Mufflers
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Mufflers

  1. #1
    Junior Member Lightning23's Avatar
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    Default Mufflers

    Is there any performance advantage changing the Standart 4" slip in mufflers to the flapper type on a 496 Mag?
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  3. #2
    Senior Member Dana Marine Products's Avatar
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    The 496 mag engine (375 HP) seems to run pretty good with a little bit of back pressure. We recently conducted some very detailed testing on a Baja 242 Islander with that very engine.

    A claim had recently been made about a 10 MPH gain from an exhaust install on this boat. Many here didn't believe it, and neither did we. The owner of the boat was gracious enough to allow further testing with accurate tools and a certified driver. The results are finished. We don't have the ink dry yet, but there is some worthy information related to your question.

    The boat did indeed run exactly the same with the stock exhaust compared to the aftermarket system that was supposed to provide a 10 MPH increase.

    The interesting thing on this boat is that we could run the boat full throttle and switch the silent choice closed with only a 1/2 MPH loss. Every boat is expected to react different to power gains and losses, but I was shocked to see such a minimal loss in speed.

    My opinion is that the 496 Mag (375 HP) engine enjoys a little back pressure. There will most certainly be a variable in results between different boats and potential speed gains. A full report will soon be available detailing our findings.

    Testing the muffler theory on your specific boat is the only way you will be able to determine the results for your boat. You may find an increase, you may not. What your boat produces will most likely not be the same as what Billy's boat produces. If you want to try it, and you're willing to run a fair test, meaning that the test will be conducted in the same air and water conditions, with a GPS speedo, I'll loan you the mufflers to try. If they work, you can buy them, if they don't, you can send them back.

    I'd like to know the results you come up with.
    Things May Come To Those That Wait, But Only Things Left By Those That Hustle.
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  4. #3
    Senior Member CoolCruzinCobra's Avatar
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  6. #4
    New here Beer:30's Avatar
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    The 496 mag would be the first internal combustion motor in history to gain any power with backpressure. Tubular headers actually provide SCAVENGING, which PULLS exhaust out of the cylinders.

    At the races, most cars are "uncorked". Open headers (at the collector(s)) or "zoomies", which are just pipes on each cylinder. Why don't they just run open ports and not even run the "zoomie" pipes? No scavenging. The exhaust pressure moving through the pipe from the last pulse pulls the exhaust on the next stroke.

    Removing the turbulators from the stock exhaust dyno'd at +7hp. Moving from stock manifolds (full of backpressure) to tubular header or performance manifolds (Stainless Marine, Dana, Revolution, etc) removes more backpressure and starts to create better scavenging.

    Introducing water into the exhaust also creates backpressure. If the water was stopped and dumped out of another port (dry exhaust), there would be even more scavenging and HP increase.

    Lawn mowers, scooters, ATVs, 4-cyl, 6, 8, 10 - it doesn't matter. They will all increase power with less backpressure. Backpressure puts spent gasses back into the cylinder(s), which corrupts the fresh intake charge. Any amount is a negative, not a positive. Minimizing backpressure with the setup(s) we have is the best we can do.
    Quote Originally Posted by gn7 View Post
    EFI is the wave of the future. There can be no denying it. Electronics have been on the leading edge of our entire lives. Not only os the magneto dead, but the standard issue CDI is wavering. Its all about total fuel, air AND spark control. Anybody that thinks its not has their head up their ass.


    2001 SleekCraft 30' Heritage SSB, open-bow mid-cuddy. 496HO / Bravo-I.
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  7. #5
    Senior Member Dana Marine Products's Avatar
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    We've dyno'd the 496 several times, both mag and HO. We've seen HP and torque increases by adding DMP exhaust on all occasions.

    The question is about a performance advantage by changing his mufflers, generally referring to a speed increase. In my opinion, there is no direct answer to the customers question other than what I initially provided.

    I could blow smoke up his a-- and tell him he's going to see a difference, but I would be a fool to say it. As mentioned, his boat may increase, it may not. Most boats over 22 feet long will not react to small HP gains such as 5-15 HP. Some will, most won't.

    With our dyno time and boat trials on 496 engines, it is our experience that the 375 HP mag engine just doesn't have alot to gain with MOST after market exhaust systems. Most cast aluminum systems offer little or no scavenge affect on the exhaust. These short runnered cast systems equipped with a 3.5" ID riser are simply too big and will most likely lose torque.

    The real question is, what are we comparing it to? If you take an older 454 Mag or 502 MPI, you can usually get some form of gain by changing the exhaust because of the inferior exhaust system you started with. With the 496 engine, this is the not the case. The 496 system is a much better flowing system compared to old school Merc manifolds. Yes, removing the 2" inside diameter turbulators will show a small increase on the dyno. But that same stock 496 system equipped with the turbulators just out ran an after market system that recently raved of a 10 MPH increase. Most people would be surprised to hear that the stock system actually ran the same compared to this aftermarket system, but the stock system ran 50 rpm's better. Not a big difference, probably close enough to call them even, but the engine didn't run any better when it was equipped with this specific aftermarket system.

    Our Dana Marine systems have been specifically designed to scavenge exhaust through a 27" long primary and a Vortex cone assembly which is sized appropriate to specific engines. A 496 engine will actually lose 4 HP on the dyno with our #5 risers compared to our #4 risers. The #4 risers have a 1/4" smaller diameter Vortex cone compared to our #5 risers. We dyno'd a 380 HP big block engine at Westech where our DMP exhaust equipped with our #3 risers (3" ID) made more HP and torque compared to their dyno headers. They were shocked. If you open them up too much, you lose power. Slap a blower on it, and this whole theory goes out the window. At that point, get the biggest exhaust system you can afford.
    Last edited by Dana Marine Products; 08-20-2009 at 10:33 AM.
    Things May Come To Those That Wait, But Only Things Left By Those That Hustle.
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  8. #6
    New here Beer:30's Avatar
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    Quote Originally Posted by Dana Marine Products View Post
    We've dyno'd the 496 several times, both mag and HO. We've seen HP and torque increases by adding DMP exhaust on all occasions.

    The question is about a performance advantage, generally referring to a speed increase. In my opinion, there is no direct answer to the customers question other than what I initially provided.

    I could blow smoke up his a-- and tell him he's going to see a difference, but I would be a fool to say it. As mentioned, his boat may increase, it may not. Most boats over 22 feet long will not react to small HP gains such as 5-15 HP. Some will, most won't.

    With our dyno time and boat trials on 496 engines, it is our experience that the 375 HP mag engine just doesn't have alot to gain with MOST after market exhaust systems. Most cast aluminum systems offer little or no scavenge affect on the exhaust. These short runnered cast systems equipped with a 3.5" ID riser are simply too big and will most likely lose torque.

    The real question is, what are we comparing it to? If you take an older 454 Mag or 502 MPI, you can usually get some form of gain by changing the exhaust because of the inferior exhaust system you started with. With the 496 engine, this is the not the case. The 496 system is a much better flowing system compared to old school Merc manifolds. Yes, removing the 2" inside diameter turbulators will show a small increase on the dyno. But that same stock 496 system equipped with the turbulators just out ran an after market system that recently raved of a 10 MPH increase. Most people would be surprised to hear that the stock system actually ran the same compared to this aftermarket system, but the stock system ran 50 rpm's better. Not a big difference, probably close enough to call them even, but the engine didn't run any better when it was equipped with this specific aftermarket system.

    Our Dana Marine systems have been specifically designed to scavenge exhaust through a 27" long primary and a Vortex cone assembly which is sized appropriate to specific engines. A 496 engine will actually lose 4 HP on the dyno with our #5 risers compared to our #4 risers. The #4 risers have a 1/4" smaller diameter Vortex cone compared to our #5 risers. We dyno'd a 380 HP big block engine at Westech where our DMP exhaust equipped with our #3 risers (3" ID) made more HP and torque compared to their dyno headers. They were shocked. If you open them up too much, you lose power. Slap a blower on it, and this whole theory goes out the window. At that point, get the biggest exhaust system you can afford.
    Very good points, and all true.

    What you are describing is VELOCITY. It's the same with intake runners on cylinder heads. It's not a matter of having restriction by running smaller ports, it's keeping the velocity of the intake (or exhaust, in this case) up to speed. With the bigger risers the exh is just swirling around and not following the path as smoothly. Tighten up the cone and you are not adding backpressure, just increasing velocity.
    Quote Originally Posted by gn7 View Post
    EFI is the wave of the future. There can be no denying it. Electronics have been on the leading edge of our entire lives. Not only os the magneto dead, but the standard issue CDI is wavering. Its all about total fuel, air AND spark control. Anybody that thinks its not has their head up their ass.


    2001 SleekCraft 30' Heritage SSB, open-bow mid-cuddy. 496HO / Bravo-I.
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