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

[EuropaTC]

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.

The guys at QED sound like your best bet. In all honesty I'm just guessing, you really need someone who's had a TC on a flow rig. Didn't Dave Vizard do a lot of work on them before he moved onto more modern stuff ?

The only reason I mentioned venturi is that I remember reading something about widening ports with DIY gas-flowing and how the wider areas lost velocity and hence fuel dropped out. It's hazy, could have been in something like an old issue of Car & Car Conversions back in the day.  I think the main message wasn't to re-shape or remove metal, just to blend in obstructions around the valve guides.

[4129R]

So a gradual linear reduction from 40mm down to 34.4mm would seem not to drop any pressure, whereas 40 down to 29.6 and then back up to 34.4 would seem to drop pressure and possibly upset the fuel/air mix.

Until I know the size of the ports where the manifold meets the head, I cannot make the flanges accurately, I can just work on the rough prototype.

But it does seem very easy to get to the ports on the head, and the inlet manifold, which are quite short, so gas flowing to the correct diameter would seem to be simple.

Alex in Norfolk.

P.S. Hamilton must be itching to get racing to get full points for the race, and hoping Verstappen takes out Rosberg on the re-start.

[jbcollier]

A good port narrows as it approaches the valve guide to increase mixture velocity and density.  The port then opens up from there to the seat as there is now a valve stem in the middle of the port and a valve head to work around as the flow goes through the port.  It "looks" wider but it's not really.

Porting is not intuitive or there would be no need for flow benches.

Welding individual flanges just on the outside may also be problematic as there may be voids and gaps formed where the flange touches the head.  This will create swirls and eddies that will negatively affect mixture flow.  Welding the flanges on the inside may be required though I'm not suggesting you do so.  You need to talk to someone experienced with welding on TC heads specifically.

[Roger]

The Federal camshafts are the type C, or SE spec.
The power you're  expecting is around that of an Elan Sprint or Europa Special, which used D  type camshafts, 40 DCOES and 10.5:1 CR.

You'll be somewhere around SE spec, or 115bhp or so, I  imagine.

[BDA]

P.S. Hamilton must be itching to get racing to get full points for the race, and hoping Verstappen takes out Rosberg on the re-start.

That was quite a race! I had the same thought as you, but I wouldn't be unhappy if Rosberg wins the championship. I think he deserves it. Verstappen is amazing! His run through the field after that stupid stop for tires reminded me of Senna at Donnington in the rain in '93. Lewis needs to watch out for him.

[EuropaTC]

(part quote)
So a gradual linear reduction from 40mm down to 34.4mm would seem not to drop any pressure, whereas 40 down to 29.6 and then back up to 34.4 would seem to drop pressure and possibly upset the fuel/air mix.

I don't think it's solely down to the diameters, my suspicion is that it's more about the available cross section for flow at any point.  As John points out, once you're at the valve guide you have an intrusion into the fuel stream, both from the guide coming out of the inlet wall, the valve stem and valve head to get around.  Although you measured 34.4 at the valve seats, you're not going to have Pi x r^2 area available because it's cluttered up with a valve.

The area available for fuel to get inside the combustion chamber is going to come from the valve diameter & amount of lift on the cam. I'd guess at the point the fuel passes the valve head it's going as fast as it ever does, which of course will help atomisation, etc. (well out of my depth now  )

None of which helps you I suppose, all just speculation. The fact is you're in the position where you've just got to give it a go and refine as you move along and things strike you.

Brian

[4129R]

Reading David Vizard's book, page 21:-

"It will be seen from Fig 9. that roughly speaking, the inlet port can be divided into three sections. The first part is tapered, the second is a parallel section. After this comes a short section which slightly flares out to the valve seat diameter. With the exception of forming the venturi and blending the tapered port section, we must avoid removing any more metal than is necessary to achieve a smoothly contoured port with a good finish."

I read this as match up the carb 40mm at the gasket joint to the start of the inlet port tube of the manifold, gently taper the port down to the diameter of the parallel section, and then slightly modify the larger bit just before the valve seat, which is best done by a specialist.

So I need to measure the diameter of the parallel bit, and make up the inlet manifold to taper evenly down to the smallest diameter of the port, and then give the head to a specialist gas flow chappie, who can smooth out the manifold and the inlet port on the head, and smooth out and enlarge the bit just before the valve seat.

It is 0'C outside, 32'F, so my enthusiasm to venture outside to start making up the manifold tubes is cooled substantially. There is international sport on the TV for the next 6 hours, cricket,India v England, then soccer Manchester United v Arsenal, then England v Fiji in Rugby. Decisions !!!

Alex in frosty Norfolk.

[EuropaTC]

G'd evening Alex, it was cold up North in Lincolnshire this morning as well, so I don't blame you for huddling round a warm TV !

I've got that book as well and I'd agree about matching the gasket to the manifold.  I think all you're looking for at this stage is to remove any obstructions and try not to leave any "gaps" which might cause eddies and fuel drop-out.  For the first prototype I don't think I'd do anything immediately behind the valve or even very much around the valve guide, I'd just try to get something that hangs webers on the side of the head and actually runs.

Then it might be worth having a shot on a dyno to see what sort of power it produces as a baseline before attempting any more work to gas flow the installation. If you can't get access to a dyno easily then maybe the stop-watch dyno will have to do, but at least then you'll be able to see the benefit from any additional work. Whereas if you just dive in and go for broke you won't know if the 140bhp (   fingers crossed ?) comes from your conversion or the gas-flowing stages ? 

Brian

[FranV8]

Hi Alex.  Practical Performance Car did a piece in the last couple of years pouring Latex into ports so that the internal port profile could be visualized.  They then sliced this like a loaf to measure the cross sectional area as it changed through the port length, using the results to steer metal removal.

I can't remember the right progression in areas, I'm sure it's somewhere on the internet though.

Perhaps its worth doing that on a Weber and a Zenith head just to see what the differences are in this respect?

Really very interesting project and thread, enjoying watching your journey here.  Hope you carry on beating your frustrations!

[4129R]

Well the long R&D continues, with trying to make up flanges out of 10mm thick ally to weld to the head, and a manifold made from 6mm ally to bolt to the flanges, and 10mm ally where the 40 DCOEs bolt on, and 50mm ally tube with a 30mm hole to make the inlet port tubes.
 
Enclosed is the progress so far.

R&D has been a mixture of finding the right machines, getting the right tools to fit in the machines, cutting bits, hole borers and milling cutters, and getting used to using the machines to their capability. Add trying to work out how much metal you can cut off the inlet side of the head, and trying to get it all to work from a gas flow point of view, and you have an "interesting" learning curve.

I now need to get the angle of dangle right for the tubes, so I need to make up a jig to keep all the bits in the right place while they are tacked together for proper welding.

Once the manifold and head have been welded, the finer grinding and polishing of the head can take place. 

[TurboFource]

Any more progress on this conversion project?

[Pfreen]

These people already have a casting.  It isn't cheap though.  https://www.ebay.com/itm/Lotus-Elan-Stromberg-Head-Conversion-for-Weber-Carburetor/401707452794?hash=item5d87a1497a:g:sywAAOSwcHRcZNpp

[Bart]

Hi Alex,

I have not spoken to John in a while (he built my engine with the Webber conversion). His email is john@omnitech-engineering.com and his cell is 001 360 820 1333

Cheers,


Bart.

[4129R]

I found it was much easier to find a second hand Weber head, but having said that, I am trying to find an engineering company to cut the inlet cam groove into the heads I bought, where the alternator pulley attaches.

Cutting back the head is a very specialist engineering project, so by the time you do that, make up the inlet manifold to attach, and weld it all together accurately, I can see where the cost comes from.

Alex in Norfolk.

[TurboFource]

Literary, thanks for the info on Stromberg heads today! It was great to talk with you!