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  #21  
Old 04-21-2014, 12:08 PM
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So much misinformation in this thread, but I am still keeping out

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  #22  
Old 04-21-2014, 01:03 PM
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Originally Posted by Skier1 View Post
Well that is your opinion ,Sorry but that is a complete load of piffle , a turbo diesel will s**t over a petrol, you obviously havent driven one. Diesels also have a better retardation due to the higher compresssion ratio. There is no way I would contemplate towing with a petrol unless I was towing a fuel tanker behind me.
Yes, that is my opinion. I have driven many turbo diesels, and a few naturally aspirated diesels. I have had a turbo diesel Passat (red badge, A6 engine) and a diesel LR Discovery. Class 3 driver's license (unlimited GVW on highway, with air brake endorsement, meaning almost exclusively diesel.

I also worked in the diesel engine industry (engineering, sales, service) for 26 years. 15 to 8000 hp.

Diesels inherently have no effective engine retardation other than friction. That is simply because while they have a higher compression ratio, they are not throttled. When the air in the cylinder is compressed, it is then decompressed, for no net work, thus no retardation. If you want to have retardation (which occurs naturally with a throttled gasoline engine) you need to include an exhaust brake of some type, Jake or otherwise. That is why those devices were designed. That device opens an exhaust valve after the compression stroke, releasing the compressed air (and making lots of noise). There are also hydraulic retarders. All designed to overcome the limitation of the diesel engine with respect to lack of engine retardation.

If you want to learn more about diesel engines and their development, and the challenges faces (including lack of engine braking) suggest you read Cruickshank's book on the Cummins engine company and the engineering development of the diesel engine concept over 75 years.

I am glad you like your diesel engine. But please don't spread so much piffle. It makes you look like a w**ker.
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  #23  
Old 04-21-2014, 01:08 PM
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^^^ As much as i agree with you on the retardation,my X5D's engine has more braking effect than any of my other cars,4.6is included.I dont have accelerometer in this car,but it will be interesting to have the decel values measured.
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  #24  
Old 04-21-2014, 01:09 PM
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Originally Posted by beamertruck View Post
Diesel will not always get better mileage, it doesnt do well in stop and go driving. Also you have to look at other factors, diesel is a much thicker fuel and is less refined, which causes it to freeze quicker, but with modern tech thats not as big a deal. One thing is for sure, if you fail to upkeep, use injector cleaner, replace the filter then be ready to replace injectors constantly. The new emission regulations have taken a toll on diesels the DPF restricts the engines ability to breathe and causes many issues if not taken care of and used properlly. If you have not driven or are used to diesel then save yourself the hassle and learn the differences before jumping in, diesel engines are also compression based and require proper warm up and a good quality fuel for proper operation. Diesels are great, they last and are powerful but you better know how to drive it.
Diesels are fine in stop and go driving, they are just better in constant load applications. Best way to achieve that steady load factor with stop and go driving is to use some form of hybrid IMO.

All internal combustion engines are 'compression based', but diesels use compression ignition. Careful on your warm up comments, as you need sufficient preheating to start, but then the engine warm up cycle is just the same as a spark ignition engine. Do not idle it, wait until you have oil pressure and drive as soon as possible, at low to moderate loads. Engine warm up happens faster with some load applied.
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  #25  
Old 04-21-2014, 01:11 PM
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Originally Posted by bawareca View Post
^^^ As much as i agree with you on the retardation,my X5D's engine has more braking effect than any of my other cars,4.6is included.I dont have accelerometer in this car,but it will be interesting to have the decel values measured.
I don't know if BMW has included any sort of throttling mechanism to enable that retardation. Would be interesting. I suspect they wouldn't, since they have gone one step further in the latest models and moved to a freewheeling feature. Now that would blow for towing significant loads.
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  #26  
Old 04-21-2014, 01:24 PM
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Now that was ugly.Diesel is using almost no fuel at idle,so it is very efficient,at long stops and at stop-go traffic.I am fairly agressive driver,but with a good restraint I can do 22-23 Mpg mixed driving in the LA traffic.I dont think that is achievable with any of the gas engines available,or with any low-mid size SUV this side of Honda CRV.
Agree that the diesel cycle is inherently efficient.

You don't have to go to a CRV to compete, though. The best way is to reduce vehicle weight. Our 2007 X3 3.0si (265 hp IIRC) regularly does 32 mpg (imperial)/26 mpg (US) on the highway. It drops closer to 28 mpg (imperial)/24 mpg (US) in mixed driving, and if I did pure city driving I am sure it would drop further. I drive efficiently, but make sure to use a good portion of the 7000 rpm limit regularly.
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  #27  
Old 04-21-2014, 01:25 PM
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Originally Posted by JCL View Post
I don't know if BMW has included any sort of throttling mechanism to enable that retardation. Would be interesting. I suspect they wouldn't, since they have gone one step further in the latest models and moved to a freewheeling feature. Now that would blow for towing significant loads.
My first car was East German "Wartburg"-3 cylinder 2 cycle engine with a freewheeling feature on the transmission,so nothing new under the sun
Actually that car was made after WWII until mid 90s in the ex-BMW factory in Eisenach,so my first car has at least BMW spirit
I have read all the documentation about M57 engine and didnt see anything mentioned for throttling under no-load,but it may be just a side affect of the EGR system function.There is a throttle body in the intake tract.
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  #28  
Old 04-21-2014, 01:26 PM
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Originally Posted by blue dragon View Post
So much misinformation in this thread, but I am still keeping out
Come on, jump in, you know you want to.
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  #29  
Old 04-21-2014, 01:35 PM
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Originally Posted by bawareca View Post
My first car was East German "Wartburg"-3 cylinder 2 cycle engine with a freewheeling feature on the transmission,so nothing new under the sun
Actually that car was made after WWII until mid 90s in the ex-BMW factory in Eisenach,so my first car has at least BMW spirit
I have read all the documentation about M57 engine and didnt see anything mentioned for throttling under no-load,but it may be just a side affect of the EGR system function.There is a throttle body in the intake tract.
I drove an early SAAB 99. They also used a freewheeling feature. Don't know much about the Wartburg, but I did know about DKW 2 stroke models built in the same time frame, and I see that there is some common parentage there as well. Small world.
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  #30  
Old 04-21-2014, 02:59 PM
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Originally Posted by JCL View Post
I drove an early SAAB 99. They also used a freewheeling feature. Don't know much about the Wartburg, but I did know about DKW 2 stroke models built in the same time frame, and I see that there is some common parentage there as well. Small world.
Yes,I think the engine was copy of DKW 3 cylinder,one with the radiator installed behind the engine.
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