If big cover over small wheel + the anti surge porting = lag city, it sounds like I'm better off upgrading cover and wheel at the same time. http://www.ebay.com.au/itm/MAMBA-Garrett-T04Z-T04R-66-3-84-mm-Compressor-Housing-GTX-Wheel-Back-Plate-/171783921595?pt=LH_DefaultDomain_15&hash=item27ff1e9fbb Maybe something like this?