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Thread: C-18 Performance Mods

  1. #1
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    C-18 Performance Mods

    I restored a 16 last year and this year I purchased the boat I plan to keep for a while, a super low hour, pristine 2005 C-18. It came with the Mag 350 MPI/ Alpha package, captains call, transom mufflers. I am in Denver and most of the lakes we run on are above 4,000' elevation. The 18 is nice with the MPI setup for changing altitude, but just not enough power at altitude for serious man fun.

    Over the winter I am planning a major performance enhancement of the power unit/drive and i wanted to see if the knowledge base here agrees with my approach to this boat. We travel a lot to different lakes throughout the west and the 18 is the perfect size boat for our use. We do a fair amount of pulling skiers and toys so the boat needs to be pretty versatile. I like everything to be fast so it needs top end. Here are my requirements:

    1. 80mph at any altitude. Retain factory fuel injection system and run on pump gas. Retain the single point water drain system.
    2. Good hole shot for pulling skiers
    3. Nice cruiser for evening wine cruises with the wife and friends. Not too loud from inside the boat, sounds great outside.
    4. A performance transom look, but with a swimstep for water/ beach loading.
    5. Not concerned about spending money to do it right
    6. Good ride, handles great at all speeds
    7. Good reliability and room for performance growth
    8. Basically, your classic sleeper that delivers surprises and smiles

    Here is my plan:

    1. Keep the 350 Mag as is (75 hours) and add the whipple supercharger kit for the late model MPI system. Add an oil cooler. I already installed SM exhaust manifolds and the mercuiser Smart Vessel Mobile. The whipple setup nets 450Hp with almost no loss at altitude and loads of torque. From what I have read, 450hp should get me to 80 no problem. I'll add Livorsi fuel pressure guage and boost gauges to the dash.

    2. The Alpha should really go because of the whipple, so I am planning on replacing it with a Bravo X 1.5. I'll pull the motor and replace the transom assembly with a new Bravo unit. I am thinking of keeping the Bravo lower because of the pulling and not go with a shortie given that top speed is not the only goal. Either a Mirage + or Hydromotive IV prop, and drive shower. While the engine is out I will probably just remove the through prop exhaust option and run transom only. The stock Corsa mufflers are quiet enough. Add Bravo sea pump and plumb for transom hose hookup.

    3. I already purchased a set of Mayfair 12" K planes. I am going to set them up so I can still fit a set of Imco steering rams on the transom and run the Brazil cable setup for the steering. Looks like the outer edge should be right over the outer chine.

    4. I want to add a pair of Eddie Marine billet swim platforms (red) under the exhaust mufflers right above the waterline. In the west you are always on a beach, and in the water, so you need to be able to get in and out from the back. I have looked at all the options and this seems to make the most sense to me. There is just barely enough room on the transom to do this along with everything else when planned together.

    5. To round things out I already acquired a Hardin marine set of billet controls, new Sony satelite/ USB/ Bluetooth head unit, wet sounds speakers, 10" powered sub, Accon pop up cleats, Accon pop up LED bow light, and steering wheel mounted trim controls.

    So here are a couple of questions. Does this plan seem to be the correct approach to achieving my goals? Would a shortie make the boat basically non-skiable? I am really shooting for an epic classic here. Something that really stands out but is good for more than just fast passes.

    Thanks for the reactions and input.

    Chad
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  2. #2
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    Hopefullyosur866 will see your post. He has tremendous experience with where you are going. Is that an "open channel" steel trailer? I have been looking for one, who makes that?
    1972 16 OB - C16B-63 - "Surface Tension" Resto Project
    1974 16 OB - DMR16106017-B - "The Mule"

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    Yes, osur866 seems to have the most experience here, along with Skilling. I have read most everything he has posted on his development. I am most interested in his opinion on stock Bravo vs shortie lower and effect on pulling skiers/ toys.

    It is an open channel trailer. It is a Trail Rite out of Santa Ana, now out of business. Performance trailer in SoCal has taken over most of their business.

    It has the folding tongue and surge disk brakes. The boat sits at a nice rake on the trailer and low in it for easy deployment. I added the ratchet tie downs and the F2 winch. I also clear filmed the fenders and forward rails to protect the paint. It tows like a dream.

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    Instead of going with a bravo water pump I would go with a crank mounted one.
    You won't have to worry about your present serpentine set up and impeller changes will be much easier. Also , I would consider drive ratio. If you were to drop down to a 1.36 that would put a lot more propellers in the mix. Having said that , there very well could be a good reason most use a 1.5 ... Also , Mercury used a 1.68 ratio for altitude so do a little digging on that subject. First and foremost you are going to want to check your bilge for cracking around the stringers where the L brackets are bolted. My 2004 18 had some cracking in the bilge area that needed to be fixed. The old saying safety first applies here. You need a full hydraulic steering setup , not the cable driven kind. As others have said , Steve will be a great resource to you !!
    better to die on your feet, than live on your knees

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    Quote Originally Posted by smokediver View Post
    Instead of going with a bravo water pump I would go with a crank mounted one.
    You won't have to worry about your present serpentine set up and impeller changes will be much easier. Also , I would consider drive ratio. If you were to drop down to a 1.36 that would put a lot more propellers in the mix. Having said that , there very well could be a good reason most use a 1.5 ... Also , Mercury used a 1.68 ratio for altitude so do a little digging on that subject. First and foremost you are going to want to check your bilge for cracking around the stringers where the L brackets are bolted. My 2004 18 had some cracking in the bilge area that needed to be fixed. The old saying safety first applies here. You need a full hydraulic steering setup , not the cable driven kind. As others have said , Steve will be a great resource to you !!

    Thanks! I will look into all of the above.

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    What is wrong with using a Brazil Manifold to control the steering rams? Is the main goal to get rid of the cable system altogether?

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    Transom Layout

    Today I laid out the transom. I confirmed that I can fit the Mayfair K Planes, Dual IMCO Steering Rams (6.35" offset) and Eddie Marine swim steps all on the transom together. The swim steps should be just above the waterline. I am going to have to make adjustments to the brackets because the transom curves and does not have the same vertical angle on the outer bracket. I should be able to just shave off the material and retap the mounting hole. The layout still allows for me to tie the boat down by the rear eyes.

    I don't think the swim steps look too bad, at least everything works together. All of my gauges, bezels, controls and speakers are platinum color so I ordered a set of the swim steps in clear anodized to compare. I got these red ones for the 16 and never put them on. So what do you think red or platinum?
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    The swim steps look good. They're only noticeable because the boat is on the trailer, but I like them. When its in the water they'll be the perfect height and look like they'll sit right on the water line. Good choice.


    The K-planes mounting plate may not fit flush to the transom. At least that's the issue I had with the trim tabs on my 22.
    You may have your own plan, but this is what I did to make them fit on mine. (See post #55)
    http://www.donzi.net/forums/showthre...O-to-502/page4
    Why is faster never fast enough.

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    Quote Originally Posted by yeller View Post
    The swim steps look good. They're only noticeable because the boat is on the trailer, but I like them. When its in the water they'll be the perfect height and look like they'll sit right on the water line. Good choice.


    The K-planes mounting plate may not fit flush to the transom. At least that's the issue I had with the trim tabs on my 22.
    You may have your own plan, but this is what I did to make them fit on mine. (See post #55)
    http://www.donzi.net/forums/showthre...O-to-502/page4

    Thanks for sharing the thread. Good solution for the spacer. They aren't flush so I am going to have to do something similar. I have to fit the swim steps too.
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    Love the plan!

    Are you sure you need to ditch the Alpha drive? Lots of guys running 400+HP strokers thru Alpha drives. If yes, I believe the Bravo is longer so you'll need a shorty. Also the Alpha SS runs good on the 18s so a short drive works.
    The cable helm has slop but it debatable if just adding the dual external rams is enough.
    Thanks, Patrick


    1996 22' Classic

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    Quote Originally Posted by Pat McPherson View Post
    Are you sure you need to ditch the Alpha drive? Lots of guys running 400+HP strokers thru Alpha drives. If yes, I believe the Bravo is longer so you'll need a shorty. Also the Alpha SS runs good on the 18s so a short drive works.
    The cable helm has slop but it debatable if just adding the dual external rams is enough.
    Pat, I was thinking that with the whipple the torque would likely destroy the Alpha, so it seemed best to just get the Bravo done while I have the motor out. I was going to pull the motor for ease of installing all the stuff on the transom, and at the same time change the gimbal assembly, remove the prop exhaust manifold, do the steering, clean the bilge, and set everything up. It is a real pain working around the motor. It is a bunch of dough to change it but the B1 just gives you more options.

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    Quote Originally Posted by Turbochad View Post
    Thanks for sharing the thread. Good solution for the spacer. They aren't flush so I am going to have to do something similar. I have to fit the swim steps too.
    FYI: If you do try the same thing, don't fully tighten the mounts when setting the putty. Just snug them up. If you fully tighten them, you will flex the mount and/or the transom and defeat the purpose of making a form fitted spacer.
    The ones I showed in the thread were my second attempt.
    Why is faster never fast enough.

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