Joe, best thing I could suggest is look up the factory rpm specs for your hemi.
Best performance will typically come from shifting at the peak POWER rpm.
On the shift that will typically bring the rpm back to somewhere around the peak TORQUE.
A canned tune is ok, but you'll ALWAYS get much larger benefits from a dedicated tune by a good operator on a dyno. Yep, take it to a good dyno tuner who can tune Diablo, and have them strap it to their dyno and tune it. It's not cheap (think $500), but real gains never are.
Maybe DynoSteve can help you? He's an Aussie ex pat now stateside, quite experienced with these. He dyno'd a 5.7 in a 300C with the factory tune while I was in the dyno cell, and I was astounded to see air/fuel ratios approching 8:1 at WOT high RPM. Those kind of numbers are ridiculous! As you know stoich is about 14:1. Obviously Chrysler runs them so rich to allow for every ounce of abuse that someone could dish out. That's why I've said before, clean up that fuel map, and there's ALOT of power to be had.
Now, my humble opinion is the canned tunes DO give you an improvement, but very slight given they also want to keep a large margin for all types of abuse. They dont want internet word spreading that an engine running their canned tune blew up (even though the guy might have been doing donuts in sand dunes for 3 hours before it finally cried enough).
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