HELP!! Need pistons questions answered ASAP

[jdbubb at ix.netcom.com (Dan Bubb)]

I think this is the general consensus that I've heard also.
One additional consideration is that if you're going forced induction a cast piston may be strong
enough for your application, but you may not be able to get the compression ratio you want with a
cast piston (cast pistons not generally available with custom crowns) and that alone may force you
to use a forged piston.
A second issue that no one has mentioned is that there are two common alloys used in forged pistons.
2618 is, I beleive, the alloy that is not suitable for street use and has given forged pistons their
reputation for piston slap when cold and wearing out rings prematurely. It is a high strength alloy
that has a higher coefficient of thermal expansion than cast material requiring sizeable piston to
wall clearance.
4032 is a more recent alloy. It's not as strong as 2618, but still stronger than cast. It's
coefficient of thermal expansion is also between cast and 2618 so it can have cylinder clearances
approaching that of a cast piston. I've heard some people say this is entirely streetable. I've also
heard some people say pigs can fly, so take it with a grain of salt.
I think the big issue with forged is simply the bigger cylinder clearance and if the manufacturer's
recommended clearance is close to stock, then there is no downside.
Not sure if this is true of VAG pistons, but a lot of cast pistons have very small thermal expansion
because they have a steel insert under the crown. Tough to do with a forging. I'll have to dig out a
magnet.
Dan

----- Original Message -----
From: "Tommy YUHAS" <h2ovwdrvr@msn.com>
To: <stetson@unrealexpectations.ath.cx>
Cc: <Scirocco-l@scirocco.org>
Sent: Saturday, April 17, 2004 3:38 AM
Subject: RE: HELP!! Need pistons questions answered ASAP


> Ok as I have been piston shopping of late building a little something
> special for my 80 Jeffs old car. I will be running a lysholm on a 16v block
> with a 20v head with a 8.5 to 1 cr and 15 to 17 psi boost. As for forged vs
> cast everyone I have talked to that I trust are telling me if you plan to
> daily drive it go cast even in a race motor on a vw the cast are your better
> option. The only option that I have been recomended forged on is if that
> motor is going to be race use only and going to be kept in the very high rpm
> range always 7500 to 9500 rpm if not it is not worth the extra cost and the
> wear and tear of rings. I still have not decided on that motor what I am
> going to do because it won't see much street use. I am going to experiment
> with the current motor at very high cr and high rev valve train going to see
> the damage I do with cast pistons while the other motor is getting built.
>
> My 81 is a 3a and I am going to keep the factory pistons and throw some mild
> boost at it for that motor and it use as a weekend play toy that is ideal
>
>
> >From: stetson <tim@unrealexpectations.ath.cx>
> >Reply-To: stetson@unrealexpectations.ath.cx
> >To: scirocco list <scirocco-l@scirocco.org>
> >Subject: HELP!! Need pistons questions answered ASAP
> >Date: Fri, 16 Apr 2004 14:22:56 -0500 (CDT)
> >
> >K then,
> >
> >A rather demanding topic I know...but I'm under the gun here.
> >
> >So....as you know, the 3A is in the shop where it was granted a clean bill
> >of health for just about everything EXCEPT the cylinder bore.
> >
> >That needs to be milled .50mm over stock.
> >
> >This means I need new pistons (the shop will not bore w/o them in hand). I
> >would like to get some nice hypereutetic <sp?> or forged and the only
> >place I'm finding for them is Autotech for........
> >
> >$750 !!!!!!!!!!!
> >
> >YEA GODS AND LITTLE FISHES!!!!!!!!!
> >
> >Right now for block cleaning, tolerence checking, magnafluxing, and boring
> >it's costing me $260 +tax. This means if I can find a cheaper piston set I
> >could perhaps get it blueprinted and balanced.
> >
> >I want to do this to this engine ONCE, no more. The engine may not stay w/
> >this Roc but I want to have a known, proven, hardened engine @ the end of
> >this fiscal blood letting that I KNOW is good.
> >
> >I have Dave @ Adirondack checking into pistons for me right now (Potter
> >can't get 'em) but will appreciate any and all info or recommendations!
> >
> >Are there any pistons from a ABA or 2.0 16v that could be used in it's
> >place? Weisco's site has them listed that seem to have the same diameter I
> >need (83mm) and the right rod length I need (144mm) and the right
> >compression (10.4-10.5).
> >
> >Any thoughts Uber-Dubbers?
> >
> >Burning up my mail accounts quotas,
> >
> >Tim
> >
> >
> >New York is a jungle, they tell you.  You could go further, and say that
> >New York is a jungle.  New York *is a jungle.*  Beneath the columns of
> >the old rain forest, made of melting macadam, the mean Limpopo of swamped
> >Ninth Avenue bears an angry argosy of crocs and dragons, tiger fish, noise
> >machines, sweating rainmakers.  On the corners stand witchdoctors and
> >headhunters, babbling voodoo-men -- the natives, the jungle-smart natives.
> >And at night, under the equatorial overgrowth and heat-holding cloud
> >cover, you hear the ragged parrot-hoot and monkeysqueak of the sirens,
> >and then fires flower to ward off monsters.  Careful: the streets are
> >sprung with pits and nets and traps.  Hire a guide.  Pack your snakebite
> >gook and your blowdart serum.  Take it seriously.  You have to get a
> >bit jungle-wise.
> >-- Martin Amis, _Money_
> >
> >
> >
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