Exhaust Headers For The Twin Cam Engine.

[ceejay]

DIY built, high quality, free flow exhaust header manifold
for the twin cam engine, (S2 elan).
Exhaust headers can also be easily removed with out the
frustration that most after market exhaust systems
suffer from.

Be warned, this article presents a different approach to what you might
be familiar with, it is thinking outside of the square. It could raise an eyebrow
or to, and may prompt a couple of questions. The answers should be in
the reading.
post link. http://elantrikbits.com/lotus-elan-blog ... cam-lotus/
Ceejay

[Chancer]

I have hand made a couple of exhaust manifolds so was quite intrigued by this article, especially the use of metal doughnuts, at first I though he was going to use them to make a segmented mandrel (we used to call them cods) for a bending machine but no apparently it was for cutting the tube as per paragraph below (how do I change the font colour to highlight it?)

Your next question after welding might be; What the heck do I do with it now? That?s easy to answer, what the welded donut allows the fabricator to do is to cut a segment out in order to create the degree of tube bend required, now that might sound difficult to do, but it is not really. Segments can be cut out with a hacksaw or an angle grinder fitted with 1mm thick cut off blade, make sure the donut is firmly clamped to work bench, vise etc.

Me again, now despite having fabricated manifolds from the description and the photos I am still none the wiser what the purpose of these doughnuts is, I think it may be to ensure a central cut so that the cross section is round and not slightly elliptical as when the two pieces are rotated against one another before re-welding they misalign but I overcome that with carefull marking out.

Can anyone explain what the use of or benefit is of these donuts, certainly lots of work has gone into them the article says that they are the key to the whole process but for me at least the article fails as it does not explain this key point, and I do have some considerable experience.

[ceejay]

G'Day Chancer.
The metal donuts simply allow a very tight, neat exhaust system to be fabricated.

Yes, most people will tend to use stock mandrel bends, which are available from
exhaust tube stockists. We also used two a three stock mandrel bent tube.

But the donuts were used to make the intricate bends and curves that may
not be possible with normal tubes. It is amazing the complex tube bends that can
be created with metal donuts.
Yes they are present quite a bit of work, and as I said in the article; "it's not
a job for the impatient person".
The design also allows the easy removal and replacement of the complete
exhaust system.
Ceejay

[Chancer]

Thanks for the reply, when i made my manifolds they were for bike engined kit cars and I sectioned up scrap manifolds from bikes that had been dropped, as you say patience was needed but the end result for me was very rewarding, it probably took weeks of evenings, my only regret is that i didnt have the money to pay for a weather/heatproof coating to protect my historical work of art, I dont even think ceramic coatings were available then.

I am still however none the wiser as to how the donuts are used, its such a shame to have composed such an informative article that i hope will encourage others that doesnt convey what they do, what is the advantage of them, perhaps I am being a bit thick?

[john.p.clegg]

Chop the Donut into 1/4 and you have a 90 degree bend,other angles are available depending where you cut them...

John

[Chancer]

Got it!!!!

Once my head was in the right place the article reads perfectly, my apologies to the OP.

The method of fabrication is pretty much what I did, I can see that the donuts can have a much tighter radius than stock mandrel bends, its a great idea that I would never ever have considered.

Anyone know where to buy some?

No cake shop or boulangerie replies please

[billwill]

Chop the Donut into 1/4 and you have a 90 degree bend,other angles are available depending where you cut them...

John

And twist one chopped piece relative to another before welding and you have 3-dimensional S-bends.

[Chancer]

Thats what i did on the BEC manifolds, loads and loads of small segments, some of the bends looked like a box of Terrys chocolate oranges on LSD!!!!!

[elanman999]

In the UK people often to use "dairy bends" which are available in various sizes with a centre line radius down to about 1.5D. These are normally in stainless steel because of the intended use.
Cheers
John

[Chancer]

We made them at the company where I did my apprenticeship as well as much more impressive dairy, brewery and process plant, its from where I recall the term "cod" for the segmented mandrels on the bending machines.

Dairy bends cost a fortune back then and were perfectly round in cross section as after forming steel balls were forced through to finally form the bore before polishing, pity I wasnt into race engines then as I could have made some slick manifolds.

How I miss that place, parctically everything was made in house so we could make anything we wanted, we even had our own garage, printers, foundry, and radiology labs including a linear accelerator.

[SJ Lambert]

I heard the name of a good stainless tube welder in Wonthaggi recently, went in one ear & out the other though........

[ceejay]

Hi Guys

There are plenty of metal spinning manufacturers around who can supply both stainless and mild steel metal donut halves in many different pipe diameters. Two halves are welded together around the OD seam, then cut to obtain the desired exhaust tube angle, then the inside join or seam can be welded, either with TIG for stainless, or Gas for mild steel or TIG for both, your choice.

It is possible to create incredibly intricate shaped exhaust headers with this method that are just about impossible to do with normal mandrel bent tubing.

The headers that are explained in the article also incorporate special steam joint (Gasket less) joints that
allow the exhaust system to be easily assembled and removed from the elan engine bay in sections. It works well as the same exhaust system was removed just recently to do a body off/engine and gearbox out of chassis to replace a failed clutch plate. Before reassembly, the joints were thoroughly cleaned and were smeared with HI TEMP RTV as a sealant... no leaks or fluffing on any of the flange joints.

Building an exhaust system as per the article does take a large amount of time....time that many people
simply do not have, so you need to make the choice - to fabricate if you have the skills and the time - or to give your credit card a nudge and just purchase a ready made system... again your choice.

If you live in Aust, the place to get your donuts and heaps of other cool automotive stuff is through the link below.
I have NO financial connection with this Co other than they are good to deal with.
http://www.elprodirect.com.au/
Happy exhausting.