I just got this email from someone, thought I'd post it.
In 1999, Chrysler deemed it necessary to change the pistons due to several
reasons. Most were the escalating transmission complaints and the quick to
replace a tranny dealers who were scamming the factory for new trannys.
Another reason was emissions, but not entirely. The actual emission output is
exactly the same as it was in 1997. In some cases it is worse.
The newer pistons are different as well as the rods. The different parts will
not interchange between years. With the lumpy cam you could run a much stronger
forged piston and have lotsa torque. It also worked very well at higher piston
speeds. The offset of this was greater thermal expansion and skirt slap. When
you soften a camshaft and everyone wants power, you have to find it elsewhere.
The intake was already close to max effiency and the heads could not be modified
without having to recertify the engine. The only other change that could be
made was to change the piston design.
What is different is that the hyperpathetic pistons are a high silicon content
design. With this they are thermally stronger to a small window. This allows a
closer piston to wall clearance which leads itself to less blowby, lower tension
rings, and reduced emissions. In addition to this, Chrysler engineers wanted to
be sure that they kept the power levels up so the wrist pin weight was changed.
You see, when you take valve duration away from the cam you have to get it
somewhere else. So, they raise the pin height in the piston to increase its
dwell time at Top Dead & Bottom Dead Center. This adds greater cylinder filling
and more squench with every revolution. Another reason why Creampuffs respond
SO well to nitrous and supercharging.
The drawback is that once the peak thermal limit has been reached for a
hyperpathetic piston, it flakes or cracks away. It literally self destructs.
It will not hold its heat treating and will shatter like glass. Forged pistons
will hold their structure, yet will actually melt at much higher temps due to
the slow annealing process in their heat treating. This is why forged pistons
are the ones of choice for all big nitrous and forced induction applications.
What can be done? You can ceramic coat the Creampuff slugs and forget the
problems, or buy a $1000.00 worth of new forged pistons. Ceramic coating costs
about $500.00 and is worth gold plating. Ford now supplies ALL its new 4.6 and
5.4 engines with ceramic coated pistons. They do this to reduce all scuffing
and to eliminate all possible piston failures with their forced induction
systems.
