Author Topic: Turbo Cooling Down  (Read 5481 times)

Offline Teutonic_Tamer

  • Forum addict
  • *
  • Posts: 4,562
  • GreasedMonkey - HoofHearted - GTI now mod'ed, ASK!
Re: Turbo Cooling Down
« Reply #10 on: 12 March 2009, 15:35 »
Does the same apply to superchargers??

Superchargers are not at all as critical for a number of reasons.  They are NOT driven by effing hot exhaust gasses, but they are driven by a belt or gear from the engine crankshaft.  This means that when the engine is turned off, the SC stops immediately, and can not freewheel like a turbo can.  Finally, SCs tend to run at speeds similar to engine crankshafts (OK, some may be half engine speed, and some may be twice engine speed too - but even at the latter, that will only be upto 12k-15k rpms) - whereas turbos spin at considerably higher speeds.  The turbo on the GTI can spin at 180,000 to 200,000 rpms !!!!  :nerd:
Sean - Independent Automotive Engineering Technician (ret'd)
-----
'06/7 Golf Mk5 GTI 5dr (BWA) DSG, colour coded,

I feel like a homo


Offline pazz

  • Not said much yet
  • **
  • Posts: 98
Re: Turbo Cooling Down
« Reply #11 on: 12 March 2009, 22:59 »
Superchargers spin "at speeds related to that of the crankshaft", they are geared (quite complex) to suit their application eg... flow rate bearing in mind crankshaft speeds etc.

A supercharger generally spins faster than 12k-15k rpm more like up to 50k rpm. But yes you are correct in thinking they dont come anywhere near to that of a turbochargers.

A supercharger doesnt use the same oil as that of the engine so isnt really subjected to the same issues related to "letting it cool down".

Quote
no special shutdown procedure is required with superchargers. Because they are not lubricated by engine oil, they can be shut down normally.
http://auto.howstuffworks.com/supercharger5.htm

But as mentioned before turbochargers obtain their power from exhuast gases flowing through a turbine, which especially after a good thrashing can tend to glow red with heat. When shutting down the engine there will be no passing airflow through the turbine, the blades/spindle/bearing (sleeve or ball) will absorb this heat and hey presto f00ked turbo.

Consider then that a supercharger receives it's energy from the crank via a belt/chain mechanism which doesnt subject the unit to nowhere near as much heat.

But as good engineer's always say, you must consider your application. Fact for fact, superchargers tend to prefer large displacement engine's, mostly due to the reason that the cranks supply ample energy - consider the rolls royce merlin AND where space is paramount (BMW Mini cooper etc). But then thats a debate for another topic.