Sidewinder 18SS LS Conversion?
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Sidewinder 18SS LS Conversion?

  1. #1
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    Default Sidewinder 18SS LS Conversion?

    I've currently got a 1981 Sidewinder 18SS with a Mecruiser 260/Alpha set up that I have been playing with for a few years now. Most of my mods have been to replace worn out parts like upgrading to msd ignition since the points distributor wore out, upgrading to a demon carb cause the quadrajet was too far gone to rebuild etc. This spring I also started picking away at the rotten wood and stiffening up the hull by adding much needed torsional stiffness with amazing results.

    This boat is also the closest thing I am going to get to a corvette, and honestly, I want to turn heads at the dock or ramp with a set of corvette coil pack covers hiding in my engine compartment, so I would like to swap in an stroked LS3 (say 540hp) and take it to the next level. I am curious if anyone has swapped an LS style motor in front of a bravo drive, what parts were sourced and where from? I also have some questions as to which bravo lower would be better to use, more specifically which lower sections are still capable of thru-prop exhaust?

    I also have no idea what to expect in terms of top end with this hull design, or how much horsepower is enough to get me to say a safe 80-90mph. I also know that I have to spend some time blue printing the bottom of the boat, but the boat also needs to be refinished so that doesn't bother me much. Any thoughts or help would be much appreciated, as there are not too many boats in my area that come even close to breaking 70mph, and the shops here are more dedicated to wakeboard boats and bowriders with 3.0l's than anything go-fast related.
    Last edited by Tdvjensen; 10-31-2013 at 05:27 PM.

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    Tim Moore has a pair of 5.3 LS based engines in his Skater. Runs good. He could probably tell you everything you need to know about what parts you'll need to put an LS in front of a Bravo drive.

    His screen name on here is TMoore.
    Last edited by FormulaZR; 11-01-2013 at 08:13 AM.


    "No, my boat doesn't need any more power" - No one ever

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    Quote Originally Posted by FormulaZR View Post
    Tim Moore has a pair of 5.3 LS based engines in his Skater. Runs good. He could probably tell you everything you need to know about what parts you'll need to put an LS in front of a Bravo drive.

    I think his screen name on here is TMoore.
    Just found your thread on your 383 ls swap. Very nice set up! I like how low the EFI intake sits compared to a carbed intake. What brand of headers did you use?

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    Here's a shot of the boat from last season.



    And a couple from this spring of the wood work/torsional stiffness I was referring to earlier.






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    Sounds like a cool project!
    To put a ls engine in front of the bravo drive isn't that big of a deal... The worst thing now is the price of the sea water pump has doubled since I did mine.
    I used a PCM/Crusader sea water pump, it bolts directly to the block where the power steering pump would normally go. The bad thing about that is you will have to mount your power steering pump somewhere else. I currently have manual hydraulic steering on mine so it's not an issue YET. I plan on mounting a power steering pump where the A/C Compressor goes and run off the A/C belt groove.
    The manifolds I used are also PCM/Crusader.
    The bellhousing and drive flange for the bravo drive bolt right on.

    If you have any questions I'll try to help. Like FormulaZR said I have 2 in a 24 Skater.

    Read through this thread.
    http://www.performanceboats.com/dyno...-question.html
    Last edited by tmoore; 11-01-2013 at 06:22 AM.

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    Here is a link to the Crusader engine, just to give you an idea.

    Crusader Captain's Choice 6.0

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    Quote Originally Posted by Tdvjensen View Post
    Just found your thread on your 383 ls swap. Very nice set up! I like how low the EFI intake sits compared to a carbed intake. What brand of headers did you use?

    Thank you. My headers are made by Rewarder.


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    Quote Originally Posted by tmoore View Post
    Sounds like a cool project!
    To put a ls engine in front of the bravo drive isn't that big of a deal... The worst thing now is the price of the sea water pump has doubled since I did mine.
    I used a PCM/Crusader sea water pump, it bolts directly to the block where the power steering pump would normally go. The bad thing about that is you will have to mount your power steering pump somewhere else. I currently have manual hydraulic steering on mine so it's not an issue YET. I plan on mounting a power steering pump where the A/C Compressor goes and run off the A/C belt groove.
    The manifolds I used are also PCM/Crusader.
    The bellhousing and drive flange for the bravo drive bolt right on.

    If you have any questions I'll try to help. Like FormulaZR said I have 2 in a 24 Skater.

    Read through this thread.
    http://www.performanceboats.com/dyno...-question.html
    I was looking at the Hardin Marine sea water pump. CP performance has it and its supposed to bolt up where the A/C compressor would go, and is supposed to line up with the normal serpentine belt. The big question I have for that set up though would be belt length, as it doesn't tell you anything about that in the description of the part, and its also not cheap. I was also thinking of running a crank driven pump. Marine Power engines also sells a 6.0L similar to the crusader link you left me, and it looks like they use a crank driven pump. My biggest questions are as follows:

    1) Which flywheel are you using and which starter motor? You mentioned that the bravo bellhousing and drive flange is great news.

    2) What kind of power are you running out of each of your 5.3's? What kind of top end do you see right now?

    3) Which bravo drives are you using, and more specifically which lower section are you using?

    The most questions I have are about rigging more than anything else. Putting the motor in and tying it to a drive and making it run isn't that intimidating to me, its setting it up right in terms of x-dimension etc. that makes me want to do a little more homework first. This isn't going to be a cheap swap, so I would like to have a decent idea of what I need to do before I start sourcing parts.

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    The setup of your boat won't be anything close to the way mine is...
    I'm running a very high X, the prop shafts are 1 1/2 inches above the bottom of the boat. Right now my 5.3s are completely stock with a little tuning, my props are way to small and i'm hard on the limiters at 103-104.
    I'm running regular Bravo I drives with Imco nose cones. I'm running stock LS flywheels and starters. The flywheels I got from Jegs for $99.

    I don't really know where the X should be on a hull like yours. The way you use your boat will have a lot to do with it, but if you're wanting to run 90 I think it will have to be pretty high. Propshaft maybe 2 inches below the bottom. That will have the motor pretty high in the boat though and you might want to look for a shorter lower.

    If you're going that fast you also need to make sure you put hydraulic steering on that thing, I think it will be a hand full.

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    Quote Originally Posted by tmoore View Post
    The setup of your boat won't be anything close to the way mine is...
    I'm running a very high X, the prop shafts are 1 1/2 inches above the bottom of the boat. Right now my 5.3s are completely stock with a little tuning, my props are way to small and i'm hard on the limiters at 103-104.
    I'm running regular Bravo I drives with Imco nose cones. I'm running stock LS flywheels and starters. The flywheels I got from Jegs for $99.

    I don't really know where the X should be on a hull like yours. The way you use your boat will have a lot to do with it, but if you're wanting to run 90 I think it will have to be pretty high. Propshaft maybe 2 inches below the bottom. That will have the motor pretty high in the boat though and you might want to look for a shorter lower.

    If you're going that fast you also need to make sure you put hydraulic steering on that thing, I think it will be a hand full.
    I definitely plan on hydraulic steering, and blue printing the bottom of my boat, and hoping for not too much of a handful lol. I think what is going to happen is the cutout/current x dimension is going to stay the same as with the alpha power plant because of exactly what you mentioned about motor height. In a perfect world, I would like the motor lower, but that's not possible as the boat is too shallow for that. I think its going to be I get it put together and in the water and play from there. I'm sure that with the extra 200 ponies I should be able to gain a couple mph, and I'll play with shortened lowers etc. as I use the boat and figure out exactly what I want. I definitely appreciate your time to answer my questions etc.

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    Quote Originally Posted by Tdvjensen View Post
    I definitely plan on hydraulic steering, and blue printing the bottom of my boat, and hoping for not too much of a handful lol. I think what is going to happen is the cutout/current x dimension is going to stay the same as with the alpha power plant because of exactly what you mentioned about motor height. In a perfect world, I would like the motor lower, but that's not possible as the boat is too shallow for that. I think its going to be I get it put together and in the water and play from there. I'm sure that with the extra 200 ponies I should be able to gain a couple mph, and I'll play with shortened lowers etc. as I use the boat and figure out exactly what I want. I definitely appreciate your time to answer my questions etc.
    As I understand, it's "better" to get as short of a lower as possible for your application; and then as spacers as necessary. I could be wrong on that, though.

    Before you go crazy on the engine/power...it *might* be better to start with a stock-ish engine (because it's cheap). That way, if it doesn't work out like you planned, you won't be out too much money. You could probably get a good running engine to experiment with for around $500. That would only cover the piston cost of an LS3 stroker.

    Tim's are both aluminum block 5.3's...I think that might be a good starting place, unless you want an iron block.


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    Quote Originally Posted by FormulaZR View Post
    As I understand, it's "better" to get as short of a lower as possible for your application; and then as spacers as necessary. I could be wrong on that, though.

    Before you go crazy on the engine/power...it *might* be better to start with a stock-ish engine (because it's cheap). That way, if it doesn't work out like you planned, you won't be out too much money. You could probably get a good running engine to experiment with for around $500. That would only cover the piston cost of an LS3 stroker.

    Tim's are both aluminum block 5.3's...I think that might be a good starting place, unless you want an iron block.
    I have also read to start short and add as required for prop shaft CL. Spacers are cheaper than lower sections. What I really should do is pull it into my shop and measure where I'm at now for prop shaft CL and crank CL and the compare to bravo drive specs. I also would like the boat to be capable of 75+ mph (ideally 80+ mph), but I'd like the boat to still be somewhat of an all around performer.

    You also make a good point about the initial engine choice. It seems like the largest initial cost I am going to have is the drive upgrade. If I am going to want to have any significant horsepower and performance, the old alpha drive isn't going to get me where I want to go, regardless of power plant. Also regardless of power plant, things like hydraulic steering are necessities and should be invested in first for simple safety reasons. I'm a speed freak, but not a speed freak with a death wish lol. I like things that work, and work comfortably. I will be investing in hydraulic steering for sure, but if nothing else its for my own piece of mind.

    All of that said, my homework now is to investigate other LS variant options, and find some specs on drives and see how that will lay out in my boat.

    The other thing I didn't mention is timeline. This is not a project that is going to get done this winter, as I have other projects and other commitments, but this is a project that I am very passionate about. Also thinking and research is cheap, plus it keeps me sane. I definitely appreciate your guys' insight and willingness to point me in the right directions.

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    I'm just thinking out loud here for initial engine choices.

    There's a guy I know with a stock-ish 6.0 in his Glastron jet boat...it runs mid 60's. Mine has 500-550 hp, and runs low 80's. Then Tim has a pair of box stock 5.3's and runs 100+ (emphasis on the +).

    I guess I'm wondering, how much power would it really take to push your boat with an outdrive to 75-80 mph?


    "No, my boat doesn't need any more power" - No one ever

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    I think a stock 6.0 would be a good place to start. I think the top speed is going to depend on drive height more than anything, I also think it's going to be hard to get it high enough in that boat. A stock Bravo is 21 13/16" from prop centerline to crank centerline, so to get the propshaft up to where it would perform good will either take setting the motor real high and reworking the transom to get the drive high enough or a real short lower or both. Another option it the Blackhawk drive, but they are getting harder to find.

    I think if I were you I would bolt the Bravo on in stock location and find a -3 lower and see how it does.

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