Originally Posted by Armstrong Off-Road
If you are off-roading get a different turbo that spools lower if you want the torque and your wastegate will just be open a lot sooner. Or you can do what I'm trying to figure out, run duals, have one at full song at say 2500rpm and then have a bigger one pull you all the way up to the high revs. BTW does any one have any ideas on this setup?
Armstrong is right, you can match a turbo to your engine that will be biased towards the low rpm range but will run out of breath at "higher" rpms. while we're on the subject, a lot of the PV (passenger vehicle) turbos are now running a ball bearing rotating assembly which greatly reduces unwanted friction and allows the turbo to reach it's speeds easier.
As far as your question Armstrong, what you described is a Series sequential setup which i don't think i've ever heard of on a PV application. It's basically two turbos mounted right next to each other with pressure-based bypass valves routing airflow to the appropriate turbo. I don't recommend even thinking about a setup like that for a PV application mainly because of packaging. But you just do not really need that kind of turbo range. you would be better off investing some time and really evaluating what you're after in your turbo and then spend the time matching a turbo to fit.