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Turbo Optra - CT12 Dyno Session Video

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Re: Turbo Optra - CT12 Dyno Session Video

Postby PrecisionBoost » Thu Apr 04, 2013 3:11 am

As far as the discussion related to intake manifold pressure vs exhaust manifold pressure I would like to make a few points.

1 )
The measurement technique used in this dyno video is flawed, a boost gauge is not an accurate measurement tool in this circumstance, the correct measurement tool is a water cooled piezo electric element inserted just before the turbine inlet. Manifold pressure has large fluctuations at high frequency, only a piezo electric element fed to a signal analyzer can give repeatable accurate measurements. The "boost gauge" only gives you a very rough indication of back pressure, it is not an accurate measurement, therefore you can not use it to compare pressure ratios of intake/exhaust. The biggest problem is that the boost gauge is connected to the manifold via a compressible gas ( air ) with a non-linear temperature change between the source and the gauge. If your rubber line was replaced with a steel reinforced line filled with a non-compressible fluid that has a small thermal expansion ratio it might be possible to get a reasonable average pressure measurement.

2 )
The measurement of ratio is only accurate under very specific circumstances, ideally in a laboratory environment. Manifold pressure is typically done in small steps while plotting both the compressor and turbine efficency charts.
That is to say they move the engine load/speed in small increments measuring the mass airflow, change in temperature and manifold pressures. They do not ramp the engine quickly, the measurements are done at a steady state where the engine is held at a particular load/speed for several seconds while the computer data logs the information to get an accurate average reading.

In conclusion, I'm not saying that this "boost gauge" measurement is useless, I am only saying that the number shown on the gauge is inaccurate and it is only a relative number. That is to say 20psi on the gauge does not indicate 20psi in the manifold, it's likely not even linear.

Example of what I'm saying:
inlet pressure 6psi - gauge pressure 6psi - actual pressure 8psi -- estimated ratio 1:1 -- actual ratio 1:1.33
inlet pressure 8psi - gauge pressure 7psi - actual pressure 11psi -- estimated ratio 1:0.88 -- actual ratio 1:1.38
inlet pressure 10psi - gauge pressure 8psi - actual pressure 14psi -- estimated ratio 1:0.80 -- actual ratio 1:1.40

Hopefully you get what I'm saying, it is a good tool to compare two turbos such as a T3 "45" and a T3 "60" or perhaps a turbo with different compressor or turbine housings so long as nothing but the turbo changes.

There will be a relative difference, but the difference will not be linear and it will not equal the real ratios.

When it comes to real automotive engineering, they use real time instruments and data logging systems, it's the only way to physically measure with precision and get repeatable results for calculating efficiency.
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Re: Turbo Optra - CT12 Dyno Session Video

Postby Tony the Tiger » Fri Apr 12, 2013 7:59 am

PrecisionBoost wrote:As far as the discussion related to intake manifold pressure vs exhaust manifold pressure I would like to make a few points.

1 )
The measurement technique used in this dyno video is flawed, a boost gauge is not an accurate measurement tool in this circumstance, the correct measurement tool is a water cooled piezo electric element inserted just before the turbine inlet. Manifold pressure has large fluctuations at high frequency, only a piezo electric element fed to a signal analyzer can give repeatable accurate measurements. The "boost gauge" only gives you a very rough indication of back pressure, it is not an accurate measurement, therefore you can not use it to compare pressure ratios of intake/exhaust. The biggest problem is that the boost gauge is connected to the manifold via a compressible gas ( air ) with a non-linear temperature change between the source and the gauge. If your rubber line was replaced with a steel reinforced line filled with a non-compressible fluid that has a small thermal expansion ratio it might be possible to get a reasonable average pressure measurement.

2 )
The measurement of ratio is only accurate under very specific circumstances, ideally in a laboratory environment. Manifold pressure is typically done in small steps while plotting both the compressor and turbine efficency charts.
That is to say they move the engine load/speed in small increments measuring the mass airflow, change in temperature and manifold pressures. They do not ramp the engine quickly, the measurements are done at a steady state where the engine is held at a particular load/speed for several seconds while the computer data logs the information to get an accurate average reading.

In conclusion, I'm not saying that this "boost gauge" measurement is useless, I am only saying that the number shown on the gauge is inaccurate and it is only a relative number. That is to say 20psi on the gauge does not indicate 20psi in the manifold, it's likely not even linear.

Example of what I'm saying:
inlet pressure 6psi - gauge pressure 6psi - actual pressure 8psi -- estimated ratio 1:1 -- actual ratio 1:1.33
inlet pressure 8psi - gauge pressure 7psi - actual pressure 11psi -- estimated ratio 1:0.88 -- actual ratio 1:1.38
inlet pressure 10psi - gauge pressure 8psi - actual pressure 14psi -- estimated ratio 1:0.80 -- actual ratio 1:1.40

Hopefully you get what I'm saying, it is a good tool to compare two turbos such as a T3 "45" and a T3 "60" or perhaps a turbo with different compressor or turbine housings so long as nothing but the turbo changes.

There will be a relative difference, but the difference will not be linear and it will not equal the real ratios.

When it comes to real automotive engineering, they use real time instruments and data logging systems, it's the only way to physically measure with precision and get repeatable results for calculating efficiency.



Precise readings is always good, but I find it rather pointless to elaborate so much into getting "precise" readings on such a varying condition. You're trying to discredit existence's readings yet you don't even know what it takes to achieve a truly useable figure. I had access to such instrument, but there was no method to standardize the conditions to make precise readings useful. With the same engine, same turbo and same power output, I could manipulate exhaust pressure readings to almost double just by running the engine through unrealistic conditions for that certain engine. I can also manipulate this figure via fuel/ignition timing and cam timing changes.

Turbine inlet pressure changes rather easily. Torque falls and pressure falls with it. Late spark timing due to octane limitations increases the pressure big time due to incomplete combustion. We know the engine runs through an RPM band and boost curve, but where do we sample our readings to gauge efficiency then? How long do we "load up the engine" to get the standardized figure to be used for efficiency calculations? 10 seconds? 1 minute? Perhaps for a 1000+ WHP car, which cannot even physically spend more than 30 seconds at full boost and full throttle before it runs out of gear at 200+ mph?

A big power street car (e.g. my Camry) does not even spend more than 30 seconds under full boost before it runs out of gearing. Heat saturation on the manifold, or obtaining a steady state condition is not a priority. Due to the nature of such engine, the engine should never be locked at a certain RPM anyway unless I was trying to use my 900WHP Camry to haul a boat up a mountain.

There is no need to get so over technical on such a loosely obtained figure. Just by choosing a different location to probe the exhaust manifold can throw off pressure readings regardless of how precise your instrument is. A manifold with stamped collector vs a 15-deg merge collector will require a different location. The key is to find a spot that "makes sense" so that it's useful for tuning. This comes from experience only. On a log manifold with centralized runners, I usually take the reading closer to the exhaust valves to check for reversion and adjust cam timing accordingly. With a long runner front facing exhaust manifold on a drag car with open DP, I take the reading deep within the turbine housing where it necks down to half its diameter. The readings are used for plotting turbine efficiency maps which is important for a drag car.
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Re: Turbo Optra - CT12 Dyno Session Video

Postby benzino » Fri Apr 12, 2013 12:42 pm

You're getting your terms mixed up. PrecisionBoost is only talking about accuracy. you're talking about precision...

Accuracy is finding as close to the true value as possible; whereas precision deals with repeatability.
Accuracy would be determined by sensor placement and precision would be determined by standardizing and controlling as many variables as possible...

Ergo, you're both right, you're both equally pretty... and you both get to go to the ball :lol:
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Re: Turbo Optra - CT12 Dyno Session Video

Postby PrecisionBoost » Sat Apr 13, 2013 11:25 pm

Tony, the point I am making ( which you support with your response ) is the measurement is a relative figure as opposed to an accurate physical measurement.

Quite simply if all variables are generally the same ( position, air/fuel ) and you start playing with different turbo configurations ( housings and wheels ) then the measurement technique with the boost gauge would be a great tool to show if the intake/exhaust manifold pressure has increased or decreased with the change in turbo configuration.

This technique is perfect when you are inserting turbos ( such as the CT12B ) which do not have published compressor or turbine maps for mathematical calculation of expected results.

My concern however is with Exist3ence's statement that:

" So now think of the opposite of that - a ratio of less than 1:1. Take for example 1:0.7. I have seen this on very efficient setups - and no it does not mean the car is laggy at all, it will actually be very responsive"

My problem here is that the measurement technique used it is not an accurate physical measurement, that is to say his statement that there are efficient responsive cars running 1:0.7 is purely speculation because the measurement tool is not accurate.

The gauge is a great tool for building systems, it is however a horrible tool for giving a physical measuement as a statement of fact.

You could however say you measured 1:1.05 initially, decreased the turbine housing size and measured an improved 1:0.9 ratio.

That is say you can say you improved the intake/exhaust pressure ratio by roughly 15% but you can not say the real ratio is actually 1:0.9

If you had an accurate measurement tool you might find that the ratio may have been 1:1.9 initially and 1:1.6 afterwards ( which is that same 15% relative change in pressure ratio )


If you want a more accurate reading you need to remove the rubber hose and gauge and replace it with a steel tube ( 8-12" in length ) and use a piezo electric pressure sensor connected to a logging tool.

Garrett ( GSE_Turbo ) uses a piezo exhaust gas pressure sensor from a ford powerstroke diesel ( EBP sensor ) which sounds like a great alternative to the high priced sensors I was talking about.

The indirect piezo sensors ( such as the powerstroke EBP ) are only good to 400 degrees C, which is why there is a need for a long tube to decrease temperature.

The water cooled units I initially mentioned can take 800 degrees C, which allows them to go right into the manifold for direct measurement.


Hopefully this will clear up any confusion, I certainly see value in the relative measurement to say the ratio has gone up or down, but it can not be used to give a physical ratio such as "1:1.2" due to accuracy of the measurement gauge and the setup.
1994 Opel Calibra 4X4 turbo ( C20LET 2.0L 16V Turbo )
2002 Daewoo Lanos
2011 Mitsubishi Lancer Raliart --- SOLD! :)
1989 Passport Optima GSi (Astra MK2 ) --- SOLD! :(
1990 Passport Optima GSi (Astra MK2 ) ---SCRAP! :(
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