Turbo manifold design.

[justin ivan]

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.
Justin Ivan


>From: Jörgen Karlsson <jurg at pp.sbbs.se>
>Reply-To: diy_efi at diy-efi.org
>To: <diy_efi at diy-efi.org>
>Subject: RE: Turbo manifold design.
>Date: Wed, 10 Jan 2001 13:25:30 +0100
>
>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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