any day. He has been building 9 second and 8 second engines for many years. Including turbo charged applications. He did my heads if you seen the pictures and bench flowed it before and after for increase of cfm. What he was saying if the valve spring are too weak and you rev it past it's range, it will bounce causing the condition you just described. This doesn't mean all single coil springs are weak on the VG motor. I just wonder why Z1 has this problem with Ferrea valves but SGP hasn't reported any problems. Ferrea valves are used in lots of high performance engines.