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

[Kevin Ford <cheryl_ford@bc.sympatico.ca>]

Graydon D. Stuckey wrote:
> 
> 
> 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
> 

The "antireversionary step" from exhaust port to exhaust manifold is 
benifical in normally aspirated engines, (preventing some of the 
exhaust pulse echo from entering the port), but with exhaust manifold 
pressure reaching 25 psi or more in a turbo engine, the pressure 
difference in the pulse is much lower. I think the slight benefit of 
the antireversionary step is outwayed by the gain in flow by port 
matching the exhaust port.

Generally, turbo engines are ported with gaining the most possible 
flow, above all other concerns.

Kevin Ford
Chase, B.C., Canada
email: cheryl_ford@bc.sympatico.ca