Merlin Heads on a 454Mag

[Lightning]

How much HP do you think Cast Iron Merlin Heads (Rect Port / Roller Rockers) on a stock 454 mag would produce over the stock GM heads? I am getting the motor rebuilt and decided to step up to these heads per the recommendation of many.

[Rubths]

How much HP do you think Cast Iron Merlin Heads (Rect Port / Roller Rockers) on a stock 454 mag would produce over the stock GM heads? I am getting the motor rebuilt and decided to step up to these heads per the recommendation of many.
I went from nice 990 heads on a semi stock motor rebuilding it with ported polished Merlin cast heads with roller rockers and the log exhuast and jumped over 100hp per the impeller rpm hp chart. I was told by my builder that if I was to switch to some nice headers I would pick up more hp and possibly another 500rpms.
You should see a 50hp gain but it would depends on how restrictive your exhuast is.

[Shallow Minded]

I've personally had a very bad experience with Merlin heads, dropped a valve seat twice. When I spoke to somebody at Merlin, he just kinda laughed when I stated it was a marine application. He strongly recommended not using them on boat motors. Just my $.02...

[steelcomp]

How much HP do you think Cast Iron Merlin Heads (Rect Port / Roller Rockers) on a stock 454 mag would produce over the stock GM heads? I am getting the motor rebuilt and decided to step up to these heads per the recommendation of many.
IMO the rect port heads, even stock GM are too big for a stock 454 Mag. Merlin oval ports, which outflow GM rect port heads, would be much better for that app. I don't know about dropping a seat in a cast iron head.

[Lightning]

I've personally had a very bad experience with Merlin heads, dropped a valve seat twice. When I spoke to somebody at Merlin, he just kinda laughed when I stated it was a marine application. He strongly recommended not using them on boat motors. Just my $.02...
The heads from Merlin are setup for cars, they need to be redone when you are putting them in a boat.

[Shallow Minded]

I agree. I had the standard stuff: inconel exhaust, SS intakes, fresh and ready to roll in a mildly blown marine application. I like to think my machinist knew what he was doing. What I do know is that it happened twice and the Merlin/World Products reaction was less than comforting when I told him my story.
I know plenty of guys who haven't had a problem, too. I just thought I'd share my experience.

[rpm2]

I have a set of fully ported Merlin oval ports along with a ported matching intake fresh and ready to go for sale. 2k plus shipping. If they are not as described, you can send them back for a full refund. They are setup for hyd roller up to .650 lift.
Heads (r_dash@charter.net)