Will the common aftermarket turbos stand up to the hideous exhaust pulse of the 13B?  Of course, the Mazda unit doesn't seem to do all that well :o(  How do you tell what kind of exhaust pulse a particular turbo will handle?  Who do you ask?
I'd be afraid to put in an "other than Mazda" turbo and subject it to the exhaust pulses we're dealing with without some assurances.
Getting spooked again .... Jim S.
 

 There are a whole lot of RX-7's running around with aftermarket turbos, and they seem to hold up fine.  There are  "single turbo" upgrades out the wazoo for 3rd gens, but who knows how long they'll last.  Most of those guys are pushing high boost, and blowing the engines in pretty short order anyway.  I don't think there's any doubt that some of the aftermarket turbo's can work, but would any of them last as long or longer than a stock turbo?  I'm not sure anyone knows.  I do know that the second gen turbo's don't seem to be doing the job.