I have over 17 grind bits & stones and 6 tools I've dedicated to just porting. I have over 30 bits that I use for polishing. I can port the exhaust manifold very well, but with the lenght of almost all the flanges I can't get the very peaks that I would love to hit. Those are the only flaws that come with porting them yourself. Of course you would get some gains, but of course the Extrude Hone is the best for flow. But I agree with you about shelling out $500 for the process. I would suggest just doing the work yourself on the exhaust manifolds. I wanted to see if I could find someone looking to get ride of them, but the chances of that are few & far between.