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Info: Forged vs. cast pistons

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Re: [gti-vr6] Re: forged pistons burn oil? how? "Jim Chu" <jimchu@erols> Tue, 4 Jan 2000 19:34:39 -0500
Re: [gti-vr6] Re: forged pistons burn oil? how? Judson Main <judson@btg> Wed, 05 Jan 2000 10:39:41 -0500
Re: [gti-vr6] Re: forged pistons burn oil? how? srsvw@pop.tiac Wed, 05 Jan 2000 11:41:37 -0500
Re: [gti-vr6] Re: forged pistons burn oil? how? Judson Main <judson@btg> Wed, 05 Jan 2000 11:58:43 -0500



From jimchu@erols Tue, 4 Jan 2000 19:34:39 -0500
From: "Jim Chu" <jimchu@erols>
To: gti-vr6@dev.tivoli
Subject: Re: [gti-vr6] Re: forged pistons burn oil? how?
Date: Tue, 4 Jan 2000 19:34:39 -0500
 
The forged slugs takes more time to expand and thus burns a little oil.
We're not talking about bellowing smoke here.  The clearance has a lot to do
with it.  Since I'm going to run 20+ psi, I want .300, but .250 is good for
a 'street' motor.

The VR6 can handle 10 psi with stock compression and 15 psi with a copper
head spacer to reduce compression and stock everything else for STREET use.

I just started the plan to assemble my 2.9L (82.5mm pistons = 2896cc and not
2861cc from 82mm slugs) motor with a 9:1 CR.  I've been sitting on the hard
parts for a while and now it's ball to the walls!  currently at 325 rhp
(10psi) and hoping for 400hp to the wheels?  I'll laugh at that when I'm
done!  Gotta pony up another $1k for forged rods.  Kiss my tranny goodbye or
do a reverse burnout after few brews, again : (

Jim

- ----- Original Message -----
From: Paul Ting &lt;&#102;ubas_up&#64;hotmail<img src=/i/dc.gif border=0 width=35 height=15>&gt;
To: &lt;&#103;ti-vr6&#64;ccsi<img src=/i/dc.gif border=0 width=35 height=15>&gt;
Sent: Tuesday, January 04, 2000 7:14 PM
Subject: [gti-vr6] Re: forged pistons burn oil? how?


> In the article located at
http://www.vag.org/techtips/tuning/tuning_pg1.htm
> the author said forge pistons will increase oil consumption.  How is this
> possible?
>
> While researching various turbo kits in te past 2 years I've been told by
> several sources to invest in a set of forged pistons.  If it is true that
> forged pistons will increase oil consumption, then are they really worth
it?
>
> Jim Chu, you have JE pistons in yours don't you?  Any change in oil
> consumption?


Date: Tue, 04 Jan 2000 19:56:13 -0500
From: veearesix &lt;&#118;eearesix&#64;mediaone<img src=/i/dn.gif border=0 width=35 height=15>&gt;
Subject: [gti-vr6] PISTONS ( kinda long)

Pistons..they suck  oops I meant the Detroit basketball team :)
Pistons , cast(stock), Forged and Hyper-Eutectic.
For most hypo apps its normal to want forged pistons. However in engines
designed to produce average or moderately high power output, cast pistons will
often produce more power than forged pistons...WHY? ( I know your asking this)
There are several reasons, First cast pistons usually develop less ring-groove
wear and have marginally less heat conductivity, keeping more heat in the
combustion chamber . 2nd They are designed to run with minimum bore clearance,
providing a more stable platform for the rings, ( LESS oil consumption, better
sealing = more power). 3rd they are often lighter then all but the best
forgings, and most importantly cheaper!
Cast is a more thermally stable alloy then forged. Thereby expanding less then
the forged when hot. Requiring  less gap in the bore. This is where oil
consumption and noise comes from( piston slap..known to make it sound like a
deisel).Pistons that fit loosely in the bore when the engine is cold will
adversely affect fuel efficiency and increase oil contamination, consumption,
and emissions. remember oil in gas = less horsepower, however when hot and
expanded with a better seal it is not  a problem..
Cast also being harder ( more brittle) is very intolerant of detonation, again
all pistons are but forged can with stand more than cast.
Developed in england are the Hyper-Eutectic pistons. ( "hyper" meaning high and
"eutectic" meaning melting point. Cast with a special material ( high silicate
level about 12 or 14 % ( the max before the metal sweats it out)) at a higher
temperature than normally used in the manufacturing process. The result is a
light piston having nearly the strength as a forged piston combined with the
desired hardness and low expansion rates of a typical cast piston.( one day we
may see ceramic pistons... they have been played with- but extremely sensitive
to detonation.)
Hyper-Eutectic offers substantially reduced piston noise over forged. Also lower
in cost falling between forged and cast.
This is just some brief facts surrounding pistons, there are many many more!
Doug


Date: Wed, 5 Jan 2000 08:24:06 EST
From: &#65;WE16VR6&#64;aol<img src=/i/dc.gif border=0 width=35 height=15>
Subject: [gti-vr6] Re: forged pistons burn oil? how?

This is an anachronism.
Older forged pistons expanded so much with temp, that they had to be run on
the looser side when cold.  This caused them to slap around a bit, and let
oil to be sucked up past the oil ring.  However, when warmed up, they would
behave themselves.
Yet, the newer forged pistons (Wiseco, JE, Ross, etc.) alloy content is much
more thermally stable, and quite close cold tolerances (~.004") can be run.
When installed correctly, they behave very much like a cast OEM style piston.
The benefit of a forged piston is lighter reciprocating weight, and greater
resistence to temp extremes.

&lt;&lt; From: "Paul Ting" &lt;&#102;ubas_up&#64;hotmail<img src=/i/dc.gif border=0 width=35 height=15>&gt;
 Subject: [gti-vr6] Re: forged pistons burn oil? how?

 In the article located at http://www.vag.org/techtips/tuning/tuning_pg1.htm
 the author said forge pistons will increase oil consumption.  How is this
 possible?

 While researching various turbo kits in te past 2 years I've been told by
 several sources to invest in a set of forged pistons.  If it is true that
 forged pistons will increase oil consumption, then are they really worth it?

 Jim Chu, you have JE pistons in yours don't you?  Any change in oil
 consumption? >>


Regards,
Todd
AWE Tuning
215-753-8203
Orderline 888-565-2257
http://www.awe-tuning.com/



Date: Wed, 05 Jan 2000 09:24:09 -0500
From: Uwe Ross &lt;&#85;we.Ross&#64;pobox<img src=/i/dc.gif border=0 width=35 height=15>&gt;
Subject: [gti-vr6] PISTONS

> Date: Tue, 04 Jan 2000 19:56:13 -0500
&gt; From: veearesix &lt;&#118;eearesix&#64;mediaone<img src=/i/dn.gif border=0 width=35 height=15>&gt;
> Subject: [gti-vr6] PISTONS ( kinda long)
>
> Pistons , cast(stock), Forged and Hyper-Eutectic.
> For most hypo apps its normal to want forged pistons.
> However in engines designed to produce average or
>  moderately high power output, cast pistons will
> often produce more power than forged pistons...

Yes, I agree, factory-type cast or hyper-eutectic would be prefereable for
most applications.

Now tell us where to get 83mm pistons for a VR6 that are anything BUT
forged...

I have a customer in Finland who lunched a stock 82mm piston in his 2.9L
Corrado.  He has some bore damage in that cylinder and will have to increase
the bore diameter.   Unfortunately, there are NO oversized pistons available
for the 2.9L from the factory.  His only option appears to be forged.

- -Uwe-










From judson@btg Wed Jan 05 10:39:41 -0500 2000
From: Judson Main <judson@btg>
To: gti-vr6@dev.tivoli
Subject: Re: [gti-vr6] Re: forged pistons burn oil? how?
Date: Wed, 05 Jan 2000 10:39:41 -0500
 
You guys.  I swear...

The JE forged pistons have a tapered design.  I was told that .150 was
easy to get with NO stuck pistons ever!  I did .200 to be on the safe
side and all I heard on startup was a little dieseling sound.  That's it.
No burned oil whatsoever.  Never a stuck piston.

Jim, .300 is WAY too much.  Call JE and re-confirm, and remember
they will make very, very conservative recommendations.

Jud.










From srsvw@pop.tiac Wed Jan 05 11:41:37 -0500 2000
From: srsvw@pop.tiac
To: gti-vr6@dev.tivoli
Subject: Re: [gti-vr6] Re: forged pistons burn oil? how?
Date: Wed, 05 Jan 2000 11:41:37 -0500
 
I hope you mean .002"!


>You guys.  I swear...
>
>The JE forged pistons have a tapered design.  I was told that .150 was
>easy to get with NO stuck pistons ever!  I did .200 to be on the safe
>side and all I heard on startup was a little dieseling sound.  That's it.
>No burned oil whatsoever.  Never a stuck piston.
>
>Jim, .300 is WAY too much.  Call JE and re-confirm, and remember
>they will make very, very conservative recommendations.
>
>Jud.











From judson@btg Wed Jan 05 11:58:43 -0500 2000
From: Judson Main <judson@btg>
To: gti-vr6@dev.tivoli
Subject: Re: [gti-vr6] Re: forged pistons burn oil? how?
Date: Wed, 05 Jan 2000 11:58:43 -0500
 
Okay, I've got my dots wrong.  I meant ".0015" and ".003" and etc.

Jud.






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