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Thread: ESE's works engine tuner

  1. #35821
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    Dynamics, dynamics, dynamics. Thank you very much Frits. Makes perfect sense.
    I might guess that a greater amount of energy translates to a greater amount of heat in this case? Maybe the pipe could be longer to accommodate a lower compression ratio or a later ignition. (Given the 2.4 million other variables stay the same)

  2. #35822
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    Quote Originally Posted by Condyn View Post
    Dynamics, dynamics, dynamics. Thank you very much Frits. Makes perfect sense.
    I might guess that a greater amount of energy translates to a greater amount of heat in this case? Maybe the pipe could be longer to accommodate a lower compression ratio or a later ignition. (Given the 2.4 million other variables stay the same)
    Whilst writing my previous post I had considered including the correlation of ignition timing, exhaust gas temperature, speed of sound and pipe length, but I decided not to make things too complicated right away. But you are perfectly right Condyn: pipe length is an important factor when meddling with compression ratios and ignition timing.

  3. #35823
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    More adventures and two stroke fun at 2Stroke Stuffing:- https://youtu.be/7B64Nhldbe4

  4. #35824
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    Quote Originally Posted by JanBros View Post
    Quote Originally Posted by TZ350 View Post
    .
    now my 50 has a 30mm carburetor. A bored out 24mm OKO.
    so is there any venturi left at WOT ?
    I am suspicious you might be right and will be looking into it some more.

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ID:	349636 Suzuki RG50. 30mm carb. WOT blue line, partially closed red line. Issue simulated on a DynoJet dyno.

    I am not sure about that 30mm carb. The bike runs well enough but after a hard run down the straight it picks up speed if I close the throttle a bit. My first thought is that by the end of the straight it is running in the over rev area and the smaller throttle setting is leaning the mixture off and heating the pipe for a bit more rpm.

    The carb has been fitted with replaceable jets for air correction. I have also replaced the straight line MX80 ignition with an Ignitec DCCDI programmable one and also made a PWM power jet thing.

    You could be right about that 30, and what it really needs is a smaller carb. I have a spare 24mm to try too.

    But I can't test anything until we are out of lock down. There is a major vaccination drive going on in the country and the city I live in is completely closed. The rest of the country less so as there is no sign of CV19 there.

  5. #35825
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    Many very fast 50cc Freetech etc use 30mm HV Lectron carbs , the trick here is that this particular carb , like its bigger brothers has a venturi radius behind the slide that is 4mm smaller than the nominal bore.
    Thus at 1/2 throttle it operates like a 24 Dia , and if the flow bench tests are the same as the bigger versions , they flow more air at WOT than the equivelant bore sized Keihin/Mik/Dell.
    Of interest as well is that the Lectron can be run up around 50* downdraft to straighten out the inlet duct without spewing fuel thru the pilot circuit under brakes , as all other carbs do except the
    actual rare carbs designed with an angled bowl.
    Ive got a thing thats unique and new.To prove it I'll have the last laugh on you.Cause instead of one head I got two.And you know two heads are better than one.

  6. #35826
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    Quote Originally Posted by Frits Overmars View Post
    Personally I am in favour of a low compression ratio for a competition two-stroke.
    I know you probably do not like this kind of questions as their is no simple answer, but I'm gonna ask it anyway :
    what would you consider low and is there some sort of correlation with BMEP ?

  7. #35827
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    Quote Originally Posted by TZ350 View Post
    More adventures and two stroke fun at 2Stroke Stuffing:- https://youtu.be/7B64Nhldbe4
    Alex' latest video prompted me to react and although I value the technical level of the Kiwibikers infinitely higher than the average Fakebook level, maybe I can avoid some mishap by posting it here as well.
    Hei Alex, as you know I like the way you promote the two-stroke engine with your videos and I am well aware that you have thousands of followers. Not everyone of those will be as experienced as you are, and I noticed a 'dangerous ten seconds' from 06:52 to 07:02, where you set the piston position with a depth gauge and then tighten the ignition nut with an air wrench. Those unexperienced followers might follow your example and ruin the depth gauge because they never saw you removing it before tightening the nut...

    Quote Originally Posted by JanBros View Post
    I know you probably do not like this kind of questions as their is no simple answer, but I'm gonna ask it anyway :
    what would you consider low and is there some sort of correlation with BMEP ?
    If I come across a question that I don't like, I can always pretend I didn't see it Jan. You learn these things on Fakebook, you know .
    What would I consider low? That is a question I never asked myself; I prefer numbers over expressions like low and high. But in order to try and answer your question let's say that a compression ratio lower than 10 is definitely low. And I am talking geometrical compression ratio, not the nonsensical Japanese 'trapped' compression ratio that is meaningless unless the exhaust timing is also mentioned (which it never is).

    Of course there is a correlation with BMEP, although I cannot confirm that it is linear. I like these low compression ratios because I get more power with them, and since power comes from BMEP x rpm, and since the optimum rpm is pretty much defined by the angle.areas of an engine, which are not influenced by the compression ratio, the power must come from the BMEP.

    To be absolutely precise, although the angle.areas of an engine are not influenced by its compression ratio, the specific angle.areas are because the volume that has to be scavenged, increases when the combustion volume is increased. So arithmetically the achievable rpm becomes smaller for a lower compression ratio. But this influence is negligible, as long as you do not go really low with your compression ratio, like 4:1 or so.

    Am I joking? Now that I write it, I wonder why I never tried it; the exhaust pipe would love it! And I have nothing to lose; a 4:1 compression ratio can't possibly damage an engine, and replacing a head if it doesn't work is a matter of minutes.

    One more thought to crank your brain:
    After the piston has closed the transfer ports on his way up, the exhaust pipe tries to shove washed-through fresh mixture back into the cylinder before the exhaust port closes.
    This shoved-back mixture raises the pressure in the cylinder and at some point this pressure has risen so high that the pipe is no longer able to shove back any more mixture.

    Now if the volume above the exhaust port is bigger, there is more room for shoved-back mixture and the cylinder pressure will not rise quite so quickly.
    The pipe can then cram more mixture into the cylinder before exhaust closure, which is good for power.
    How can we make the volume above the exhaust port bigger? By fitting a head with a bigger combustion chamber volume....

  8. #35828
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    I have built 8 different pipe designs for a specific vintage air cooled engine, and think I have arrived on something usable. I was stuck on long headers (around 35%) for a few designs with the thought of delaying the diffusers action on the bad transfer geometry. The first pipe I built with a 33% header worked WAY better instantly. (Random tangent I know)

    I think that I am sold on trying a lower compression ratio on my next engine with much efforts in making the pipe suit.
    The compression ratio is currently 15:1. Being that it is air cooled I am gathering a lower ratio might be beneficial in more than one way.

    This is an interesting perspective/logic Frits. I have always associated a high exhaust port with bad trapping and lower cylinder pressures, without thinking of the pipes roll.

    Another thought I have is the extra spilling that my vintage engine likely has, and the effect that has on this theory. I have read and think I understand Neels literature on contact discontinuities. If an engine has a garbage trapping efficiency, a lower compression ratio with a larger area in the cylinder for the smeared up pipe to be pounded back into, it may wasted space?

    My thought process is probably wacky.

  9. #35829
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    Quote Originally Posted by Frits Overmars View Post
    The pipe can then cram more mixture into the cylinder before exhaust closure, which is good for power.
    How can we make the volume above the exhaust port bigger? By fitting a head with a bigger combustion chamber volume....
    Or running a lower exhaust port.....

  10. #35830
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    Quote Originally Posted by Frits Overmars View Post
    An 11:1 compression ratio with early ignition may well behave just like a 15:1 compression ratio with late ignition, but once again it depends on the efficiency of the pipe.
    Hi Frits,
    would the pipe in these two cases be of the same shape? Of course this depends on the exhaust gas temperature,
    so the question is, what happens to the EGT by lowering the compression ratio?
    I wonder what pipe a 4:1 cr requires?

    Btw I am doing 50cc endurance racing (mainly a 8h race in Germany) and I am reading this threat (and on Pitlane) for some years now, but all the answers I had were already asked and answered. Thank you for sharing your knowlege. It is better than all the 2T books I have bought.

  11. #35831
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    Before I take anymore material out of the combustion chamber I am looking for some suggestions from people with more up to date experience with 2 strokes and methanol than my clumsy 1970's experience with Meth and RD's.

    The engine is an air cooled 1971 Kawasaki F81M rotary valve 250 with a 70mm bore being prepped for post classic road racing.

    Un corrected compression ratio is currently 15:1, squish 1mm. Fuel 25% Methanol, 5% Acetone, 70% 96 petrol. The plan is to keep adding Methanol until the cylinder head temperature hovers around 70deg C.

    The question is, what is a sensible compression ratio and the sort of spark plug heat range to use with Meth.

  12. #35832
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    Wow , a sudden burst of interest over one small comment - but its a big can of tasty worms.
    To jump in on the first question , yes there is a direct correlation between BMEP and static compression.
    As BMEP rises so is the Delivery Ratio , and or Trapping / Scavenging Efficiency. These variables all ultimately increase the amount of clean A/F in the cylinder prior to EPC.
    Thus as these effects become more efficient the dynamic compression increases , and the law of diminishing returns begins to affect the optimum static compression that can be used.

    Then the next influence is fuel quality/octane and makeup.
    A general approach is that leaded race gas is optimised by lots of com , minimal advance and very lean mixtures.
    Unleaded /pump low octane fuel is the dead opposite - it hates com , likes advance and makes best power when on the richer side.
    Thus the old Elf 130 was run up at 18.5:1 and was combined with minimal advance and around 700* + in the header ( not in the spigot like the Aprilia had )
    The later GP bikes on FIA unleaded were fastest with a max of around 15:1 , way more advance and richer jetting , simply due to the fuels characteristics.
    This approach lowered the pipes bulk average wall temps , and thus those designs changed to suit.

    Low com does increase the available cylinder volume above EPC , and does lower the compressing losses BTDC , but these elements pale into insignificance compared to the detonation resistace
    that is set by the compound effect of the com and the extra advance this lower com number will allow.
    Programmable ignitions make finding the optimum advance relatively easy on the dyno , but then finding the best power com involves the nighmare of making a bunch of inserts with nothing changed
    but the cc , and then having to reconfigure the ignition for each change.

    But sadly even in the case of changing from 12:1 to 16:1 there will be a huge difference in chamber geometry - and thats another can of worms as well.
    Nothing is easy when operating on the outer limits.

    Edit - the other question was related to the effect on EGT by dropping com - in this case EGT will rise as more of the finite energy within the trapped fuel is released into the header instead of heating the piston/water.
    But this is directly offset the other way by adding timing , so its an endless circular function trying to find the best combination.
    Ive got a thing thats unique and new.To prove it I'll have the last laugh on you.Cause instead of one head I got two.And you know two heads are better than one.

  13. #35833
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    TeeZee , having done tons of work using Meth before I had grey hair , I wonder mainly why you are using Meth as an aditive to petrol.
    By far the best results for an aircooled is to maximise the natural cooling effect of huge amounts of rich Meth mixture going thru the engine.
    Using 90% Meth , 5% Acetone , 5% petrol means you can run identical com to Avgas as you would in a watercooled cylinder , and have no heat soak related power loss.
    The effective octane of this mixture is around 130 , but you must have a cold ( 11 ) plug and as much grunt as you can get with the ignition if running +20% rich with high com.
    Nowdays this is easy , run the ignitech at 14.2 charging volts and parallel up the outputs of a DC CDI P2.
    I used a huge Crane ignition coil designed for CDI use in NASCAR race engines as it has the only two things that will increase spark energy in a DC CDI , very low primary resistance and high inductive reactance.
    Ive got one if you want to give it a shot.
    This setup pulled nearly 5 Amps from a P2 that previously ran at around 1.5A on a normal single coil - a massive increase in ionisation and burn time energy.
    Do it right and 16:1 is a walk in the park for your application.
    Ive got a thing thats unique and new.To prove it I'll have the last laugh on you.Cause instead of one head I got two.And you know two heads are better than one.

  14. #35834
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    Quote Originally Posted by wobbly View Post
    TeeZee , having done tons of work using Meth before I had grey hair , I wonder mainly why you are using Meth as an aditive to petrol.
    By far the best results for an aircooled is to maximise the natural cooling effect of huge amounts of rich Meth mixture going thru the engine.
    because the bike is used in endurance racing and he does not want to pit every 15 minutes for refueling ?

  15. #35835
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    Nah we dont do much endurance over here, and Rob isn't getting any younger for that sort of malarkey. None of us are.
    I've been told. Dreaming`s free.
    Think I'll go, back to sleep.
    Everybody listen, voices in my head
    Everybody listen, do yours say, what mine says?

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