Turbo manifold design.

[Seth]

Corky Bell agrees with the separate flange theory, if that matters to
you.  He shows hand fabricated manifolds manufactured with one piece
flanges. Then the flanges are cut with a hacksaw between each individual
port to reduce cracking. 

-Seth

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.
> 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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