Cant view the pic but are these the corkscrew type baffles? If so, I had them in my boat and picked up several MPH by cutting them out. Stock 330hp 454.

On CP perfpramance's website under the muffler section the have a test on a 25' Daytona with a 502 mag. The boat did drop 12 db, but it also dropped 200 rpm.

The Hardin Marine one at the top looks the same as the double X.

http://cpperformance.com/products/Exhaust/024.htm

Do you have a wesite or phone # for them?

slip-ins
 

I installed a pair that look the same as in the pic, If I remember right I got them from Rex Marine. They seem to work well for me. I had to do something,I think it sounds good. I'm still not sure how it would do on a db meter and I don't think it would get the approval of most tree hugger types. I will say,I do boat where there a little sensitive and nobody's bothered me so far. As for performance loss I only ran it on the trailer without them. But I feel the boat performs as it should with a stock 7.4.

I tried them on my 502 mag. and lost 200 rpm, and also the tailpipes got so hot you could even touch them normaly they are only warm to the touch. I drilled a bunch of holes in the center plate and that helped a bit, but i only use them when there is a chance of a problem.
They do cut the noise down quite a bit.

I inquired about the same mufflers at CPPerformance. They said 100-150 rpm loss. I said No Thanks.

Splashandburn,
GGB advertises in the classifieds under exhaust.
They also have a website. GGB.CA. I think.
Wait a while for it to load.
Greg

Pantera572, did you complete the installation of these mufflers yet? If so, have you had a chance to try them out and which ones did you buy, the Extreme Variable Exhaust for the High Flow Louver?

Bam, Bought the extreme variable.
Looks like it will be done in two
weeks. I'll post pictures and my thoughts asap.