@shane_3800 I get what you are saying, if there is no limit to the level of stress and endurance of the block and rotating mass, then for the given 6 litre capacity as OP you could also create
“
A”: An entirely new induction path, customise a significantly upgraded fuel system, fabricate custom drag race headers to suit custom made cylinder heads that have a revised CSA.
Supposing further that money were no object (NB OP not overly keen on cost of lifting the lids etc) the brick wall is not any of the above. It is GM’s accepted engineering that limits the factory block and rotating assembly according to proven stress and endurance. Bearing in mind OP definitely doesn’t want to rebuild every few drag runs, quite the opposite.
GM warrants (NA 6.0 and 6.2) alloy short block to 480 and 319 T7 FI 6.2 block to 620 ft lbf but internally for the LS9 daily at just over 600 GM specifies incredibly exotic parts including forged metals and alloys in the rotating assembly.
All that’s to say I agree when the sky is no limit with all the money and specialty / custom engineering maybe also consider modified heads. But given limited resources and clearly defined parameters of stress and endurance limits, an overhauled crack-tested block TPP honed with forged rods and pistons (possibly crank) defines the next practical level for a performance build.
Apart from purely academic reasons, why would you anyone want, never mind pay for all the paraphernalia at “
A” above to suit larger CSA / head design if just hand tidied stock heads and a well planned build will outperform the bottom end?
Above point builds on my tuning pressure video posted here earlier - that also reflects the prevailing engineering trend in all ICE - VVT (and lift) wins convincingly over variable length and cross section runners not just for performance but for a road car most importantly efficiency through the RPM. BMW, Porsche, MB, Fiat (Ferrari) proved that over the past 20 years.
Apart from obvious mild hand porting and valve job (you get included else for quids with exchange o/haul heads) CNC / race heads are, for all reasons above, a huge waste of time effort and money and should be relegated to one of the overpriced last items to consider for a streetable sub $20k LS build in 2021.