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

[4129R]

Proper cutting fluid helps. I also found the incomplete circle makes it much easier, but with a decent cutter, it is quite quick. 5 mins maximum for a 40mm hole, even with changing sides so 5mm from each side.

32, 33, & 35mm cutters on order.

I will be using 5/16 stainless bar for the studs, then only thread them enough so they tighten before they run out of threaded hole. Not sure which type of Loctite for S/S to ally.

[4129R]

So far, I have cut back the head Z/S ports to the main head block, made 8 holes for the 4 pairs of studs to attach the new manifold, made lots of prototype flanges with 32mm holes to attach the manifold to the head, made a 4 x 40mm hole 10mm thick ally flange to attach the 2 x 40 DCOEs, and now I am playing with my new lathe trying to make 4 x tapered tubes from 40mm to 32, to  go between the Weber and the head flanges.

Cutting the tapered tubes on the lathe is only a challenge because I cannot yet find the right internal cutting tool to put in the lathe. Several ordered on eBay should be delivered for this weekend.

For a timing point of view, I reckon it takes 6 hours to machine the head and drill and tap the 8 stud holes, about 2 hours to make the 4 hole Weber flange, about 2 hours to make the 4 head flanges, about 4 hours to make the 4 tubes, and then the tubes need to be welded to the flanges on a jig, and then the ports and inlet tubes polished.

Total cost about £50 for the ally tube and plate, probably £100 for the polishing, about £50 for the welding, and a minimum 10 hours with the milling, drilling and lathe machine.

I am worried that the 1 & 2 ports will not match the 3 & 4 ports for air flow, due to the angles of the ports cast into the head, and the 2 40DCOEs will therefore need different jetting. Time alone will tell.

Is it worth it? Well, I either throw 7 Z/S heads away, sell them on eBay for not a lot, and but 7 Weber heads on eBay of varying quality and fault, or go down this route. Quite which is better, time alone will tell.

Will a 40 DCOE Federal head, with Federal cams, be much better than the Z/S head? I have no idea, but it should sound the part with the intake roar, and should be much easier to gas flow, and should have much more variation on the carb set up for various stages of tuning. 

When the 4 tapered tubes are done, when I have the right internal cutting tool for the lathe, I will post photos of the parts ready for welding together.

Alex in Norfolk, with a garage full of ally swarf.   

[BDA]

I admire your gumption! Can't wait to see your pictures!

One of the great benefits to converting the Z/S head to a Weber head is that porting can be much more accurate since the  intake runners are shorter and a porter would have much more control over the grinder throughout the length of the runner. It would be interesting to have your head ported by someone who is experienced with Weber heads when you're done so he could compare a traditional head with yours.

[Roger]

It looks like you have left the breather box containing part of 3 and 4 inlets in place.
Why not cut the box off completely?

[4129R]

It looks like you have left the breather box containing part of 3 and 4 inlets in place.
Why not cut the box off completely?

I think I will explore that route next to see what is involved, and how else to vent the breather which used to go into the air filter box.

Alex in Norfolk.

[Certified Lotus]

Alex, I'm a little late in reading about your adventure but it seems that you are headed in the right direction.

I have some weber head photos that might be of use to you.

About two years ago I was asking a lot of questions (on Elan.net as I was rebuilding an Elan S1) about the twin cam weber head regarding the casting and where the water and oil ways were located exactly in the head as well as the thickness of the casting walls in certain areas. Couldn't get detailed enough answers so I sourced a used head that was no longer usable and had a machine shop cut it apart and mill away one area of the head. After media blasting and filing the entire head (knife edge sharpness where it was cut) I painted the water ways blue.

Here are the results:

[4129R]

It is what lies in the square bit on the left of this photo which is the mystery.

I have Weber heads, so I know the dimensions of the inlet port tubes, but getting them even in size and shape, and to work properly with good air flow, is the challenge.

Plus getting the machining time down to an acceptable level, for both cutting away the Federal head, and making up the 5 flanges and the 4 tapered tubes.

Getting a cast manifold is only really economically feasible if large quantities are requires, and the casting would still need the flanges made flat by machining, the carb fixing stud holes drilled and threaded (5/16 UNC), and the port tubes gas flowed, so making up the manifold from 5 flanges and 4 tubes seems the easier and cheaper option at the moment. Welding it together will need a jig made to hold it in the right position while the parts are tacked together.

This is quite a challenge for someone who is used to working in wood rather than metal. Learning milling and lathe cutting techniques is interesting. The ally sticks to cutting tools and blades unless you frequently dip or coat them in cutting fluid, which seems a bit like gearbox oil.

I was using a hand held jig saw to cut the 4 hole carb flange to shape after cutting away as much with the 40mm hole cutter as possible. The jigsaw blade soon got clogged with molten ally until I frequently dripped cutting fluid on it, and then it cut through 10mm ally plate really quite quickly and accurately. 

Hopefully the internal lathe tool is on its way so cutting the tapered tubes can continue.

Her indoors is getting a bit frosty, but at least she knows where I am; just follow the sound of 60's &70's music, and I will be close to the source drilling and milling away.

Alex in Norfolk.

P.S. thanks for the cutaway photos, they may be of help, but I think the Federal Z/S head is quite different, but only on the side I am cutting away.

[Certified Lotus]

The cut away head is from the UK. I had it shipped to me in the US. I was just showing you exact locations of water and oil ways in the casting of a weber head. I don't know how different they may be on a stromberg head.

[RoddyMac]

Omnitech takes the breather box off completely.  You should be able to see some of it in the video they have on their website.  The last time I saw one of their converted heads it was already in the car (Elan) so all I could see was the top of the motor. 

http://omnitech-engineering.com/category/automobile/engine_development

[4129R]

Thanks very much for that link.

Taking the box off reveals 3 strange extra holes. From the look at the manifold he has, it looks like he just blanks those holes off. I think 1 of those connects to the block with the strange rubber tube you get in the head gasket set.

The manifold has a complicated curve in its face. I wonder if that can be made into a straight line crease between the two planes.

I see much more ally swarf on the garage floor soon !

Alex in Norfolk.

[4129R]

I started cutting away the breather box next to 3 & 4 inlet tubes.

First I started using a milling machine. It was far too slow, and all I succeeded in doing was wrecking 1 long milling cutter which cost me £60.

So I attacked the cast ally box with a small hand held angle grinder and a 3lb hammer. Much quicker.

Then all I have to do is smooth off the cut edges to give a flange to mount a flange plate on.

Without cutting back 3 & 4 inlet tubes to the same length as 1 & 2, I ended up with unbalanced inlet port tubes, and a bad K shaped change of direction on 3 & 4 which you could not rectify with any amount of porting or polishing. So, to make the inlet port tubes balanced for length, diameter, shape, and polishing, the vent box has to come off.

When the vent box is removed, you end up with the vent from the block which is normally connected to the head with a rubber tube, and a vent down from the cam cover area, with no connection to anything, so I am thinking on making a plastic T piece, and fittings to the block and underside of the cam cover area, and venting them into a catch tank if I am not using the standard inlet air filter to which the head vent is normally connected.

I will downsize photos and post soon.

Next I will screen capture the Omnitec photos to see where they mounted the studs to attach the manifold to the head, and start drilling holes for the same head stud fixings.

Alex in Norfolk.
 

[4129R]

Photos of cutting off the breather box with an angle grinder.

I cut back the face too far cutting into the cam cover, so when I do this for real, I will have to face the head carefully about 5-6mm further out.

You can see after cutting off the breather box, the ports are the same length, the same shape, and very easy to polish.

The manifold plates and tapered tubes have been made up as a prototype to see feasibility. If all 4 tubes will be the same length and all point in the same direction, the manifold may be easy to cast up. I will make 4 long tapered tubes and a decent flange to attach to the head, and see if the cast head is easy to produce.

Alex in Norfolk.   

[BDA]

Great stuff, Alex!

[andy harwood]

Wow!
This is very interesting. Thank you for photographing and sharing.
It appears with the right tools, this is a doable modification.
The tapered intakes look great.

[4129R]

You need a compound lathe to taper. The bit moves at an angle of 3' for the long tubes, and 5' for the shorter tubes. I worked out the angles using a circular saw and cutting plywood to the right shapes. The circular saw has accurate calibrations so you know exactly the angle you are cutting to the nearest degree. It is very accurate.

You have to taper the insides of the tubes first, as the lathe chuck cannot hold the tapered outside end.

Once I have the right recipe, I will do most of the cutting myself and get a proper machine shop to do the final facing, as it is very difficult to get all 4 flange mounts in exactly the same plane without a very big milling machine or grinding machine.

I actually used the lathe to face 3 & 4 ports as the milling machine won't fit, it is too small. I put the milling bit in the chuck of the lathe, and moved the whole cylinder head at right angles to the cutter as the cutter rotated.

I will get the hang of it all soon.

Cutting the tapered tubes is actually very quick providing you get the tube exactly square in the chuck. I rotate the chuck by hand to see if there is any wobble or run out before starting the lathe.

Alex in Norfolk.