Port and polish - how smooth is too smooth (mating surfaces)

[ragajungle]

Hey all. I am working on a mileage monster - I am porting and polishing and gasket matching the 2.0L SPI for my Merc Tracer. I have all the intake and exhaust ports practically so I can see myself in them. I also worked to clean the mating surfaces up and someone pointed out that

"If the head mating surfaces are too smooth it could compromise the seal"

Is this accurate? I have always been under the impression that cleaner and smoother is better.

Any advice is helpful.

-Mike

 

[Rick]

Found this...

http://www.underhoodservice.com/Article/84847/component_connection_manifold_destiny.aspx

According to one aftermarket gasket manufacturer, the recommended surface finish for the intake manifold and cylinder head mating surfaces should ideally be 30 to 60 microinches Ra (Roughness Average). Another gasket manufacturer said anything from 20 to 80 Ra should be good enough.

Unlike the super-smooth surface finish that’s usually required for late-model MLS head gaskets (20 Ra or less), the surface finish for most intake manifold gaskets isn’t as critical. Even so, it must be smooth, flat and clean, with minimal pitting and waviness.

 

[ragajungle]

Thanks Rick. Good read, I long suspected GM was using orange bull-sh*t and not actual coolant lol... now I will just have to figure out how to determine "microinches"

 

[rookieshooter]

It's been years since i ported and polished heads. But the school (Old School BTW) was not to make a mirror finish on the intake ports, reason. The gas droplets atomized better if they came in contact with a more rough surface then mirror.
I'm talking standard porting sanding drums.