Pistons, Hypereutectic or Forged Options

[sjhenry1075]

Hey everyone, so I'm starting to purchase all the parts for my build (2056) and I'm now choosing the pistons. Just a side note, I will not be racing this car. It's a 2056 w/ 9.1:1 CR, 86a cam, dual 40 IDF's, and built up 2.0 heads. My question to everyone is, forged or Hypereutectic? What is everyone else running?

[ChrisFoley]

Hypereutectic is fine for an engine combo like that.
If you were making that into a race engine with higher compression I would recommend JE forged pistons.

[sjhenry1075]

Hypereutectic is fine for an engine combo like that.
If you were making that into a race engine with higher compression I would recommend JE forged pistons.

Thank you Chris. by the way, I recently ordered your cable system for dual carbs, I heard it's amazing. Thank you for the ultra fast shipping!

[Al Meredith]

The 2056 is the way to go . I have built several and all have KB pistons . Check the internet for the top ring clearance . The KBs run hot at the top and require a larger gap I think about 24 thou instead of the typical 16 thou.

[sjhenry1075]

The 2056 is the way to go . I have built several and all have KB pistons . Check the internet for the top ring clearance . The KBs run hot at the top and require a larger gap I think about 24 thou instead of the typical 16 thou.

Great advice, thank you! Since they run hotter, should I add an external oil cooler?

[VaccaRabite]

The 2056 is the way to go . I have built several and all have KB pistons . Check the internet for the top ring clearance . The KBs run hot at the top and require a larger gap I think about 24 thou instead of the typical 16 thou.

Great advice, thank you! Since they run hotter, should I add an external oil cooler?

Probably. But not until you have built the engine and see if you need it.

Pistons running hot will be seen in the heads, not so much in the oil. At least you won't see it in the oil till way after the heads are cooking.

Zach

[pek771]

Get forged pistons. Cast with a lot of silicone alloying element are a crapshoot.

[Superhawk996]

Get forged pistons. Cast with a lot of silicone alloying element are a crapshoot.

(IMG:style_emoticons/default/av-943.gif)

Cast pistons widely used in production engines for decades upon decades without issue. A 50 year old T4 VW engine for street use doesn’t require forged pistons.

[JamesJ]

A "street car" will benefit from forged pistons depending on your driving style. Are you planning to "hot rod" it on the street or do any spirited street driving? Go with the forged pistons.

[Superhawk996]

Guess those 345 HP LS1 engines are (IMG:style_emoticons/default/stromberg.gif) with their cast pistons. (IMG:style_emoticons/default/confused24.gif)

If OP has money to burn and just can’t sleep at night without knowing he has forged pistons in an antique VW engine . . . Sure spend the money.

Who knew piston choice is as polarizing as the oil choice threads (IMG:style_emoticons/default/av-943.gif)

[ChrisFoley]

Forged pistons are noisier than hypereutectic cast. They grow more as they heat up which means they have to fit more loosely. Piston knock is louder than excess valve lash.

[emerygt350]

Yeah, having to wait for thermal expansion and price is why I went with hypers on my 302. In an air-cooled engine where you are dealing with even more thermal expansion there is no way I would go for forged unless I were planning on boost. Particularly a 50year old motor that's going to make these kinds of ponies.

I would also add that things can go south pretty quick on one of these and reducing the cost of the build might make that next oops less painful.

[pek771]

I see no one has asked what sort of cylinders is the OP using? When the gasoline becomes even worse than it is now, then what? Porsche designed the newer cylinders and pistons to expand and contract at the same rates. The old stuff, like my old 2.2 six cylinder had cast iron cylinders and forged pistons. When you decide in 5 years to go in a different direction, it makes the couple of warm up minutes fairly inconsequential. You think the real hot rodders use cast iron 94 mm cylinders, or Nikkies?


I could be wrong about this, but I don't see where forged pistons are noisier than cast outside of warm up. Yes, cast piston have been used for years. Gasoline had lead in it also.

[Superhawk996]

Porsche used plenty of cast pistons in the early air cooled sixes (except S variants). I could stand to be corrected since I don’t have the Bruce Anderson book in front of me but my recollection is forged pistons for S variants, 930s, and RS variants of the early motors.

There are a couple flavors of forged piston alloys which also include high silicon content to improve thermal expansion and improved scuffing resistance. Forged pistons are generally heavier than cast and can place more stress on rods at high RPM. So there’s that downside to forged.

The discussion of Nickies is not relevant to what the OPs original question. I think we can all probably agree Nickies P&C sets are pretty sweet but they come with a hefty price (~$4k). It’s easy to spend other peoples money. Chris provided an appropriate answer to the question that was asked - what to use on a mild 2056 street build. No discussion of hot rodding. No discussion of forced induction future upgrades. No discussion of extending redline beyond 5500 RPM.

Leaded gas or Unleaded gas has no relevance to the piston material selection. Octane ratings do come into play at high compression ratios (let’s say >10:1 for the sake of this discussion). There are plenty of modern cars that run > 10:1 cast pistons (LS1’s) with the aid of fuel injection and knock sensing. The OPs proposed compression ratio is well documented to be OK on pump gas with our T4 air cooled engines. Any engine that is improperly tuned and detonating & knocking will quickly destroy pistons whether forged or cast.

On the plus side for hypereutectic is not only the improved noise aspect but also the slight improvement they offer in reduced emissions since they run tighter than forged pistons. Not a huge thing for us hobbyists but it was a major factor for the OEMs as they tried to deal with emissions reduction mandates. Might be worth something to those that still have to deal with emissions certs in select states like CA.

Like so many things in life, a one size fits all solution - really isn’t a solution at all.

OP asked a legit question. I’m not trying to argue that forged pistons aren't good in the right high performance application, but rather that they are not necessary for a mild 2056 street build.

Cast pistons are well documented in many naturally aspirated engines north of 400 HP. To say that forged pistons are necessary in an VW T4 2056cc engine that will be lucky to produce 130 HP is a disservice to the OP.

[Geezer914]

I used AA Pistons with their biral cylinders.

[JamesM]

I used AA Pistons with their biral cylinders.

A lot of people like to crap on AA Pistons parts for some reason.

I have them in my 2056 along with multiple data logs of pulls to 7k RPM and 7 years of autocrossing with it. I have yet to scatter them.

Worth mentioning though that forged tend to be lighter. I was witness two engine builds that were 100% identical in parts use aside from one getting KB pistons and the other having JE forged. Both running identical Megasquirt systems and optimized on a Dyno. The JE motor made about 5hp more at peak.

[914werke]

I used AA Pistons with their biral cylinders.

How did you get them to seal? (IMG:style_emoticons/default/idea.gif)

[Superhawk996]

Worth mentioning though that forged tend to be lighter.

Let’s be very careful with terminology.

Forged piston material is denser due to the forging process.

Therefore if the piston geometry is 100% the same between cast and forged, the forged piston will be heavier.

Yes, it is true a performance oriented forged piston may be lighter in some cases (but not always) because they may have shorter piston skirts, thinner piston domes, etc.

Particularly in the case of shorter forged piston skirts, combined with the higher thermal expansion, this makes the cold start piston slap even noisier.

I tried to quicky find the weight of KB Hypers vs JE Forged but came up empty handed searching their online catalogs. If someone is truly wanting a lighter forged piston, be sure to do your homework and contact the vendors directly for tech data.

Lest anyone think I am opposed to forged pistons - I do have a set of 100mm JEs with CNC thinned domes awaiting a special build. As stated previously, forged pistons have their applications but are not mandatory for a mild 2056 street build.