AAN intake manifold

[|Maku|]

Hy guys!

A few weeks ago my S4 AAN manifold was welded and polished. After the job was done, some local guys said that its not a good idea to polish intake manifold because then air and fuel wouldnt mix good enough. I polished only those egdes that go into cylinder head, so that there wouldnt be any obstacles.

What do you specialists think about it?

Greetings, Marko!

[Keeper of The Kitten]

I have heard this said about normally aspirated (not turbo) engines, it is true that a rougher surface promotes better mixing. This is true for a carburettor.

...but the Audi is a turbocharged engine and with fuel injectors that are quite near to the cylinder head, so I think it is not a big problem.

Polishing in the exhaust is a good idea to reduce buildup of carbon.

__MDC__

[Greg_S]

It is recommended that a rough surface is left to help the air to mix better with the fuel. If you search the threads there were some good links on the subject

[SteveH]

Only the inlet ports into the head need to be left with a rough surface. This helps to prevent fuel droplets pooling on the port walls. As already mentioned, it will not be an issue in the inlet manifold as there is no fuel in the airflow at this point. In fact, a smooth surface on the inside of the inlet manifold should help airflow.

[volcano rs]

you hit the nail on the head steveh great minds think alike .why does air need to have turbalance in the manifold when it hasn't mixed anything yet ? only the inlets ports have to be slightly rough .

[Keeper of The Kitten]

Exactly what I was saying! With carburettor type engines the intake is "wet" along it's whole length, whereas the system we have puts the injectors at the head ports - so the whole intake runs "dry"

__MDC__