Turbo manifold design.

[Jörgen Karlsson]

Berndt wrote:

> Jörgen Karlsson tapped away at the keyboard with:
>
> > The stock manifold has separate flanges, but since the manifold
> is pretty
> > strong it does not flex anyway.
>
> It should. That's how you cope with the different expansion.
> The stiffer the manifold, the greater the stress on the manifold
> attachment. The manifold should only be strong enough to contain the
> exhaust gases. :-)

I agree, but tell that to Audi.

> With an allow head and steel manifold, you automatically have to
> cope with different rates of expansion.

Where the thermal expansion of steel are about half of the thermal expansion
of aluminum, at least if my memory serves me right and the information
wasn't corrupted in the first place. Since the full lenght flange will
always be hotter then the head this is good, the problem occurs when it gets
more then twice as hot as the head. One calculation I did was that the
flange plate will grow 1.9mm in it's full length when it is at 350ºC,
compared to 20ºC.  The head should grow around 2mm if the area around the
exhaust ports stabilize at 200ºC. The tubing of the exhaust manifold on the
other hand will expand 4.2mm compared to room temperature, that is at 700ºC.
By checking the color of the stock manifold after a few miles at 150mph I
find that the temperature of the exhaust manifold is even higher then that.


> If each runner is
> individually-flanged, then the stress is reduced because the runner
> flexes individually. Only a small amount of stress results in each
> flange because it's fixed in at least two places.

On a common turbo manifold the runners cannot flex idividually, if they
could there wouldn't be much of a problem. All expansion adds up in this
case even if I have separate flanges. The difference as I see it is that the
studs has to take the force of 2mm of expansion at 700ºC, compared to 0.1mm
if I use one large flange. The relatively cool flange will keep the stress
of the studs.

Individual flanges are very easy to make, the problem is that I don't think
that it will work. It hasn't before and I don't think that it will now. The
big common flange is a few hours extra work for me.

I am more sure then ever about this

Jörgen

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