Dissection of the LS Engine

Discussion in 'Chevy' started by Toobuilder, Sep 28, 2012.

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  1. Oct 26, 2012 #21

    Toobuilder

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    The broad goal is to replicate the performance of the 300 HP Lycoming. So I'm looking for 300 or better @ 3000 RPM or less. In theory, the BMEP required is within the reach of current LS engine technology. This is why I'm driven to the biggest displacement I can get as it relaxes the BMEP requirement. A 427 "only" needs a BMEP of 185 to reach my goal, while that 500 inch monster would do it with 158. This is speaking of the final configuration, of course - the engine in this thread is just a learning exercise.

    concerning your last question, you're speaking of bell housing and front accessory holes between the LS series and the Chevy V6? Off the top of my head I don't think there is a 6 that shares the LS pattern. Even among the V8's, the LS has a unique pattern. It's close to the traditional SBC, but one hole is off. That said, the car guys will bolt the older transmissions up anyway.
     
    Last edited: Oct 26, 2012
  2. Oct 26, 2012 #22

    Jay Kempf

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    The 300HP Lycoming being the io-540? Weights similar? I have a 470 here and it's a porker. My 928 4.5L v8 is over 500 lbs and the 470 is heavier than that. SBC is much lighter than either I am thinking.
     
  3. Oct 26, 2012 #23

    4trade

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    Turbo charger with moderate boost level will give same amount of hp/ torque, and it give lower assembly weight too. New turbos cost less than 1/10 of that stroker kit.
     
  4. Oct 26, 2012 #24

    Toobuilder

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    Yes, the angle valve 540. It's lighter than the big Conti, but still no flyweight. Very preliminary comparison between a DD LS engine and the angle valve 540 show a slight edge to the aircraft engine in weight, but it should be close enough. That is subject to change as I learn more about the LS. For example, I just weighed the power steering pump, alternator, mounting bracket and belt tensioner (all an assembly as used on the LS), and it showed 38 pounds. Even with the significant advances in weight reduction in the Gen III through V engines from GM, there is still a LOT of easily shed fat for an airplane application.
     
  5. Jan 7, 2013 #25

    Toobuilder

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    So there has been some progress on the mule engine. I have spent way too much time machining up a prop adapter to mate to the back of the crankshaft. This is not meant to be flown, just something to hang a prop on and evaluate on the ground.



    [​IMG]


    [​IMG]

    Turned out fairly well, but the fact that the crank to adapter bolts are loaded in shear right at the threads is a little scary. I think it will be OK with light props on the ground, but dowel pins would be needed to drive a flight propeller with any piece of mind.
     
  6. Jan 7, 2013 #26

    BBerson

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    That prop adapter looks good. Is it steel or aluminum?

    I just made a similar prop adapter for my monster .67 liter V- twin Honda. Mine is aluminum.
     
  7. Jan 7, 2013 #27

    Toobuilder

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    This one is aluminum as well. The drive lugs are 4130 though.
     
  8. Feb 20, 2013 #28

    RJW

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    I’ve been out for a while. Just want to say good work. Any news?

    I haven’t had a chance to run the inverted DD SBC lately. Been busy working on a light gearbox.

    Rob
     
  9. Mar 28, 2013 #29
    Hi Toolbuilder, glad to see you are making some progress since the last time I was at this site.

    I've got a thought rambling around on propellors for conversions. I'm not stating this as a fact, just something we might get some opinions on. Everyone relates to conventional wisdom on propellor speed.............that being a propellor must only turn in the 2700/2750 rpm range or less. Further, conventional wisdom tells us that the larger and slower turning prop is the most efficient. I think that props are designed with the 2750 max in mind because many aviation engines can only produce reliable HP
    up to that range. Given that the power curve on an automotive engine begins to exponentially improve at that point..........whereas the aircraft engine is gasping to produce another 10/15 hp...........maybe we should look at the auto engine slightly differently than we look at the airplane engine equation.

    In simple terms what I'm wondering is if we set the limit of an autoengine at say 3000/3150 rpms and use a smaller prop.......could we gain sufficient power (say 50 hp) to make a different pitch (and smaller diameter) more efficient. The amount of additional horsepower available in this rpm range is what makes it interesting when compared to the Lyc and Continental. I don't think the LyCons can provide the additional needed power and longivity at that rpm to swing a much coarser prop.

    Any thoughts on that........
     
  10. Mar 29, 2013 #30

    Toobuilder

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    There seems to be a consensus that shorter, higher RPM props are efficient at cruise, the trade off is a loss of static thrust at low speeds.

    Ive been talking to John Harmon a little bit and as a consequence become more familiar with his Rocket III... Essentially a clipped wing, single place RV-4. Such an animal might make a fine testbed for a simple, fixed pitch V-8... Impractical, but low risk. A light, high RPM prop might prove out to be a fine solution. Sure, you may not be able to get in and out of a 1000 foot strip like a stock RV, but how many of us are really restricted to such a runway anyway?
     
  11. Mar 29, 2013 #31
    One of the things about the internet is that some times things get said and eventually are assumed to be fact. I have always heard that a longer slower turning prop is better(?) more efficient (?) etc. I have absolutely no frame of knowledge to base an opinion on, other than thats what I've been told. I remember that for many years (decades), it was somewhat an accepted fact that an engine with a longer stroke would make more torque than an engine of equal size that had a shorter stroke and bigger bore. Physical science disagrees with that notion and says that power equals pressure against an area times the distance it moves decides the outcome............so the longer stroke theory has begun to fade as people become more knowledgeable.
    Given that a propellor is basically a lever, I have now begun to wonder if there is not more to the propellor efficiency than just accepted ideas. I realize its not exactly the same, but is it close enough to be useful? My thought is whether an engine that is limited to a small horsepower increase in the 2700-3000 rpm range might well be better off with the larger prop because it cannot generate enough additional power to use a shorter coarser prop. On the other hand, if an engine is just coming into a range where it produces lots more power......might it not be better to capitalize on that power for takeoff by using a coarser (shorter) prop? This brings me to the next step in my question. Most people wanting to adapt a V8 think they must use a reduction drive. I'm against that notion because of the cost and additional weight.I do advocate for a short shaft driven adapter between the engine and prop.Rather than the additional weight of a reduction drive, why not add a prop governor? Could/would this not be a more effective, more efficient, and somewhat lighter alternative?
    Again I would like some thoughts on this idea....................
     
  12. Mar 29, 2013 #32

    autoreply

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    Unfortunately, it's basic physics that determine (and limit) the prop size issue. A smaller prop moves far less air and thus doesn't produce as much thrust for given HP.
    So, at low or zero speed, your thrust is much lower. That is a big problem during take-off (longer runways).

    At speed, the effect is much less severe. In fact, 500 HP @ 300 kts with a 30", properly designed prop has almost the same efficiency as a big prop.
     
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  13. Mar 29, 2013 #33

    rv6ejguy

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    At these rpms, hp increase is pretty linear, even on traditional aircraft engines. At Reno, the Sport Class guys are turning around 3200 without issues and the F1 guys around 4000. Life is not going to be as good at 3200 vs. 2700 most likely however. Really, the simple solution to the DD auto engine equation is simply adding a turbo and intercooler for about 25-35 lbs, of extra weight. Running very low boost for takeoff and normalizing in cruise will give you a decent power to weight ratio even down around 2700 rpm where you could use conventional and available propellers. The turbo reduces the noise nicely too without the need for mufflers.

    With all the TV problems with PSRUs and their extra weight and cost, DD has some nice attractions. The turbo DD concept is proven on Subaru engines and Gary Spencer's atmo Ford V8 Long Ez works very well and has well over 1000 flight hours on it now.

    The stock LS6 makes about 250hp at 2700 rpm. With a turbo, really simple to get 300 at the same rpm. I don't see the need to use an LS7 or a custom built and expensive, punched out LSX to get the job done. Crate LS6s are pretty cheap and no need to make any internal mods IMO.
     
  14. Mar 29, 2013 #34

    PTAirco

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    If you want to know if big props really are more efficient, just look at what's sitting on top of Bell 47 helicopter and see it take off vertically. Now sit a Debonair on its tail and watch it try to do the same. Same engine.

    I suppose with direct drive and small props and increased rpm, there is a point when the benefits of higher power at higher rpm no longer produce an increase in thrust and that's the cut-off point. Simple intersection of curves; power produced and thrust produced. I doubt that it lies much beyond 3000 rpm for engines that are likely candidates for conversion.
     
  15. Mar 30, 2013 #35

    autoreply

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    I think in a certain type of airframes (light but fast), the trade-off is vastly different. They have room for a vastly more powerful engine with slightly less static thrust (TO performance) further aided by the possibility to move certain components (cooling, turbo's) to other C of G positions. The advantages of direct-drive are well-worth it for those airframes.
    In most airframes though, indeed, you're limited to aviation engines, or automotive engines with a big, heavy, complex, troublesome PSRU.
     
  16. Mar 30, 2013 #36

    PTAirco

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  17. Mar 30, 2013 #37

    stol

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    That dyno sheet looks VERY realistic to me.... To make it a 300 HP @ 2700 RPM motor will take 12-14 PSI of boost from a Turbocharger or 16 PSI from a Supercharger..... And that hardware will weight more then 35 lbs...
     
  18. Mar 30, 2013 #38

    rv6ejguy

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    Right you are, I was sleepy today and looking at torque...:emb:

    Ok, with about 40-45 inches, we could make around 260hp, putting in the same league as as an O-540 but I think the installation would weigh a good 50 lbs. more minimum.
     
    Last edited: Mar 30, 2013
  19. Mar 30, 2013 #39

    PTAirco

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    And I was getting hopeful there, thought I might be looking at the wrong chart. I am still leaning towards direct drive for my biplane nonetheless. I know it's not the ideal candidate -slow and draggy - but practicality and cost are the main mission. Which rules out turbos, which I agree are a good way to boost power in a direct drive engine (especially here in CA, with heat and mountains), but the cost of those is about the same as good reduction drive.
     
  20. Mar 30, 2013 #40

    cheapracer

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    True but a simple, cheap cam and exhaust change can really get the numbers up at any RPM point you need and I believe you would be able to aproach the numbers suggested by rv6ejguy.

    It would take nothing more than a phone call to Crower or Crane etc. camshaft companies to verify it.

    You can go further to achieve those numbers as well such as stroker cranks with short rods but of course when it gets to there the money needs to happen.
     

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