FYI. I have listed on ebay, item number: 180502126237, one pair of 496 Mercruiser exhaust risers that I had sandblasted and then polished.

How much horsepower will thoses add?

Whatever you would like to hear!

where did you get that done and how much did it cost you if you don't mind me asking? I've got some as well.

I'm putting the 496 manifolds and risers on my Scarab. In buying the manifolds I ended up with extra risers. A friend sandblasted 4 pair and I gave him $60. I polished them myself. 220, 400, 600, 1000, 1200 and finally 1500 followed by polishing them with stainless steel rosin on a bench grinder. So most of the work is my own labor. The small dent that shows up in the pic is small and was there in the powdercoat too. I have another set that I haven't polished but has a bigger dent from being dropped by mt buddies friend. He paid me $300 for that set but I still have them.

I got mine back from the sandblaster today. I used a stainless steel polishing kit and buffed them with metal gloss compound, but they don't look anywhere near as good as yours.