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Thread: 496 Mag Exhaust Manifolds, Performance?

  1. #1
    davis777
    Anyone have any reccomendations for upgrading the stock 496 Mag exhaust manifolds and risers?
    I currently have a stock system with Corsa diverters and a Y Pipe.
    I have looked into Custom Marine's Sport Tube system, and they look bitchen but pricey at 4K
    What about Eddie Marine Thunder, Gil Marine or some others?? Custom Marine boasts 50-60HP gain. Would you see some gain from these other Manifold Mfrs. if the Mag could breath better. Merc claims they are high performance manifolds and risers and the EMI Thunders look alot like the Merc stock manifolds. I have the standard 375HP 496 Mag and I just can't justify $4,500.00 for the Custom Marine Headers and install costs, I would rather spend 11K and pick up a fresh 496HO version.
    Any suggestions,
    Thx,
    R-

  2. #2
    carreraboat
    try this
    http://tpmarine.com/
    ask for don i think he has some in stock and some performance numbers he has done some lake testing

  3. #3
    Sweet Addiction
    Does anyone have some real world Data for these. They sound like they are in my budget. Really thinking about getting headers so I need some feed back.

  4. #4
    shadow
    Anyone have any reccomendations for upgrading the stock 496 Mag exhaust manifolds and risers?
    I currently have a stock system with Corsa diverters and a Y Pipe.
    I have looked into Custom Marine's Sport Tube system, and they look bitchen but pricey at 4K
    What about Eddie Marine Thunder, Gil Marine or some others?? Custom Marine boasts 50-60HP gain. Would you see some gain from these other Manifold Mfrs. if the Mag could breath better. Merc claims they are high performance manifolds and risers and the EMI Thunders look alot like the Merc stock manifolds. I have the standard 375HP 496 Mag and I just can't justify $4,500.00 for the Custom Marine Headers and install costs, I would rather spend 11K and pick up a fresh 496HO version.
    Any suggestions,
    Thx,
    R-
    If you want a cheap easy way to get the best out of your stock exhaust,
    removed the turbulator plates between the riser and manifold.Take about 20 mins and people have claimed 3mph gain.Second if you take the manifold off and port them they will free up some flow.The runners between each port have quite a bit of material that can be removed.I'll sllok for a pic.

  5. #5
    shadow
    Heres a pic of the turbulator between the manifold and riser.
    Choked down to 2" you can remove the 4 nuts holding the risers on,lift the riser up,remove the turbulator plate.
    The gaskets are reusable if not damaged,you can also run a bead of high temp silcone around it for insurance.
    http://www.hotboatpics.com/pics/data...CF1482-med.JPG

  6. #6
    shadow

  7. #7
    Sweet Addiction
    so maybe your telling me that aftermarket headers are a waste of money. Ok, listen to my problem first and see if you can justify what is going on, and see if I was going about fixing it the right way.
    Ok, I am running the 496 mag, I am spinning a Bravo 1-24 pitch, I was running about 4700 RPM.
    I took the prop in for lab work, too out the turbulators, and went back to the lake. I lost about 4 mph, and was only running 4600 RPM.
    So I though to myself, why not buy some header to free up some HP, and get a couple of hundred RPM's back which would put me where I want, and not mess with the prop anymore.
    So does adding aftermarket headers justify what I am trying to do, or does my theory suck.

  8. #8
    shadow
    I,d say if you got the $$ and want to spend it.Have at it.I wouldn't mind a set myself.
    Definately will enhance performance,How much?All depends on which type,and the boat/set up.
    If you were running 4700rpm and had the prop worked and went down to
    4600 and lost 4 mph i'd be looking into the prop situation and who did the work.
    Theres no reason that if you were spinning a 24 @ 4700 prior to having the prop worked on you shouldn't have been able to atleast pick up a couple hundred rpm.
    I'd first find the prop that gets you to 5000rpm-5200rpm with your current set up then work on modifacations to your engine and prop from there.
    You can't fix a prop issue with exhaust manifolds or headers.
    Just my 02.

  9. #9
    Sweet Addiction
    Well I know eveyone is taking the turbulators out, but for some reason I keep thinking maybe that had something to do with it, but probably not. Well I am going to do some testing with and without the turbulators and write stuff down, if I don't see any change I am going back to the prop shop and have them shave it down some more. I will probably work on the headers later anyway.

  10. #10
    shadow
    Good idea. Run it with the turbulators in & out and that will answer that.
    Then from there you will know where you stand with your current prop.
    Good luck and keep us posted,there are plenty of curious 496 owners here.

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