There is a lot of controversy about how to protect your new rebuilt engine during initial start up, on the dyno, at the track or on the street. With high levels of flat tappet cam failures this has become an area of much concern. Without going down the road of flat tappet cams and lifters, proper lubrication is something we have direct control over. Using a special non-detergent oil for engine break-in has been around since the 50's and even earlier. Many like to dump their favorite additive in for break in yet are still using a high detergent oil. Many of these additives like GM OES and STP are heavier than your motor oil and they may sit in the oil pan too long before fully mixing with the oil and getting to the right place like on the cam lobes before damage can take place. Break-in oil is not only important for flat tappet cams but for all engine parts that are protected by your lubrication system. Rather than claiming to be an expert and maybe be giving bad advice I decided to provide some links from the experts and you can decide for your self. Happy reading.
https://www.youtube.com/watch?v=teDgJgPeeeU
https://www.speedwaymotors.com/the-t...lly-help/53663
https://www.youtube.com/watch?v=BM_sM9tsmoY
https://vpracingfuels.com/tech-talk-...hy-it-matters/
https://blog.amsoil.com/why-you-shou...rts-equipment/
https://www.enginebuildermag.com/2019/08/break-in-oils/
https://www.hemmings.com/stories/bre...the-right-oil/
https://butlerperformance.com/i-3164...html%3Fq%3Doil