Maldo

this is from KB web site


Hypereutectic -vs- Forged Pistons


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.

crashbox455

Maldo beat me to it.

i can't say that i know anything for sure, but i'm impressed enough with the tech articles on KB's website that i'd be comfortable with letting them choose my pistons for me. i suggest you all take a look.

basically, if John Irb thinks it'll do, i'll take his word for it.

prisoner881

If I were doing this for money reasons I would agree with you, but I'm not. If forged were the best way to go, I'd go with it regardless of cost. As you stated, considering the total motor costs, forged vs. cast doesn't change the cash that much. However, I'm looking at hyper pistons because they may offer advantages in less blowby and oil consumption. Or, you might say that I'm trying to not consider forged because of the disadvantage of requiring extra piston to wall clearance.

Someone already posted the contents of the KB piston website article on hyper pistons, and it lays out a great deal of the information on why I'm looking at them. Of course, I don't consider KB to be entirely -- ahem -- objective in this matter because they're one of the primary makers of hyper pistons. Just as I would expect them to suggest hyper pistons, I'd expect Speed-Pro, TRW, and so forth to suggest only forged pistons because that's what they're pushing. Only here can I get some (hopefully) objective responses to my question.

prisoner881

This is my thinking as well. I thought, which would be stronger? A purpose-built cast hyper piston, designed to handle 600hp turbo applications, or an off-the-shelf generic forged piston? Costs for the super-duper cast piston might well exceed the cost of a generic forged piston, so it's not cash savings I'm after. In a word, it's convenience. I don't want to be adding a quart of oil every 2000 miles, it's as simple as that.

EddieP

Actually, KB makes forged pistons also... just like Speed-Pro/TRW produce cast hyper pistons.

jonaddis84

Soooo...the twin turboes whining and blow off valve arent signs of a beast under the hood?

prisoner881

Heh heh...I like the way you think.

However, you've touched on another reason why I'm going with turbos as opposed to just a regular centrifugal blower. You can hear a blower car idling a mile away, even with the "quiet" gears on some blowers. I've sat next to really radical turbo Buick GN's and, until they get on the loud pedal, you never hear the hair dryers. Sure, if somebody powerbrakes you'll hear 'em spooling up, but that's unavoidable. I just want a motor that idles smoothly, is as maintenance-free a stock engine, gets good gas mileage when I drive it sanely, but has gobs of Ford-eating horsepower under the hood when I ask for it. Oh, and I don't want to refill a bottle, either.

That has turbos written all over it. Besides, with me being the engineering type, I have a thing for mechanically elegant designs. Turbos are more efficient than blowers, and that appeals to me. Anyone can bolt on a blower, but turbo cars are a rare and special thing when it comes to V8 horsepower these days.

prisoner881

Yeah, but KB's Silv-o-lite line is their premiere line, and I expect them to push them.

jonaddis84

Good points. I just thought it sounded funny at first, I understand though. Someday Id like a set (or maybe a single) or turboes blowin my LT1. Until then NA+N20 is all for me.

Another point that should be addressed. I just heard from a local engine builder round here that there are "two" different types of Forged pistons.

1. West coast
2. East coast

he said, for what reason I forget, that the East coast is a premier piston (wiseco, TRW, and one other). reason being is you can run a much tighter PTW clearance, I think he said almost .07" or maybe a little more than the "west coast" slugs. He spoke that the way to tell the difference is the color of the aluminum, the east coast are a much more dull gray than the more shiny west coast.

Anyone else heard this before?

BIGBADBOWTIE

Just putting this out there. I am in the boat with Damon.Kb hyper slugs in a flat top 355 solid roller motor. I turn it 7000 rpm on a 150 shot of go fast gas. Runs like a champ.

rskrause

I was just yesterday taking a look at my new JE "blower/nitrous" pistons before bolting things together. The instruction sheet said something to the effect "these pistons are made from a 2618 aluminum alloy that contains no silicon" (maybe I am not getting the number right). Hmmm..........

Rich Krause

nosfed

prisoner881

Doesn't this sound like some sort of misprint? I'm no metallurgist, but I thought even forged components had some silicon in them.

Injuneer

See item #2 on the JE 2618 instruction page:

http://www.jepistons.com/pdf/piston_instrc2618.pdf

On the other hand, if you look up the specs for 2618:

BIGBADBOWTIE

Nice hotrod Fred.... :-) Very nice.

back to the regular broadcast.