"Clamshell" exhaust manifolds 1

[aberlin]

Hi,

Does anyone know anything about this type of exhaust manifold, like manufacturing methods and construction techniques used to make it or the benefits of a dual-walled manifold (pictures dont reveal but it has a second 'skin' within, and an apparantley consistent air gap between the two). Has anyone ever worked with these, have specs? I am only familiar with cast exh manifolds and am curious.
googling yielded only unrelated designs.


The pictures (have more if needed):

http://i26.photobucket.com/albums/c135/moshimasu/clamshell/DSC_0517.jpg

http://i26.photobucket.com/albums/c135/moshimasu/clamshell/DSC_0524.jpg

Thanks in aticipation,
Alex

 

[GregLocock]

Reasons you might use one include keeping the exhaust hot, and quiet.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[Warpspeed]

I have had success placing very closely fitting fabricated mild steel covers over factory cast iron manifolds. They are very effective at reducing heat radiation.

But I wonder at the problems of differential expansion if the whole thing were to be welded into one piece. There would at least need to be a slip joint around the outlet pipe, or perhaps some concertina wrinkles strategically built into the shape.

 

[OP800]

I believe Ford uses this type in some models of it's vans.

 

[mattsooty]

These are called dual skin manifolds and are used with close coupled catalysts to allow faster light off after cold start.

They are becoming more popular as emissions reduction during the open loop portion of afterstart and warm up becomes more of a constraint to passing an emissions drive cycle.

MS

 

[aberlin]

So what exactley allows these manifolds to produce a faster light off than, say, a cast manifold with a ceramic heatshield around it, also close coupled to a cat. thanks for the input so far people. I will post up some videoscope shots to show you some interesting internal structure.

 

[aberlin]

Here are some videoscope shots of the insides. Only one of the three manifolds I looked at had a strange wire mesh sandwiched between the two skins

http://i26.photobucket.com/albums/c135/moshimasu/clamshell/sandwich2.jpg

http://i26.photobucket.com/albums/c135/moshimasu/clamshell/sandwich1.jpg

http://i26.photobucket.com/albums/c135/moshimasu/clamshell/runner3.jpg

http://i26.photobucket.com/albums/c135/moshimasu/clamshell/runner2.jpg

http://i26.photobucket.com/albums/c135/moshimasu/clamshell/inner_skin.jpg

thanks for looking.

 

[mattsooty]

I havent looked at the piccies but the reason is simply that less heat is lost to and through the manifold because of the insulating propeties of the dual skin.

MS

 

[aberlin]

I see, thanks. Do you know how this type of manifold is manufactured?

 

[Warpspeed]

To get faster converter light off, the idea is to make the exhaust manifold out of very thin material with very low thermal mass, and insulate it somehow.

A heavy cast iron manifold made from several kilograms of iron, when stone cold, will continue to draw the heat out of the exhaust gas for a considerable time until it reaches "normal" operating temperature. Initial temperature rise at the cat will therefore be slower with a heavy cast manifold.

 

[Peter7307]

I understand BMW cars also use this type of manifold so an email to them may provide a lead.

Cheers , Pete.

 

[DonSund]

As far as manufacture:

Flanges: WaterJet, Laser cut, Punched, Flattend if nessesary

Inner Skin: Either Drawn (two halves) or fabricated tubes ie header. Mig, Tig, or Laser seam welded.

Filler: Knitted ss wire cloth, or possibly packed wire mesh used with a form.

Outer skin: appears to be a Stamping (two halves), possibly would not have to have solidly attached to inside tubes as they are surrounding them and there is a filler in between to dampen any forced vibrations. Could possibly be spot or projection welded over the insides.

There are lots of possiblities / strategies to attach the outside skin. You would have to evaluate cost vs durability on that one.

Don

 

[aberlin]

Thank you Don, that's exactley what I was looking for.

 

[Hurls]

It seems like this exhaust manifold would work well in a turbocharged engine.