I think this is out of Sport Z Magazine (I got it off of My350Z):
Given this info., I think I'd put the NISMO at the top of my list. Good power AND torque, and doesn't give up anything at the bottom end (big plus). I also like the way it sounds the best (personal preference). You can hear sound clips of these exhausts and more here:Exhaust Shootout notes:
They used two cars (2% Hp difference).
Car 1 Baseline = 233.2 Hp - 222.6 ft/lbs torque
Car 2 Baseline = 237.5 Hp - 224.0 ft/lbs torque (stronger engine - lighter wheels)
All manufacturer's systems Hp and torque numbers were lower than advertised. Not a surprise.
Borla (car 2) = 8.2 Hp - 2.7 ft/lbs torque (peak values)
A top end system. Little HP increase until the 5600 rpm to 6500 rpm range. Lost HP & torque below 1800 rpm. 60mm (error actually 58mm). Weighs 52lbs. 1 million mile warranty. Installation - Hard (17 pieces)
5Zigen (car 2) = (-3.4) Hp - .02 ft/lbs torque (peak values)
Lost Hp, no real torque gain. Most expensive. Loudest. 58mm pipe. Lightest @ 25lbs. 1 year Warranty. Installation - Medium
Stillen (car 1) = 8.1 Hp - 7.3 ft/lbs torque (peak values)
Hp and torque increase starting at 3000 rpm to redline. Lost a little HP & torque below 1800 rpm. 60mm pipe. 74lbs - 10lbs heavier than the stock system. Lifetime Limited Warranty. Installation - Easy
Injen (car 1) = 7.6 Hp - 5.1 ft/lbs torque (peak values)
Small torque loss at 2800 rpm. Torque gain starts at 3300 rpm. Small Hp increase starts at 3300 rpm, max Hp from 5800 rpm to redline. Major loss in Hp and torque below 2200 rpm. 49lbs.
1 year Warranty. Installation – Easy
Nismo (car 1) = 6.3 Hp - 4.5 ft/lbs torque (peak values)
Torque increase starting at 3000 rpm. HP increase 4800 rpm to redline. No power losses below 1800 rpm. 54lbs. 3 years, 36K miles id installed by Nissan dealer. Installation - Easy