Myth or reality
08-02-2007, 11:40 AM
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Originally Posted by pennetta' post='454495' date='Aug 2 2007, 02:26 PM
Specifically the idling lets oil run over the turbo bearings, which gets heated up by both normal friction and by conductance of heat from the exhaust side of the turbo. Non-synthetic oils would fry at these elevated heat levels, the term is coking, and go into thermal breakdown.
If you drive normally its not needed. If you just beat the piss out of the car and are stopping immediately thereafter (like running the cops and ditching into a garage) then let it idle for a minute or two.
If you drive normally its not needed. If you just beat the piss out of the car and are stopping immediately thereafter (like running the cops and ditching into a garage) then let it idle for a minute or two.
While it is no longer necessary to have a cool down period, it can't hurt.
08-02-2007, 11:52 AM
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Originally Posted by juventus' post='454470' date='Aug 2 2007, 01:41 PM
The second "Myth" my friend told me was that the air conditioner, when on, eats up about 40 horse power units. Is this true?
A typical car at freeway speeds uses about 30hp. In other words, it needs 30hp to overcome drag and drivetrain loss.
If you turn on the AC driving on the freeway, you now need 70hp to maintain speed.
Assume your car gets 30 mpg on the highway. If the 40 hp number was true, if you turn on the AC, your fuel economy would be cut by more than half to 13 mpg.
08-02-2007, 12:54 PM
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One more "sniff test:"
A typical car at freeway speeds uses about 30hp. In other words, it needs 30hp to overcome drag and drivetrain loss.
If you turn on the AC driving on the freeway, you now need 70hp to maintain speed.
Assume your car gets 30 mpg on the highway. If the 40 hp number was true, if you turn on the AC, your fuel economy would be cut by more than half to 13 mpg.
A typical car at freeway speeds uses about 30hp. In other words, it needs 30hp to overcome drag and drivetrain loss.
If you turn on the AC driving on the freeway, you now need 70hp to maintain speed.
Assume your car gets 30 mpg on the highway. If the 40 hp number was true, if you turn on the AC, your fuel economy would be cut by more than half to 13 mpg.
08-02-2007, 01:11 PM
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Originally Posted by iversonm' post='454544' date='Aug 2 2007, 02:52 PM
One more "sniff test:"
A typical car at freeway speeds uses about 30hp. In other words, it needs 30hp to overcome drag and drivetrain loss.
If you turn on the AC driving on the freeway, you now need 70hp to maintain speed.
Assume your car gets 30 mpg on the highway. If the 40 hp number was true, if you turn on the AC, your fuel economy would be cut by more than half to 13 mpg.
A typical car at freeway speeds uses about 30hp. In other words, it needs 30hp to overcome drag and drivetrain loss.
If you turn on the AC driving on the freeway, you now need 70hp to maintain speed.
Assume your car gets 30 mpg on the highway. If the 40 hp number was true, if you turn on the AC, your fuel economy would be cut by more than half to 13 mpg.
08-02-2007, 01:39 PM
#15
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Originally Posted by juventus' post='454446' date='Aug 2 2007, 06:03 PM
I have a friend who owns an Audi RS4 turbo. He told me to let my 535i stand idle for 2 minutes after driving before i switch off the engine. Is this right?
BTW he loved the way the 535i drove. He thought tat it felt like an M3.
BTW he loved the way the 535i drove. He thought tat it felt like an M3.
Yes, most of all if you decide to go for a remap
08-02-2007, 02:33 PM
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Originally Posted by Tangled' post='454572' date='Aug 2 2007, 04:54 PM
The fact that you're talking about horsepower (as opposed to torque) tells me you have no idea what you're talking about. There amount of parasitic drag that come from running the AC should be about the same through the powerband.
Your AC compressor cycles on and off to provide a nearly constant amount of cooling power, regardless of the rpm. Only the duty cycle changes.
Since we are talking about a constant amount of cooling power, power is absolutely the correct unit.
08-02-2007, 03:22 PM
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You can get a 'turbo timer', which is basically a little box (usually really small) that turns the car off automatically after a pre-set time after taking the key out, so you don't have to sit in your car waiting for 2 minutes.
08-02-2007, 03:23 PM
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Originally Posted by iversonm' post='454625' date='Aug 2 2007, 03:33 PM
Based on your statement, cooling power would be is proportional to rpm. If automakers built cars like that, your car would get colder as you increased rpm. You seldom here you SO state, "Downshift, honey. It's hot in here."
Your AC compressor cycles on and off to provide a nearly constant amount of cooling power, regardless of the rpm. Only the duty cycle changes.
Since we are talking about a constant amount of cooling power, power is absolutely the correct unit.
Your AC compressor cycles on and off to provide a nearly constant amount of cooling power, regardless of the rpm. Only the duty cycle changes.
Since we are talking about a constant amount of cooling power, power is absolutely the correct unit.
08-02-2007, 03:42 PM
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Originally Posted by Tangled' post='454654' date='Aug 2 2007, 07:23 PM
Wow, do you know that horsepower is related to engine speed, that it's an abstracted unit of force when it comes to engines?
While they interact with each other, they are quite distinct concepts.
08-02-2007, 03:44 PM
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Originally Posted by The Parrot' post='454454' date='Aug 2 2007, 12:42 PM
in generaly i would always recommend it to any turbo car driver. its more good practise and may keep the turbos better for longer .