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

[4129R]

I am exploring the feasibility, and cost, of cutting off part of the Zenith inlet manifold, and welding on a 45DCOE Weber manifold for a Lotus Twin Cam head.

It looks possible and relatively cheap compared with the cost of a new head (£3,000 ish) and the cost of a decent second hand Weber head North of £1,000, which usually is wanting some machine work, guides, valve seats etc.

I was told by a Lotus engine specialist that the cost of cutting off the inlet and grafting on a new one would be prohibitive, but I am not so sure.

If I find a cost effective way of doing this, how many of you out there would be interested in doing this? I was thinking of getting an inlet casting made up that could easily be welded to the cut back head, and if I get someone to make the casting, they would want to know how many castings to make. The greater the number of people interested, the more the cost of making up the mould for the casting would be divided up, making it cheaper for all.

I tried to contact an engineering company in the US who did this years ago, but I got no reply.

Alex in Norfolk.

[BDA]

Was Omnitech (http://omnitech-engineering.com/category/automobile/auto-article/lotus-port-tuning-for-volumetric-efficiency) the folks you called? Dave Bean was the first I heard of who was selling them. It wasn't cheap and I highly suspect he took orders for Omnitech. I would guess there are shops on your side of the pond who at least used to do it, but I wonder if the engine has gotten too old for many people to want such a high dollar mod. I would also think there are fewer Stromberg heads in Europe and thus even less a market for it. For your sake, I hope I'm wrong.

Let us know what you find out.

[Grumblebuns]

I need to speak to my machinist and get his take on the feasibility of the project.

Rather than weld on the Weber manifold, anyone see why they can't be bolted on instead, assuming the casting around the intake area is thick enough.

   

[4129R]

Cutting off the old manifold flush with the head is trickier than say 1" away.

A bolt on would be much easier. I wonder what will happen when the 8 holes are drilled and tapped into the casting. Will it go into the waterway?

Alex in Norfolk.

[EuropaTC]

A bolt on would be much easier. I wonder what will happen when the 8 holes are drilled and tapped into the casting. Will it go into the waterway?
Alex in Norfolk.

Would it matter if it did ? I suppose if you were using bolts it would be a problem, but I would expect a permanent stud would be ok. It's not as if you'd be pulling the manifold section on and off, it would most likely be a fit and forget installation.

I haven't seen a Stromberg head close up but I can't imagine why it's not feasible if the later head was a modification of the original design.  It might be expensive to cast a section unless you were doing a hundred, but a fabricated item might be cheaper for one or two items. If you can weld it yourself or get a cheap source of welding, say an exhaust fabricator,  then I would think it's an economic project. If you have to go to a machining shop then I'm more doubtful.

Brian

[BDA]

I'm pretty sure Omnitech bolted a Weber inlet manifold to a modified Stromberg head. Besided having better carbs, there were advantages in porting the input runners because they were shorter so there was more control of the grinder and bur and thus a better job.

[EuropaTC]

Well BDA, ya got me curious.....  and I reckon you're right.  These look familiar ?   

[4129R]

I had contacted Omnitec. No reply.

If I were to use brass or stainless steel studs into the head, if they went into the waterway, they would not corrode, so would be replaceable.

I remember old Minis had brass 1/2" nuts on the exhaust/inlet manifold studs to stop corrosion, so it must work, even with high exhaust temperatures.

All the old Elans in the UK had Zenith carbs, so there would be a market in both the US and the UK for a bolt on inlet manifold.

I have a scrap Zenith head here, so I will explore possibilities. I even bought a 45DCOE cast aluminium inlet manifold on eBay which was for a Zetec engine to see if I could use that. It had TURBSOPORT cast into the manifold. It seems the casting people (Chinese?) could not spell. I will contact Turbosport, who are not too far away from me, to explore options of casting a special manifold, costs, feasibility etc.

Alex in Norfolk.

[LotusJoe]

I'm pretty sure Omnitech bolted a Weber inlet manifold to a modified Stromberg head. Besides having better carbs, there were advantages in porting the input runners because they were shorter so there was more control of the grinder and bur and thus a better job.

I also recall in my conversations with Bean that the Stromberg head was a good candidate for Weber modification. He machines off the Stromberg intake and bolts on a Weber manifold. The question is it worth the $1350.00 for the conversion plus another $798.00 for the Weber carburetor setup (Bean also sells). 

[4129R]

Well BDA, ya got me curious.....  and I reckon you're right.  These look familiar ?   

The captions on those photos look the wrong way around to me.

Alex in Norfolk.

[4129R]

Apparently you don't need to weld the cast alloy, it is more like soldering using an aluminium filler rod, and oxy-acetylene to heat up the surfaces and melt the rod.

But if a bolt on manifold is cheap enough, it cannot take long to cut off the old manifold, machine the head flat using a milling machine, drill and tap 8 holes, and put liquid gasket in place to seal the joint.

Alex in Norfolk.

[BDA]

Brian, that's the way I remember it.

Joe, is that current information from Bean? His website is WAY out of date. Regardless, I think it would at least be an interesting exercise to call them over at Bean and ask about it. Bean used to have a machine shop - he built my engine - but I don't think he has one any more. That certainly isn't to say that he doesn't or couldn't farm out machining projects to a shop. For that matter, that may have been the way he built my engine! 

[4129R]

The question is it worth the $1350.00 for the conversion plus another $798.00 for the Weber carburetor setup (Bean also sells). 

$1,350 seems a ridiculous price for 2 hours work in a machine shop and a cast manifold. Most cast manifolds retail around £120 + VAT which at post Brexit exchange rates equates to around $175.

Alex in Norfolk.

[LotusJoe]

Brian, that's the way I remember it.

Joe, is that current information from Bean? His website is WAY out of date. Regardless, I think it would at least be an interesting exercise to call them over at Bean and ask about it. Bean used to have a machine shop - he built my engine - but I don't think he has one any more. That certainly isn't to say that he doesn't or couldn't farm out machining projects to a shop. For that matter, that may have been the way he built my engine! 

I'm taking the information off Bean's website. I know it is very old so I would not be surprised if the prices have increased, assuming he still offers the modification. Alternatively there is always the conversion to SUs. And there is also a conversion to a Weber 38/38 downdraft. Both of those don't require modification to the head. 

[4129R]

If anyone in the USA is on speaking terms with Omnitec or Bean, and they would be kind enough to give them a ring to find out if they have any manifolds left, I need 7 inlet manifolds to convert all the Zenith heads I have accumulated here.

I can get the machining done locally, and the manifolds would only be gathering dust on a shelf somewhere.

Alex in Norfolk.