Turbo spin down time Observation..
06-03-2001, 04:08 PM
#1
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Turbo spin down time Observation..
I ended up ripping out the stock airbox finnally and installed a Cone Filter till i get a New Aluminium one.
With The GT25 you can still hear the turbo spinning after the engine is shut off.
Even letting it idle for 2-3 minutes before engine off, It still spun for about 45 seconds...
Hmm very low friction...
Not to forget no oil circulation at that stage either...
Just observation..
With The GT25 you can still hear the turbo spinning after the engine is shut off.
Even letting it idle for 2-3 minutes before engine off, It still spun for about 45 seconds...
Hmm very low friction...
Not to forget no oil circulation at that stage either...
Just observation..
fun fun fun
06-03-2001, 08:46 PM
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low friction? low efficiency (at those RPMs)
The engine provide a huge restriction to airflow when it stops. The turbo should stop spinning due to the backpressure.
If the GT25 keeps spinning that long past shutdown it's because it doesn't produce any boost at those low rpms. If it did, it would use up its energy earlier. Instead, it ceases to be an impeller and just spins.
This is not necessarily a bad thing, as Corky points out, an engine that produces a lot of boost up top won't work down low.
If the GT25 keeps spinning that long past shutdown it's because it doesn't produce any boost at those low rpms. If it did, it would use up its energy earlier. Instead, it ceases to be an impeller and just spins.
This is not necessarily a bad thing, as Corky points out, an engine that produces a lot of boost up top won't work down low.
06-03-2001, 10:11 PM
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So my engine won't work in the low rpm???
According to the dyno, there is not much different in my A4 vs a stock one..
hmm strange...
Back pressure from what?? Engine is stopped..
probably one of the cylinders has both exhaust and intake valves open, ie:Overlap cycle...
hmm strange...
Back pressure from what?? Engine is stopped..
probably one of the cylinders has both exhaust and intake valves open, ie:Overlap cycle...
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06-04-2001, 08:20 AM
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yeah, that's what it sounds like
At really low turbo RPMs, that is. I wouldn't worry, the low efficiency area is probably at very low turbo RPMs, ones which may not even come into play during operation.
It is possible tha tthe engine stops with one cylinder in the overlap position. It is probably unlikely though, since turbo engines don't have much overlap because it allows boost to be lost.
It is possible tha tthe engine stops with one cylinder in the overlap position. It is probably unlikely though, since turbo engines don't have much overlap because it allows boost to be lost.
06-04-2001, 11:39 AM
#10
Neat. With or without overlap, since turbos are not positive displacement pumps, it does sound
like the momentum and less friction via the ball bearings kept it spinning for sometime. I never seen that happen with a solid bearing turbo - which sometimes I have observed to be stopped when engine is idling. Or it is perhaps that your turbine wheel is too heavy. That'll be bad ;P
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