Here is some more info you I just found in one of my engine H/P books.
Hope it may help,
jm
[TABLE="width: 645"]
<tbody>[TR]
[TD="colspan: 8"]Moving upstairs, two cylinder-head variations for the 3.8L V-6 are available. The early ’94-’95
engines had a single intake port, while the later ’96-2004 engines had a Siamese intake port with
two runners feeding one intake valve. One runner supplies the cylinder with air at low RPM, and
then the secondary port kicks in extra air at higher RPM. The timing of this addition is managed by
the EEC-IV engine management system.
In 1996, the deck surface of the cylinder head was changed, providing more material around the
bore, improving head gasket sealing. For performance use, the best head gasket to use is the
Corteco gasket. It’s an MLS design, incorporating an outer layer of steel, with an inner core of
copper. The flexibility built into the head gasket means no more reliability problems from shifting
head gaskets. The stock head bolts are torqued-to-yield, one-time-use bolts and should be
replaced with ARP bolts which increase clamp load on the gasket, enhancing the sealing qualities.
Using all these techniques eliminates head gasket problems associated with the 3.8L V-6 for once
and for all.
The standard 3.8L cast connecting rods are useable for moderate performance applications, but
they aren’t considered reliable past 5,500 rpm and 300 hp. The ’94-’95 engines use a shorter
connecting rod than the ’96-up engines, the longer rod allowing a raised pin in the pistons, and a
lighter assembly. Aftermarket rods are available for the 3.8L from Scat and others. These need to
be matched with the correct compression distance on the piston (the distance between the
centerline of the piston pin and the top of the piston) and dish volume in order to achieve the
desired compression ratio. Forged pistons are available from JE and others to suit a variety of
applications.all.[/TD]
[/TR]
</tbody>[/TABLE]