You can turn the full load screw up to increase rack travel at WOT. It's recommended that you install a pyrometer beforehand. I also recommend converting the wastegate actuator from vacuum to pressure control, to eliminate computer interference in your boost management. I've applied all of these treatments as well as some mild port work to the cylinder head, and the car is just as quick as the six cylinder diesels. Add larger pump elements, a bigger turbo and an intercooler, and the car will really wake right up.
Unfortunately I'm not aware of any dyno charts showing the stock configurations of either powerplant. This is the best I can do for the 603. You can see that the peak torque shows up rather low in the rpm range, which is why these diesels feel so quick around town.
I put a 2.5" turbo back straight pipe on it today, getting windows tinted tomorrow. Putting 17" take offs on it. Got new halo headlights and new tail lights. Next I'm getting a pyro and boost gauge and I'm turnin the pump up
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