The easiest way is to install a boost controller in the wastegate hose. They are fairly inexpensive and work well. Adjustments are then quick and easy. 14psi is just fine for the 603.

Please forgive my ignorance, but how does a boost contoller work hooked-into the wastegate hose, how does this work or affect boost? Also what would you say is the upper, yet safe limit on boost for these engines, if 14psi is no problem how about 16psi?

I have a medium intercooler that I'm planning to add and use that to add more boost later.

Thanks,
Bill

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Stable Mates:
1987 300TD 310K mi (Hans)
2008 Jeep Grand Cherokee OM642 165k mi (Benzrokee)