I think the information here is a bit fragmented. First, hours on any performance engine between top end freshening is going to be somewhat dependant on how the owner is running it. If it sees lots of hours at 4500+ rpms, and its a 500efi it will need springs checked and replaced sooner than a average motor that sees less than 25% of its hours at 4500+ rpms. The real reason the 496 engines can go longer on top ends is because the valve spring is a better piece and the camshaft has lobe ramps that are easier on the valve spring and valve train. We have done so much valve train research that was used to develop our new valve train on our new Raylar BigPower head for the 496 engines that I can say surely that the valve train life on any 500 efi motor can be greatly increased by just changing over to a new valve spring like Comp Cams #26120 beehive-ovate wire single spring and recommended retainer. It is similar to the new special Eibach-Raylar valve spring we developed for our head. Because its a single -no dampner or inner, it runs cooler and quieter and that translates to more hours without spring degradation or breakage. HEAT IS THE ENEMY OF ALL VALVE SPRINGS!! Rub to pieces of metal together at high speeds and frequencies and you will have valve springs wear out sooner than single springs that are cooler at all operating ranges. Its not rocket science just good solid engineering and metalurgical knowledge. If this type of valve train is rigged on a 500 EFI or similar big block the engine life at even high rpm percentage use will be greatly extended to something more like 500 to 750HRS. Thts also provided the user does recommended engine service and oil changes coupled with normal recommended temperature operating ranges, and stays below redline rpms.

Ray @ Raylar