Ive got 60k miles on my 305 TPI. 20k of that was mildly supercharged(6psi). So, two questions: When should I start to worry about lower end rebuilding, and how much power can a stock 305 lower end take, without upgrades?

 

You should have had thicker head gaskets installed with the supercharger. These lower the compression on the engine to prevent it from throwing rods.

The stock lower end will be ok as long as you don't beat on it all the time.

 

Heh, well I dont beat on it with a stick or anything, but I am something of a leadfoot, and dont turn down races when they are offered to me. As far as rod throwing, the supercharger was too mild for me to worry about. I did blow the headgaskets early though(at least I thought so at about 50k miles), the supercharger certainly adds more strain. If I ever get an engine that I am happy with, as far as stability goes, then I still plan on 12-15 intercooled psi, in which case it would be wise on my part to lower compression down to about 9:1.