Big Block Billy

Ditto ! Inconnel exhaust ! Marine engines have very high exhaust temperatures because the motor is working hard. @ $200-$300 a set, they are some of the best parts for a boat motor.
Cheap exhaust valves will only result in a future failure. Even the inconnel valves should be changed if pitting is found where the head and stem meet. Like the Stainless headers, the metalurgy eventually changes in the valves, especially if subjected to reversion. Only use used valves that have been thoroughly inspected, and ground. If in doubt throw them out. Same thing with valve springs, buy the best that you can afford, to keep the motor alive. My friend's boat with the 572's dropped a valve. It had a cracked guide, and an intake valve fatigued and let go. In the end, doing things right is the only way to go. Instead of going boating we should have had the heads re-done, or rebuild both motors instead of just one. Now he needs a motor.

lowflyin

That's exactly what happened to the motor that my present 502 replaced, even cracked the deck on the block...all was destroyed except the forged crank. I didn't hear of inconel valves until this new motor was complete. So I guess now you know why I have this concern about the integrity of the valves. Does Mercruiser use these?

PatriYacht

Mercruiser uses Inconel valves in all of their high perf engines. They used to put them in everything from 370hp up. I'm not sure if they use them in the 496 black motors but everything from 500hp up uses them.

Big Block Billy

You're not alone with the 502 having valve failure. They have the same heads as the 454's. And the same Eaton GM 2.19 +1.88 car valves. And make more power which equalls more heat on the valves. Better quality valves should be used with nice big valve margins. forget about necked down "race" valves. It know it would suck, But maybe consider pulling the heads and doing an valve job with the Inconnel's . If you want more power go with the 2.25 intakes. Going with the bigger(1.90 exh.) valves isn't worth it. Especially if you have to have hardened seats installed. Whatever you do durability is better than what it costs, and better than short lived power. I'm still trying to get that through my head. Talk to the machine shop and find out what valves were installed. Some inexpensive valves made in Brazil are made from a very good grade alloy, and are better than the GM's. Any good valve should have markings on it near the top of the valve stem. They may have the alloy #, or Manufacturer's name on them. You may get lucky. BBB

lowflyin

Thanks guys. Actually the motor that self destructed WAS a 454, but since I needed a block anyway I went with a 502 this time. For right now I think I'll run what I've got since it's brand new and only has about 10 hrs since the build, but I'll probably pull the heads after this coming summer. I was thinking about going with more cam anyway. Are you guys saying I should go with inconel exhaust and leave the stockers on the intake? And...do you think there is a noticable increase to be had from going to 2.25 intakes?

z.zuperboat

Go with the manley severe duty intakes.

formula31

I second all this valve stuff, having broken my share of motors due to valve failures. Inconel or Feria exhausts and Severe Duty intakes. I went from 1.19 intakes to 2.25. No noticable difference in boat speed for me.

lowflyin

Thanks for the info. Yeah, I guess bigger intakes is one of those things that makes a small increase on paper but not enough to notice by itself. When I do the heads again I'll probably still go bigger anyway though. It might work better with the bigger cam I'll be using. You know how it is...it all helps in the big picture.

Big Block Billy

Like most improvements, what works for you is what you want to do. Unfortunately what works well in someone else's application may not serve you well. All you can do is get some input from others, and ultimately make an informed decision for yourself. Based on the big picture, BBB