Just the run of the mill burr's available at the hardware and parts store. I really wish I had a set that were longer. I just have the ball, cylinder and pine cone shaped ones. A friend of mine that does professional porting (Nick for GH) says I need to get an egg shaped one as it's what he uses most, and also showed me a set that would certainly be nice to have but the limited amount I'd use them I couldn't justify purchasing. I'm going to make him cringe again when I lap the valves again, lol.
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Rebuilding an OHC Pontiac 250 with EFI and a Turbo