of course its possible to make more than 500hp from a 616. its just a matter of how much you are willing to spend. forged rods from Pauter, forged pistons from Wiseco or JE, ceramic coated pistons and chambers by Swaintech, custom billet crank from SCAT, Dart ductile sleeved block, 8mm super-stroker dieselmeken pump, custom manifolds from Wilson manifolds or Stainless headers, compound turbos, custom cam from Colt cams, and larger valves from Supertech. plus plenty of little custom bits and bobs. you could likely get over 600 from that set up, now for the low low price of ~30K$ or more. the only reason not to is there are better architectures to start off of. the only reason i chose to stick with the 617 architecture is for the challenge and satisfaction from actually getting real power after all the custom work needed.

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1985 300D om617: 8mm M pump 175cc 5200rpm, holset he221w @ 30psi, large A2W ic, compounds on the way.
KD9AFT
A&P