All of the kits I've seen, some manifolds, and a lot of turbo set ups have the compressor on the passenger side. Why??? You have to route the downpipe under the turbo, right by the oil return line, instead of just going straight down like if the compressor was on the driver side. Charge piping has to also go under the turbo when the compressor is on the passenger side. You have the downpipe, oil return line, and charge piping all snaking under the turbo, when it can all be avoided by mounting the compressor on the driver side. I've always hated this design and always wondered why all of the kits use it this way, there must be a reason.

 

Couple reasons.
People like the a/c.
Most radiators dont have an opening in the middle to allow for compressor/turbine housing placement.
Putting a filter on it would require a good amount of crazy piping to run into the tire well to avoid a/c and power steering.

Guess that pretty much sums that up.