Here's a bit of info taken directly from the Federal Mogul site.
I have a set of their Speed Pro Hypereutectics (H345NP30) in my 355 Chevy. And will definately be using a 100 shot that will be controlled to only come in at WOT where there is enough fuel to help prevent the dreaded nitrous-lean condition.
(Casting differences from std and hypers are highlighted in
italics) The hypers have silicon imbedded in them to help deal with heat and pressures.
Speed-Pro’s cast hypereutectic material is a relative newcomer to the performance market, and has several attractive features. Our hypereutectic pistons operate perfectly with standard ring end gaps and have conventional ring land locations. When compared to traditional cast pistons, which are not designed for performance use, the hypereutectics are significantly stronger, particularly in the highly loaded ring land, skirt and pin bore areas.
Our FM244 Alloy contains 16.5 percent silicon and has excellent tensile and fatigue strength. This material’s improved thermal characteristics, its greater hardness and the increased resistance to scuffing permit tight bore clearances which help minimize noise on cold engine start up. This quiet operation, along with a lower cost are the primary advantages over a comparable forged piston. These pistons are an excellent choice for street performance, “claimer” oval track engines and bracket racing use. They will also work well in moderate supercharged applications and are suitable for towing and marine use.
Here's the link...There is also a section near the bottom to help youdecide which type of piston is right for your application.
http://www.federal-mogul.com/cda/content/front/0,2194,2442_2905_6800,00.html
