In my opinion: polish the exhaust so carbon is less prone to stick to it, but dont polish the intake. Just leave a 'semi-rough' finnish. Some say this is good so "fuel doesn't fall out off suspension" but imo, thats nonsense. The reason why I leave it semi rough is the fact that it creates a small turbulent boundary layer sticking to the walls, leaving a larger laminair flow in the middle of the port. You allways get turbulence/eddies on the walls of the port which will disturb flow. If you can make those eddies smaller there will be less disturbance. When you're a race expert, and know *exactly* how the flow in the port flows, its different since you then might be able to make a very good port shape where there is hardly any turbulance in the first place. In those cases polishing will be good. In the DIY porting, leave a semi rough surface.

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P131, '65, B20B+M47. P131, '69, B20E+AW71L+LSD. (www.tinustechniek.tk)