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  1. #1

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    O ring style diesel conversion head for high rpm.

    Hi all,

    Has any body successfully used an O ring style diesel conversion head for high rpm or racing use?

    The only example that I have seen was in an RC Pylon racer using a Thunder Tiger Pro 46 and whilst it ran very well I have no idea as to the longevity of it.

    So, can the standard Viton seals stand up to the high compression and heat that can be found in the upper rev bands of most engines?

    Thanks.


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    RE: O ring style diesel conversion head for high rpm.

    Rec

    Thats really hard to say seeing we dont know what goes on up there ,

    what is the argreed temp of a leaned out contra piston , unknown ?

    I seem to remember Dave Gierke saying on a glow it was 470 F ,, on a Diesel would you say it was cooler than a glow?



    230 C is very hot , you can temper steel at 250 C,

    people often do

  3. #3
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    RE: O ring style diesel conversion head for high rpm.

    To me there is more black castor build up on a high revving diesel than on a typical glow engine running on full castor fuel. So the head temperature might be higher on diesel engines compared to glow.

  4. #4

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    RE: O ring style diesel conversion head for high rpm.

    Bob Davis (Davis Diesel Development) made diesel heads for ducted fan engines back in the day.

    He would be qualified to answer this one.

  5. #5

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    RE: O ring style diesel conversion head for high rpm.


    ORIGINAL: fiery

    Bob Davis (Davis Diesel Development) made diesel heads for ducted fan engines back in the day.

    He would be qualified to answer this one.
    Hi Derek,
    ************** yes that is true but note that even the ducted fan entry on the web site only gives mention to low noise, low fuel consumption, big props etc.

    And that is all good and fine but the devil is in the details, do they rev out to 22 000 rpm and beyond, and for how long? And do I spy a tuned pipe on that ducted diesel on the site?


  6. #6

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    RE: O ring style diesel conversion head for high rpm.

    I can tell you this much and that is that back when we were flying ducted fan with new K&B .81 we lost the barrel in the carburator in flight so the fuel had to jump across the open throat. It's safe say, that imakes for very lean. The plane was flying too fast to land and so it stayed in the air for over 20 min. before we could land it. After the engine was opened we found no parts failure except for major piston wear. The piston could slip through the cyclinder with ease. However, we do not use common Viton rings.
    Bob Davis, Owner - Davis Diesel Development

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    RE: O ring style diesel conversion head for high rpm.

    Thanks for the reply Bob, I appreciate it.

    Non standard seals, never knew that!

  8. #8

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    RE: O ring style diesel conversion head for high rpm.

    Recyled flyer I do not know what material Davis O rings are I guess his "Trade secret" like the Coca cola formula

    I have NEVER heard of anyone mentioning a failure of his O rings, regards martin

  9. #9

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    RE: O ring style diesel conversion head for high rpm.

    If the muffler is cooler than a glow doesnt that mean the engine is too

  10. #10

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    RE: O ring style diesel conversion head for high rpm.


    ORIGINAL: 123Cat

    If the muffler is cooler than a glow doesnt that mean the engine is too
    Not really, combustion in a model diesel takes place very rapidly and entirely within the engines combustion chamber whereas methanol is still expanding when the exhaust port opens.
    A flame front can be seen under favourable conditions exiting that port so imagine how hot the muffler would get as compared to the completely spent gases of a diesel.
    The interior of a diesel head could well be hotter as a consequence.

  11. #11

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    RE: O ring style diesel conversion head for high rpm.

    123 cat I would say so, run a glow no muffler you see a flame front still burning when out the exhaust, diesel no, combustion complete, , when I measured diesel temp on engine maybe 195 to to 225 tops , glows hotter you do not want to put you finger at end of a glow exhaust or grab muffler martin
    on glow at least 25% of fuel wasted this way no work, hence diesel fuel economy

  12. #12

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    RE: O ring style diesel conversion head for high rpm.

    Just by having a quick look around the net has revealed to me that ambient temperature air squeezed at 18:1 compression ratio will yield 647ºC but that is a temperature that is briefly visited and may not reflect on the cooler outside of the engine.

  13. #13
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    RE: O ring style diesel conversion head for high rpm.

    Chris, when 60 degree air is compressed to 363 PSI it generates 1,000 degrees of temperature but only while it is being compressed, the friction between the molecules causing the heat. At TDC the surrounding metal rapidly cools the air unless fuel has been injected into it. At 1,000 degrees the air actually glows a dull red.

    The compression ratio in our Diesels about 13.5 to 1 or less. My Saito .80 has 14.4 to one and will start and run with no assist at all. It will turn a Bolly 13.5x8 at 8,700 rpm but is over compressed. I don't think they would stand up under 18 to 1.
    Farmall 240 the final issue of the Farmall C, Super C, 200, 230 series.
    122 Cu. In. 22 hp. A small tractor that would do big work due to its 10x36 inch rear tires.

    As competition improves products, the differences between them get smaller and smaller

    Club Saito member #5

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    RE: O ring style diesel conversion head for high rpm.


    ORIGINAL: Hobbsy

    Chris, when 60 degree air is compressed to 363 PSI it generates 1,000 degrees of temperature but only while it is being compressed, the friction between the molecules causing the heat. At TDC the surrounding metal rapidly cools the air unless fuel has been injected into it. At 1,000 degrees the air actually glows a dull red.

    The compression ratio in our Diesels about 13.5 to 1 or less. My Saito .80 has 14.4 to one and will start and run with no assist at all. It will turn a Bolly 13.5x8 at 8,700 rpm but is over compressed. I don't think they would stand up under 18 to 1.
    Ah this old chestnut Dave, Imust do the math myself but I have seen figures quoted for model diesels well beyond 13.5:1.

    Clarence Lee from the Davis web site -
    " ............. diesel engines run as high as 22:1!"

    Model Engine News Web site -
    "A rule of thumb says that the typical diesel mix will go bang at a C/R of around 18:1, " and " compression ignition engines will need to get up in the region of 18:1.."

    From the Pacific North West Combat Diesel site -
    :a well broken-in diesel will run typically on compression ratios of around 17 or 18 to 1"

    My MVVS glow runs at 11:1
    with zero nitro fuel so I maybe this is about geometric vs trapped compression ... again.


  15. #15
    Moderator Hobbsy's Avatar
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    RE: O ring style diesel conversion head for high rpm.

    Chris, if what you say is true our model Diesels would run on pump Diesel with no ether. This Case 430 has 17.5 to 1 compression ratio and generates 485 psi compression pressure and will start un aided in all but sub zero weather. For sub zero it has a glow plug in the center of the intake manifold to warm the air as it flows through the manifold. If you use ether on this one while using the glow plug you'll have to go over to the neighbors to get the air cleaner back.


    Type: J.I. Case

    Fuel: diesel

    Cylinders: 4

    Valves: -unknown-
    Bore/Stroke: 3.8125x4.125 inches [97 x 105 mm]

    Displacement: 188.4 ci [3.1 L]

    Cooling: liquid

    Air cleaner: oil bath

    Compression: 17.5:1

    Rated RPMs: 1750

    Starter type: -unknown
    Farmall 240 the final issue of the Farmall C, Super C, 200, 230 series.
    122 Cu. In. 22 hp. A small tractor that would do big work due to its 10x36 inch rear tires.

    As competition improves products, the differences between them get smaller and smaller

    Club Saito member #5

  16. #16

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    RE: O ring style diesel conversion head for high rpm.

    Hi Dave,
    the trouble with the figures I quote, and quite possibly the ones that you quote also is that there is no method of measurement shown.

    Geometric compression ratio, the one that is mathematically the easiest to find, is the most common and the most inaccurate of all.
    Swept volume + head volume / head volume does not take into account how much of the swept volume is actually trapped for use.

    In two strokes the volume of above the exhaust port is what is trapped, plus a slight residual pressure wave gained from below it, and its far harder to measure and as a result not often quoted.

    In any valved engine be careful as to when all the valves close to give you exactly what is trapped, it's no use quoting a perfectly correct geometric compression ratio if the valve overlap runs into the compression stroke, and a lot of engines in fact do this.

    The gas pressure is what counts, not what the ruler tells us - and I am sure that some of the others will extend on this further.

    Thanks mate.

  17. #17
    Moderator Hobbsy's Avatar
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    RE: O ring style diesel conversion head for high rpm.

    You are correct, here in the Stites, you get that, it is called the corrected compression ratio when taking the port/valve timing into consideration. On some engine tests C. Lee calculated the compression and stated the corrected ratio..
    Farmall 240 the final issue of the Farmall C, Super C, 200, 230 series.
    122 Cu. In. 22 hp. A small tractor that would do big work due to its 10x36 inch rear tires.

    As competition improves products, the differences between them get smaller and smaller

    Club Saito member #5

  18. #18

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    RE: O ring style diesel conversion head for high rpm.

    ok group just a tidbit, was reading the 400 page plus manual that came with my Dodge truck with a cummins diesel and up comes a scary page
    RUNAWAY , If the tubo lube oil has a bad leak into the turbo if that happens
    Step 1 turn of the key this shuts down the fuel and injection pump hence NO FUEL FED INTO ENGINE INJECTION SYSTEM OFF
    Step 2 block off air or use fire extinguisher sprayed into air intake, Wonder why they do not have an emergency shut down, just a flap to cut off air, some engines do

    The engine in this condition is running wide open on that nice mix of lube oil and air pushed in by the turbo, just like a wide open throttle on our model engines
    (except no governor will speed to self destruction)

    Compression ratio 16.7 to 17.4 depending on engine (Cummins)

    conclusion- diesel is diesel if compression ignition regardless of fuel makes no difference if model engine or full size martin


  19. #19

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    RE: O ring style diesel conversion head for high rpm.

    Martin, and the original 6.5 litre Ford and Dodge's ran at over 21:1.

    The use of a turbo is a wild card and probably takes that 17:1compression piston set in your Dodge truck back up to around 20:1 at full boost.

    Anyway, no further entries about high speed model engines with diesel conversion heads?

    The K&B 81 is worth finding out about though!


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