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lifespan of an LS at high HP? (ie marine use, 200-500hp) OR the HP to last 400hrs

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lifespan of an LS at high HP? (ie marine use, 200-500hp) OR the HP to last 400hrs

 
Old 05-15-2019, 04:51 AM
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Default lifespan of an LS at high HP? (ie marine use, 200-500hp) OR the HP to last 400hrs

Can anyone share some insights into the lifespan of an LS engine (in particular the 4.8/5.3 gen 3's hence posted here) in a non-car type application, such as put into a boat let's say?

I've seen industrial engines based on the older chevy small blocks that put out less than I might expect (say 175hp for a 350cid or 1/2hp per CID sustained) and i'm not sure for what design life of hours but i'm often curious how well an LS would hold up in the same use since I thought even the industrial ones at that power used stronger internals than normal engines.. Whether stock or even modified/ie are you hitting the limits of something like the connecting rod life or the bearings or... what really are the weakpoints for SUSTAINED high HP output?

I'm not looking for crazy or extreme builds like four digit power for a few dozen hours, but for something like a performance pleasureboat i've seen 400-1000 hours of life thrown around as a goal for some other engines so i'll use that. What would you expect to be the weak points of a Chevy LS asked to do 400 hours of service at outputs of like 200hp, 300hp, 400hp, 500hp? (perhaps the latter two with some turbo boost or whatever, as engine life is often better on some boost than something required to spin higher RPM's) Then would anything radically change if trying to last 1000hrs instead?

Even 200-300hp i'd be happy with I mean, the bigger power figures are more curiosity. I'm sure more is doable, but whenever I see big figure marine motors it's tens of thousands of dollars, i'm looking for more the budget power category or mods not too expensive. :)
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Old 05-15-2019, 08:16 AM
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The marine BBC engines I used to build were recommended to be refreshed at about 400 hours, but those were stupid engines. Rings and springs were the main wear items, lifters were usually replaced every other refresh but I don’t know that it was ever really needed or just a CYA thing. .

I have not built any LS engines for marine use, but i don’t think 800 hours or more would be unattainable. It just depends on use and maintenance. 100 hours at WOT and 5500RPM is a lot different than 100 hours chugging through no wake zones.

The most popular power adder seems to be the PD blower (ie roots or twin screw), but when sized properly, turbos work really well. IIRC, the main thing about turbos in a marine application is heat management, especially in an enclosed hull.
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Old 05-18-2019, 05:04 PM
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Contract Chris Straub and talk to him. Last I knew, he supported a lot of the marine performance guys and he may be able to give you some insight and guidance.
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Old 05-19-2019, 12:39 PM
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Originally Posted by columnshift View Post
Can anyone share some insights into the lifespan of an LS engine (in particular the 4.8/5.3 gen 3's hence posted here) in a non-car type application, such as put into a boat let's say?

I've seen industrial engines based on the older chevy small blocks that put out less than I might expect (say 175hp for a 350cid or 1/2hp per CID sustained) and i'm not sure for what design life of hours but i'm often curious how well an LS would hold up in the same use since I thought even the industrial ones at that power used stronger internals than normal engines.. Whether stock or even modified/ie are you hitting the limits of something like the connecting rod life or the bearings or... what really are the weakpoints for SUSTAINED high HP output?

I'm not looking for crazy or extreme builds like four digit power for a few dozen hours, but for something like a performance pleasureboat i've seen 400-1000 hours of life thrown around as a goal for some other engines so i'll use that. What would you expect to be the weak points of a Chevy LS asked to do 400 hours of service at outputs of like 200hp, 300hp, 400hp, 500hp? (perhaps the latter two with some turbo boost or whatever, as engine life is often better on some boost than something required to spin higher RPM's) Then would anything radically change if trying to last 1000hrs instead?

Even 200-300hp i'd be happy with I mean, the bigger power figures are more curiosity. I'm sure more is doable, but whenever I see big figure marine motors it's tens of thousands of dollars, i'm looking for more the budget power category or mods not too expensive.

Cheap 250hp run all day long get an aluminum 5.3L with a nicely spec'd marine cam that will run the LS3 springs. If you want to go harder farther Id look at a larger oil pan and baffle set up. Give canton a ring or get handy with a welder. 10 quart pan ought to be plenty

If you want to get to that 400 range? I'd run an aluminum 6.2L again with a nicely sped'd marine cam on the LS3 springs, should go 800 hrs at 5000 RPM. Oil volume upgrades as above recommended. Its not that LS motas have oil issues but extended high RPM is going to need redundancy to be safe and keep cool so 10 quart or a dry sump would be hugely beneficial for long term running. I'd stay away from boost unless your look for 500+ at the prop and willing to run race gas. Add cubes instead based on 6.2L block a 414 or something should net you 450 at the prop with a mild marine cam using an endurance lobe and run all day on pump gas for 800 hrs

The tune up is going to be key to your long term reliability. Your going to want to seek out the most competent tuner in your area and follow their guidance with regards to fuel system set up.

Last edited by cam; 05-19-2019 at 12:42 PM. Reason: tune!!!
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Old 05-24-2019, 05:15 PM
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Originally Posted by KCS View Post
The marine BBC engines I used to build were recommended to be refreshed at about 400 hours, but those were stupid engines.

I have not built any LS engines for marine use, but i donít think 800 hours or more would be unattainable. It just depends on use and maintenance. 100 hours at WOT and 5500RPM is a lot different than 100 hours chugging through no wake zones.

The most popular power adder seems to be the PD blower (ie roots or twin screw), but when sized properly, turbos work really well. IIRC, the main thing about turbos in a marine application is heat management, especially in an enclosed hull.
Stupid meaning stupidly powerful? What power outputs did you see with a 400hr lifespan? (i've seen four digit ones with far less hours I mean)

I know they still sell the 496 big blocks as ~330hp inboards of a sort, I know there is some engineering point where even if you CAN do the power with a smaller engine, the longevity suffers... the same reason that Ford is making what is it some new 7.3 liter gas or something for the medium duty gas and I think superduty pickups now when we haven't had big blocks for almost two decades practically... i'd love to get more details of where the tradeoff for that is, for where an LS may no longer be the best solution.

One big reason for blowers in marine is the off the line torque for the holeshot, it's why they also like diesels or use transmissions with a low gear on many propellers. I had it in mind using something like a TH350C potentially in a thai longboat design. (others use car and pickup transmissions effectively in this role, and if you've seen what a 300hp outboard costs you'll see why i'd like to do this on the cheap. :^)


Originally Posted by vettenuts View Post
Contract Chris Straub and talk to him. Last I knew, he supported a lot of the marine performance guys and he may be able to give you some insight and guidance.
Thanks for the suggestion, assumes https://straubtechnologies.com/ this guy after a search for straub marine LS.


Originally Posted by cam View Post
Cheap 250hp run all day long get an aluminum 5.3L with a nicely spec'd marine cam that will run the LS3 springs.

If you want to get to that 400 range? I'd run an aluminum 6.2L again with a nicely sped'd marine cam on the LS3 springs, should go 800 hrs at 5000 RPM.

I'd stay away from boost unless your look for 500+ at the prop and willing to run race gas. Add cubes instead based on 6.2L block a 414 or something should net you 450 at the prop with a mild marine cam using an endurance lobe and run all day on pump gas for 800 hrs

The tune up is going to be key to your long term reliability. Your going to want to seek out the most competent tuner in your area and follow their guidance with regards to fuel system set up.
My main goal was at least 250hp but the thought of running more power on E85 is compelling but that's a waste if not forced induction... I wanted reliable power for 400 hours before needing a rebuild and was wondering how far I might tip the can.

Why LS3 springs? Just curious if something special.

My race gas is E85 - I live in Minnesota and it's available absolutely everywhere. I'd rather boost a 4.8/5.3 to make efficient use of the size than pay the premium for the 6.0/6.2 tax since everyone wants the extra cubes. :) The cost difference pretty much pays for the turbo, and this is in part an excuse to play with tuning under high load and other crap. (note this boat project is a good 2 years off MINIMUM as I have nowhere to put it right now, but i'm just indulging my LS interest early by doing research) In part i'm wondering whether a 4.8 on a bit more boost would be just as reliable on a 6.x on less boost because things like crank and rods should be same strength I assume, effective pressure on rod journals and all that again the same, valvetrain loads same, etc...

I'm aware turbos can make people get greedy - the goal was not too greedy, but I wasn't sure if these engines would last at WOT loads even at designed HP to be blunt so the turbo isn't even a for sure thing - I was curious why else a 6.2 might better last 400hp than a 4.8L on lighter boost. Heck I thought making power at a lower rpm with like 7-9psi might outlast turning higher RPM. A lightly boosted turbo 4.8L with around 400hp if it would last 400hrs would be like a holy grail I mean but even 260hp is still a solid 'outboard'.
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Old 05-24-2019, 07:18 PM
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Honestly you're on the wrong forum, There are boat forums and the swaps have been done many times.
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Old 05-25-2019, 06:56 AM
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Originally Posted by columnshift View Post

Thanks for the suggestion, assumes https://straubtechnologies.com/ this guy after a search for straub marine LS.
Yes. Chris can hopefully provide some guidance and points of contact.
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Old 05-25-2019, 03:05 PM
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Originally Posted by columnshift View Post
Stupid meaning stupidly powerful? What power outputs did you see with a 400hr lifespan? (i've seen four digit ones with far less hours I mean)

I know they still sell the 496 big blocks as ~330hp inboards of a sort, I know there is some engineering point where even if you CAN do the power with a smaller engine, the longevity suffers... the same reason that Ford is making what is it some new 7.3 liter gas or something for the medium duty gas and I think superduty pickups now when we haven't had big blocks for almost two decades practically... i'd love to get more details of where the tradeoff for that is, for where an LS may no longer be the best solution.

One big reason for blowers in marine is the off the line torque for the holeshot, it's why they also like diesels or use transmissions with a low gear on many propellers. I had it in mind using something like a TH350C potentially in a thai longboat design. (others use car and pickup transmissions effectively in this role, and if you've seen what a 300hp outboard costs you'll see why i'd like to do this on the cheap. :^)




Thanks for the suggestion, assumes https://straubtechnologies.com/ this guy after a search for straub marine LS.




My main goal was at least 250hp but the thought of running more power on E85 is compelling but that's a waste if not forced induction... I wanted reliable power for 400 hours before needing a rebuild and was wondering how far I might tip the can.

Why LS3 springs? Just curious if something special. High service life. LS3 springs are about as stout as your going to get that will run the hours you want without needing replacement.

My race gas is E85 - Ethanol is hydrophilic and readily absorbs water so its not a good wet environment fuel. 91 oct straight gas will serve you much better. If your going for boost e85 makes some sense but you will have to put a lot of care into the fuel system and keeping the fuel free of soaking moisture up. If your going to leave the boat in the water for days on end you will likely have a lot of issues with E85 fuel getting spoiled. I live in Minnesota and it's available absolutely everywhere. I'd rather boost a 4.8/5.3 to make efficient use of the size than pay the premium for the 6.0/6.2 tax since everyone wants the extra cubes. The cost difference pretty much pays for the turbo, and this is in part an excuse to play with tuning under high load and other crap. (note this boat project is a good 2 years off MINIMUM as I have nowhere to put it right now, but i'm just indulging my LS interest early by doing research) In part i'm wondering whether a 4.8 on a bit more boost would be just as reliable on a 6.x on less boost because things like crank and rods should be same strength I assume, effective pressure on rod journals and all that again the same, valvetrain loads same, etc...

I'm aware turbos can make people get greedy - the goal was not too greedy, but I wasn't sure if these engines would last at WOT loads even at designed HP to be blunt so the turbo isn't even a for sure thing - I was curious why else a 6.2 might better last 400hp than a 4.8L on lighter boost. Heck I thought making power at a lower rpm with like 7-9psi might outlast turning higher RPM. A lightly boosted turbo 4.8L with around 400hp if it would last 400hrs would be like a holy grail I mean but even 260hp is still a solid 'outboard'.
I suggest natural aspirated because of the fuel concerns listed above mostly. You can run race gas with no eth and boost. Pump 91 on boost is not going to hold together well under extended high RPM runs imo. At least not while making high power levels. Where a large cube 6.2 based build will run happy ALLLLLLLLL day long making 400+ power with ease on pump 91. Heck it will run for years and years.
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