05-04-2013, 12:02 PM | #45 | |
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Really interesting discussion. Some useful info on engine design:
http://www.epi-eng.com/piston_engine...y_contents.htm Volumetric efficiency: http://www.epi-eng.com/piston_engine...efficiency.htm Quote:
http://www.epi-eng.com/piston_engine...on_engines.htm Torque charts for a few engine designs: |
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05-04-2013, 01:32 PM | #46 | |
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But heres a link to a different forum, if you scroll down the page you`ll find a guy called Mash3 stating the same number for the S54. http://www.m3forum.net/m3forum/showt...=236058&page=3 Not the most credible source maybe, but the best i can give you her and now. |
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05-05-2013, 09:41 AM | #48 |
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A peak VE of 115% for a street car?
I am sorry, but I am not buying it Further, something seems off with the chart. A VE curve should mirror the shape of the torque curve. In this chart, peak VE is achieved around 3500RPM while the S54 has its torque peak around 4900RPM... Last edited by CanAutM3; 05-06-2013 at 05:44 AM.. |
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05-05-2013, 03:53 PM | #49 | |
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The graph for the one cylinder engine reflects well the half revolution (from 360 to 540 degrees) power stroke and then the negative torque required for the compression cycle. There is also a small dip in the torque to push the exhaust gases out and then torque remains slightly negative to suck the charge in. It is also interresting to see that on the 6 cylinder engine, even if the power strokes overlap, it is not sufficient to overcome the torque consumed by the compression strokes (still some negative torque). Only as of the V8 does the instantenuous torque always remain above zero. Last edited by CanAutM3; 05-05-2013 at 04:02 PM.. |
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05-07-2013, 05:43 AM | #50 | |||
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We are deep into all of the complexities that led to me revising my original response. To be more precise at this point would mean applying the math to properly model the system. Il'l have to take a look at the graphs that Boss330 posted to see if they cover what I am saying. |
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05-07-2013, 06:32 AM | #51 | ||
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T = P * A * S/2 * sin Teta T = Torque P = Cylinder pressure A = Piston Area S = Stroke Teta = Crank position angle where TDC=0 Quote:
My understanding of the torque output of an engine is the mean output of all the cylinder pulses for a given RPM, as would be measured on an engine dyno. Peak torque is the highest mean output over the entire rev band. IMO this definition is consistent with manufacturer published data and all published dyno charts. With this definition, cylinder count for given displacement, volumetric efficiency and stroke values should not have an impact (except for friction losses). However, looking at instantaneous torque, I agree, a bigger piston will yield a greater momentary peak torque. As I mentioned previously, I don't think this number properly reflects the capabilities of an engine and it is not a number that is comonly used to descibe an engine characteristics. Looking forward to read your interpretation of Boss330's graphs . Last edited by CanAutM3; 05-07-2013 at 10:46 AM.. |
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05-22-2013, 05:20 AM | #52 |
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How about them using Variable-geometry turbocharger/s its popular in diesels were the technology can cope with the lower exhaust temperatures.
But Porsche said they have solve the problem with the use of VGT on gasoline engines ,the 997 Turbo uses it and i guess the newer 991 Turbo to. http://en.wikipedia.org/wiki/Variabl...y_turbocharger |
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05-22-2013, 07:49 AM | #53 | |
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05-23-2013, 06:11 AM | #54 | |
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I have read here and there that BMW is testing that type of setup and i think that would make sense as you can have a broad powerband. I dont think the VGT turbos used in many diesel cars is that expensive but the ones used in the 997 Turbo may be so as the metal needs to cope with the higher temps. So say that they use one VGT Turbo instead of two or three conventional they maybe able to cut cost and that could be a smart idea as a VGT turbo act as a smaller and bigger turbo in one for a broader powerband without the comlexity of two or three turbos that may be sequential controled. |
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