This is an interesting read.
Here is my personal experience:
I have a 2005 LLY. It has basic twins, 30% injectors, LBZ cp3 and built trans. Lots of other small stuff, but that is what is making the power. When I finally figured out my low rail pressure issue, A scored fuel rail letting fuel leak by race valve, my HP went from 530 to 675 with no change in tuning. I drove it hard and made lots of 1/4 mile passes. I knew the rods had bent a bit due to how it acted on cold start up. I drove it another 100k miles on a 600hp tune daily. Finally decided to refresh it.
Since I had low mileage LBZ rods and a set of low mileage LLY pistons, I used those to rebuild it along with all the standard stuff for a rebuild. I figured I would tune it for 650hp and be happy all day long. I drove that motor just over 35k before I broke a piston. Here's the difference between the two motors. I actually used the 650hp on the new motor a lot. I don't mean drag racing or street racing because I did that a lot with the first motor. I had around 15k miles of towing on the 650hp tune. Was a lot of fun, but it eventually broke a piston.
The moral of this story is this:
You hear everyone say their stock motor dyno's 600-700hp and lives all day and they beat the crap out of it. 10 seconds here, 15 seconds there of full power. Try using the that full 600+hp for more than 15 seconds at a time such as pulling a 3 mile 6% grade at 20k combined running 80mph and I promise that stock motor will not last very long. I have climbed hills on my 650 tune where the boost was at 40+ for 2-3 miles. And that is why I broke. Stock pistons have a certain life span. I would say maybe 20 minutes of total run time at 600hp and they are done. Just an estimate
My best advice would be this. If you can't afford to do it twice, don't build it at all and be happy with the lower horsepower. My lbz is fully built and spends its life in the 800hp range. It has broken twice. There is no safe horsepower. Stock motors have broken cranks and pistons on stock tuning. If you do build, build it for a 1000hp, and run it at 700hp and it may last a while for you.
