383, 454 Gas V8 engine sources- any experience?

Discussion in 'Gas Engines' started by Toolate, Sep 9, 2013.

  1. El_Guero

    El_Guero Previous Member

    You would be better off getting a boat that was designed for slightly more speed, rather than trying to push a brick ....

    Just my 2 cents.

    Wayne
     
  2. Toolate
    Joined: Sep 2013
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    Toolate Junior Member

    Yes- that is it and I dont expect more than 16kts or so. I am fine with that.

    The top one was recently sold and it had been repowered with a 6.1 gasser. I couldnt find out performance #'s though.

    Any thoughts on what GM might offer direct that would help? Prefer to stay small block.
     
  3. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    The "delivery weight" version of your boat can be pushed to about 20 MPH. A delivery weight boat is dead nuts empty - nothing in the tanks, a single crew member (skipper), no anchor, no dock lines, no cushions, not even curtains on the windows. Once you add the usual elements, (anchor, rode, fire extinguishers, fuel, water, a cooler full of beer, etc.), the speed drops down, often fairly quickly. You boat has some "capacity" so you still can run 17 MPH with a modest load (normal equipment, supplies and a couple of crew).

    The boat does best with 200 to 250 HP. Applying more then this is just a fruitless attempt at a physical impossibility, based on hull shape.

    Again, I wouldn't order directly from GM, mostly because they charge twice as much as anyone else. All of the GM packages (305, 350, 350 Vortec, 383 Vortec, etc.) are available through the marine rebuilders or distributors at a considerable savings, usually with the same guarantee.

    A bone stock, second gen, carbureted 350 (two piece main) will produce 220 to 240 HP. This is the cheapest way to go and parts are very plentiful, plus they're easy to work on, without special diagnostic tools. A Vortec version will have fuel injection, which is a more reliable induction setup, but also more expensive and more difficult to work on. These will produce slightly more power, usually about 250 - 260 HP. The EFI option adds about$1,500 - $2,000 to the price of the base engine. Contact FirstMateMarine.net and look at what they have. You can get a 355 small block (slightly punched 350) with 360 HP, which of course is way more then you need, but if you must have it . . .
     
  4. Toolate
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    Toolate Junior Member

    Thanks PAR,

    I spoke to that company and they are sending me some information although the web site was down and I called and spoke to their technical department who referred me to their sister company (as he called it) Blue Print Engines. Getting some info on their 355 and 383. Any experience with either of these companies? I appreciate your time and thought on this.

    I looked at some of your designs to by the way. Very interesting stuff- would love to quit my life and just build wood boats but the bills keep coming....

    Not looking to make a racer out of her, just give her a little life and a steady 16kt cruise is reasonable as far as I have heard with these hulls. There is apparently a 30' Sisu with some huge engine that makes over 30kts in the lobster boat races in maine. I can only imagine what the fuel economy is like.
     
  5. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Blue Print is a company I've dealt with many times and their marine division is FirstMate. Blue print is an engine rebuilder, making stock replacement and higher performance versions as well.

    You don't need a performance engine, again simply because of the amount of power you need to drag all the water you'll need to drag at higher speeds. A stock 350, producing 240 - 260 HP will offer the best economy for the speed range you want, assuming the boat isn't overly burdened with junk and crew (most are).

    A stripped down Sisu, with 700 - 1,000 HP will scoot pretty good, but it'll drag half the local harbor along with it and you can watch the fuel gauge move at gallons per minute.

    It's a physics thing, not an amount of power thing. The hull just isn't shaped to do well, much over 14 knots. You can force it (as I've mentioned) but it'll trim poorly, fuel usage will dramatically rise and the boat will get progressively skittish, as speed rise. It's not a proportional change, as you might think. For example, if you double the power you have right now, you'd be lucky to see 18 maybe 20 in dead smooth water. That's a hell of a price to pay for a few more MPH.
     
  6. Toolate
    Joined: Sep 2013
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    Toolate Junior Member

    And double the fuel consumption. I get the whole hull speed concept.

    So moving on from that. Would you say that it would make sense to go for a little more power so the engine wouldn't be working so hard?

    Compare a 350 V8 to a 383 pulling the same load at the same speed- different RPM's because the larger engine will make the same power as the smaller engine but at a lower RPM. Which will use less fuel?

    I have heard arguments on both sides of this. Some say yes, some say that fuel will be burned and converted to motion at the same rate so an oversized engine is a waste of $. Also heard that the added size of the trans/shaft will make the larger engine less efficient at a given speed.

    I am not sure on this but either way believe that a gas engine is likely to be happier the slower you run it for extended periods and so will the people in the cabin with it...

    I think, for the record, the cost difference between engines (5.0, 5.7, 6.0) is about $1800 for each increment.
     
  7. powerabout
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    powerabout Senior Member

    you need to keep the v8 under 3000 rpm otherwise big fuel consumption
    I have repowered a few singles where a 454 used less fuel than the 350 it replaced at the same cruise speed due to this factor
     
  8. rasorinc
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    rasorinc Senior Member

    Well you got an answer. With the hull you have speed is limited. If you can lay under the boat and take pics of the bottom looking up and maybe run a string line from stem to transom so you could see where it is not level and how far it is off level, there is a chance you could form a V filler form out of fiberglass that you could attch to the existing hull giving you a V bottom which would allow more speed. A lot of work..........not simple to do.
     

  9. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    A V bottom addition of some sort, will not help this hull. In fact it is a V bottom now, just not a lot of deadrise. Maybe 5 degrees at the transom, which is typical for this hull type, which is a warped bottom. This is an old school hull form, much like a sea skiff shape, just with tucked up buttocks aft, to permit lower speed economical operation.

    It's more a matter of gearing the available power for these hulls, if efficiency is desired, within the limitations of her speed potential. A slow spinning prop on a torque laden, but also slow turning engine is the ideal setup, though not especially typical for a gas installation. A big loppy diesel would be best, but heavy and expensive. Next up might be a long stroke, big block, geared to run at modest RPM. The cost effective setup is a small block, gear to swing a bigger prop slower, within the power band of the small block.

    A 350 and a 383 are basically the same, except the 350 has a 400 crank installed and a "30 over" bore, which increases the 3.48" stroke to 3.75" and the cylinder diameter to 4.03". This is a common over bore on this conversion, for example a 30 over bore, on a stock 350 makes it a 355. You also create what we call a square engine, meaning the bore and stroke are nearly the same (1.24 bore/stroke ratio on a stock 350, but a 1.07 ratio on a 383). This is fine for a street engine in a car, but not so much on a boat and delves into a well debated discussion about ideal bore/stroke ratios.

    Generally, you want a fairly long stroke, to develop torque, but you also increase piston speed, heat and other issues (induction efficiency, power density, etc.).

    Building a torque monster is something that any engine builder can do. You'll lose upper RPM performance and throttle response, but this is what you want, a fat, torque maker, spinning relatively slow. This is easier with a longer stroke engine. You'll pay dearly for this and the net result may be a few MPH gain in speed, with an engine just lopping along. So, if building a custom engine, look to get a large stroke to bore ratio.
     
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