It can be argued that the Vortech's are more efficient (as far as charge temperature is concerned), but it's proven they are more reliable. Can't beat the gear driven impellers (Powerdyne's are belt driven and can/will break in time, or under heavy abuse). 3 year standard warranty isn't bad either. Go Vortech.
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'91 LX Hatch, 17 ROH ZR6's, lowered, 3.73's, offroad H pipe, SN Cobra cat-back, ASP pullies, 14° timing, C&L 76mm MAF, 170A 3G, B&M Ripper on a T5
Best ET: 14.593 @ 94.62 2.292 60'
1991 LX Hatch 5.0L