Gains from port & polish
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Nebraska_e28
- Beamter
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Gains from port & polish
How much is there to be gained from port matching & a mild polishing on a stock b34 running 12psi? Is it worth the effort?
Things like boundary layers in airflow make simple statements such as "smoother is better" untrue. Turbulence in the boundary layer actually results in more air making it into the cylinder than a purely smooth surface does. You also get better air and fuel mixing with non-polished intake port surfaces.
You can polish the exhaust ports if you want I suppose, but they'll carbon over pretty quick so I don't see the point there.
Porting has more gains than zero if done correctly and competently. Whether it's "worth it" is kind of subjective. The m30 isn't particularly starved for airflow in the mid-range, but runs out of ability to feed the engine as the revs climb. You'd need to change the cam at least along with that porting to get the full benefit.
You can polish the exhaust ports if you want I suppose, but they'll carbon over pretty quick so I don't see the point there.
Porting has more gains than zero if done correctly and competently. Whether it's "worth it" is kind of subjective. The m30 isn't particularly starved for airflow in the mid-range, but runs out of ability to feed the engine as the revs climb. You'd need to change the cam at least along with that porting to get the full benefit.
Polishing 
You want some turbulence in the intake to help mix the A/F, exhaust will carbon up as already stated.-
Coldswede
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In general, manufacturers do a good job on port shaping and airflow numbers, it is very efficient way to increase the engines power for a one time engineering cost and little if any manufacturer cost. BMW seems to do a good job on their porting.
As Jeremy said, laminar airflow is much more "slippery" than any polished aluminum and some turbulence is good for fuel/air mixing and keeping the mixture from wetting the port walls too much.
Effective porting can be done but it is time consuming and requires good record keeping and a flow bench. There is someone on the board who is working on this project who has the tools and expertise.
I'm not sure anyone has ever proven port polishing to be beneficial.
As Jeremy said, laminar airflow is much more "slippery" than any polished aluminum and some turbulence is good for fuel/air mixing and keeping the mixture from wetting the port walls too much.
Effective porting can be done but it is time consuming and requires good record keeping and a flow bench. There is someone on the board who is working on this project who has the tools and expertise.
I'm not sure anyone has ever proven port polishing to be beneficial.