You say 400Hp now but what about in 6 months?
Anywho, Lets start out saying that "nothing can survive detonation". Most all the stock components can mechanically handle the stress and tension forces applied at torque levels around 500- 600 Ft/lbs or more. It is the vibrations and wave after wave of shock do improper flame speeds, pre/post ignition, incorrect timing curves, etc that warrants the forged pieces that can handle the forces that co reside. P.S. If you think you can tune your car good enough to put 600Hp on stock components then mo power to ya!
Now moving past that part of it, If you truly are not going to keep buying larger and larger turbos, because you can just bolt them on, then the stock crank and rods are good for about 500HP at the FW.
Say you need to replace your crank, well then do a price compare between a 4340 Chinese crank and a stock replacement. Two years ago, I bought a stock stroke 4340 CAT crank for $400. Stock rods are pretty cheep if you need to replace yours (doubtful), but there are good rods for appox $500. The added expense in going forged for your rotating assemble is the getting a neutral balanced harmonic balancer and flexplate together around $600.
I will say billet steel center mains caps is no brainer if you have to machine anyways.
Most important is the engine builder, most competent shops do not have a clue how to build a BuickV6. Yea some on here will say “WHAT I built mine in the sand box outside and it has been running for 30 years”, but there are countless accounts of builders setting up the tolerances too loose or not checking the rod side clearance, or something. SO do a good job at picking the engine machine/builder. Make sure he has some proof to building strong Buick engines.
As to the 400 RWHP combo – that can be had on this forum with a few strokes on the key board. Any modern 61 – 62 mm turbo can provide enough air flow on a set of cleaned up stock heads. OH go with a roller cam, I know it is appox $800 more, but dang it is nice to have in a street/strip application.
Good Luck
