I think they both do basically the same. The Haltech with the Cobra is a beautiful unit JMHO but pricey for me, so I chose the Vortex with the Power Duct. Best bang for the buck. Besides, I had to buy 2 sets. /phpBB/images/smiles/icon_cry.gif
I have 2 C5 with the Halltech, and I couldn't be happier. (paid for both of them) I haven't had any other system, so I can not honestly offer a comparison. That said, I would buy the Halltech again. Best looking system, and my Z06 picked up 3 MPH and .4 in the quarter. Best time of 12.42 @ 115.97 with a 2.19 60' time. Having participated in a dyno day here in So Cal, it appears that each of the "bottom breather" systems appear to be close in performance gains. My 2K coupe - auto runs 12.9 @ 109 with the Halltech and powerloader.
I am a very happy camper.
I still cant decide which one to get , I've had two Halltechs and they were top notch , but maybe its time to try something different?
2001 Black ZO6
Best 1/4(so far) 12.5 at 112
B&M Ripper Shifter
RM racing Nitrous(not installed yet)
1985 white Corvette coupe(auto)
1998 Silver Corvette coupe (M-6)
2000 NBM Corvette Coupe (M-