whats the general consensus on the amount of power these blocks can handle? (if kept detonation free of course)
Back in the 90's before the advent of "boards", a turbo Buick owner by the name of Fred wanted an answer to that question as well.
He was a member of the GN/TTYPE list and had access to an engine dyno. He built a production 4.1 block over a period of many months as he accumulated the necessary parts which was not an easy task back then?
The rotating assembly was all stock parts, none of them forged, he just hand picked the best available.
The real challenge was finding and obtaining the supporting parts to develop enough power, as the goal was 700 HP.
He did reach that goal and barely surpassed it when the block let go and ended the project.
Based upon his efforts, I built my first 4.1 with a girdle and hard block and this was before affordable forged cranks and rods were available. I ran this at the track for a few years in the low 10's, and sold the engine. Second owner used it hard for a few years and sold it to a person that beat the hell out of it but never hurt the block.
With the advent of forged cranks and rods, we no longer used girdles or hard block on stock blocks, but we do install 2 steel center caps.
At the time Fred did his testing, very little data gathering info was available, and do not recall details on his fuel supply or injectors, as there was very few supporting parts available.
My experience has show the 700 HP level can be reliable with the current tuning and data products available.
A street driven GN with 700 HP available is very hard to recon with especially if this power/torque can be utilized with proper traction.