Keith Black Hypereutectic 383 Pistons (Part Number KB-100) - $24.65 each SRP Forged 383 Pistons - $56.63 each TRW Forged 383 Flat Top 2VR Pistons - $41.00 each Going on a 383 Superram Daily Driver car.....with a max of 150HP shot of nitrous. I was orginally going to go with the SRP pistons...but read this in a book. "one advantage of the cast piston over the forged piston is that it requires less piston to bore clearance and in a high performance street engine, for instance, this will mean quieter operation, better ring seal (less piston rock) and frequently more power beacuse of it. High-performance street engines work from idle through to 5500 rpm much more than they do from 5500rpm to 6500rpm. If an engine is not going to be constantly turning high rpm cast pistons are the better option. " Its an old book, so maybe pistons now a days are different....which is what I wanted to find out. I thought hyper pistons would be a good middle ground.....but if what is said above is not really true, or not true anymore, or not something to worry about...I'll get the forged pistons...probably go ahead and get the SRPs instead of TRW. Any input please.

hypers and nos do NOT mix, never use them unless its just a mild engine, forsure go with the SRP's there a excellent piston and will handle the spray no problem

what about the whole piston to bore clearance blah blah. Just ignore it and go with the forged? Definetly the max rpm i'll be hitting is 6500 rpm.

Hypereutectic pistons are fine for 150HP shot of the juice.

Forged pistons are only needed for a 450+HP motor, plus a 250HP shot of nitrous.

The term hypereutectic means that the casting of the piston has a higher level of silicon in it.

What we call a regular cast piston is a eutectic. The 'hyper' part just means there's more than 11% of silicon in the piston.

By using higher amounts of silicon in the casting, the piston has better thermal characteristics than that of a regular cast piston. IE, it's more resistant to melting from heat. Kinda like a forged piston.

A forged piston is just that, it's heated to a very high temp after it is cast. This causes the aluminum to become very hard. They have the highest level of heat resistance. That's due to there expanding ability.

Because of there ability to expand, you must allow more clearance so they don't seize themselves to the cylinder walls as they heat up and get bigger. And they usually require more ring gap because of how small they become when they cool. Otherwise the ends of the rings would be touching at start-up, and that would be very very bad.

The piston rock is caused at start-up from the pistons being smaller, and having more room to move. Once the pistons warm up, and swell, then the clearance is smaller, and they sit tighter in the cylinders.

I think hypereutectic pistons got a bad name for the same reason that EFI did when it first came out.

A bunch of beer drinkin' old timers were sitting around sayin' "Why can't they just leave stuff alone? All this new stuff is confusing us. If it's confusing us, then it must be bad. So let's tell everyone how bad the new stuff is."

AJ

383 Block, Scat 9000 Crank, Eagle H rods, AFR 190 (maybe 195) heads, LT4 hot cam, SuperRam system, T56 tranny, 12bolt rear end with 3.73 or 3.42 gears, ~10.1 comp. and the 150hp max nitrous shot. Hyper pistons or forged pistons? Daily driven, want it to last as long as possible, taken to track every now and then.

You have that part mostly correct. "Hyper" means "above" or "over". So, a hypereutectic aluminum alloy has a silicon content that is "above" the eutectic point (the % at which the alloy will be liquid above a certain temp, or solid below that temp - no liquid & solid "slush", or two-phase mix). In metalurgy, that is illustrated in what is called a "phase diagram".

That isn't quite right. The silicon makes it stronger. Since it is stronger, it can maintain the same required minimum strength at a higher temp. (The temp at which melting occurs is irrelevant - by that time, you're dead. Liquid starts to form at the same temp for both materials, anyway.)

FWIW, what we call "cast" and "hypereutectic" are both made with a casting process; the methods have to vary slightly to keep the hypereutectic material molten so it will flow properly into the mold.


Way off. They are made out of a different alloy entirely. The material is forced into shape without being molten, which induces grain flow, which is a big factor in making them stronger. Rough machining, stress relief, and final machining follow. Other processes may be involved, depending upon the design.


They are stronger, due to the material and forging process, in the same way hypereutectics are (explained above).


Close. Because they will withstand more heat, they must be allowed to expand more.

Enough for now...

for a power adder i'd use forged everything

Forged definitely. I believe SpeedPro (I think) has a new forged piston out that does not expand as much with heat so it can be fitted to the bore tighter. Look in the Summit catalog. I believe thats where I read it. I have seen KB hypers last just fine in 500hp+ motors WITHOUT nitrous or supercharging. If you are going to do either of these I would definitely go forged.

Yeah I was wondering if there were any forged pistons that didnt expand as much. Not sure if they existed or not. I'll look at a few catalogs and see if i can find anything.

five7kid, excellent information! I think all the misnomers regarding Hyperuetectic vs forged pistons need to be revisited. I run KB Hyperuetectic pistons with a 100 shot of squeeze in a 400+ hp motor only and have not seen any unusual adverse affects. I'm not saying this is the very best scenario but on a buck to ET level I believe there a good choice. Some of us just don't have a John Force budget.

IMHO
Metalax

Where is AJ coming from? The rings don't butt together cold, that is the gap you have when you build the motor. The reason for larger ring gaps in todays schemes is that the extreme heat from nitrous will close the gap.
Forged pistons are more malible and absorb the shock of detonation that can happen easy with spray. Hyper pistons are strong and don't expand much, but they are brittle.
Short story
You want quite long lasting street car with minumum spray go hyper.
If your building a play car for a lot of strip abuse forged is the way go.

For that matter, "forged" pistons are initially cast as well, before they're forged. It's also possible to have a forged a piston with a hypereutectic alloy, but it's not common.

Holy crap old post! 2002! LOL

Use forged for any application using laughing gas. I can almost guarantee you'll lift the top ring land off the hypereutechtics after a number of decent length nitrous runs. The top ring will butt together and you'll have a piston that looks like the picture on the KB silvolite website under 'special clearance requirements'. If you push the limit on compression ratio I'd recommend the forged units, even without giggle juice.

Yes all the aluminum or steel is cast/melted it could then be poured in to a mold for a cast product or poured in to ingots/blanks that are then forged into shape.