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Thread: A work of pure genius! - Brilliant "Revetec" Engine

  1. #241
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    Quote Originally Posted by manolis
    the RoadLoad program is for those who have not your excel nor your background, especially for the youngsters.
    Yeah, it is a pity mine needs Excel. I have been learning VBA to make it a stand alone program.

    Quote Originally Posted by manolis
    Here is a plot for your discussion (I have ‘stolen’ the basic BSFC plot from internet and added the rest).
    Ah, that's what we need. You can see that engine is actually at it's most efficient at medium load at about 2,500rpm. Highway cruising is a medium load for most cars (light load for really powerful cars)

    You can see with the curves that Manolis drew that light loads it would be most efficient at ~1200rpm (downhill cruising).

    But at higher loads like going uphill, it is most efficient operating about 3,500rpm.


    Quote Originally Posted by revetec
    My point is that if you produce better torque in a lower in the rpm range (which will lower the point in RPM when the engine labours) then you can use taller gearing which then saves fuel.
    That isn't right. Can't you see your own car is the perfect example. It's peak torque is 4800rpm yet it is quite efficient operating low in the rev range. Your car has a performance engine, and it doesn't labour at low rpm. If you retuned it with a very mild cam, so you got peak torque at 3,000rpm, do you think it would make your fuel economy any better?

    If an engine has enough power to pull a tall enough gear to allow it to operate at it's most efficient cruising rpm, then it has power to do it. It doesn't matter that it's peak torque is at 1000 or 8000rpm. So long as it has sufficient torque down low to pull the necessary gear ratio to get it to cruise at it's most efficient rpm.

    You should be able to tune your Revetec better (generally tuning and better breathing etc), and get it to run higher in the rev range. This will move your peak torque higher and make a big improvement in horsepower. Doing this shouldn't reduce the torque it's producing low in the rev range much at all (it will reduce it a bit, but not much - not enough to cause you to need to select a lower top gear ratio).
    Last edited by pneumatic; 10-27-2006 at 12:14 AM.

  2. #242
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    You're moving around the point again....I am not talking about peak torque, I'm talking about low down torque.

    Your quote:
    So long as it has sufficient torque down low to pull the necessary gear ratio to get it to cruise at it's most efficient rpm.
    Your quoting what I'm quoting but then you argue the point against it.

    My Caprice has good torque at low RPM and it cruises very nicely at 100kph with the engine doing around 1,300rpm. If a small engine had higher torque down low then instead of being geared to cruise at 100kph doing 2,500rpm, it can be geared taller before it labours, to maybe operate at 2,000rpm. Which saves fuel.
    Do you agree because I'm sure that you get better fuel economy in 5th at 100kph than in 4th, or manufacturers would not bother putting an overdrive gear in the transmission?
    Last edited by revetec; 10-27-2006 at 01:08 AM.

  3. #243
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    Quote Originally Posted by revetec
    Your quoting what I'm quoting but then you argue the point against it.
    No, we just don't quite understand what each other is saying. I like what I said, that's why I wrote it

    If a small engine had higher torque down low then instead of being geared to cruise at 100kph doing 2,500rpm, it can be geared taller before it labours, to maybe operate at 2,000rpm. Which saves fuel.
    So why do some manufacturers put in an overdrive that makes the engine sit on 2,500rpm, and not 2000rpm?

    Part of the answer is that in some cases the car that sits on 2500rpm doesn't have the torque to sit on 2000 in top gear. But a lot of the time you will find they actually do have the power to do that.

    The other part of the answer is the engine might not be at it's most efficient at 2000rpm anyway. Manolis's BSFC diagram shows that.

    So what I am saying is there are no clear rules of thumb.

    Do you agree because I'm sure that you get better fuel economy in 5th at 100kph than in 4th, or manufacturers would not bother putting an overdrive gear in the transmission?
    Yes, but not all overdrives are equal either. Manufacturers set-up the gearing so the engine will run at it's most efficient rpm, and be able to pull the tall gear. What I am saying is this rpm varies, and it is almost always below where the engine makes peak torque anyway.

    You see you want to be able to accelerate past the cruising speed. If you are cruising at peak torque, then your acceleration will get slower and slower the faster you go. Part of this is because the wind resistance gets greater, but another part is that you are running down the torque curve. The combined effect is rapidly slowing acceleration.

    If you cruise below peak torque, then your acceleration may not get slower. The wind resistance will get greater and try to slow your acceleration, but you are running up the torque curve, so you are getting more torque to combat the greater wind resistance. So you may actually end up accelerating faster. And this is what you want. When you go to overtake you at least want the acceleration to stay constant. And it's great if the acceleration gets faster and faster.

    On the other hand if you have an engine that the acceleration gets less and less as you try to overtake, it gets a little worrying. You have to plan the overtakes and drop down gears more often, but even when you drop down gears your running on the down slope of the torque curve again (but an even steeper down slope - as you are higher in the rpm).

    Does that make any sense?



    Ok, the thing you said that started all this is that because the Revetec makes good torque down low, it will be better than an engine that makes it's torque higher in the rev range. This is not correct. This is what I object to. I think I have explained the reason why pretty well, but maybe not
    Last edited by pneumatic; 10-27-2006 at 04:27 AM.

  4. #244
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    Brad,

    take a look at the plot of Brake Specific Fuel Consumption.
    It was posted exactly to expain that the higher gear (and so the lower revs) is not necessarily equivalent to lower consumption.

    Take for instance the case of the brown heavy load curve.
    Suppose you are driving on a long uphill road with constant speed V Km/h.
    So the resistant the engine has to win is constant (let say P1 KW).
    To keep the V speed you can:
    1. Use 1st gear in gearbox and keep the engine revving at 5000 rpm (pressing as necessary the gas pedal). For each hour you consume P1*0.35 Kg of fuel -as the empty red cycle indicates.
    2. Use 2nd gear in gearbox, keep the engine revs (pressing properly the gas pedal) at 3600 rpm. As the resistance to the car motion is the same P1 KW, according the plot your fuel consumption becomes: P1*0.3 Kg / h (the specific consumption at 3600 rpm and 600 units of torque is 300 g/KWh). So you save some 15 to 20% of fuel compared to the case with the 1st gear.
    3. Use 3rd gear in the gearbox, keep the gas pedal completely pressed to keep the engine revving at 2400 rpm. Now you have a consumption of around P1*0.35 Kg/h, which is as much as with 1st gear and 15 to 20% more than with the 2nd gear.
    With 4th and 5th gear the car cannot continue moving with V Km/h and just decelerates.
    So the rule "use the longer gear ratio for economy is not applicable here.

    Taking the case with the medium load (the blue dashed curve) you see the same things, i.e the consumption is
    with 1st gear : P2*0.52 Kg/Kwh
    with 2nd gear : P2*0,33 Kg/Kwh
    with 3rd gear: P2*.275 Kg/Kwh
    with 4th gear: P2*.320 Kg/Kwh
    while 5th gear cannot keep the V speed and the vehicle decelerates.
    As you see the best economy - in this case - is achieved with 3rd gear, neither with 2nd nor with 4th (the "rule" says 4th).

    In the case of the light load (red curve) the 5th is the gives the best economy with P3*0.280 Kg/Kwh or (P3*280 Kg/Kwh)/V if you prefer the consumption in Kg / Km.

    So, according the speed of the vehicle and the resistance of the road, using the BSFC plot of the specific engine you can decide for which gear of gearbox to use.

    With the BSFC plot of a specific engine and given the gearbox ratios, you can decide when to shift gear in gearbox to get the best economy. With the RoadLoad program you can decide when is the best moment to shift gears in order to move as fast as possible.

    It seems reasonable to create BSFC plots for Revetec engines in order to compare immediately their economy to any other engine's economy, without general rules and long lasting discussions.

    Pneumatic,
    I was thinking to transfer the RoadLoad from Q-Basic (originally created) to Visual Basic but I never did. If you want the QBasic code to use it as the base for your V-Basic RoadLoad just say so.

    Thanks
    Manolis Pattakos

  5. #245
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    so... engineering people, is it possible to install this into a Fiat 500? With it's low weight, it should be pretty fast, but you'd have to create custom mounts.
    I'm dropping out to create a company that starts with motorcycles, then cars, and forty years later signs a legendary Brazilian driver who has a public and expensive feud with his French teammate.

  6. #246
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    Quote Originally Posted by manolis
    It seems reasonable to create BSFC plots for Revetec engines in order to compare immediately their economy to any other engine's economy, without general rules and long lasting discussions.
    I agree (and said the same thing pages ago). We can argue theory forever, but what we need is some actual test data on this engine.

    Manolis, thanks for the offer on the Roadload program. Unfortunately I haven't learnt VB (stand alone version), so wouldn't know what to do with the code yet

  7. #247
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    Kingofthering,

    In order to keep the existing mounts of Fiat 500, I erased some zeros from the Sepcific Fuel Consumption Plot.
    As it is now, the BSFC plot seems not far from the BSFC plots of the current 1000 cc auto engine, with the torque in Nt*m.
    A plot like BSFC is the way (i.e. the tool) to think about consumption and then about maximizing economy.
    By the way one more animation regarding PRE was added to the pattakon web site at http://www.pattakon.com/pre/droplet.exe. Comments?

    Thanks
    Manolis Pattakos

  8. #248
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    well... It seems that this engine has been discontinued, the website is gone.
    I'm dropping out to create a company that starts with motorcycles, then cars, and forty years later signs a legendary Brazilian driver who has a public and expensive feud with his French teammate.

  9. #249
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    For your information...Maintaining Constant Speed with a accuracy of +/- 5%



    The graph shows an increase in fuel consumption after peak torque is reached.
    Last edited by revetec; 10-31-2006 at 09:35 PM.

  10. #250
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    We should get Revetec, Pneumatic, and Manolis a hotel room.

  11. #251
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    Ha ha!

  12. #252
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    Quote Originally Posted by revetec
    The graph shows an increase in fuel consumption after peak torque is reached ie. 3rd gear - Approx 60kph@4,300rpm and 4th gear Approx 80kph@4,300rpm and an increase in fuel consumption below 1,400rpm where the flat torque really starts.
    Where did that graph come from? And how did you come up with those gear speed to rpm conversions?

    The graph says it is a 3L V6 Taurus, but not whether it is the Vulcan motor;
    12 valves 3.0L V6 155 h.p @ 4900 rpm, 185 lb.-ft. @ 3900 rpm.
    or the Duratec motor;
    24 valves 3.0L V6 200 h.p @ 5650 rpm, 200 lb.-ft. @ 4400 rpm.

    So whether peak torque is reached or not depends on which motor, but they are pretty similar so that's not much of an issue.

    Now lets say the graph is for the first 4 gears of the 5 speed manual (which wouldn't make any sense, it's probably for the 4-spd auto). But assuming the manual would give the lower gear ratios.

    "3rd gear - Approx 60kph@4,300rpm" is completely wrong. 3rd @ 60kph in a taurus is only ~2,500rpm. Why you chose 60kph I have no idea.

    Similarly "4th gear Approx 80kph@4,300rpm" is wrong. 4th @ 80kph is about 2400rpm.

    But those speeds you picked also don't make sense. The graph shows 4th gets the best economy at 52kph. This would be about 1600rpm. This just proves my point, where peak torque is has nothing to do with at which rpm the engine is most efficient.

    You can clearly see that the most efficient point of 1600rpm is no-where near the peak torque of 3900-4400rpm of the taurus engine.

    That is what I have been saying. An engine needs enough torque to run down low, but having peak torque low isn't a "good" point for a normal car engine, and it doesn't relate to good fuel economy.

    Does this make sense

    Rockefella - I'll spend a night at the Paris Hilton if your paying
    Last edited by pneumatic; 10-30-2006 at 09:49 PM.

  13. #253
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    Brad,

    I see the graph, I cannot see the difference from the Brake Specific Fuel Consumption plot.

    A typical car needs some 18 to 20 PS to move with constant speed of 100 Km/h on a level road. Let say it takes 25 PS for this heavy V-6 3.0 liter car to move with 100 Km/h.
    A 3 lit car engine is reasonable to provide more than 150 to 200 PS, lets say it provides only 150 PS.
    So, at 100 Km/h on level road the car needs less than 1/6 of its maximum power output (i.e. it operates at very light load).
    According the 3rd gear curve of your plot, at 100 Km/h, the engine revs at peak power, so itneeds only 25/150=1/6=17% of its available power and torque at the same revs with wide open throttle.

    BSFC plot says the same: at light load (red dashed line) the best economy is achieved with 5th gear, the 2nd best economy with 4th gear and so on.

    So?

    If the graph of LabMath were made for uphill road, the curves would be a lot different (for instance, and depending on the road slope, at some speed the 3rd or the 2nd gear would provide better economy compared to 4th or 5th gear).


    PS1. Brad. It seems the discussion goes to an end. I do not know who ‘Pneumatic’ is. But what I know, after the long discussion in this thread, is that Revetec needs a Pneumatic.

    PS2. Rockefella:
    If Pnematic can compromise with ATHENS HILTON instead of PARIS, they will have also the chance to drive, feel and test the Pattakon prototype cars to tell people for them. In return, I will pay for the suite(s).

    Thanks
    Manolis Pattakos

  14. #254
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    As regards external dimensions of Junkers-PRE 500cc

    In another discussion I had to show how small the Junkers-PRE engine is. I finally sent this slide.



    Scooters have even more space. The width is less than rear tyre width.

    In case of twin cylinder 1000 cc Junkers-PRE (crankpins at 180 deg) the image is still valid, with the left cylinder ‘hidden’ by the right one.

    Thanks
    Manolis Pattakos

  15. #255
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    The graph came from "The Georgia College of Tech Engineering" Maybe you all should contact the professors there and have a talk with them. It was the 24 valve engine, picked because of its flat torque curve.

    It's fitted with an auto.
    gear ratio 1st gear: 2.77:1
    gear ratio 2nd gear: 1.54:1
    gear ratio 3rd gear: 1.00:1
    gear ratio 4th gear: 0.69:1
    Differential with a gear ratio of 4.266 to 1.

    That was what was in the paper. If you don't agree, take it up with the college professor.
    Last edited by revetec; 10-31-2006 at 08:20 PM.

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