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| Skilgreining á afli https://www.bmwkraftur.is/spjall/viewtopic.php?f=7&t=65218 |
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| Author: | Alpina [ Sun 23. Feb 2014 12:45 ] |
| Post subject: | Skilgreining á afli |
Ansi áhugavert verð ég að segja,,,,,,,,,, Hear is what I know about cams and the engine. First, for street drivability BMW engineers did not leave anything on the drawing board!!! Second, HP is not directly measured with a dyno, it is dependent on engine torque and simply calculated, from the torque measured on an engine dyno or delivered through the drive train to the rear wheels. Third, the HP math is a simple calculation: HP = (lb-ft X RPM)/5252. That is why EVERY engines HP = lb-ft torque at 5252 RPMs. So the only way an engine can have more HP than torque is to spin the motor faster than 5252 RPMs. Also, simply moving the torque peek to higher RPMs will make the engine generate more HP at the higher RPMs but it is not without a cost. That is, you can do just about anything you want to an engine and it is almost impossible to significantly increase the maximum torque developed without either increasing the engine size or charging volume efficiency with a 4-valve head or forced induction to increase the charge volume for the engine size!! Engine torque is developed based on an engines ability to utilize the full throttle air/fuel ratio and charge volume in the cylinder. Since the air/fuel ratio is pretty much a known quantity for maximum power and the cylinder charge volume/compression are the limiting factors in reality there are only a few variables for charge volume. Those are, cylinder size to accommodate a greater volume, intake flow and the resonance of the intake flow for cylinder filling over the RPM range. The intake flow resonance is want causes an engine to have a torque peak with less torque on both sides of the peak due to the intake flow inefficiency. So a naturally aspirated engines of a given size can be modified to move the torque peak(intake resonance point) around by changing the intake runner length, port size, cam duration, overlap etc. but in the general sense if an engine of a given size develops more HP it is only because you have modified the engines intake resonance point to move the torque peak to a higher RPM, always at the sacrifice of torque developed at the lower RPMs. The only way to increase torque on both sides of the torque peak without increasing the engine size is forced induction!! Also, simplest way to increase the torque at the rear-wheels is to lower the diff gearing. However if you look at a M5, S38/5-speed/3.91:1 diff the car/engine gearing is at the limits. The M70/S70/6-speed/3.15:1 diff has some room for improvement however if you go too far a super low 1st gear can reduce 1st gear performance and the increase in cruise RPMs will hurt fuel mileage and cause extra engine wear. |
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| Author: | D.Árna [ Sun 23. Feb 2014 12:59 ] |
| Post subject: | Re: Skilgreining á afli |
Skemmtilegt innlegg og mjög áhugaverð lesning! |
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