Turbo manifold design.

[Jörgen Karlsson]

Justin Ivan wrote:

> Not sure if I agree with everyting that you are saying. When the
> flange is a
> single piece, essential all (really just a large portion) of the
> expansion
> takes place at the ends of the flange, the material in between constrains
> the flange from expanding towards the center. When the flange is
> separated,
> each port can expand in 2 directions, therefore has more flexibility.
> If someone can debunk this please do.

If the manifold had looked like an ordinary V8 header I wouldn't have
anything against using separate flanges, it would be far better then using
one large flange. An ordinary header usually has pretty long runners in thin
material that are pretty flexible.

In my case the distance between the ports are 86mm and the runners are
routed the shortest possible way to the runner next to it, turbo exhaust
manifolds must also be made from a bit heavier tubes then ordinary headers.
To prevent cracking I used high quality tube bends and welded it with
electrodes made for the specific material.

This makes my manifold very strong, to make the ends of it flex 2mm requires
a lot of force. A lot more force then I would trust the manifold studs with.

When we use separate flanges the temperature of the tubes in the exhaust
manifold decides how long the manifold will be. From room temperature to
700ºC the manifold will grow 4mm.

If we use one long flange that is bolted to the head, the temperature of the
flange will decide the length of the manifold. Since one side of this flange
is bolted to the engine that I guess are 200ºC around the ports, one side
are welded to the runners and 80% of its surface are exposed to the air I
would guess that it will have a temperature somewhere in the middle of the
200º engine and the 700ºrunners. Hopefully closer to the engine temperature.
I think that the flange temperature will be around 250-350ºC. Since the 1/2"
thick flange will be a lot stronger then the red hot runners of the manifold
it will not be affected much by the runners will to grow 4mm when the flange
only has grown 1-2mm, the runners will hopefully take the beating without
cracking to often.

Since the cylinderhead will grow with temperature too the flange and the
head will hopefully grow about the same amount.


Jörgen

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