and still the standard by which all other carburetors are measured. It is unsurpassed for full-race use, yet its infinite tune ability by way of interchangeable calibrated parts allows it to be tailored to suit any engine and application.[/color] Hardly enough can be said about the DCOE. Its features include: ball bearing throttle shafts, piston type accelerators pump circuits, a wide variety of throttle bore sizes.. and, of course, the excellence that is Weber.

Ed, are you just against the use of Holbay rocker cover and twin DCOEs or against the fitting of the Holbay engine complete with said cover, twin 40s, and the rest of the Holbay set up.
I am in the process of restoring my alpine which came to me with the Holbay setup. I'm mot a purist so i'm not too bothered about being original. Personally I think the twin 40s look impresive, but I remember when I had an Alpine about 15 years ago, it had Holbay engine and the carbs were allways a pain, so i'm hoping this time will be better.
What effect would the 28/36 DCD have on a Holbay engine?

Well here I can reply to both posts at once, firstly the Weber blurb. They obviously have shifted lorryloads of DCOE's over the years and yes, by the Lord Harry they look impressive and it is likely that they perform well ( ON THE RIGHT ENGINE ) but on an Alpine motor tricked up to look like a Holbay they are a complete waste of time. They are over the top. Over carburetting an engine is the surest way to lose power and economy. David Vizard will tell you how people have fitted these monstrosities to 948 cc Racing motors and he's beaten them with a 1.5 inch SU by miles.
Looks good .................and that's about it. Macho stuff eh?
By the way he's managed to extract 144 hp at the flywheel of a 1275 bored out to 1380 which is more than anyone else has managed to do to date. How he's done it is all in the book.

If you have a genuine Holbay engine I virtually guarantee ( don't take my word for it Chris has already told you that they ran a Holbay with twin 150CD's and it went just as well ) that it will make more power with a suitably jetted 26/36 DCD. The thing is everyone thinks that what looks good is important. Engines don't care what carbs look like, only owners do.

My whole point is just this I'm not knocking the DCOE, I'm just saying that it is being used because it "looks the business" its a Macho charisma on the cover of Power Max, let's a do a wheelie thing, that we should have grown out of years ago. I mean have you seen and heard the state of some of these cars that have appeared sprouting DCOE's because " they look the business"? I wonder what things will be like in 10 years time.

Please everyone take a step back, get David Vizard's book, question your own motives and empower yourselves to learn what is really important to make power from your engine. Listening to the sound of your exhaust/ induction under bridges is not "special tuning" Until you can change this old mindset that manufactures have taken advantage of for donkeys years nothing will change ( and I've been saying the same thing for at least 20 years now, It's all in the Horn "Not going Holbay" remember.

More on Ram Charging if we get a chance to break out of these shackles!!!
Regards Eddie

I didn't reply that well to your post mackem so let me add that I'm not against the use of the Holbay Engine with all it's attendant pieces. It is after all said and done, an historical part of the Alpine's heritage.
There are many fine examples in the club that run and perform as intended, and must be hugely enjoyable to drive.

If the engine is the proper unit it should have Holbay pistons as a matter of course. These are Hepolite Powermax flat top pistons. Without the dish in the top of the piston the compression ratio is raised. This a a very good thing.

Raising the compression ratio alone will produce considerably more power as long as detonation is avoided. My 1592 cc engine was bored out to 0.030" ( about 1640 cc ) and fitted with these pistons. The cam I'm using is standard Series 1V though, so you could say I've gone part Holbay and the CR is about 10.5 to 1 which is as high as you could dare to go on a street car, especially with unleaded fuel, although now with Tetra boost available I can mix my own 98 Octane 4 star leaded fuel, so I will be able to advance my ignition back to the proper settings this year.

Also with the benefit of closing off the water heating to the manifold I should be seeing a considerable increase in power. All these things are INVISIBLE but these are the type of mods that make power.

As long as you know why you are doing a mod to your car I'm happy, what I'm not happy with is the number of people fitting bloody great big carbs to a practically standard engine and then wondering why it's missing and running like a pig.

But I would say that if you are willing to be a bit different and fit a Weber 28/36 DCD to your Holbay you will not be disappointed at all. It may not look as good but you'll be too busy overtaking to notice.
Good Luck with it, let us know how you get on.
Regards Eddie

Has any one got one of these 28/36 DCD carbs fitted? if so, what do you think of it?
Which manifold would be needed to fit 28/36 to Holbay head?
I would like my car to drive like a sports car should. I will fit the DCOE,s and see how it goes, If not happy I would give the 28/36 a go provided I can get a suitable manifold.
Would love to fit a Ford 2.8 V6

Problems with twin 40s are almost always down to poor or innacurate setting. I have the proper Holbay set up, with a few tweeks Pertonic ign,power coil, port mods, electric fan, and fine tuned the set up on a rolling road.By rejetting the carbs & using an exhaust gas analiser a reading of 124 BHP was achieved, this could have been higher but at .a loss of low down torque. I have aspare Head Im modifying, matching ports etc. it will be interesting to see if I can achieve any significant improvement on this. By the way its scary watching your pride and joy doing 80 with the door open and the tester sat with one foot on the ground!!