I have the GGB Extremme "Transom Mount" on my 525efi and love them. They made a big difference in the exhaust noise level without affecting the performance or top speed. Mine we installed by the dealer when I bought the boat. Shoreline Marine in VA.

My motor in my 272 Baja made 944 hp (blown 540)on the dyno,boat runs almost mid 90's. I'm using stainless marine 3's with 5 inch tails adding water at very end. The boat was SO loud I could not tolerate it,the ggb clampons made it tolerable,it actually idles better and it lost NO top end. Lofty sold me the mufflers and fred also had them available at trick marine,Smitty