Polish & Porting Heads

[mtnfir]

Another question ya'll. Now that my motor is completely disassembled for a top end rebuild, should I have my heads ported and polished or flowed? I'm guessing that they are one in the same, but is it really important? If it is, how much does it typically cost, and what is the typical power gain or benefit in general?
thanks
Carl

[jluetjen]

What model engine are we talking about? What's the camshaft that's going to be used in the finished project?

As far as the typical power gain and benefit, you can do a search on "porting" and read up for a couple of days. My conclusion after researching the subject and analysing a lot of data is that in general it won't get you anything unless everything else is maxed on out. To put it differently, if airflow through the ports is what's holding the engine back, you'll gain HP by porting and polishing. If there are other restrictions or constraints (like airflow meters, mild cams, etc) which are limiting the fair flow, improving the porting won't get you much. Not to mention, compared to your average Detroit engine (pre-DOHC, 4 valve designs), a 911 engine is ported really well. The ports are straight, have no obstructions and in general have well designed cross sections. While it's not impossible to find some gains, in general they'll be small and hard to achieve.

[Steve@Rennsport]

Carl:

Stock Carrera heads support power levels to 330+ HP so they will not be a restriction for you,....