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X5 E70 (2007 - 2013)
E70 BMW X5 produced between 2007 and 2013. Discuss the E70 X5 with other BMW owners here.

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  #26  
Old 02-24-2008, 07:42 PM
oilbelcher oilbelcher is offline
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Quote:
Originally Posted by jcl10 View Post
There are a few different concepts being muddied here, IMO.

I agree with you that we 'feel' torque. However, you cannot dismiss hp. We feel torque because it produces a change, ie acceleration, and we can sense changes better than we can sense absolutes. However, torque at low rpm is not as valuable or the same as torque at high rpm (although it is convenient). In very simple terms, you will feel the acceleration, but still take longer to get to your destination, since you are going slower. That is because when you make the same torque at higher rpm, you can take advantage of gearing. Consider two engines, one diesel and one gasoline, making the same torque but at different rpms. Each driver floors it. They both accelerate relative to their torque curves. However, the gasoline car is out in front and gets there sooner, due to gearing.

You are instead considering two engines at the same (low) rpm, with the diesel engine making more torque. Yes, it will accelerate quicker at those low rpms. If you don't like shifting, it can be very handy. But unless it produces the same hp as the gasoline engine, it will be slower, since you will accelerate to something like half the rpm limit of the gas engine, and then you're done.

If we really wanted to get into this we should discuss torque rise, which is the number that causes you not to have to downshift as you slow down, pulling up a hill. It is increase in torque as the rpms drop, essentially.
all very good points; I was trying to summarize a lot in very short amount of text. I am only saying why most people quickly and wrongly dismiss a diesel engine to relatively low HP, and don't understand anything about torque. It took me a while to grasp the concept between HP/Trq. It is only certain conditions that you can let a diesel trump a gas engine, as far as performance. But both are different animals, and have their different applications. This does start to change though as you turbo charge a gas engine. When you look only at performacne (ignore efficiency), a good turbo gas engine gives you the best of both performance worlds.

I also learned why HP drops so fast in a diesel after roughly 5000 RPMs: the piston starts to travel faster than diesel fuel can burn/explode in the cylinder, so engine "runs out of breath". Diesel fuel burns slower than gas. I thought it had more to do with the fact that diesel engines run at much higher compression ratios, and the way they are constructed.

BMW is saying you can get most of that performance, and a good deal of effiency gains. But both performance and effieincy is very open to interpretation, and even each person will have a different perceptions as variables change... so this then makes the price/value equation quite difficult to measure. I want to see diesel take hold in the US, but don't want to pay through the nose just to get it.

It is just unfortunate that the car makers who specalize in diesel are based in Europe with mostly European cost structure in Euros (at least for engines of the German cars), so the weak dollar is causing havoc on their business cases and projects margins with this new product intro. I just can't wait until the US manufacturers are forced to join the diesel party. If anything, MB/BMW/VW/Audi will eventually help with this.
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  #27  
Old 02-25-2008, 09:16 PM
newbie2bmw newbie2bmw is offline
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It is my first visit to this forum and I have already learnt a lot in one day. Thank you for explaining the concepts in layman terms. Thanks to Olibelcher and Jcl10.
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