Converting a Zenith/Stromberg Head to a Twin 40 DCOE Head

[kiwiokie]

Was the integrated intake manifold originally a cost saving measure?

[4129R]

Was the integrated intake manifold originally a cost saving measure?

I cannot see how making up molds for two different heads, the Z/S version and the Weber version, can be cost saving.

I would have thought making molds for two different bolt on cast ally manifolds would be a lot cheaper.

I cannot see any reason for making the carb flange and inlet manifold part of the head casting. It makes no sense to me at all. 

Alex in Norfolk

[EuropaTC]

Was the integrated intake manifold originally a cost saving measure?

I cannot see how making up molds for two different heads, the Z/S version and the Weber version, can be cost saving.
I would have thought making molds for two different bolt on cast ally manifolds would be a lot cheaper.
I cannot see any reason for making the carb flange and inlet manifold part of the head casting. It makes no sense to me at all. 
Alex in Norfolk

I suppose it depends on the circumstances at the time, remember Colin Chapman was supposedly famous for wanting to shed all possible weight and achieve minimum production costs so I'll guess he looked at all options.

A separate manifold would mean fitting studs, more machining operations, gaskets and assembly time plus marginal weight increases (this from a guy who allegedly said "why are you letting those washers go for a ride on my car ?" so if you were never planning to have anything other than webers on your car, there is a case for all-in-one.

Back in 1962/63 when setting out with the Elan it probably seemed logical to have a single casting, especially if he could flog them to Ford with an attraction of reduced assembly-line time.  It's only much later when the US emissions kicked in (?) that he had to find an alternative to webers, and he did try to convert all Elans to stromberg heads around 1969-ish. If that had worked out ok with the UK market I doubt we'd ever have had dellorto equipped Europas, both the Elans & Europa would have ended their days with Strombergs and the same base casting.

With our 20/20 hindsight and knowing that Lotus would need to offer variations 7 years down the line it does make sense to have a head casting with separate manifolds, but back in 1963 I'll be the accountant vetoed it !

Brian

[jbcollier]

The switch to Strombergs was for two reasons.  Firstly for emissions, Stromberg would assist manufacturers meet emissions standards.  Something Weber wouldn't do until years later.  Second, the Stromberg heads with non-emission carbs put out the same power as the Weber heads for production tuned engines.  Stromberg carbs were MUCH cheaper so, for a while, both Euro and Federal production engines came with Strombergs.  The Euro market protested which led to the reintroduction to production cars of the Weber/Dell head.

[Roger]

They only had to make moulds for the inlet manifolds, not the entire head. They always were separate moulds.

[4129R]

After much machining of the cast inlet ports on the head, I have now come to a halt on R&D as I have hit 4 problems, 2 of which are considerable, and 1 of these is a deal breaker in my mind.

If I didn't cut off the breather box, 3 & 4 ports had a nasty K kink in them, so it had to come off.

The Problems:-

1) There is a iron plug in the head, which presumably plugs a waterway casting, which gets in the way of machining a flat surface. It will protrude about 1/2" proud of the flat surface. This can be overcome with making a round cut out in the flange which needs to be bolted to the head.

2) There is an oil breather from the head, and another breather from the block, which need to be linked and vented into the inlet air filter or a catch tank. So a plastic T piece needs to be fitted to the head when it is fitted to the block, similar to the existing rubber tube.

3) When cutting the head flat to get a completely flat surface on which to bolt the manifold, you cut in to the camshaft area in the top of the head. This could be solved by a 60' change in the plane of the flange to be bolted to the head which Omnitech did,, but this needs complicated machining to both the head, and to the flange to be bolted to the head.

4) I think this is the deal breaker. After machining the face of the head flat, and I was cutting 10 thou off a time until I got a flat surface, there is not sufficient meat left in the head casting to drill and tap holes for stud fittings. I was hoping for 6 full turns of the 5/16" UNC thread. I don't think I can find sufficient places where this depth in metal remains after machining the face of the head flat. I have drilled many holes into the head in suitable fixing places, but very few are now suitable.

I looked at the manifold Omnitech had bolted to the head, worked out where their holes were drilled, but there just was not enough meat there to cut 6 turns. With the shear force of the 2 x 40DCOEs wobbling up and down, you need decent a large number of fixings for the manifold to the head. I think 8 studs would be good, 6 a bare minimum, but I can only find about 3 decent fixing points, and these are all in a line in the middle of the inlet port, so not of sufficient top and bottom spacing to prevent shear from the inevitable carb wobble.

Therefore my research will stop unless I get some inspiration to solve these problems.

I have taken a photo of the 4 problems listed above, and will post mid week when I can reduce the file size of the photo.

My investment in time has been considerable, about 12-14 days so far, my investment in machinery has been a lathe £1200 with cutting bits, a milling machine about £750 with milling cutters, and a belt sander machine about £200 with the sander belts etc. I just hope I
 find things to use these for to justify this expense. Well, as they say, nothing ventured, nothing gained, and if you don't try, you will always be wondering "what if".

My next challenge is to get the soda blaster working so I can clean up all the rusty and dirty parts easily. Cleaning cast ally is the challenge, so I will try to work out how to use the pressure blasting cabinet I have bought. I had to buy an extractor fan to join to the side to remove all the dust, as when you start blasting, you can see FA without extracting the dust.
 
Alex in Norfolk.
 

[EuropaTC]

You sound a bit down Alex, and to be honest I'd probably feel the same.  But, as my old boss used to say "research isn't easy, if it was it wouldn't be research". Or something like that anyway.

There's going to be a way forward, it's just a case of finding it. Someone else has done this trick so it must be possible. Let's see some photos of where you've hit snags and maybe we'll have a lightbulb moment. I think you've done well so don't give up just yet.

Ideas, first thoughts and no doubt all to be discarded but maybe it will spark something else that will work.

You say the wall is too thin to take a stud, ok, one way out of that would be to cut say a 1/2" hole and then weld in a small (but thicker) plate for drilling/tapping. It will reduce the waterway behind it, but probably not enough to matter.

The other, and this might be ridiculous but I don't know until I see the area, is to overlay with weld to bring it up to thickness. So far I'm assuming your aim to get a flat surface has been by removing metal, maybe adding some is one way forwards. Aluminium is easily MIG welded and that can put a lot of metal down quickly, far more than the usual TIG approach.

This is too interesting a project to pack in just yet ! 

Brian

[4129R]

I have coloured in the problem areas on the head. I will post photos soon when I can downsize.

Red are the holes with insufficient thickness.

Green are the holes with about 6 UNC thread depth.

Black is where I have broken into the cam chamber. Just welding a piece of 5mm x 5mm bar would sort that out.

White chalk is where the oil breather comes down from the head into the old vent box. Drilling a 15mm hole and sticking a tube in that would work easily.

Blue is 5 areas where I could weld 6mm or 10mm ally bar with already drilled and tapped bolt holes in it. they will be each side of the 4 ports, which seem very equally spaced.

Photos probably Monday evening. My other computer has photoshop elements on it which I use to downsize the photos.

Alex in Norfolk

P.S. I seem to have found another way of downsizing 3Mb photos.

[4129R]

I have a better idea.

Make up identical flanges in 10mm ally plate, drill and tap 5/16" UNC threads, and weld the flange plates to the head using a jig to keep them in the exact correct position.

Then use the same jig as part of the jig to make the manifold for welding.

So the sandwich will be head, 10mm plate, gasket, 6mm plate, tapered tube, 10mm plate 40 DCOE.

I will make the flange plates and the jig next weekend to see if this is possible.

Alex in Norfolk. 

[jbcollier]

A single plate welded to the head will not be sealed "behind" the plate.  You would have to weld multiple plates; and then machine them all to the same plane afterwards.  There's a good reason Omnitech uses a CNC angled "cut" and you have found it.

Stock, there is not much to choose between the Stromberg and Weber euro set-ups though the Webers may be a little quicker revving.  If it is power you are after, fitting flat-slide motorcycle carbs to your Stromberg heads will easily meet/exceed the air-flow capabilities of 40DCOEs, perhaps even ITBs.  When the slide is fully raised there is virtually no restriction all.

[EuropaTC]

Hmm, I can see you've been having fun drilling holes !

As John says, a plate welded on top will have problems although not insurmountable.  I'm struggling to envisage the geometry to some extent and that gives rise to concern about exactly how you'll get a plate welded over the 4 inlet holes. One snag will be the need to weld/seal the bores at the plate/head interface. It could be do-able but depends on the tig torch you have I suppose.

It's definitely blue sky stuff but looking at what you have makes me think of a weld overlay.  Not practical with TIG welding but aluminium mig welds quite easily and although it would be expensive in terms of wire I could see 3-6mm of weld metal going down over the length of the head without too much problem and very quickly.  That would give machining and tapping clearances without any snags that I can see and a solid base to work forwards from.

How deep are those red holes, would another 3mm give you sufficient thread ?

Brian

[RoddyMac]

Looking at the machining that Omnitech does compared to your head, it looks like they dont mill the inlet tracts completely flat.  It looks like their intake manifold has a bit of the intake tract cut into the angled portion.  I wonder if this keeps more material on the cylinder head.  It also looks like they did the machining via CNC, the little bulges for the cam studs look untouched.  I'm sure you could machine them off then build them back up with weld, but that involves welding. 

I also do recall reading somewhere that the reason Omnitech didn't weld a manifold or a plate on was due to warpage when welding.  Also, you would lose any heat treatment to the head. 

Also, I had a thought about the stud engagement, could you machine up some blind threaded bosses and weld them into the head?  Drill or machine out a pocket with a step, then weld in some top hat section bosses?

Rod

[4129R]

So Plan B, to make up 10mm thick flanges, with 5/16" holes already tapped into them to take the studs, continues.

These flanges are to be welded to the head around their entire perimeter to give an airtight seal.

Technical Problem:-

The venturies in the 40DCOE are supposed to be 32mm diameter for standard state of tune.

The valve seats measure 34.4mm diameter at the combustion chamber. 

Having machined the inlet tubes off the head to the first flat face available, the inlet ports at this place are 29.6mm diameter.

I made the holes in the flanges 32mm diameter.

Question:-

When I make up the flanges, and the inlet tubes for the manifold, the tubes start off at 40mm as that is the size of the carb at the flange. I reduced the tubes from 40mm down to 32mm by careful machining. When I get the ports gas flowed so the manifold and head match up properly, do I get the ports on the head where the manifold bolts on, increased in side to 32mm, 34mm, or leave them at around 30mm which is what they are.

If they stay at 30mm, I am going to have to make up another set of flanges and tubes, which is no big deal now that I have the tools and the method. 

The heads will have standard Federal spec cams, I can get the compression increased slightly by planing the head, but otherwise, with just gas flowing, 40DCOEs correctly jetted, and a tubular exhaust manifold, I would class the engine as stage 1 tuned, and I would expect around 120-125 BHP.

Does anyone out there know about port sizes, or should I consult a Lotus Twin Cam head porting expert?

Alex in Norfolk

[EuropaTC]

Hi Alex,

I see what you meant in the other thread about metal on your workshop floor !

I'll be honest and say I have no idea what the answer is to the port diameter questions, all I can comment is that it's not always a case of opening everything up as wide as possible, sometimes the venturi effects come into play.  But quite honestly I've no idea if it applies in this instance.

I know it's potentially dangerous to take measurements from drawings but there's a sectional elevation in the manual regarding valve guides and followers which might give a clue as to the OEM design. If you look it does change sections in a few places and I could convince myself that it's not the same diameter as the inlet valve. Take a look for yourself at the image.

But the bottom line is that for best results you need someone who knows what they're talking about, and that's not me I'm afraid. I think if I were doing this I'd try to measure a weber head along the inlet tracts and see how that compares with what you're trying to do. If you haven't a "spare" weber head in your collection, I've got one in my workshop that I can try and measure up for you with some inside calipers. It won't be 100% accurate but it'll give an idea of the shape.

Brian

[4129R]

Just invested in David Vizard, tuning Twin Cam Fords to see if there are any clues there.

I think I will call in at QED and have a chat when I pick up my ally seats from Loughborough. Quorn is very close, about 4 miles away, and on my way home.

Logic would say that a smooth transition from 40 down to 34.4 would give the best gas flow. I think the venturi effect is only needed to pick up the fuel. I would have thought once the fuel and air were mixed in the carb, a smooth air flow would be all that was needed into the combustion chamber. 

Alex in Norfolk.