We run full wet exhaust on ours. Either E-Tops, Stainless, Sweepers or Full stellings. We have all of them on the shelf so we can tune with what the client will be using. You can NOT tune an engine with car headers and have it be remotely close in the boat. Car headers also ad 80-100hp over a stock set of E-Tops. One reason our dyno seems more "honest" than most. We run pyrometers as well.
Here is our system, if you have any questions just give me a shout 518-644-3080
header-tailpipe-big pipe through the wall-outside into a huge concrete "muffler" sounds very similar to MDG setup.
those 575 pictures are probably 20 years old from our old website lol

Love it. I’ve always hated boat engines tuned with car headers. Seems risky to me for the tune.

We used my 50 gallon drum.. Im not 100% sure how we hooked it al up..

Bob Lloyd at Full Throttle Marine built a big silencer box with a bunch of marine mufflers coming out the top. I would imagine the water could be collected out of the bottom if desired..

That seems like a lot. Was this on a 1000+HP build? Smitty and I only saw a 22HP loss going from dyno headers to E-Tops and adding a flame arrestor on my NA builds.

What was your HP and cam spec?

The more overlap you’re running, the more a short runner boat exhaust will hurt.

584HP to 562HP
237/243 LS114

900hp blower motor yes

So Im buying 2 industrial grade silencers with 8" inlet/outlet to mount on outside wall of new dyno room for normal dynoing. Im also burying a 1500 gallon plastic tank that water from dyno brake is going to gravity drain into.Going to add extensions to top of both vents on that tank and when I dyno wet exhaust there will be a second set of exhaust holes thru the wall, will expand tailpipes from 4" to 8" pvc with 90s turning into the risers on tank. IF there isnt a clear expansion/size change on a tailpipe from its 4" or 5" and its extended with SAME diameter pipe, youve now created athe wolrds longest collector, Smitty