What levels of "Bar" readings should I be getting?
11-24-2005, 05:23 PM
#16
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Originally Posted by TB993tt
I understand and agree with what you are saying, but where does the temperature and the affect it has on mass fit into it - because the ECU reads mass and not boost it allows the boost to increase when temp is hot and air is less dense and reduce when it is colder and air is denser - that is what I see in practice 
11-24-2005, 05:30 PM
#17
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We realize that Bosch uses a MAF to measure the air mass or air density to get the fueling calculations for our engine. As temperatures lower the air gets more dense, thus more fuel is brought into the system. Air is also more dense at lower elevations. Engine load is basically a function of how much air is entering the engine vs the position of the throttle.
The 996TT might read .7bar on the boost gauge, but different functions of the ECU will vary the boost. It has been reported many times as the air temps are lower that the ECU will allow more boost or basically allow more load in a given set of parameters. Saying that .7bar is what the ECU allow 100% of the time is just not the case in Motronic programming. The boost can be manipulated with an minor adjustment to the wastegates. The "stock" ECU will vary the boost output like with higher than 94 octane fuel.
It is a published fact that if a turbo engine goes over I-70 in the Rocky Mountains the turbocharger shaftspeeds will reach 30-35% higher than at sea-level. The engine doesn't realize the turbo's are spinning faster, with modern ECU's and altitude corrections for fueling, the turbochargers will make the required air until boost parameters are reached in the ECU maps, to open the wastegates. With one exception, while running in a overspeed condition while trying to meet the boost parameter, the compressor wheel begins to lose its efficiency or the ability to generate sustained pressure levels. At this condition, heat is generated, the engine will sense the rise in air temps and will reduce timing and open the wastegates at maybe .6bars thus lowering the turbine shaft speed. Many turbochargers have met there fate, as temps have increase in the compressor housing, coupled with a over-speeding shaft, a compressor wheel will burst.. Typically the wheel will crack right in half.
The short answer is that most of the time .7bars-.8bars is the norm, however if one was to install a accurate boost gauge one will actually see faster higher transient spikes in boost levels settling down to .7-.8 bars..
The 996TT might read .7bar on the boost gauge, but different functions of the ECU will vary the boost. It has been reported many times as the air temps are lower that the ECU will allow more boost or basically allow more load in a given set of parameters. Saying that .7bar is what the ECU allow 100% of the time is just not the case in Motronic programming. The boost can be manipulated with an minor adjustment to the wastegates. The "stock" ECU will vary the boost output like with higher than 94 octane fuel.
It is a published fact that if a turbo engine goes over I-70 in the Rocky Mountains the turbocharger shaftspeeds will reach 30-35% higher than at sea-level. The engine doesn't realize the turbo's are spinning faster, with modern ECU's and altitude corrections for fueling, the turbochargers will make the required air until boost parameters are reached in the ECU maps, to open the wastegates. With one exception, while running in a overspeed condition while trying to meet the boost parameter, the compressor wheel begins to lose its efficiency or the ability to generate sustained pressure levels. At this condition, heat is generated, the engine will sense the rise in air temps and will reduce timing and open the wastegates at maybe .6bars thus lowering the turbine shaft speed. Many turbochargers have met there fate, as temps have increase in the compressor housing, coupled with a over-speeding shaft, a compressor wheel will burst.. Typically the wheel will crack right in half.
The short answer is that most of the time .7bars-.8bars is the norm, however if one was to install a accurate boost gauge one will actually see faster higher transient spikes in boost levels settling down to .7-.8 bars..
11-24-2005, 06:14 PM
#18
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Originally Posted by Dock
I don't think the 996 Turbo will allow the boost to exceed ~0.7 bar regardless of temperature.
Greetings,
--Pierre
11-24-2005, 07:02 PM
#20
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Originally Posted by Kevin
The short answer is that most of the time .7bars-.8bars is the norm, however if one was to install a accurate boost gauge one will actually see faster higher transient spikes in boost levels settling down to .7-.8 bars..
11-24-2005, 07:29 PM
#21
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Originally Posted by Kevin
Pierre, that because you really installed a GT2 engine in your last rebuild 
Seriously, the pic above was taken a few years ago (in 2002, I think). The car probably had like 50-60'000 km at that time, and that speed was sustained, not just a short little peak.
Sorry to slide a little bit off-topic, but I went to Germany 10 days ago to test my new engine (and exhaust) on the Autobahn. Result: 323 km/h indicated and it had a tad of potential left.
Greetings,
--p
11-26-2005, 06:29 PM
#23
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Originally Posted by Woodster
Pierre,
You don't think your stock turbo goes more than 200 mph do you?
You don't think your stock turbo goes more than 200 mph do you?
But anyway, this is the indicated speed. Real speed is a tad lower, so below 200 mph. I'm now on snow-tires, so I'll have to wait a few months for the next top-speed test. 
BTW, beautiful snow here today in Minnesota.
Greetings
--p
Last edited by Pierre; 11-27-2005 at 07:24 PM.
11-26-2005, 11:47 PM
#25
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FWIW
Shortly after taking delivery in Illinois, I took a road trip to Telluride, Co. via Albequerque, NM. In Sante Fe, NM. approximate altitude 5000 ft. I would see .8 bar. I would get .2 -.3 bar just pulling away from a stop light in traffic. As I neared Telluride, approximate altitude 9000 ft. I would see .9 to 1.0 on a stock turbo. I presumed that what the gauge was showing was "gauge" pressure rather than " absolute" pressure. This would explain the higher numerical values.
Cheers,
Shortly after taking delivery in Illinois, I took a road trip to Telluride, Co. via Albequerque, NM. In Sante Fe, NM. approximate altitude 5000 ft. I would see .8 bar. I would get .2 -.3 bar just pulling away from a stop light in traffic. As I neared Telluride, approximate altitude 9000 ft. I would see .9 to 1.0 on a stock turbo. I presumed that what the gauge was showing was "gauge" pressure rather than " absolute" pressure. This would explain the higher numerical values.
Cheers,
