The GLM website says that their manifolds take 6 seconds off of the planing time of a 21 foot bayliner.

http://www.glmmarine.com/manifolds/testresults.html

Wait... it's a 22 inch bayliner.

Hey Lib... what did you hear bad?

fund, use blue hylomar, it does not harden, it will reduce further corrosion. I have used it on all water surface gaskets and blower gaskets for several years. It was made for Rolls Royce jet engines, aluminium safe, and if you do disassemble, the gaskets just peel off.

never mind, I see you are considering headers, I would recommend revolution, do a search here, most everyone is happy with price and performance

The only bad thing I've heard was someone complaining about the quality of the casting. They said there was a lot of casting flash inside the exhaust runners. It was a posting on another website. Judging from the guy's other posts, he seems to have an opinion about many things. Everything else I've heard has been good. FPB magazine did a test of the manifolds, and picked up 3mph on a 21' sport boat with a 350 Chevy and Merc drive.
They changed the manifolds right at the ramp.

I have also looked into getting a set for my 7.4L, but i would like to see some dyno results for something, he has no info other than "increased performance".

Fund razor,

I just bought the Aluminum version from him for my rebuild project. There was some white stuff in 2 of them but I wouldn't really complain about it. Just rinsed them out. They look better then stock Mercruiser and came w / all mounting hardware, plugs, etc. I went w / Aluminum to save the weight. My Mercruiser manifolds gave out in ~ 2.5 years and took both engines with them...Figured I try these out and check them every year.

I also liked the fact he actually answers his phone. He did not make any HP increase claim but said his customers had noticed an improvement. I will never really know as I am building 2 new engines and changing everything else.

I went ahead and pulled the trigger.

Two complete set ups for less than 750.00 was hard to pass up from a guy with a good reputation who answers his phone.

I went with the cast iron.
Did your mercs go out so fast because you are in salt water?