#3---- Hypereutectic or Forged? | 1/27/2012 |
Hypereutectic -vs- Forged Pistons
(Reprinted from KB-Silvolite website http://www.kb-silvolite.com)
Hypereutectic pistons are used in some original equipment engines. They are favored because of reduced scuffing, improved power, fuel economy and emissions.
Hypereutectic 390 refers to a unique aluminum piston alloy that contains dissolved and free silicon. The material can be T6 heat treated to high strength and stiffness. Non-heat treated 390 hypereutectic alloy aluminum has slightly less strength than conventionally cast F-132 aluminum.
With this in mind, we caution the reader about the use of non-T6 heat treated O.E. design hypereutectic pistons for high performance. Silvolite and others do make replacement-type hypereutectic pistons that are worthwhile for stock replacement applications. Original equipment design is almost never suitable for performance applications.
The KB line of hypereutectic pistons were designed around the 390 alloy. The result is a high performance part intended to give the performance engine builder access to the latest in piston technology.
Forgings have long been the mainstay of the performance business and did well in the big cubic inch engines of the 60’s. Now, with focus on peak cylinder pressure timing, ring sealing dynamics, cylinder air tumble and swirl, combustion chamber science, and extended RPM ranges, we need to consider some new piston options.
The KB T6 hypereutectics are considerably different than the forgings. The KB pistons have shown improvement in power, fuel economy, cylinder sealing, service life, and cost effectiveness. The reduced thermal expansion rate allows the piston to be run with reduced clearance. A tight piston is less likely to rock, make noise, and burn oil. A rocking piston wears rings and increases blow-bye. The close fit of the KB piston allows the piston rings to truly seal, minimizing blow-by.
The design flexibility enjoyed by the KB series of pistons has an advantage over present day forging practices. The die for a forged piston must be designed so it can be easily removed. This limitation makes it difficult to make a light weight piston without sacrificing strength.
The KB pistons' utilization of the permanent mold with multiple die parts allows undercut areas above the pin hole and material distribution in the skirt area that stiffen the entire piston unit. The forged piston requires thick skirts to achieve comparable piston rigidity. A rigid piston rocks less in the cylinder and improves ring seal.
The forged pistons' thick skirts add weight. The design of KB pistons gives us the option to build the lightest pistons on the market.
Some current KB pistons are not super light for several reasons. If the piston is to be used as a stock replacement, more than a 10% weight reduction will mandate that the engine be re-balanced.
Common sense suggests that the introduction of a new product be extra strong at the initial release. As the product becomes accepted, weight reductions are scheduled as regular product upgrades, as justified with actual race testing.
There will always be a market for custom forged pistons. Small runs of forgings are more economical than small runs of permanent mold pistons because of the complexity of permanent mold tooling. Where quantities justify, expect to see future KB pistons developed that are lighter and stronger than anything else on the market. Machined head profiles are easily changed with our CNC equipment so we will stay current with new cylinder head developments. Volume production is expected to keep the price reasonable.
Our pricing policy has given the impression to some that we are building an economy, or in between, piston. The truth is, we are striving to build the "State of the Art" piston that is best, regardless of price. Reasonable pricing is just an added benefit.
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