I won't do anything radical unless I have the car in front of me. NA engines are a bit more forgiving of "ball-park" calibrations but boosted engines need to be carefully watched. Of the people I know doing chips, they tend to fall in this same area.
I will do the basics once I know what I'm dealing with (displacement change, injectors, cam specs, etc.) I ask that the owner to scan the car under certain driving conditions to dial in those basics (BLM, WOT O2, idle). Beyond that, it's a shot in the dark.
Certainly, if you have access to a dyno for the more detailed tuning it's very helpful. After that you have to go to the track to do any final power tuning. Dyno tuning will get you 90% there. The proof is at the track. Seat of the pants tuning is good for about 50%. Now take that chip and put it in another car. Will it work as well? Only the dyno and track know.
Beyond that, many tuner comes up with calibrations that work well on a given combination and can feel confident in giving it to you without fine tweaking. Perfect? Probably not, but good enough.
You have to exclude calibration changes that are made just to get the damn car to run from this conversation.
[This message has been edited by TK (edited 08-09-2003).]