RE: head gasket, any mods while I am in there?

["Graydon D. Stuckey" <graydon@apollo.kettering.edu>]

On Sun, 7 Jun 1998, Jeffrey J. Goggin wrote:

> >In message <Pine.SOL.3.91.980606174629.1963A-100000@apollo> "Graydon D.
> Stuckey" writes:
> >> ...  but I found out that the exh ports were _much_ smaller
> >> than the gasket so I gasket matched the exh ports.
> >
> >BZZZT!
> >
> >They're meant to be smaller.  The lip is quite deliberate.

I won't presume to second guess the Audi engineers, but I really doubt it 
because there's very little consistency to the geometry in how the ports 
mismatch the gaskets.   It looks to me like a simple manufacturing 
tolerance issue. Not too terrible, but certainly not something I'd want 
to have on my car.

> Not necessarily ... I'm in the process of preparing a head myself and while
> the exhaust ports are also smaller than the manifold gasket, the manifold
> gasket is itself smaller than the manifold. As such, enlarging the port to

Hmm, I didn't find that with my OEM one-piece exh manifold.   The ports 
on the manifold were alaso smaller than the gasket, and approximately the 
same shape as the port in the head.   That is one reason why I don't 
think the factory was concerned with any anti-reversionary lip.

> match the gasket still preserves the anti-reversionary lip ... of course,
> this can vary from head-to-head & manifold-to-manifold.  That said, getting

The more I work on Audis, the more I think that Audi has alot of 
variation in their manufacturing process.   I guess as long as they can 
build cars, and their spare parts fit, then that's OK though.

> task and much of any potential gains to be had can be lost if this detail
> isn't addressed ... but Graydon already knows that and being Mr. Meticulous,
> I'm sure he's addressed this as well.  :^)

Your confidence is amazing! :-)   To expound further on my original 
statement, I ported the exh ports in the head out to within 0.5mm of the 
gasket, and I will open the exh manifold up to the gasket, so I'll have a 
0.5mm antireversionary step all around the port.

Does anyone know any design guidelines for how big that step should be?  
My guess, based on my experience with flow distribution in a tube leads 
me to the .5mm step since the flow out there will be very low, and that 
may be the reason that the reverse wave travels along the wall.  Any 
ideas or thoughts?

Later,
Graydon D. Stuckey

"There's alot more to Jazz than just wrong notes"