I am looking for turbo that will bolt to my 4-bolt TA headers and to a 4" downpipe. Would also be nice if compressor outlet would match my CAS V1 intercooler w/o adapter. Would that be a big turbo? Probably.
most precision downpipe flanges.. for example are 3 5/8" vbands.. so they aren't 4" per say.. it's more important what Vband size you have rather than the pipe itself. a 4" is over 100mm exhaust wheel inducer which is larger than almost any turbo out there except for the biggest.
any T4 4 bolt turbo will "bolt to" your headers. "almost" Any T4 4 bolt with Precision "h" high flow cover or equivalent compressor cover will bolt to your headers and your intercooler pipe. The center section makes there difference there... with anything larger than a 76mm being a problem.
Keep in mind, that a T4 4 bolt 60mm turbo will also bolt up.. but against the exhuast bolt up or v-band is the unknown.