The most important factor of any stressed part, factory or aftermarket, is HOW MANY STRESS CYCLES THE PART IS SUBJECTED TO".If you take a 40 year old factory rod that never sees more than 4000 rpms, say a 440 from a C body, that rod has never been stressed, providing it was well tuned and properly maintained. A HP factory rod has probably seen too many banzai runs and now you are using it in a racing situation. It is only a matter of time and luck before a failure.