Hypereutetic v Forged

I have used Keith Black Hypereutetic pistons at .010 over with 10/1 compression for the last 20 years or approximately 50,000 miles without using any Castrol Syntec 5-50 oil. They are better than cast and cheaper than forged. Good luck

I used K.B. for years, they are fine in a street application. Be aware,the top ring is gapped larger as it is closer to the top of the piston.

quote:

Originally posted by Horace Cope:
Needing to order a new set of pistons for my 351C and debating which is the best way to go.

Used forged pistons in my previous engine build with no problems. However I notice a lot of the suppliers, especially here in the UK, list about 5 types of Hypereutetic to about 1 type of forged.

Also notice the Hypereutetic are much more keenly priced so if I can save a bit of money without compromising the build I will.

Car will be fast street with no track use so are there any good reasons not to go with these hypereutetic pistons. Anybody had good or bad experiences with them

Types I'm looking at are Speedpro and KB.

Cheers
Horace

Hyper-eutectics are cast. For the detail-obsessed, 'eutectic' is the amount of proprietary additives -like silicon- the molten mix can dissolve. 'Hyper' simply means they added a bit more than that amount & mixed it in. There are also often steel struts inside to further control heat expansion. Their main advantage is less heat expansion= tighter clearances so less cold-start blow-by and better emissions numbers. Not as strong as forged so if you run high compression (10:! or more) or beat on the motor, you may have trouble making cast pistons live. "Fast street" means different things in different areas... They work fine if you understand their limitations. They do NOT like big loads of nitrous, for instance.

From Wikipedia. A hypereutectic piston is an internal combustion engine piston cast using a hypereutectic alloy–that is, a metallic alloy which has a composition beyond the eutectic point. Hypereutectic pistons are made of an aluminum alloy which has much more silicon present than is soluble in aluminum at the operating temperature. Hypereutectic aluminum has a lower coefficient of thermal expansion, which allows engine designers to specify much tighter tolerances.
The most common material used for automotive pistons is aluminum due to its light weight, low cost, and acceptable strength. Although other elements may be present in smaller amounts, the alloying element of concern in aluminum for pistons is silicon. The point at which silicon is fully and exactly soluble in aluminum at operating temperatures is around 12%. Either more or less silicon than this will result in two separate phases in the solidified crystal structure of the metal. This is very common. When significantly more silicon is added to the aluminum than 12%, the properties of the aluminum change in a way that is useful for the purposes of pistons for combustion engines. However, at a blend of 25% silicon there is a significant reduction of strength in the metal, so hypereutectic pistons commonly use a level of silicon between 16% and 19%. Special moulds, casting, and cooling techniques are required to obtain uniformly dispersed silicon particles throughout the piston material.
Hypereutectic pistons are stronger than more common cast aluminum pistons and used in many high performance applications. They are not as strong as forged pistons, but are much lower cost due to being cast.
Hypereutectic pistons can be forged, but typically are only cast, because the extra expense of forging is not justified when cast pistons are considered strong enough for stock applications.
Aftermarket performance pistons made from the most common 4032 and 2618 alloys are typically forged.

If it were me I'd be looking at the Ross forged flat top pistons. Besides durability they have at least 3 other things going for them. They have "full-round" endurance racing style skirts, helpful in keeping the thin cylinder walls intact. They have narrow ring grooves for modern thin piston rings. They sell for a good price at Summit Racing.

Hyper pistons have no business being in a serious performance engine, they were designed for mass produced low emission tight clearanced moderate output 100k mile warranty'd EFI daily driver computer controlled vehicles using knock sensors

(they're delicate)

Hyper pistons do not hold up to severe duty, period.

2618 alloy is nearly indestructible, uses larger clearances & expands more than 4032 which is more temp/dimensionally stable

I'd rather have a standard eutectic or slightly Hypo-eutectic piston than a Hyper

I am sure that a lot of people have good experiences with hyper pistons. I am not one of them. I ruined a motor with a broken hyper piston. I always spend the extra to get forged pistons just for piece of mind from that point forward.

they just haven't had a bad experience, yet

notice in the wiki link they state that special processes are required in production to evenly distribute the silicon throughout the mix

I've used cast, hyper-cast, and forged.

The forged pistons are really overkill and unless you are going to drag race this car and hit it with 200hp worth of nitrous, they are definitely over kill.

The Keith Black hypertutonic is a good piston and all that you need.

I have them in my 347. In that engine, the interesting thing about them is they weigh 347g vs the 521g of the stock forged piston.

The engine balancer just didn't believe that and kept weighing them, saying "this just can't be".

In the early 70's one of the trick pieces to put into a Pro Stock small block was super light pistons like this.

They all had to be "carved" out of the forged pistons by hand to get them that light. Now you just open the box and install them.

The piston pins are 102g for these pistons too.

The engine revs like it is an electric motor with an aluminum flywheel.

I vote KB pistons.

I can only say that when I had 2 SS intake valve heads break off and wedge themselves into the intake ports, my forged pistons took a serious beating but held together just fine. My camshaft had stopped rotating due to a sheared drive pin.

Mark