I think the solder will stick to pretty much any steel that cranks would be made of as long as it is shiny clean. Yes it would be heavier than epoxy, but not a lot more than steel, which it should be if machined correctly in the first place. I heard throttling may improve, but overall speed may not, by too much. I have done the solder thing, and radiused the back of the window, and sharpened the edges, and only got 200 and 300 rpm extra in unpiped motors. Still it is better than nothing, if it idles, and ramps up better.