mark 4 454 with 049 large ovalport heads that have larger valves installed. I keep getting bad leak down results after 20 -30 hours run time . I am getting 20-30% percent leakage on most of the exhaust valves (stainess). plug readings look good a full throttle. am I burning lean damageing the valve or seat? do I need inconel exhaust valves for a NA engine? will inconel valves hurt the valve seats? My cams are 112 centerline with stainless marine exhaust that mixes water past the transom. the exhaust valve do not seem rusty from reversion. any ideas?????

Did you check to make sure it has hardened exhaust seats?

The original engines in my current boat, the previous owner was talked into putting some older heads on it. As luck has it one set did not have hardened seats. To make matters worse they put one head on each engine. I only had 20-30 hours on the boat before it had zero compression on a cylinder.