It's all about knowing what you want from the start...Mainly to save buying several turbos till you find ideal spec.
I'm taking this route simply because i'm starting out mapping and would like to get an idea of how each size of turbo behaves etc.
Ideally i'd rather have a larger turbo running a percentage of it's capabilities rather than a small turbo being pushed to it's limits. If you push a turbo to it's limits you run the risk of creating a lot more heat as once past it's peak efficiency the turbo will basically become a heat pump. You can lower temps with bigger intercoolers etc but it's still not ideal. Also considering a bigger turbo will give more power with the same boost pressure as a smaller one as it's physically moving more air at the same pressure (which is why just bolting on a bigger turbo with no ECU changes is probably a bad idea)
There is actually a minefield of information on turbos. I can just pass on information as I learn it myself as I've learned a lot from the Saab crowd who have been mucking about with turbos for years.
Also never overlook other supporting hardware. Even something as simple as an exhaust downpipe can have a huge influence on the car and what you can do. I recently did a remap on a car that has identical components to mine (apart from a home made looking very restrictive looking also, downpipe) and it's an identical map (safe stage 2 aero map) I've had no problems whatsoever....however he's melted a set of plugs...My theory so far is the downpipe is so restrictive that it's not allowing heat to escape fast enough. There may well be something else such as the FPR not supplying enough fuel to the injectors causing a lean mixture (dangerous...very) which could be something as simple as a split/leaky vacuum pipe from the manifold to the FPR.
Another reason I want to run a bigger turbo is because I want the lag...simply because of the Saab gearbox being a weak link (engines will take 500bhp before needing any internal work)...It's torque that kills the boxes and a late spooling turbo will shift the powerband up the rev range to effectivly limit the torque, I do have a boost limit set in first and second to have some form of safeguard to the box.
Another thing to note about converting N/A to turbo and it'll have been said a million times before...standalone management or a proper remap. I've heard of people just bolting up a turbo and hoping the ECU will adapt...not likely...what is more likely is ECU see's positive manifold pressure/high MAF reading and shit it's pants ....also not be able to supply enough fuel or correct ignition map and back to the lean mixture thing. That usualy equals remodeled pistons etc
Basically research is key when playing about with forced induction
Feel free to ask away and i'll help with what little i've learned so far
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