Rotax 503 ... 1 or 2 carburetor ?

Discussion in '2-Stroke Aircaft Engines' started by dominique, May 25, 2019.

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  1. May 25, 2019 #1

    dominique

    dominique

    dominique

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    Hello
    For my current project (http://da01ulm.free.fr) the choice of the engine is not yet final. The general configuration of the aircraft imposes a light engine around 40 45 kg with at least 40 hp
    I'm thinking of the Rotax 503 and I wonder if there is a big difference in reliability and ease of tuning between the 1 and 2 carburetor versions
    Do you have an idea ?
    Thank you
    Dominique ... sorry to use google translator !
     
  2. May 25, 2019 #2

    pictsidhe

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    Twin carbs need balancing or the idle will be horrible. That isn't difficult on a twin.
    Reliability is much the same.
     
  3. May 25, 2019 #3

    choppergirl

    choppergirl

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    Jet ski carbs so you can do aerobatics and fly upside down.
     
  4. May 25, 2019 #4

    dino

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    The idle is always horrible anyway.
     
  5. May 27, 2019 #5

    Armilite

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    ====================================================================
    First, Rotax's UL Engines have been based off Skidoo Snowmobiles Engines, which have used Rotax Engines since 1963. In 1993 they switched over from Single Spark Plug Nippon Denso CDI Ignition over to Ducati Dual Spark Plug CDI Ignition. Early Rotaxs used Bosch Points Ignitions. The 185UL to 503UL are all Piston Port Engines.

    You have to not only Look at HP@rpm made usually Max 6500rpm and Total Engine Weight FWF.

    Rotax 503UL Twin (50hp@6500rpm) 10.8cr with Rotax's Muffler, 62.3hp@6500rpm with R&D's Tuned Pipe!
    http://www.rotaxservices.com/dyno.html#7

    Rotax 447UL Twin (40hp@6500rpm) 9.6cr with Rotax's Muffler, 52.4hp@6500rpm with R&D's Tuned Pipe!
    http://www.rotaxservices.com/dyno.html#15

    Rotax 377UL Twin (35hp@6500rpm) 9.6cr with Rotax's Muffler and used a Single 36mm Bing 54 Carb. To my knowledge R&D never made a 377UL Tuned Pipe. The 377 is also called a 380 in Snowmobiles, and there was also a 380HO (High Output) 2004+ Sold only in Sweden an Alaska that I have found! The Standard 377/380 used 9.6cr with a 30mm Carb in Sleds were rated 36hp@7000rpm, the 2004 380HO used 11.2cr and 30mm Carbs and was rated 48hp@7000rpm. The 2004 380HO with an aftermarket Tuned Pipe Dynoed 57.26hp@7000rpm, was still making 52hp@6500rpm.

    Rotax 277UL Single (26hp@6250rpm) 11.8cr with Rotax's Muffler, were 30.5hp@6250rpm with R&D's Tuned Pipe!
    http://www.rotaxservices.com/dyno.html#14

    Today, Skidoo still makes a 550F which came out in 1993 which is a Reed Fed Engine. Depending on what Type of Reduction Drive you want to run, the US/Canada 550F's Top PTO Case have been Doctored, bottom Half of Case has the Provision 8 Bosses. The early 550's 2003 to around 2006 came with 34mm Carbs, 9.6cr, and Dynoed 70hp@7000rpm, later ones were detuned with Smaller 30mm Carbs, and even later ones eventually used different Cylinders with Smaller Ports. Today I think their rated 58hp@6800rpm.

    I see you live in France. In Russia, they still make almost all of these Older 90's Rotax's under the RMZ Line of Engines, but the 277, they do make a 250 Single with a Provision 8 Case. Their 550F has a Provision 8 Case.
    http://russneg.ru/Dvigatel-RMZ---550-2-karb--sov--smazka-Dukati-S40500550_110t.html

    If you use 11.5cr, with Proper Size Carbs for your Engine, with a Good Tuned Pipe (Wide Band) Designed for 6500rpm, it takes on Average 7cc to make 1hp! So for example, a 503 is 496.9cc. 496cc/7cc = 70.8hp!

    277UL(268.8cc) 268cc/7cc = 39.2hp
    377UL(368.4cc) 368cc/7cc = 52.5hp <- Remember, 380HO with aftermarket Pipe made 52hp@6500rpm!
    447UL(436.7cc) 436cc/7cc = 62.2hp
    503UL(496.9cc) 496cc/7cc = 70.8hp

    462UL(463.0cc) 463cc/7cc = 66.1hp
    532UL(521.3cc) 521cc/7cc = 74.4hp
    582UL(580.9cc) 580cc/7cc = 82.8hp
    618UL(617.2cc) 617cc/7cc = 88.1hp
    670(669.2cc) 669cc/7cc = 95.5hp

    You can use this Calc also. https://www.mk5cortinaestate.co.uk/calculator3.php
    Example: Rotax 277UL actually Dynoed 25.4hp@6000rpm with a Muffler. 25hp@6000rpm = 65% Volumetric Efficiency. My Skidoo 670 with a Stock Tuned Pipe Dynoed 115.7hp@7750rpm = 94%. So a 277UL(268cc) going from 65% to 95% @6000rpm = 36hp, 268cc at 95% at 6250rpm = 37hp, and 268cc at 95% at 6500rpm = 39hp. Hence the 7cc Rule of Thumb said 39.2hp.

    380HO with aftermarket Tuned Pipe 57.26hp@7000rpm. Still made around 52-53hp@6500rpm! 368cc at 7000rpm at 94% = 57hp, 368cc at 94% at 6500rpm = 53hp! 368cc/7cc = 52.5hp!
    380HO 57.26hp at 7000rpms.jpg 380HO 2004 AD 36HP.jpg 380HO 2004 AD 48HP.jpg
     
  6. May 27, 2019 #6

    Vigilant1

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    The OP asked a simple question: Which is better, 1 or 2 carbs for a Rotax 503?
    Now I know it is possible to cover the history of Rotax engines and never answer that question.
     
    poormansairforce, BJC and FritzW like this.
  7. May 28, 2019 #7

    Armilite

    Armilite

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    ============================================================
    All the Rotax Fanners and Free Airs are less than 45kg = 99.2lbs
    On a 503 Single vs Dual Carb can make a 3-4hp Difference depending on Carb Size used.
    They all Idle rough below 2000rpm varies with Prop used. If you use a 377 to 503 with a Rotax C or E Gear Drive you can use an RK400 Clutch which will let it run Smoother at lower Idle rpm. I don't remember the rpm when the RK400 engages at, I want to say 2350rpm, so No Prop Loads till then. Balancing any Engine can also Help. No difference in Reliability and ease of tuning.
     
  8. May 28, 2019 #8

    Armilite

    Armilite

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    ============================================================
    Actually, he made muliple Questions and references. "Heading 503 1 or 2 Carb?"

    "For my current project (http://da01ulm.free.fr) the choice of the engine is not yet final. The general configuration of the aircraft imposes a light engine around 40 45 kg with at least 40 hp
    I'm thinking of the Rotax 503 and I wonder if there is a big difference in reliability and ease of tuning between the 1 and 2 carburetor versions
    Do you have an idea? "

    So I gave him some Options with Examples, what did you give?
     
  9. May 28, 2019 #9

    Armilite

    Armilite

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    Today, we are seeing some EFI kit's on the Market by Ecotrons, and MegaSquirt, etc, which should give you a little better GPH, make Starting your Engine easier, run Smoother, and Fix any Carb Icing problems.
    https://www.ecotrons.com/small_engine_fuel_injection_kit/400cc_to_800cc_engine_fuel_injection_kit/

    There is also other brands of Snowmobile Engines(20+) that could meet your 45kg Weight & 40HP criteria. Not all can use a Gear Drive, but most can use a Belt Drive. Like JLO made Singles from 100cc to 396cc. So did Sachs, both were made in Germany. They were used on many different brand Name Sleds, on Water Pumps, Generators, Garden Tillers, Weed Wackers, Utility Carts, etc. So you might find them in France used on many things.

    If you want to use just a Muffler and 6500rpm then figure 10.5cc for 1hp. 40hp x 10.5cc = 420cc+.

    If you use a Tuned Pipe and 6500rpm you can use 7cc x 40hp = 280cc+. Which gives you many different Engine Options.

    All the different(20+) Sled Engine manufactures made a 292cc Single, it was the most popular Sled Engine. The Highest HP 292 Single was the Yamaha 292 that was a Reed Fed Single.

    Today, Rotax isn't making any New 503UL's so used is your only choice, and the Simonini Victor Singles, Reed Fed, using 9.5cr, set the World Bar for Airplane use. But they aren't cheap. Made in Italy so not too far from you. http://www.simonini-flying.com/index.php?lang=en

    368cc = 44hp@6500rpm using 9.5cr using a Tuned Pipe! Victor 1 362cc/7cc = 51.7hp
    382cc = 48hp@6500rpm using 9.5cr using a Tuned Pipe! Victor 1 Plus 382cc/7cc = 54.5hp
    400cc = 54hp@6500rpm using 9.5cr using a Tuned Pipe! Victor 1 Super 400cc/7cc = 57.1hp Best!!

    The Simonini Victor 1 makes at 5,500rpm 38.8hp or 28.56kw and at 6,000rpm 42.0hp o 30.91kw. So probably around 40hp@5750rpm.

    My used $85 JLO L372 (80mm x 74mm) 372.1cc, and IF you take out the Iron Sleeve and Nikasil the Shell gives you a minimum (86mm x 74mm) 430cc. I got about $350 in it so far for all New Gaskets & Seals, Bearings, etc. I got a NOS Head & Cylinder for $115 Shipped in that total. I still have to buy a New Carb, Rope Recoil, and Electric Starter & Lithium Battery, and a few Nuts & Bolts/Studs I want to replace. I'm sure I will be under $750 for the Motor if I rebuild it the normal way, and probably under $1100 if I go the Nikasil Route. Any of the current Belt Drives made for either the Honda/Briggs/Clone or Rotax's could be Adapted to work on a JLO. If you want a 4 Stroke I would look at these New Honda/Briggs/Clone Singles that go up to 626.3cc today. A 440cc+ Single could probably be Built to make your 40hp at 5000rpm.

    JLO L372 - L380 COVER 1.jpg HONDA ROTAX JLO PTO BOLT PATTERNS.jpg 1970 Arctic Cat Panther 372 JLO Rockwell Engine - 1.jpg JLO PTO SPEC'S 125mm 45 Degree 4 Bolt.jpg JLO 340 PTO CASE.jpg

    That's 23hp@3600rpm. They use Small Carbs, Restrictive Air Filters & Exhaust with low Compression.
    Vegas 625.jpg
     

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