E-ZooZoo One,
looks like there are now 2 choices for flowmaster.
Standard 40 Series - Two Chamber Mufflers
This is the most “aggressive” sounding street/strip muffler that Flowmaster offers. If you're looking for attention, this one will get you noticed. The standard 40 series has an “aggressive rumble" and will generally resonate inside the vehicle around 1800-2000 rpm’s, and again at 2400-2600 rpm’s. Constructed of 16 gauge aluminized steel and fully mig-welded for maximum durability.
and
40 Series Delta Flow -Two Chamber Mufflers
This two chamber design incorporates Flowmasters patented "Delta Flow" technology. The "Delta" deflectors result in increased scavenging for better performance and reduced interior resonance over the standard 40 series with a nice growl outside the vehicle. Sounds great on late model performance cars with catalytic converters. Constructed of 16 gauge aluminized steel and fully mig-welded for maximum durability.

but shows the same part #942544 for both .do not know why. there are no other choices with 2.50" in/out same side. shawn