Quick Head Port & Polish Question

[malone]

Should I leave the polishing to exhaust ports only? For TDIs, I believe polishing intake ports are acceptable as long as the swirl port design is left alone, but for TDs I'm not so sure. I realize that in a IDI head fuel is injected outside of the intake air stream, but I would assume that air swirl/tumble is still important for the later mixture with low pressure fuel. Comments?

[935racer]

With the TD's I would think its best to do both, I think the intake would benefit from a good polish. I'll match them all at least mark.

[SMOKEYDUB]

The turbo will make it tumble :wink:

[Northboundtrain]

I'll match them all at least mark.

Do you mind explaining what this means?  I'm trying to learn all I can about porting and polishing.  Thanks

[Baxter]

Match porting is where you match manifold to the ports on the head.
Simplest way to do it is to colour the area around the port with a black marker.
Place the gasket over the studs and using a scribe then mark out all the metal protruding past the gasket.
Then, with a die grinder remove metal till the gasket matches the head.
repeat for all ports on head and manifold.
Basically your removing steps that could impede the free flow of gas in or out of the engine.

[Northboundtrain]

Thanks, I was wondering how that was done.  Does the gasket ever compress and squeeze out into the port?  Is it worth polishing the manifolds too?

[Baxter]

Yep, Manifolds too.
Don't go mad, I generally just give stuff a quick fettle while the heads off.
Im no engine modifier by a long shot, just a general repair garage.
Not dealing with modifying heads daily I can't tell where the weak spots are, you gotta be careful porting heads as you can grind through into the water jacket or oil ways... not good!
Just take out rough edges, casting marks and blemishes and a quick tidy up is enough for me.
Another trick is to "waste" the valve guides to improve flow, some people grind the whole lot off that protrudes into the port, okay on a rarely used and regularly stripped race engine, not good for a daily drive!