Luis,
In a passenger car with mufflers and tailpipes, header tuning isn't going to matter. A properly tuned exhaust system counts on an open system. Putting mufflers and tail pipes on a header system will negate any real performance gain. This is why so many of us are pleased with our cast iron 3 into 1 shorty headers. Just relieve as much back pressure as possible and enjoy your ride.
Jim
