15 to 20 minutes at 2500 rpms. I actually fluctuate a bit, I'll change the idle speed every 5 minutes....up to 2800, down to 2200, etc. The key is to NOT let the idle go too low, or oil pressure will be inadequate, and also the lifters may not rotate (remember cam rotates at half crank speed). If they don't rotate, the cam is toast. Once 'worn in', they establish a wear pattern and everything is happy in the engine. I've never lost a camshaft using this method. I immediately change the oil and filter after cam break-in, getting all the metal particles, assembly lube, condensation, etc. out of the engine. Fire it back up, set the idle and timing, then work on the jetting. Naturally, while it's running during the initial break-in, keep an eye on water temp, oil pressure, and potential leaks. Helps to have two people. ALWAYS use a muffled exhaust for break-in (even on racing engines that don't normally use one), it greatly reduces the chance of strange noises getting obscured. I find it easier to hear the engine's internal clatterings if you wear ear plugs too, it blocks out the external noises.
Bob
