Umm... if you mean to get to 250hp a/m then you would need higher not lower compression pistons, but that would be just plain stupid because squeezing that much power out of D16Z6 is pretty damn hard, the stock compression is great for turboing (only like 9:1 if i remember right), but you would want to get forged pistons at the same compression, and forged rods etc, block guard... blah blah blah...

If you want to turbo, thats your best option, but personally, I'd go for an engine swap, either a B18C if you can afford it, or a B18B. And then work from there. I have a D16Z6... and that's what i plan to do.