While working at AMS engines we would dyno about every second day. Just by locking out the distributor on a healthy street engine would stabilize the curve and would add a automatic 10hp. Not to sure what this guy is talking about since the common knowledge after 100's of dyno tests shows the timing is more stable so helps increase power. With a big stall converter the advance is going to be all in anyways so the main variance is not having weights and springs to flop around. Never once heard in my decades of building that it cost 20-30 HP. No logical reason for it to. The logical reasoning and proof shows otherwise. Can ask any of the top builders in the world. It's also well known that retarding the timing at the top of every gear can pickup MPH so if the timing does happen to drop a bit by swell that can be a positive advantage. Possibly one distributor that they used has a issue which caused negative results on a full throttle dyno pull. Most Mopar guys have known forever that they love a super fast advance getting all the timing in ASAP. That was the benefit of the light weight springs. When timing was all in by 1800RPM what exact full throttle timing curve is even happening lol. Honestly for going fast who really cares about picking up some performance under part throttle low speed rides. We aren't pulling a dang trailer up the mountains in our Hot rods lol. Which may be the point that's being refered to since it is a possibility to pickup some potential very low speed performance with a vaccum advance curve that adds extra timing. Both very different scenarios. One that really doesn't matter much in a full throttle race car. The other is to help save at the pump. I've tried both several times on my own street and race vehicles. The higher performance ones idled and ran much better with locked timing. The mild ones have a vaccum advance for increased economy but it's a noticeable difference in which ones have the more stable timing under heavy throttle.