Hyperutectic pistons don't expand like cast and forged pistons do, so they
run with a tighter piston to wall clearance. Zinc in motor oil is the high
pressure lubricating/anti-scuffing agent. It's what lubricates when there
is metal to metal contact. It's an extreme pressure lubricating agent
found in all motor oils in different amounts.
Mike
At 05:39 PM 2/11/2000 -0600, you wrote:
>fawcett@uism.bu.edu wrote:
>
> > Hmmmmm... Yeah I'm interested. The only problem I'm aware of with
> synth's had
>
>I expected to drum up some interest w/that so I dug up the book. Here's
>what it
>says:
>
>On page 164 under a section called "SYNTHETIC OIL"
>
>"Synthetic oil is a relatively recent development, especially in its
>application to
>racing engines. It has been tested, and for most applications, it doesn't
>seem to
>harm the engine. However, it also doesn't offer any advantages if the
>viscosity is
>kept constant. Most synthetic oils are thinner than standard oils. Also
>if the
>engine already has scuffing problems (valve tips, etc.) synthetic oils
>wouldn't be
>recommended based on our testing because of their lack of sulfur. Lack of
>sulfur
>can be counteracted by additives. Refer to your service manual for specific
>recommendations. If our engine build-up recommendations are followed, you
>should
>not have a scuffing problem in the engine."
>
>Their engine build-up recommendations include a very tight piston-to-wall
>clearance
>per the magnum spec. Also, I understand that at least the 360 motors are
>prone to
>scuffing in the lower portion of the cylinder bores. My Challenger's 360
>had bad
>scuffing in this location.
>
>I wonder if this has anything to do with the magnum engines using
>Hypereutectic
>pistons (do they??). I know that the magnum engines piston to cylinder wall
>clearances are much smaller than most older engines. The spec says 2
>thousandths I
>believe. I just ordered a set of KB hyper's for my Challenger motor
>rebuild - when
>I get them back from the machine shop - I'll check to see what the
>instructions say
>- I seem to recall a warning about those particular clearances and about a
>special
>anti-scuff coating. Maybe the lack of sulfur does something to this
>coating???
>
>Anyone know for sure?
>
>Latr,
>
>Shane
>
>ps: Remember folks - I'm just the messenger 8-)
>
>--
>'96 IndyRam w/lots of mods (mine)
>'96 IndyRam w/lots of options (wifes) - also a numbered (#142) "Track Truck"
>'74 Triple-Black Dodge Challenger Rallye 360 home-brew EFI R&D vehicle
>'68 Black Corvette Convertible 427 (For Sale)
>
__________________________
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