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Discussion in 'Firewall Forward / Props / Fuel system' started by Armilite, Aug 10, 2019.

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  1. Aug 12, 2019 #21

    GeneG

    GeneG

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    I'm not sure if the lifan is available in horizontal shaft. That would make a substantial difference to me.
     
  2. Aug 12, 2019 #22

    GeneG

    GeneG

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    Sorry, Double post
     
  3. Aug 12, 2019 #23

    Vigilant1

    Vigilant1

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    ? The Lifan engine listed in the link in the original post is a horizontal shaft engine (and the Harbor Freight 670s are available as horiz or vertical shaft).
     
  4. Aug 12, 2019 #24

    GeneG

    GeneG

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    It's obvious I didn't follow the link. I would still go for the Predator because of the displacement and they have good customer service policies. Just don't tell either that it is for aircraft use.
     
  5. Aug 12, 2019 #25

    pictsidhe

    pictsidhe

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    VE can and does exceed 100% since about the 60s. F1 and NASCAR are up around 120%. The trick is to acoustically tune the intake and exhaust.
     
  6. Aug 12, 2019 #26

    pictsidhe

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    If you are going direct drive, you should either lose the flywheel, or bolt the prop to it. Having the crank twixt the two is a really idea. If you delete the prop, you need a frictuon fit for the prop adaptor that will take around 7x engine torque. This is to absorb the engine pulses.
    If you go for a redrive setup, you need to be very careful about matching the engine, flywheel, redrive and prop. Anyone who says otherwise, which sadly includes many redrive manufacturers, does not understand the engineering required. A reliable redrive doesnt have to be complex, but it does have to be baby bear's porridge. A mishmash of parts is very unlikely to work.
     
  7. Aug 12, 2019 #27

    Armilite

    Armilite

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    ==================================
    Internal combustion engines:
    Volumetric efficiency in an internal combustion engine design refers to the efficiency with which the engine can move the charge of fuel and air into and out of the cylinders. It also denotes the ratio of air volume drawn into the cylinder to the cylinder's swept volume. [1] More specifically, volumetric efficiency is a ratio (or percentage) of the mass of air and fuel that is trapped by the cylinder during induction divided by the mass that would occupy the displaced volume if the air density in the cylinder were equal to the ambient air density. The flow restrictions in the intake system create a pressure drop in the inlet flow which reduces the density (unless boosts like turbos or superchargers or cam tuning techniques are used). Volumetric efficiency can be improved in a number of ways, most effectively this can be achieved by compressing the induction charge (forced induction) or by aggressive cam phasing in naturally aspirated engines as seen in racing applications. In the case of forced induction volumetric efficiency can exceed 100%.

    There are several ways to improve volumetric efficiency, but system-wide approaches are used to realize its full potential.

    Many high-performance cars use carefully arranged air intakes and tuned exhaust systems that use pressure waves to push air into and out of the cylinders, making use of the resonance of the system. Two-stroke engines are very sensitive to this concept and can use expansion chambers that return the escaping air-fuel mixture back to the cylinder. A more modern technique for four-stroke engines, variable valve timing, attempts to address changes in volumetric efficiency with changes in the speed of the engine: at higher speeds, the engine needs the valves open for a greater percentage of the cycle time to move the charge in and out of the engine.

    Volumetric efficiencies above 100% can be reached by using forced induction such as supercharging or turbocharging. With proper tuning, volumetric efficiencies above 100% can also be reached by naturally aspirated engines. The limit for naturally aspirated engines is about 130%;[2] these engines are typically of a DOHC layout with four valves per cylinder. This process is called inertial supercharging and uses the resonance of the intake manifold and the mass of the air to achieve pressures greater than atmospheric at the intake valve. With proper tuning (and dependent on the need for sound level control), VE's of up to 130% have been reported in various experimental studies.[3]

    2 Strokes:
    Now, what Percent is my Skidoo 335 20hp@5500rpm? (78mm x 70mm) 334.6cc.

    Now, what Percent is my Skidoo 340 26hp@6500rpm? (78mm x 70mm) 334.6cc.

    Now, what Percent is my Stock Skidoo 670, 115.7hp@7750rpm? (78mm x 70mm) 669.2cc.

    4 Strokes:
    A Stock Harbor Freight Predator 420cc Single is 13hp@3600rpm. What Percent is it?

    Peak Flow Calc says 71%-75%

    420cc Single Modified for Racing. Dynoed 34.83hp@5750rpm. What Percent is it?
    Peak Flow Calc says 420cc making 34hp at 5750rpm is 118%-121%.
    https://www.mk5cortinaestate.co.uk/calculator3.php

    =================================================================

    A 460cc Single, Modified for Racing. Base Mods (Air Filter, 34mm Carb, Hi-Rev kit, Header) + CR bump to 11.0cr. Dynoed 37.37hp@5000rpm. What Percent is it?
    Peak Flow Calc says 460cc making 37hp at 5000rpm is 135%-138%.

    Honda 420 Dyno.jpg HONDA 460 DYNO TEST 1.jpg

    SKIDOO 93 Stock 670 115.7HP 7750RPMS.jpg
     
  8. Aug 12, 2019 #28

    GeneG

    GeneG

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    Tuned extractors are all fine and dandy until you want a reasonable power band.
    The wider the band, the less extraction you achieve and the more weight/space you add. The negative pulse of a megaphone has a very narrow range and is dependent on the length of the expansion chamber. The valve timing of 4 stroke engines would be very interesting - variable valve timing may help. High RPM's and long intake runners would be required for that kind of packing of the fuel charge.

    Can you provide links to the 120% you are quoting please?
     
  9. Aug 12, 2019 #29

    Armilite

    Armilite

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    =================

    About the same. Cost Depends when on Sale, 614cc vs 670cc. I have read where some people who have had both used on Airboats and used as Mud Motors, thought the Lifan was better. For Airplane Conversion you're going to Replace all the Weak Parts if you do it right.
     
  10. Aug 12, 2019 #30

    GeneG

    GeneG

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    I find no information on the extractor, or intake length/diameter or flow velocity which would let me understand a packing of the cylinder.

    Looking at extraction curves you may notice that under 5000 RPM you net no real gains.

    upload_2019-8-12_12-43-6.png
     
  11. Aug 12, 2019 #31

    n3puppy

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    There is really no way to tell what your VE percentage is in the examples you asked about unless you actually measure airflow.

    I see where you posted this dyno printout for a Rotax 377 engine (380HO?)
    https://www.homebuiltairplanes.com/forums/threads/377ul-377-380-380ho-tuned-pipe-plans.27503/

    It shows 57hp@ 7000 rpm @102 CFM
    The math on 368cc @ 7000rpm flowing 102CFM = 112%Ve

    Your peak flow calculator has very different estimates from the real world experience you posted

    From Peak Flow using Known HP
    368cc @7000rpm @ 57hp. - Estimated VE = 94% an error of 18 % points over actual 112%

    From Peak Flow using Known airflow
    368cc @ 7000rpm @ 102CFM - Estimated HP = 68HP an error of 11HP (19%) over actual 57hp

    Clearly the calculator is using a rather simplistic calculation in the back ground. It appears all that it does is divide airflow by 1.5 to estimate HP. Not very realistic given engine dynamics such as compression ratio that vary HP without changing airflow

    I guess the authors note at the bottom is true
    Please note, the Horsepower figure is a rule of thumb approximation, unlike the Flow Rate figure
    Seems like BMEP would be a much better way to compare engines if you know HP and RPM - given the errors of the Peak Flow Calculator

    8C3A0B6A-D706-4B4F-9AAC-8DFE712F35B4.png
     
    Last edited: Aug 12, 2019
  12. Aug 14, 2019 #32

    Armilite

    Armilite

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    =====================
    You can figure HP (3) ways:

    1. Use the Ball Park General Rule a Porting Specialist told me, if using 11.5cr, Proper Size Carb, a Good Tuned Pipe, and turning it my UL 6500rpm, it takes on Avg 7cc to make 1hp. 377/380 is 368cc/7cc = 52.5hp. Notice, 380HO, made 52hp on the Dyno Sheet at 6500rpm!

    2. You can use the PLAN Formula and BMEP, it will be within 1-2hp also.

    3. My Stock 670 Dynoed 115.7hp@7750rpm uses 11.5cr, and comes in at 94% with the Peak Flow Clac. At 94% and using 6350rpm what Rotax Ricks 670 is rated at with his Tuned Pipe it makes 92hp, and at 94% at 6350rpm the peak Flow Calc says it should make 94hp. I don't think Rick is running 11.5cr, I think he said he lowers it a little with thicker Gaskets. How much I don't know.

    The 380HO(368cc) at 6500rpm at 94% = 53hp! Dyno Sheet shows 52hp. Only using 11.2cr, not 11.5cr!

    Simonini Victor 1 Supper 400cc, rated 54hp@6500rpm. 400cc at 94% using 6500rpm = 58hp! 400cc/7cc= 57.1hp. The Simonini is only using 9.5cr. IF, you use the General Rule of Thumb, +1.0cr = 2hp, 9.5cr to 11.5cr = +2.0cr = 4hp. 54hp + 4hp = 58hp! Is all this Aproximate Numbers, Yes. It's called a Ball Park Figure. No (2) Engines even Dyno the same.

    All we really care is how much HP were making at Max rpm!

    By using the Peak Flow/HP Calc you can see if it's as efficient as it can be. It's nice if you have same Type Engines to compare, like 377/380 vs 380HO, 670 vs 670HO, Muffler vs Tuned Pipe vs Aftermarket Tuned Pipe and a Dyno Sheet to look at. There are many parameters on an Engine that all affect hp made.
     
    Last edited: Aug 14, 2019
  13. Aug 14, 2019 #33

    Armilite

    Armilite

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    ===================================

    I wish I had a Small Engine Dyno or access to one. I would love to Dyno all these 4 Stroke Add-on Parts to really see what works and what doesn't. Same with these 2 Strokes.
    https://www.dynomitedynamometer.com/snowmobile-dyno/snow-dyno_installation-video.htm
     
  14. Aug 14, 2019 #34

    Vigilant1

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    You could just make a simple hub for the output shaft and then use calibrated clubs to get a very accurate reading of the available HP at any RPMs you want. It works, it is cheap, it is simple, it is self-calibrating, and (best of all) it is very credible. Frankly, I think the vast majority of dyno runs/graphs we see online are BS--you can get any results you want to buy, and commercial shops get more business if they produce higher numbers. But with calibrated clubs and a legit optical tachometer there's very little opportunity to fool yourself or anyone else (short of outright fraud).
     
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  15. Aug 16, 2019 #35

    Armilite

    Armilite

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    ===========================================
    If it was Simple everyone would be doing.

    I have never seen a Dyno that uses a Club. I have seen Water & Inertia Dyno, and one using an Electric Gen Head. I heard of a Club Prop for test running an engine. For the Type of Testing, I'm talking about a conventional Dyno would e best.

    Makeup some set Standards you want to for 4 Strokes like Hp@ 4000rpm, Hp@4500rpm, Hp@5000rpm, Hp@5500rpm. 2 Strokes are Industry Standard Hp@6500rpm. These Honda/Clone GX390+ Singles almost all use the same Head/Valves and almost all use similar 8.0-8.3cr.

    1. Dyno Stock 4 Stroke Engine at 3600rpm, then Dyno at Max Rpm you want to use, Max 5500rpm.
    2. Dyno Stock Engine without Air Filter, then Dyno with a K&N Type.
    3. Dyno Stock Engine without Stock Exhaust, then use the different aftermarket Tuned Headers. You have to Tuned the Header for your Max rpm.
    4. Dyno with Bigger Carbs.
    5. Dyno with different CR's, like 9.0cr, 10.0cr, 11.0cr. Someone made a nice Head Milling Spreadsheet. 11.5cr is as high as I would go whether 4 Stroke or 2 Stroke.
    6. Dyno a Ported Head.
    7. Dyno a Head with Big Valves.
    8. Dyno with some different Cams.

    You do have these different Honda/Clone Race sites to give you some ideas. Example: If you need a 25hp Engine. The Stock Duromax 18hp@3600rpm 440cc Single comes in at 95% Volumetric Efficient. Same 440 at 95% at 4000rpm = 20hp, at 4500rpm = 22hp, at 5000rpm = 25hp, just turning it Higher rpm. Now, how much % Increase 5-15% are you going to Gain if you do just the Base Mods, K&N Type Air Filter $30, Header Exhaust $40, a Bigger Carb $40?

    440 at +5%.
    440 at 100% at 3600rpm = 19hp
    440 at 100% at 4000rpm = 21hp
    440 at 100% at 4500rpm = 23hp
    440 at 100% at 5000rpm = 26hp
    440 at 100% at 5500rpm = 28hp

    440 at +10%.
    440 at 105% at 3600rpm = 20hp
    440 at 105% at 4000rpm = 22hp
    440 at 105% at 4500rpm = 24hp
    440 at 105% at 5000rpm = 27hp
    440 at 105% at 5500rpm = 30hp


    Small Honda/Clone Dyno.


    Do it yourself Bike Dyno.
    http://www.gofastforless.com/tools/dyno.htm

    Honda/Clone Header kit $25 on eBay. Can you make your own, Yes.
    HONDA GX390 CUSTOM HEADER EXHAUST KIT GENERATOR GO KART MINIBIKE DRIFT TRIKE.

    AIR FILTERS.jpg 34mm Flat Side Carb eBay.jpg DYNO 3.jpg DYNO 2.jpg DYNO 1.jpg
     
  16. Aug 16, 2019 #36

    Vigilant1

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    They are very common among people who are modifying airplane engines. Very accurate, very cheap. If you haven't heard of "calibrated clubs" it may be because they are less commonly used for those developing engines for cars, etc where it is more convenient to take the measurement at a wheel/tire, etc. But where you have an engine with a prop hub already on it and you are interested in the available power it can make at airplane RPMs (say 2000 to 4000), calibrated clubs are a great answer. No need to build a fancy hydraulic or mechanical brake, just use the air that is everywhere.
     
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  17. Aug 16, 2019 #37

    n3puppy

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    You seem to have missed the substance of my post

    The Peak Flow Calculator data is wrong for a 377/380
    .
    That means the the Calculator can be wrong for all engines

    The 377/380 in question DOES NOT have a 94% volumetric efficiency.
    The 377/80 in question DOES NOT pump 86 CFM
    It uses lots more air much and requires a bigger carb/carbs to support the higher airflow.

    The 377/380 dyno graph clearly shows that for 57hp@ 7000 RPM
    The true VE is 112%.
    It pumps 102CFM of air
    Peak Flow calculator says 94% and 86CFM
    A 19% error (102 / 86)

    377/380 Dyno graph clearly shows that making 52HP@6500 RPM
    The true VE is still 112%
    It pumps 95CFM of air
    Peak Flow calculator 92%VE and 78CFM
    A 22% error (95 / 78)

    Would you accept
    22% error in Altimeter readings indicating you can fly lower around radio towers ?
    22% error in Compass headings when trying to find an airport for gas?
    22% error in Air Speed saying you can fly slower when close to stall speed near the ground?
    22% error in Published VNE indicating you can fly 22% faster before the wings tear off?

    Since we are discussing engine modifications -
    Would you accept a 22% airflow error when trying to properly size a carburetor for an engine? In this case you need 22% more carb flow than the Peak Flow calculator would indicate.

    Personally, I would not want to spend my hard earned dollars on a carb smaller than required.
    An undersized carb would certainly reduce overall flight performance, potentially turning a well designed aircraft into a dog.

    That's the kind of mistake that can be made using false data from the calculator
     

    Attached Files:

    Last edited: Aug 16, 2019
  18. Aug 16, 2019 #38

    n3puppy

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    More evidence of the inherent errors in the Peak Flow calculators HP/VE/Airflow predictions

    Look again at the "Test Mulle" dyno graph at 7500rpm
    Horsepower has dropped from 57hp back to 52hp (same as 6500rpm)
    Yet Airflow has increased from 102 to 104 CFM

    It is well known that a two cycle will lose HP as "it falls off the pipe" at high RPM. That is why HP is dropping off after the peak 57HP at 7000rpm
    Yet the Peak Flow Calculator is predicting MORE HP because airflow is increasing from 102CFM@7000rpm to 104 @7500 rpm

    Reality
    368CC 52Hp @ 7500RPM pumps 104CFM = 107% VE
    Peak Flow Predictions
    368cc 104CFM @ 7500RPM = 70HP!!!

    70hp predicted / 52Hp reality = a 35% ERROR

    I'll bet not many people would want to spend a lot of money on a Prop that is pitched for 35% more HP than the engine is actually putting out ........ 150E3882-C7F6-4649-BDB4-EF2C50B57512.jpeg E62110D7-63A5-4C5B-86DC-EBD1D1FF9BF6.png
     
  19. Aug 16, 2019 #39

    n3puppy

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    Have you ever wondered why all those engines seem to have a 94% VE?

    It is what is sometimes called an Engineered Coincidence. It happens when actual variable data in formula is locked to a fixed value. (Rule of thumb)
    In this case, it is obvious that the authors "Rule of Thumb" saying 1 HP requires 1.5 CFM of air is forcing errors vs real world results - Significant errors in the area of 20%

    In the 377/380 engine the dyno clearly shows that at 7000 rpm 1 Hp requires 1.79 CFM (102cfm/57hp). A 19% difference
    That is why Peak Flow displays the large errors it does for this engine.

    Peak Flow Calculator has no compensation for things like compression ratio, ignition timing, combustion chamber shape, engine temperature, friction losses etc. that can affect HP.

    None of those things affect Volumetric Efficiency (Airflow)

    Peak flow assumes Combustion Efficiency is 1 HP = 1.5CFM. As you say, no two engines are alike. That goes triple for the chances of every engine ever made requiring 1.5CFM per HP.

    BMEP still seems a much more accurate method of predicting engine performance than Airflow from a "rule of thumb calculator" BEMP is a proven engineering principal

    I suspect there might be a true engineering correlation between BMEP and how effective an engine burns fuel. ( CFM/HP ).

    It may be buried somewhere in the BFSC numbers often seen in dyno prints. BFSC definitely is a measure of how efficiently an engine burns fuel/air
     
    Last edited: Aug 16, 2019
  20. Aug 16, 2019 #40

    n3puppy

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    Exactly right - pretty common in Aircraft circles - even if it is a little old school.
    But some in some parts of the world- It's even "Government Approved"
    https://www.casa.gov.au/file/79221/download?token=AieuSbZB 6E4B9608-6382-4AB3-A4ED-DB453994F543.jpeg 2C1FA31F-697B-4047-A7AC-DB417807FEE7.jpeg
     
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