?? cast hypereutectic pistons ??
Dave Simunov
Can anyone comment on cast, hypereutectic pistons ('93+)
vs. the forged aluminum pistons ? What exactly are they made of?
What does hypereutectic mean ? Is there a significant reduction in
strength ? Can they handle supercharging adequately ? Any help would
be appreciated.
Dave
Brian Kelley
In article <3379A9...@mailgate.navsses.navy.mil>,
Hypereutectic pistons are made of a combination of silicon and aluminum
(I think above 12% silicon is called hypereutectic, and below is hypoeutectic),
where silicon is dissolved into the aluminum.
I read somewhere that hypereutectic alloys act as insulators (the silicon),
keeping the piston cool. I don't know about strength reduction, but one would
think that having 1/10 to 1/5 of the piston as silicon might reduce its
strength somewhat, but I could be wrong.
I have heard people mention that the '93+ pistons have characteristics
that would increase the potential for melting (i.e.: by being
hypereutectic), but I haven't heard any REAL story of someone blowing holes
in their '93+ pistons because of supercharging.
p.s.:
This information could be wrong, so
anyone else with more knowledge, please correct me.
Brian
--
Brian M. Kelley
bke...@ultrix6.cs.csubak.edu
http://www.cs.csubak.edu
Marc Warden
In <3379A9...@mailgate.navsses.navy.mil>, Dave Simunov <sim...@mailgate.navsses.navy.mil> writes:
>Can anyone comment on cast, hypereutectic pistons ('93+)
>vs. the forged aluminum pistons ? What exactly are they made of?
>What does hypereutectic mean ? Is there a significant reduction in
>strength ? Can they handle supercharging adequately ? Any help would
>be appreciated.
>
> Dave
>
> sim...@mailgate.navsses.navy.mil
Hi Dave.
All other things being equal, a cast piston is weaker than a forged piston.
In casting, the metal grains are arranged in a random order. In forging, the
grains are in a less random order from the flowing action that takes place
when the forging hammer impacts teh piston blank and causes the material to
flow into the forging die and take on the shape more closely resembling a
piston and not some lump of hot alumimum. The resulting grain ordering
lends strength to the part.
The pistons are alumimum, though I don't know what "hypereutectic" means and
my materials references are not handy.
According to what info I've been able to gleam from reading the Mustang mags,
hypereutectic pistons can live with supercharging as long as one is careful.
These pistons can't tolerate detonation and detonation in a supercharged
engine will kill these pistons very quickly.
And even if one finds a way to eliminate and prevent detonation, there is a
upper limit to how much boost one can throw at these pistons.
It appears that around 6lbs of boost is a reasonable compromise between HP
and engine longevity.
Now I don't doubt that there are some out there who've managed to crank up
the boost and have so far not suffered because of it, but that can be
attributed to the small (but not insignificant) differences between engines
even engines that come off the same production line.
Besides, reading between the lines, even if one was blessed with
exceptionally strong hypereutectic pistons in his car, there are other
components that are subjected to stresses above and beyond the call of duty
in a supercharged engine. The piston pins, rods, crank, and just about every
other rotating or recipocating part also receives additional stress, even if
it's just additional heat.
I'm sure one wouldn't be comforted by the fact the hypereutectic pistons were
unharmed and still attached to the rods, and the rods to the crank,
but the crank was laying on the ground underneath the engine...
Sincerely,
Marc Warden (ma...@ibm.net)
Mike Burress
>
> Hypereutectic pistons are made of a combination of silicon and aluminum
>(I think above 12% silicon is called hypereutectic, and below is
hypoeutectic),
>where silicon is dissolved into the aluminum.
> I read somewhere that hypereutectic alloys act as insulators (the
silicon),
>keeping the piston cool. I don't know about strength reduction, but one
would
>think that having 1/10 to 1/5 of the piston as silicon might reduce its
>strength somewhat, but I could be wrong.
> I have heard people mention that the '93+ pistons have characteristics
>that would increase the potential for melting (i.e.: by being
>hypereutectic), but I haven't heard any REAL story of someone blowing
holes
>in their '93+ pistons because of supercharging.
>
>p.s.:
>This information could be wrong, so
>anyone else with more knowledge, please correct me.
>
> Brian
If memory serves you are correct - hypereutectic pistons have a
silicon level that is above the amount of silicon that the aluminum
will absorb. These pistons exhibit good thermal characteristics and,
if I remember correctly, better scuff resistance. However, it's still
a cast piston. Good rebuilder pistons but perhaps marginal for
high revs or supercharging.
Mike
Remove the leading 'z' in order to e-mail
me. Trying to foil spambots <g>
Gregory Scott Banish
On 14 May 1997, Marc Warden wrote:
> In <3379A9...@mailgate.navsses.navy.mil>, Dave Simunov <sim...@mailgate.navsses.navy.mil> writes:
> >Can anyone comment on cast, hypereutectic pistons ('93+)
> >vs. the forged aluminum pistons ? What exactly are they made of?
> >What does hypereutectic mean ? Is there a significant reduction in
> >strength ? Can they handle supercharging adequately ? Any help would
> >be appreciated.
>
> All other things being equal, a cast piston is weaker than a forged piston.
>
After I picked up my '93 LX, I spoke with one of the Ford engineers that
works in reciprocating parts (engine group) about what's in my 5.0. I
was told that the pistons are indeed cast, but that the new material is
head and shoulders above the older material, making them just fine for
mildly boosted applications. (My concern will eventually be
turbocharging.) As a bonus, I learned that the Con Rods are *much*
better because Ford pulled out some old 289 tooling to save money which
happened to be better than the current parts. These new (old) con rods
are supposed to be really good and the only thing that one may want to
add would be a brass bushing in the little end to make the pins full
floating. ...but since I'm probably going to be looking at a .030" over
rebuild with the turbo, I'll be getting new pistons anyway...
ok, I'll stop babbling now.
~gb
**************************************************************************
"What's the difference between a Corvette and a porcupine?"
"With the porcupine, the pricks are on the outside..."
**************************************************************************
Phil Ross
Finally, A question I know the answer to!
Hypereutectic aluminum allows contain more silicon than will stay
disolved in the aluminum grains after the aluminum alloy cools below
it's lowest eutectic point (it's solidification point). Some of the
silicon parcipitates out of the solution and forms silicon "nodules" at
the grain boundrys of the alloy grains. The chief advantage of these
alloys is their greater wear resistance, as the silicon is very hard.
These alloys are not new, in fact Chevy Vega aluminum blocks were
die-cast from 390 alloy (a hypereutectic) at GM's Massena, NY foundry in
the early 70's. However, hypereutectic alloys are not used, unless they
are necessary, because they are more difficult to cast and much more
difficult to machine (due to the silicon).
Now you know more than you ever wanted to know about hypereutectic
aluminum alloys!
lawrence heath
Basically these are cast pistons that have more silicon than can be
normally dissolved in the aluminum matrix. This leaves silicon nodules
(very small) in the aluminum. Also this means that these pistons can be
run pretty tight with respect to piston to wall clearance. One thing that
should be rembered is that these pistons run at a lot higher temp in the
ringland area. As a consequence you will need to run a bunch more ring end
gap, .023 to .025 in a standard 4.00" bore as apposed to .016 to .018 with
a forged piston. This means that these piston need a bit more warm-up to
get to operating temp. Also means that rings run at a good bit higher temp,
this in my mind can't be a real hot setup (no pun).
Yes these pistons are a bit stronger than regular cast pistons, but a good
bit weaker than forged. We have some friends that run these in limited
late model cars and seem to due quite well. But let me also say that when
these pistons come apart there isn't going to be much left. The last
engine that I saw that broke there wasn't a piece of piston left that was
bigger than a piece of pop corn. When these pistons do come apart they do
so in a big way.
--
Lawrence Heath
Lawrence Heath Racing Products
lgh...@sunline.net
Dave Simunov <sim...@mailgate.navsses.navy.mil> wrote in article
<3379A9...@mailgate.navsses.navy.mil>...
> Can anyone comment on cast, hypereutectic pistons ('93+)
> vs. the forged aluminum pistons ? What exactly are they made of?
> What does hypereutectic mean ? Is there a significant reduction in
> strength ? Can they handle supercharging adequately ? Any help would
> be appreciated.
>
> Dave
>
> sim...@mailgate.navsses.navy.mil
>
it is i
You've never seen a hypereutectic blown apart because of supercharging?
I'll send you a few if you'ld like. In most cases though it's not the
pistons fault. Read the reply by Marc Warden again. It's well thought out
and quite accurate. Note the boost limit, also leave your timing alone make
sure you don't EVER lean out..
Have Fun,
Probe
brand...@condor.navsses.navy.mil
Not quite... I wanna know more :)
I believe this is also the same process Porsche uses for sleeveless aluminum
blocks... and that this can result in a very wear-resistant bore IF quality
control assures a consistent product (GM's downfall, I believe).
Also, what's the end result in piston strength - how much better is this
than a run-of-the-mill cast piston, and how close is it to a forging when it
comes to strength, fatigue resistance, resistance to detonation damage, etc...
Probe Industries
It gets worse.
When comparing a hypereutectic alloy to forgings you also have to consider
the alloy and manufacturing process used for the forgings. Some aftermarket
forgings are made of 4032 alloy (Trw, Wiseco and some others). Most high
dollar forged pistons are made of 2618-t6. Essentially the differance is
4032 has 10% silocon and 1% copper. 2618 has 10% copper and 1% silicon..
To make matters worse, with the exception of TRW and a couple od other
aftermarket piston makers, all use forgings made of extruded billet bar
stock. That's like Probe, Ross, JE, Arias, Venolia... This allows the
manufacturer to dictate grain flow of the forging, which results in a
stronger piston. Net, net what we end up with is a material that can be
made thinner with an increase in strength.
One cannot compare cast, or hypereutectic pistons with forged. It's sorta
like comparing Heather Locklear to Nelda Glick. It's just not fair to the
cast pistons.
But, you can't compare the TRW stuff to the lightweight aftermarket pistons
either.
As an example the 302 flat-top TRW weighs about 620 grams, a Probe weighs
about 460 grams. Now 33 ounces at 10,000 rpm weight 20 tons. So the
expensive stuff takes a ton of stress off the bottom end.
All that being said, Each one of these designs has an application where
they will be perfectly serviceable.
You have two problems, as a customer.
1> There is a fair amount of overlap on application.
2> No matter which one you really need, some salesman will lie to you about
which one belongs there.
All I can say is good luck!
Probe Industries
Chuck Fry
In article <01bc6bbc$e1398c40$45b1...@lzozl.ptw.com>,
Probe Industries <*pr...@racepages.com> wrote:
>When comparing a hypereutectic alloy to forgings you also have to consider
>the alloy and manufacturing process used for the forgings. Some aftermarket
>forgings are made of 4032 alloy (Trw, Wiseco and some others). Most high
>dollar forged pistons are made of 2618-t6. Essentially the differance is
>4032 has 10% silocon and 1% copper. 2618 has 10% copper and 1% silicon..
One key difference between these alloys is that 2618 has a high
temperature coefficient of expansion (tempco), so it requires a loose
fit at room temperature to meet the required clearances when fully
warmed up. This means you get piston slap when cold, and you generally
have to baby the engine til it warms up. 4032 has a lower tempco that
allows for a tighter fit at room temperature.
Another key difference is that 4032 and the hypereutectics are more
brittle, and thus more sensitive to detonation. 2618 is more malleable,
thanks to the extra copper.
IMHO 4032 and the hypereutectics are really best suited for street
engines, 2618 for race engines. But as the guy from Probe said, there's
a lot of overlap between applications.
-- Chuck
--
Chuck Fry -- Jack of all trades, master of none
chu...@chucko.com (text only please), chuc...@home.com (MIME enabled)
This space for rent... NOT.
LSparks709
For an informative in depth explaination between pistons visit the Keith
Black -Silvolite webpage at www.kb-silvolite.com.
Hope this helps