The factory exhaust is a tri-y and tunes to a very wide rpm band. The header looks to be a 4 to 1. It will tune to a narrower band thats probably at a higher RPM.

When you run an open header you need to put an extension after the collector to get the tuned RPM right. Typically it should be from 10 to 20 inches long.

Looks great,

Kevin

87 Turbo Intercooled Raider, roller cam, torsen rear diff, LSD front diff, lockup auto with modified converter, V6 brakes, low transfer case gears...