Sounds shady to me...

Without any info on the type of supercharger, the fuel management / enrichment, boost level, etc... I can't give a meaningful estimate on the hp or tq increase.


Speaking in very broad terms:

Centrifugal superchargers tend to give more top end power. On a Vortech SC'd B16A2 for instance, the big cam feels ungodly huge, but otherwise, the powerband from 4K down feels virtually identical to stock.

Eaton / Lysholm/ Roots-type superchargers tend to boost torque curves throughout the rev-band, losing efficiency in the high end. Basically, most JRSC'd B-series simply feel as though they are blessed with much more displacement.

That's the best I can manage, based on what I've heard from you this far. To be frank, $600 new in box says to me that :
1) The SC is hot (aka stolen property).
2) It's an Ebay vundershiße. :dunno: