Piston choice: hyper or forged???

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360duster

360duster

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Hi Guys,

i have to choose which Pistons i use in my engine.

Specs: 408 SB, 75 % street driven in a 68`Valiant, target is 400-450 HP, no nitrous use planned, max engine speed 6000 rpm. Compression will be around 10:1 with dished Pistons and magnum heads.

So which Piston would you use? Hypereutectic or Forged for this build?

Ok, the hypers are cheaper. And i´m a little concerned about the bigger clearance forged pistons need, does it create a big noise?

Otherwise the forged ones are stronger - better for future upgrades?

How much horsepower can a hypereutectic Piston handle?

Maybe you can give me some information about the pros and the cons, thank you!

regards

Michael
 
I run forged TRW pistons in my 340, been told forged is the only way to go.
 
I would go forged for alittle more $$, the added clearance isn't really an issue, you might have a slight "gurggling" when cold, but thats music to your ears knowing you have strong pistons, & if you ever decide to juice it, your good to go, the HP limit on forged pistons is way up there, WAY up there, lets just say they will laugh at 600 HP, i'm sure you'll never see those #s.
 
Yeah, I'd agree with JoeDust here.....unless the money is super tight. Plus, if it's truly a 75/25% street to strip ratio.....that's actually quite a bit of racing! I've got TRW's in my 340.....it's comforting to know they're bulletproof.
 
Are you running a cast or forged crank? Hypers with the cast crank on a hydraulic cam mostly street motor should be fine.

Forged pistons are stronger because the aluminum is more dense and have a better grain pattern in the metal. Hypereutectics are a high-silicon alloy cast piston. This makes them stronger than an OEM type cast, but they are cast nonetheless.
 
I think I heard that hypers are stronger yet more brittle than most cast pistons......
 
No hypers in a 4" engine. The piston speeds are too fast for them to live well over 5Krpm. I just got a kit with SRP forged, dished (flat tops available). The kit is for under 500hp, and was under $1300 shipped. (Not balanced..)
 
Forged or cast, too many broken hyper's for me.

I'd rather have a stock piston, than a hyper.

I have a set of old .030 TRW's that have outlasted two 318 bores now.....
 
I wouldn't even consider using a cast (Hyper) piston since you plan on spinning it to 6k. The piston speed on a 4" stroke engine spinning 6000 rpm is about the same as a 340 stroke engine spinning 7500 rpm. That's way too much for cast pistons.
 
cudavert said:
I think I heard that hypers are stronger yet more brittle than most cast pistons......
Click to expand...

Yup, this is true, the key to the hypers is it doesn't take on heat, so it doesn't exspand much at all, so you run tighter clearances, but the heat has to go somewhere, so it targets the top ring, thats why it needs a looser end gap, the downside to a hyper is its brittleness, its damn near like glass, they don't just break under hard conditions like cast or forged, they "explode" in pieces, i've run hypers in a .060' 360 with a tight wall clearance, i rapped it many times over 6K with no issues, but i like nitrous, hypers don't, a cast piston will take it more then hypers will.

Go with forged & don't look back, they will outlast your kids lol. Most of us older dudes remember back in the 70s 80s when many 446s were running around with good ol'e TRW power forged pistons, they were like the energizer, they kept going & going & going, thats all we had back then, & the engine wore out before the pistons did.
 
Thanks at all for the input!

a little more info about the engine as c130 chief mentioned: cast crank 4", hydraulic cam, nothing exotic, really a budget build because i need so much other parts to convert the car from /6 to SB.

But you guys are right, if i ever decide to get better cylinder heads or maybe nitrous then the forged pistons are the way to go.

@cudavert: you are right, 75/25 is a lot of racing, maybe it´s only 85/15. The car is not my daily driver so it won´t get much miles at street, and so the race part is higher.

Thanks again, i appreciate your help very much.

regards Michael

Kopie von IMG_8323.jpg
 
I'm not understanding.....sorry to post on your thread. I do understand that forged are stronger than the hyper's but why are there so many stroker kits with hyper pistons? Are they selling inferior parts that will not last in a stroker application?
 
63dartman said:
I'm not understanding.....sorry to post on your thread. I do understand that forged are stronger than the hyper's but why are there so many stroker kits with hyper pistons? Are they selling inferior parts that will not last in a stroker application?
Click to expand...

I wouldn't characterize hyper pistons as inferior. If you do a google search for forged vs. hyper you'll find all kinds of debate on the subject. Your choice needs to be based on facts and intended use.

Here's KB's explanation: http://kb-silvolite.com/article.php?action=read&A_id=5
 
63dartman said:
I'm not understanding.....sorry to post on your thread. I do understand that forged are stronger than the hyper's but why are there so many stroker kits with hyper pistons? Are they selling inferior parts that will not last in a stroker application?
Click to expand...

Cast are the weakest. They are light and can take some abuse, but will flex and break in a modrate build. plus, most designs are stock based and simply not that good for a modern build. Hypereutectics are a cast piston. But they are a much different casting process and material. So they are very light, and stronger than a std cast design. But, in that strength are a couple caveats: They are harder, like tool steel vs iron. That means stronger, but much more brittle. They are also much more thermally stable. Meaning they dont expand much when warm so you run the piston to wall clearances fairly tight. Last, they are designed to reflect the heat of combustion back into the chamber. That means in some designs the top ring gets hotter and needs to have a wider ring end gap to avoid the ring ends butting and damage. Forged are the top of the line. But again, different materials and designs. There are some that are very heavy, some that are old designs, and some that are modern in material and design, and pretty light. As each piston gets stronger, it can cope better with the stresses of life in a cylinder. The cast piston will pull apart in a 4" arm engine because it's no strong enough to withstand the speeds above about 4K. A hyper piston will also fail this way if the rpms is high enough. Mathematically that's around 5500. the kits that have them are cheaper, and the hypers are cheaper pistons... You ALWAYS get what you pay for. Or dont get what you save. So for anything with a 3.79 stroke or larger, I wont use a hyper. I do use hypers all the time in factory stroke engines with very good results.
 
63dartman said:
I'm not understanding.....sorry to post on your thread. I do understand that forged are stronger than the hyper's but why are there so many stroker kits with hyper pistons? Are they selling inferior parts that will not last in a stroker application?
Click to expand...

Good question dartman, I'll see if I can answer it.
Whether we're talking about steel or aluminum the process of forging is essentailly the same. Raw molten material, lets talk aluminum, is poored into blocks then as they're cooling large rollers or presses or even hammers form the material into solid dense blocks. The forging process aligns the grain structure of the aluminum all in the same direction and this alignment makes for a very strong product. At this point the piston is machined out of the block of material and viola ya got a forged piston. Hyper/cast pistons are machined out of the molten material after it's been poored into rough castings and allowed to cool and since there was no forging involved the grain structure of the aluminum will be in all directions therefore not as strong. Forgings are also heavier because the material is more dense, molecules are packed tighter together, than castings.

Terry
 
demon seed said:
Good question dartman, I'll see if I can answer it.
Whether we're talking about steel or aluminum the process of forging is essentailly the same. Raw molten material, lets talk aluminum, is poored into blocks then as they're cooling large rollers or presses or even hammers form the material into solid dense blocks. The forging process aligns the grain structure of the aluminum all in the same direction and this alignment makes for a very strong product. At this point the piston is machined out of the block of material and viola ya got a forged piston. Hyper/cast pistons are machined out of the molten material after it's been poored into rough castings and allowed to cool and since there was no forging involved the grain structure of the aluminum will be in all directions therefore not as strong. Forgings are also heavier because the material is more dense, molecules are packed tighter together, than castings.

Terry
Click to expand...

Very good explanation, simple and not too many details.:supz:
 
Thanks alot for all the info. I'm just running a stock stroke 360 zero decked for speed pro hyper's with clearwater magnum heads. I was worried I may have problems with my piston selection. Of course it's all tore down right now due to operator error on the connecting rods......that's another story:) I am going to assume that my pistons should be fine for my intended use. I only want to rev to 5500-5800 5 or 6 times a year at the track.
 
Hi Guys, one more question:

i read in the book "how to build big inch stroker SB´s" that the Pistons (for example the KB 356) will stick out of the deck a little and will require machining to clear a closed chamber head. This build was with a block that was not the standard deck height, but i calculated his measurements with my block and think the same will happen with my production 360 block. Did anybody use the KB 356 or IC 745 Pistons in a similar build and can tell me if it´s true that the pistons stick out of the hole? Want to use magnum heads, dont want to run into trouble, machining the pistons will require new balancing........can you help me again???

regards Michael
 
I turn 6500 with KB hypers in a 410 4spd valiant.

I turned 7200 or so with a 340 too w/KB hypers as well.

they work great.

A newer 'quality' forged piston will be lighter than you're typical hyper, unlike old trw forgies that weigh a ton as stock replacements.

If you are gonna hit it hard with nitrous or push past 7500rpm 550hp Then forged is a good idea, but under this hypers due just fine.
 
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