It depends on what you use to do it with. I was using a 1" drum sander hooked up to a pneumatic dremmel. Took a couple of minutes to do a rough grind, then went with a lighter grit to finish it up. Then polish it. I don't know what pengaru used, but probally something similar.

looks good man!!! https://www.nopistons.com/forums/pub...DIR#>/wink.png

Looks great.. https://www.nopistons.com/forums/pub...#>/biggrin.png



Just as a precaution for those who will do this, be careful about removing material where the throttle plates seat on the runner. and when polishing make sure you don't remove the black or grey (I’ve seen both) paint looking stuff where the throttle plates sit it you have any at all or you will have a leak around the plates that can cause you somemajor idle issues...

yeah I stay off the periphery of the plates, just everything before em.

I don't know, the project was done over a few days since I had to take a break to have the holes filled @ the welder. I used a plain old dremel with sanding drum and flapper wheel bits. Then after thats finished it gets attacked with some fine grit wet/dry sandpaper, sanding parallel to the direction of air flow. This is necessary IMO because the rotary tools remoe material by grinding perpendicular to the direction of airflow, which is not exactly the surface finish you want here. I don't do any further polishing, after the wet/dry paper it looks pretty good... but you don't know how hard it is to sand cast aluminum in a small closed space using your fingers and a small piece of sandpaper til you try it. Fingers were sore for a few days following that one.

my hands got so tired doing my manifolds https://www.nopistons.com/forums/pub...IR#>/wacko.png