I think forged pistons are way over used. For some reason people think the first thing you have to do when you start a rebuild is get TRW forged pistons. The factory used cast pistons almost exclusively until recent years. Cast pistons are better than a forged piston for a street car. A cast piston is more stable with regards to thermal expansion than a forged piston. The cast piston will run quieter due to reduced piston rock and the ring seal will last longer due to a closer piston to cylinder wall clearance. A cast piston is lighter than a TRW forged piston and will be easier on the crank and rods and will make more power considering the rest of the combo being equal. A cast piston in most street strip machines will run trouble free for many years and would be a better choice than a forged piston. A factory replacement cast piston will work just fine in most street strip applications. The hypereutectic piston was developed to increase the strength of the standard cast pistons and still run a tight clearance. Basically the hypereutectic process involves adding more silicon to the alloy material and the casting process is changed some what. This makes the thermal stability even better and the piston is harder which makes them more resistant to wear and scuff. One of the properties of the hypereutectic piston is they retain more heat in the top of the piston than a standard cast piston. This is the reason that the top ring gap is critical for this type of piston. This is actually good from a power out put view point as retaining the heat you make more power. You will have a problem with any piston if you gap the rings too tight. Beck Racing Engines here in Phoenix use the KB Hypereutectic pistons in all their high performance crate engines up to 500 HP and they guarantee their engines too. The Big three are now using the Hypereutectic piston in their factory production vehicles more and more. I have seen these cars work fine with small amounts of boost and N20. Now with that said the cast pistons do have their limitations. I do not recommend using a standard cast or hypereutectic cast piston in a forced induction or N20 application. Also if you plan on making over 500 HP and plan to do regular racing then step up to a forged piston. The aluminum alloys and forging processes have improved over the years to reduce thermal expansion and attain a closer piston to wall clearance, but they still require about twice the clearance of a cast piston. For forced induction, N20, or naturally aspirated high power machines you need a forged piston as the cast pistons do have their limitations. My main point is, in many applications it is a waste of money to use a forged piston in a street machine when a cast piston will do a better job and last longer.
Tim C
65 LeMans, 3550lb. D-ports and a flat tappet cam, 10.90@121
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Tim Corcoran
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