Piston Material

[Todd Mann from Fastech]

I am looking for a good grade of alum. to make pistons out of for a Hy-po engine. Any suggestions?

[TheePres]

7075 Alum

 

 

Oops!! was thinking rods. No suggestions on piston itself.

[Tom Szelag]

Not sure what a "hy-po" engine is, but...

 

You'd want something with a high yield stress I'd imagine...which brings us to the 2xxx and 7xxx series. Also needs to retain that strength at temperature, so that leaves us with 2xxx. And probably good fatigue properties and controlled fracture toughness... 2124-T8

 

That's just my suggestion though. Make sure all its properties meet your design points.

 

If temperature isn't a big issue but you still want high yield stress and good fatigue and fracture properties, 7475 is another option.

[TheePres]

quote:

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Ross Racing pistons are forged from 2618-T61 aluminum alloy

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quote:

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These pistons are forged from either 4032 or 2168 aluminum alloy and are precisely CNC-machined to their final configuration

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Read more on this at SummitRacing.com

[Tom Szelag]

Hmm 2618, haven't heard of that. Nor 2168. Might have to look into that for a project of mine.

 

Ok looked on Matweb. 2168 doesn't exist, I guess its a typo.

 

2618 looks pretty similar to 2124. Same fatigue strength. 2124 is better for overall yield stress. CTE is same for both. I guess the question is how their strength is impacted by heat and that you'd have to look up elsewhere.

 

2618 seems like a real oddball alloy though and I'd imagine you might have some difficulty getting something. 2124 isn't overly common (not as much as 2024) but you should be able to come accross some.

[Guest CNC Apps Guy 1]

You NEED forged Al. Aluminum Precision Products here in Cali makes them. Look under the Closed Die Forgings secion of the site.

 

HTH

[Tom Szelag]

Why do you NEED forged aluminum?

[Greg Williams]

Airborneman,

 

In my previous life I worked on an engine project

all pistons are made from 2618A

[Tom Szelag]

What benefits oes this 2618 have over other alloys?

[Guest CNC Apps Guy 1]

In a word.... STRENGTH. Not that you can't use bar but, pistons are a very damanding application, are subject to BRUTAL forces and in my experience forged pistons will yield longer life, better wear, less porosity, etc...

[TheePres]

Also read that hy-po pistons are made from "Hyperuetectic Forgings", whatever that may mean.

[Todd Mann from Fastech]

Thanks everyone it's been a really crazy weekend. Lots to do. This sight is the greatest I really apprisiate all the help.I will look into these at the first of the week. Thanks agian.

[Fred @ Slate Industries]

Tom

Everything I have ever used in my Dirtbikes and Snowmobiles are Forged...

BUT, I like the way you question WHY,

and think outside the Box.

[CAM-mando]

http://www.propelledmarine.com/hypereutectic.htm

[Joels]

i machined some forged compressor wheels for Garrett turbo and they were great best aluminum i saw in 23 years!!!

[Tom Szelag]

Have yet to get into the senior level classes dealing on the mechanics of forgings. But i'd think that its essentially the same as roll forming something. You create plastic flow around the edge of a material. And yea, that's great. Makes for a strong durable part.

 

But on something like a piston where you need a very precise fit, aren't you machining away that outer surface anwyway?

[Guest CNC Apps Guy 1]

You're skimming it. What gives a forging it's strength is that you've essentially taken more material, crushed it into a smaller shape. So, if you take a 4 x 4 x 4 piece of say 7050 and weigh it, it will weigh a certain amount. If you take a 4 x 4 x 4 Piece of Forged 7050, the forging will be heavier. The forging's density is greater by a noticeable amount.

 

HTH

[Moonlightmachining]

to give you all a little more info, on our competion motors, mainly 6B Cummins, we making close to 2000 hp with 5.9 liters. Needless to say nothing lasts very long. I am devloping a billet piston so we can experiment more with bowl shape. Also making bi metal piston, titanium or A286 cap with an alumium skirt. Thanks for the advice. Keep it comming.

[Psychomill]

quote:

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Also read that hy-po pistons are made from "Hyperuetectic Forgings", whatever that may mean.

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Not necessarily. Hypereutectic pistons are cast pistons. The difference between this piston and the normally cast piston is basically the amount of silicon content. They add more to it thereby increasing its strength and thermal expansion control. These pistons are in between 'cast' and forged pistons.

 

The decision to use these pistons will depend on your application and use. How 'Hy-po' (should be 'Hi-Po') of a motor are we talking here? If you're looking to be all motor, then these types will be fine. But the hypereutectic piston is quite a bit more brittle (due to its increased hardness). So if you're looking to build a blown, turbo'd (with hi boost) or nitrous motor, you may be better off with a good forged piston. Hypereutectic pistons don't do well with knocking, pinging or otherwise violent combustions.

 

If you're looking at 'all motor' on pump gas, (keeping CR down to 10.5 or less with maybe some limited amount of nitrous or boost), then go with them or a cast piston. I've never machined my own (other than modifying the tops) so I'm not sure of the effects or details. Like James said though, porosity may be an issue. Do your homework on expansion rates, as well as skirt designs, ribbing and top (dome, flats) to control it. If you run it too tight, you'll gall the cylinder (or seize it), if you're too loose, you'll end up with excessive knock and blow by.

 

 

PS: Hi-Po is an 'old' term for "Hi Performance"

 

[ 07-25-2005, 12:03 PM: Message edited by: Psychomill ]

[ChuckM]

Most of your forged performance pistons are either going to be 2618 or 4032. 4032 is the higher silicon piston (~12%) and is generally used in normally aspirated or mild nitrous/boost engines.

 

2618 is only ~.25% silicon. Mainly used in high heat engines, it doesn't have the scuff resistance of 4032 and requires more piston-to-bore clearance due to the thermal expansion. Wouldn't be something I'd want for a street engine. Right at home in a heavily boosted/nitroused track-only engine though.

 

The newer hypereutectic alloys are suprisingly tough though. As long as you can keep an engine from detonating, they can manage the heat without much fuss. They are brittle though.

 

-Chuck

[Guest CNC Apps Guy 1]

Moonlight, did some work with a Stainless deck and Aluminum skirt and results were very good. We were able to dish out the deck and get a great burn. The stainless was darn near indestructible. About 1 million miles in the dyno and no pitting.