I've just received my short Zetec inlet manifold, (Ebay purchase). It matches the head perfectly and the quality of the casting is very good apart from some small 'lips' on the ducts which I will easily remove. However I am wondering if there is any benefit to be gained by polishing the ducts? They are currently 'as cast'.


Cheers Mick

The inlet ports should not be mirror smooth and should be rough. If they are smooth i believe that the fuel will condense onto the walls. Rought inlet ports will cause some turbulance to keep the fuel and air mixed.

Exhaust ports on the other hand can be as smooth as you like.

David

I think the shape and size of the ports is far more important than having a mirror finish on them.

When I used to tune my 2 stroke kart engines ,it was said that a reallly smooth finish can cause drag to the air flow , and a slightly rougher finish causes little eddies in the flow where it comes in contact with port wall with the result that the air is kind of flowing on air pockets rather than rubbing full on the port wall.

But it's all a bit of a 'black art' , and probably hard to prove either way , but my 1st comment about the shape and size still stands........


Until the next poster shoots me down in flames........

Yes, a little rough is best on inlet ports for the same reasons that a golf ball with dimples travels further than a smooth one,but don,t ask me why. Completely agree with shape and size.Try to match the ports in the head with the inlet and outlet manifolds as best you can, this can only help with airflow.Thats also my experience from tuning two stroke engines many moons ago.

Rough surface helps prevent the boundry layer seperating and aids laminar flow.

If you really want to get into the "black arts" of porting look here:

http://mototuneusa.com/think_fast_intake_porting.htm

Interesting read...but..!?... hows do you go about making a standard port smaller! Its a lot easier to take material away than it is to put back!

Andy

Used something called 'Devcon' aluminium filler ,have used it to make the transfer ports in a 2 stroke barral smaller , it never fell out!!

Thanks for the replies

Knobbly it is then

Mick