GM LFX V6

Discussion in 'General Auto Conversion Discussion' started by pfarber, Apr 26, 2019.

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  1. May 4, 2019 #41

    pfarber

    pfarber

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    The O540 angle valve (300hp) produces 583 ft-lb at 2700

    I don't see the problem. I would apply less torque that this. Yes, there might be more torque at a lower RPM as I haven'e seen a O540 torque curve.

    Any auto engine is a compromise. And the work to delete VVT would fly smack into the reliability/return argument. Delete VVT, reprogram ECU, deal with internal oil rerouting and make the cam/cam gears work or keep it and *possibly* have 'to much' torque?

    Explain to me how the VVT delete is a better option? No, not far flung 'what ifs'.. but compare the ACTUAL work to be done vs just keeping it stock. I'm all ears if there is a beneficial case to deleting VVT that can be made
     
  2. May 4, 2019 #42

    pfarber

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    This link is absolutely useless and provides nothing of value regarding inverted engine designs.
     
  3. May 4, 2019 #43

    wsimpso1

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    Listen to Bruce, he grew up in Chapter 1.

    It is not so much that getting a prop to work at low rpm and high torque causes problems with the engine as it that the prop that works at low rpm and high torque is tough to make run well for you at higher rpm and power, like for takeoff and high cruise. A constant speed prop that will is efficient at 75% torque and 50% rpm (37.5% power) can be run at more like 75-100% power, but it will have big blades and run at poor efficiencies in climb and cruise. And fixed pitch prop, well, if it pulls the above low power setting well, at full throttle it will only run a to 57-65% rpm before you get to 100% torque. If that is OK, have at it, but most of will be really unhappy with anemic takeoff and climb performance...

    Billski
     
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  4. May 4, 2019 #44

    TFF

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    Unless the VVT is timed to how an airplane uses power it would probably be out of sync of the powerband you want. If it’s in some hunting mode where it can’t decide what is right, that would be annoying. An airplane engine is more like a irrigation pump engine. It just drones along at one set rpm to get you there. There are exceptions like aerobatics, but even then they rarely vary 500 prop rpm. The need of a powerband that is wide does nothing for you.
     
  5. May 4, 2019 #45

    Hephaestus

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    Last time I played with microsquirt I remember it's a pretty basic lookup table to set vvti timing adjustment. Setting a basic static number to deactivate it would be simple, minor tuning could be easily accomplished as well.
     
  6. May 8, 2019 #46

    pfarber

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    So stuck in 1960's technology? I got that impression. EFI, VVT, DI, ECUs are all things that GA engines need more than ever for fuel economy and performance. The old myth that auto engines are not tested as well as aero engine has been a lie for over a dozen years.

    So yeah, I'll listen to anyone, but just being an old head mean little if you are stuck in the past.
     
  7. May 8, 2019 #47

    pfarber

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    If its there, then why not use it? It delivers definite performance gains and who wouldn't want a variable cam in an engine that would see multiple power bands?

    VVT is over 15 years old. Its not new and its been pretty well hammered out.

    Seeing that deleteing it (and simply not via software, but a hard lock) doesn't have ANY benefits over either keeping it or simply using it as most standalone ECUs could use it.

    At this point the issue is stay with the LFX or move to the LV3. I think the LFX would have height issues with the DOHC covers and would be slightly heavier than the LV3 (DOHC vs 2v push rods).
     
  8. May 8, 2019 #48

    Toobuilder

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    Aircraft engines have a "powerband" of about 300 RPM.
     
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  9. May 8, 2019 #49

    Hephaestus

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    Most seem afraid of it, I wouldn't be - but aviation world is extremely conservative on these matters. People were discussing ill conceived engine mods to eliminate it, I was suggesting more that you could code it out with less trouble
     
  10. May 8, 2019 #50

    wsimpso1

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    You are not listening to any of us...

    We have only been trying to explain a few things to you:

    We know that car engines as sold are great for cars, and some might indeed be wonderful for airplanes. The ones we know about are robust in airplanes. Others may or may not be so terrific...

    Props limit you in several ways. The biggie is that all fixed pitch props on any one airframe have one indicated airspeed/rpm/torque relationship. Your useful rpm band is narrow indeed. Go constant speed, and your range gets bigger, but you will still have only about 25 to maybe 35% of the engine's speed range useable for climb and level flight. Reach further down in the rpm range for cruise, and full throttle capacities will be significantly weakened.

    Gains made good in the airplane are thus modest at very best and more likely zero, and at a cost of complexity and weight. That generally translates to more build fuss, less payload, and poorer reliability. We have watched it before, you are not the pioneer.

    If you insist upon telling us that you are the smartest guy in the room, we will let you be. We will look forward to the progress reports, and hope that we do not have to read about you in the accident reports.

    Billski
     
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  11. May 8, 2019 #51

    Toobuilder

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    As someone who has a lot of time trying to eke out efficiency and performance from a Lycoming, I'm wondering what kind of improvements you expect? I'm doing EFI on my Rocket and expect easier operation, but I'll be pleasantly surprised if the EFI provides a noticable performance boost over the ancient Bendix fuel injection.

    I have many, many hours droning along LOP, tweaking ignition timing just so, and I have found that a Lycoming, even with it's archaic combustion chamber and induction system, cranks out some pretty respectable efficiency numbers.

    The fact is, running wide open, pulling maximum load for hours at a time is a tough mission for any engine... And the Lycoming happens to do it pretty well.
     
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  12. May 8, 2019 #52

    Himat

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    Scope for “modern” technology in an internal combustion aircraft engine may look like this:

    ECU, EFI/electronic ignition: Ease of operation and if proper done better reliability. Does maybe little for performance but can improve fuel economy to best achievable for all pilots. Old carburettor systems are work intensive to operate to max efficiency but not necessarily inefficient by design.

    VVT, probably not. That is for extending the power band and improving fuel efficiency over a larger power and rpm band. Not that useful for engines that operate at mostly one speed and power.

    DI as in direct injection. Yes, if compression ignited an made to run on Jet A1. That is Diesel engines. Petrol DI is for fuel economy at part/low load as I understand it. Not much use in an airplane.
     
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  13. May 9, 2019 #53

    pictsidhe

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    I'm still wondering how it is easier to program an ECU to use VVT than to just lock it wherever works best at your chosen RPM. Sounds like hours of extra dyno tuning to me, not to mention needing a VVT compatible ECU.

    Maybe I'm just stupid. Could someone explain it to me in dummy terms?
     
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  14. May 9, 2019 #54

    wsimpso1

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    I do not want to speak for pfarber, so I will describe the benefits of VVT and DI and then why it is of little to no benefit in an airplane.

    Cars and trucks are mostly driven at low power settings. Even highway use is at modest power. A big chunk of the EPA and Euro fuel economy cycles is at idle and very modest rpm. So the carmakers want an engine that is VERY efficient at low power and rpm.

    But customers hate a doggy car. In normal driving it should launch well and go up to traffic speeds, both in the city and on highway driving quickly and without feeling like it is straining. When you step on it, it should GO!

    How to do all of this? Use a small engine with breathing and fueling and ignition that is very efficient at idle and at slow, modest throttle, then boost it for the tiny amount of heavy pedal it gets. Cam and injection timing for efficient idle and low power are quite different from high power. Variable valve timing and big turbine small compressor turbos let you have both ends. Gas Direct Injection also lets you run higher compression ratios for more efficient low power operation, but does you little if any good over port injection at high manifold pressures and higher rpm. This give really good fuel specifics at medium torque and modest rpm.

    Now all of that is great in cars where you can hold a gear and transmit whatever the engine makes to tractive effort at speed. Customer uses modest pedal, the computer rolls in a lot of throttle and some boost and shifts up the tranny at low engine rpm.

    In an airplane, well, if we are at power settings most cars and pickup trucks use on the highway, we are descending or flying at the very low end of our level flight speed range. Most of our flights are at higher power, and we definitely need big power for takeoff and climb. Most of our flight will be at 50-75% of our possible power. Our usual ground idle will turn the prop at 1000 rpm, or we won't even move when we let go of the brakes. VVT and DI will run little if any of our operating cycle and sure won't generate benefits. The right turbo for our work is sized for steady state and good behavior up into the teens, which is way different from the automotive turbo.

    And if we really wanted to run 30% power in cruise, where VVT and DI shine, we would have to make compromises in the prop that would make full power either impossible (with fixed pitch props) or would make it really inefficient (in constant speed props), thus making for lousy takeoff and climb performance.

    I can see the argument for leaving the VVT in the plane if that rocks your boat. It is an extra thing to get right, but so would be pinning the gadget and deleting the sensors and actuators... DI at high power settings has had its issues, and again, for a one-off, I can see the argument for keeping it instead of converting, and accepting the issues instead of potentially introducing new ones of your own. I do not see VVT and DI making a more usable or efficient airplane. I would not do it that way. This is not my airplane... have at it, but know it is not for performance and maybe not even for cost, but because you wanted to do a different engine yourself.

    Billski
     
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  15. May 9, 2019 #55

    mm4440

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    at 8:32
    A 496c in. LS based normally aspirated pump gas street engine; 600+ hp but look at the first, 2800 rpm dyno numbers. 316 hp, 592 #' TQ.
    NRE is local to me, big power engine and car builder. With a direct drive and lower red line, lighter valve springs for lower stress on valve train could be used. I do not think you need to change the cam. A big inch LS means an aftermarket racing block and other parts. Inverting a V-8 is straightforward, you make sure oil can drain to an external sump tank that connects the valve covers and a suction line to the inlet of the oil pump. A dry sump is not needed but can be done with GM parts. Simple is better.

    Murry
     
  16. May 10, 2019 #56

    Toobuilder

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    Can you do 496ci with an aluminum block now? If so, good news. Last time I checked, big inches required an iron block
     
  17. May 10, 2019 #57

    mm4440

    mm4440

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    Yes, RHS and Dart have tall deck aluminum LS race blocks to name just two. Up to 4.185" bore and 4.6" stroke is possible. There are LS heads that can feed the big engines. Longer cylinder sleeves are the key to using the long strokes so the piston does not come part way out of the bore at BDC. I think the weight of the V-6 is being underestimated and there is relatively no aftermarket support. It can work fine if it is kept close to stock. Personal opinion, simpler is better. A good used V-6 might be a bit lighter and less expensive.
    1000+ HP with turbo/supercharging LSs is done all the time. PSRU(?) and prop from a turbine; sport class racing? Twin engine? All it takes is time and money.
    Murry
     
  18. May 10, 2019 #58

    pfarber

    pfarber

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    All good points made by many. I explained initially that *I* do not want to re-engineer anything. A car motor is not a perfect fit (the MAIN reason being weight, not performance) in an airplane.

    The concept of an inverted v8 is is just a non-starter. RPM is not the problem. Shear weight and lack of desire to re-invent the motor are considerable deterrents.

    The LFX may not be the best engine (the LV3 is looking good but according to GM lit. still uses VVT).

    Since I haven't read anything that is a show stopper regarding either engine, time to look and see what kind of cores for rebuild are available and costs.
     
  19. May 10, 2019 #59

    pfarber

    pfarber

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    The O540 angle valve (300hp) produces 583 ft-lb at 2700

    The O-540 is gonna weigh less, and most likely have the same or less fuel burn.

    Whats that NRE motor cost? Less than a O-540 rebuilt for an E-AB???

    Yeah, that motor is nice (I don't know) but its not a solution to any problem here. Now you want to invert it??? Enjoy your expensive experiment.
     
  20. May 11, 2019 #60

    mm4440

    mm4440

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    Hi, a quick look at overhauled 300 hp Lycs: ~ $35,000. I think a big inch LS based DD 300 hp engine could be built for about that price in all new parts, maybe less. If you want a pro to build it for you, good luck. Never tell them it is for an airplane. It should outlast a Lyc and be much less expensive to overhaul. There was someone developing such an engine at Oshkosh some years back. I think he ran out of money. E-AB means the freedom to experiment.
     
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