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Thread: ESE's works engine tuner

  1. #28111
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    Quote Originally Posted by Frits Overmars View Post
    That would imply that the blowdown period lasts all the way from exhaust opening to where the piston reaches the exhaust floor. Then at the end of blowdown,
    the transfer ducts will be completely filled with exhaust gases, and it will take a similar amount of time and crankshaft degrees, i.e. from BDC to transfer closure,
    to expell those exhaust gases again. In other words: the 'scavenging' will be performed with exhaust gas only. I can guarantee that no engine will run like that.
    Of course you're right.
    Could we postulate that, at peak power RPM, blowdown is complete by first transfer opening? Wouldn't that be the ideal situation for best power?

    Assuming (and hoping) that your exhaust duct diameter is smaller than the bore, then the duct volume will be a lot smaller than the cylinder volume. And this would imply that part of the washed-through charge makes it into the hot exhaust header before being shoved back by the pipe effects. Not quite what you want.
    Yes, I was mistaken in thinking that Wobbly had said that duct length is usually about 1 x bore. He actually said 2 x bore. In which case my duct is very short, and as you said, must negatively affect washed-through charge.

    Should the volume of the duct be related in some way to the capacity of the cylinder? Would the efficacy of the pipe effects also be a factor, since this must affect the volume of washed-through charge?

    If I find a way to extend the duct on my (water-cooled) engine, can I assume I must also find a way to cool it?

    Thank you for your advice.

  2. #28112
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    Quote Originally Posted by lodgernz View Post
    The exhaust duct of this engine has a bit of a bottleneck about halfway down, whose CSA is about 66% of the port window area.
    If you got an exhaust port that is too small for sufficient blowdown (undersquare engines with single exhaust f.e.) reducing the cross sectional area behind it will make things worse. I have seen engines benefiting over the whole power band from grinding the flange diameter bigger as 90%.
    So the percentual approach needs a sidekick: a rule of thumb how big your exhaust area must be according to your cubic capacity.

    This rule of thumb might be found using Time Area or Wobblys approach to get the area of carb, transfers and exhaust in the same ballpark. But this ballpark gets wide whilst comparing a bunch of high bmep engines...

    A friend told me that in an old version of Mota, there was a good working formula for the needed exhaust window size and exhaust flange diameter. Anyone here that knows the maths behind it?

    Happy Holidays
    Chris

  3. #28113
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    18th April 2017 - 23:08
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    V-twin

    Hey all
    I'm doing some work with the exhaust systems, I am thinking of doing a few different for testing.
    The first system I have thought of is with a shorter register to cylinder B, don’t not know if it's stupid but felt like it might be good,
    but what do I know about 2-cylinder applications or V twin for that matter.
    Thankful for thoughts and ideas!

    It will be a variator engine with peak at 15800 rpm (2x50cc 41 stroke)

    Muhr
    Attached Thumbnails Attached Thumbnails exhaust 12.pdf   exhaust 8-Scene 4.pdf  

  4. #28114
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    Quote Originally Posted by lodgernz View Post
    My cylinder has been decked and raised, so the bottom of the exhaust port is already 2mm above BDC, but of course this has not reduced the duct volume. In fact, by the time I widen the top of the port, the volume will be even larger.
    I hesitate to try and raise this floor further by other means, as I know of no published experimental data on the effects of the floor being higher than about that amount. I believe Jan tried 2mm on the RSA125 with some improvement but did not go any further than that.

    ...
    Rotax Max kart ( engine without gearbox ) original cylinder - 2.2mm barrier.

    And two other pic: pressure at partly open EX port and reed petal shape at different rpm. From old book, but interesting theory and experimentation.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  5. #28115
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    Someone help me!

    I´m redesigning my crankcase as i had a HUGE volume due to ~20mm spaced upwards cylinder.
    I´m reading '1.3' here in the thread.

    Is that cylindervolume x 1.3 ?

    In my case 211x1.3=274,3cc

    Or have i misunderstood the way to calculate it?

    Rgds
    Patrick

  6. #28116
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    Quote Originally Posted by SwePatrick View Post
    Someone help me!

    I´m redesigning my crankcase as i had a HUGE volume due to ~20mm spaced upwards cylinder.
    I´m reading '1.3' here in the thread.

    Is that cylindervolume x 1.3 ?

    In my case 211x1.3=274,3cc

    Or have i misunderstood the way to calculate it?

    Rgds
    Patrick
    (slagvolym + vevhusvolym "bdc)/ vevhusvolym "bdc= comp


    in your case (211cc) 703,3cc BDC = 1,30001422

  7. #28117
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    Quote Originally Posted by TZ350 View Post
    Attachment 334208

    Got my Arduino Nano project working Ok on the test bench.

    Computer programming, who said an old dog can't learn new tricks ...... Woof.
    Always impressed by what you do TZ, good doggy, very clever.
    Factual Facts are based on real Fact and Universal Truths. Alternative Facts by definition are not based on Truth.

  8. #28118
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    Quote Originally Posted by FastFred View Post
    Always impressed by what you do TZ, good doggy, very clever.
    he told me he would get more done if his tired sons helped him out(-;
    i'm over buckets

  9. #28119
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    Quote Originally Posted by Muhr View Post
    Hey all
    I'm doing some work with the exhaust systems, I am thinking of doing a few different for testing.
    The first system I have thought of is with a shorter register to cylinder B, don’t not know if it's stupid but felt like it might be good,
    but what do I know about 2-cylinder applications or V twin for that matter.
    Thankful for thoughts and ideas!

    It will be a variator engine with peak at 15800 rpm (2x50cc 41 stroke)

    Muhr
    I recon that your setup would be used for "moped" drag racing?
    Anyway, it looks to me that such a wheel would have a rather high moment of inertia. Perhaps you could improve your results using a different wheel setup?

  10. #28120
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    Quote Originally Posted by Muhr View Post
    (slagvolym + vevhusvolym "bdc)/ vevhusvolym "bdc= comp


    in your case (211cc) 703,3cc BDC = 1,30001422
    Thanks!

    I had it all confused there for a while

  11. #28121
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    Quote Originally Posted by _____ View Post
    If you got an exhaust port that is too small for sufficient blowdown (undersquare engines with single exhaust f.e.) reducing the cross sectional area behind it will make things worse. I have seen engines benefiting over the whole power band from grinding the flange diameter bigger as 90%. So the percentual approach needs a sidekick: a rule of thumb how big your exhaust area must be according to your cubic capacity. This rule of thumb might be found using Time Area...
    Chris, from your text I gather that in your 'undersquare' engine the bore is bigger than the stroke, but that is usually called oversquare.
    There has been confusion over this before but if we stick to long-stroke and short-stroke instead of undersquare and oversquare, we can avoid this ambiguity risk.

    Regarding your suggestion to base exhaust duct cross flow areas on blowdown time.area, that is what I keep preaching. But as I wrote on the previous page, Wobbly's approach has its reasons too.

    PS: good that you signed your post with your first name; I would not have paid attention to scribblings from an anonymous contributor .

    Quote Originally Posted by katinas View Post
    And two other pic: pressure at partly open EX port and reed petal shape at different rpm. From old book, but interesting theory and experimentation.
    Благодарю вас Katinas

  12. #28122
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    Quote Originally Posted by lodgernz View Post
    Of course you're right.
    Could we postulate that, at peak power RPM, blowdown is complete by first transfer opening? Wouldn't that be the ideal situation for best power?
    In disregard of Ryger phenomena with a single exhaust port and huge rpm, I'd say yes it would.

    Should the volume of the duct be related in some way to the capacity of the cylinder? Would the efficacy of the pipe effects also be a factor, since this must affect the volume of washed-through charge?
    Yes, and yes again.

    If I find a way to extend the duct on my (water-cooled) engine, can I assume I must also find a way to cool it?
    That would be good.

  13. #28123
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    Quote Originally Posted by teriks View Post
    I recon that your setup would be used for "moped" drag racing?
    Anyway, it looks to me that such a wheel would have a rather high moment of inertia. Perhaps you could improve your results using a different wheel setup?

    It may look like they are heavier then a standard wheel but the are actually significantly lighter, and friction is relatively low.
    Having said that, I do not know if it's something I'm going to use. However, I wanted to make sure it was possible if you wanted to.
    I do not know what to do with the engine the trip is the goal.

    Maybe it will be something to go to the store with.
    Attached Thumbnails Attached Thumbnails exhaust 14.pdf  

  14. #28124
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    Frits, I have a question about your FOS pipe, before I knew about this thread someone sent me a link to http://www.underdogsracing.com/fospipe/ I used it to calculate a pipe, but used the 5 stage experimental calculator thinking it would be better. The pipe was almost complete, but got stolen from my place along with a lot of other things. My question was should I make the same pipe again, or should I use the original FOS formula? With the 5 stage calc I came up with this.
    The hp figure is a bit generous I think, it's a Simson S51 motor, with a different sleeve to accomodate a 44.98 mm piston, which is due for rebore now, 6 transfers with okay scavenging now, it was really bad before but I need to work on it a bit more and fix the transfer timing to 130°, either using jbweld or by machining 1 mm from the cylinder base (it's 134° now), running a 28 mm pwk carburetor and a reed valve from minarelli horizontal which I think has insufficient area for the given carburetor, but I'm not really sure how to calculate needed reed petal area. Husaberg had posted it should be 0.8 reed petal area per 1 carburetor area.
    Kind regards from Bulgaria, Jordan.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  15. #28125
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    hello mr vannik is engmod2t compatible with any windows?Thanks

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