Now, would he be raising the compression ratio or lowering it. I think by increasing the volume of the combustion chamber area he would be lowering compression RATIO, but increasing actual compression values by getting more air into that area due to increased bore and piston. It is harder to see the actual compression without testing it while the engine is running. By broken I would think too tight of ring gap or poor pistons, but by you saying that you are running down the highway normally and they break I would say detonation. The TBI is tuned for a stock 350 and it isn't a very smart fuel injection. By increasing the size and air flow at the same time I think it got too damn dumb. Sorry I really don't like TBI at all. The thing is, check your timing and use some premium or bump up the fuel because at that speed/load likely lower rpms, some throttle tip in possibly, it is quite prone to detonate. The timing is high because you aren't baggin on it and the stock TBI just ain't cutting it I guess. OR maybe it just doesn't like you and it wants to die and be laid to rest??