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On the ports how much of the "bump" on the floor can safely be removed before bad things happen. Should it just be smoothed or can you pretty much flatten it to the floor?
(Boy, I had to do some digging to find these pics.)Anyway, there is a good amount of material around the bottom of the SL6 valve guide, you can grind it flush to the roof of the port but doing that removes some important guide support, basically side to side valve stem support.
There are thin sections in that area so the trick is to work down the bump with-out working too much material off the back bowl wall or off the bottom of the two dips that run to either side of that guide bump. I tend to reduce the size of the bump without shortening the guide length more then .250, that takes the end of the guide to the same level as the shallow dip. I leave some slender side support or rased area right around the guide hole.
Well, here are the pics, click to get a bigger image. (bigger file size, about 70K)
DD
<[img scr="http://www.dutra.org/pictures/engine/parts/crossection-sm.jpg">
