Went out and collected some data the other day. Found some interesting things even though my laptop decided to eat it's hard drive and I lost the logs. Things to note:
- No settings have changed since the last posted logs
- There was a -.3*F calibration difference between the T1 and T2 thermocouples that was accounted for before this post
- Ambient temperature was 61.3*F as recorded by the T1 thermocouple in free air.
- The vehicle was brought to 180*F coolant temperature before recording driving conditions.
The first pull was a peak of 24psi manifold pressure through 2nd and 3rd gear with temperatures of:
T1 (compressor inlet)-
- 76.2* when activated
- 66.2*F minimum
- 80.6*F maximum
- 74.6*F average
T2 (compressor outlet)-
- 159.6*F maximum
- 101.5*F minimum
- 137.0*F average
The next pull was a repeat of the first except coolant temps were 196*F at the start. Temperature data for that pull is:
- 80.1*F when activated
- 91.7*F maximum
- 70.5*F minimum
- 82.2*F average
- 174.0*F maximum
- 88.0*F minimum
- 119.5*F average
I did notice/record after the second pull, before my laptop crapped it's hard drive, that P1(compressor inlet pressure) was reading 10.2psia (-7.1in/hg) and P2(compressor outlet pressure) was reading 41psia (27.3psi) at 6500rpm. I don't want to call those values 100% accurate just yet because I can't back them up with logs, but I thought I would do some calculations anyway for giggles.
Using a formula I found on this site for compressor efficiency
I rearranged it and plugged in my values.
Efficiency = Tin + [Tin x [-1 + (Pout/Pin)0.263
Efficiency = 70.5 + [70.5 x [-1 + (41/10.2)0.263
Efficiency = 70.68%
Pressure Ratio = 4.02
If you look at the compressor map, PR of 4.02 is WAY off of it and a 70% efficiency at that PR would be unbelievable.
( 60.22K )
Number of downloads: 3
I hate to speculate, but let's say the pressure data was in fact accurate. Could that efficiency be possible at that pressure ratio? Did I use the wrong equation, or screw it up somehow? I will definitely be trying to back this up, or prove it wrong as soon as possible.
Trevor, something I thought was interesting was the T2 values after doing a pull while I was checking the meter. They were still very high but steadily creeping down. When I checked the meter the first time T2 was creeping down from 103*F and stopped at 88*F after about 2 minutes. When I checked the second time T2 was at 122.2*F and was creeping down to about 108.8*F before I shut it down after about the same 2 minute period. If I would have let it continue to idle temps probably would have equalized around 88*F like before. I'm guessing the temps remained high after the pulls because of heat soak in the J-pipe.
The reason I mention that is because I remember a thread a while ago where we were talking about what heats up the air from a turbo, either the compression of air, or transfer from exhaust heat. I'm certainly not trying to offend, but if I remember right we were discussing whether or not most of the heating was done through compression of the air charge. If I'm mistaken I apologize, but wanted to explain things just in case.
If you interpret the numbers above you can see that, sure, there is a little bit of heat transfer because after the first pull when I was checking the meter inlet temps were in the 74-76*F range, but the outlet was around 88*F after I allowed it to normalize. A 12-14*F increase in temp just from heat transfer seems reasonable. However, under boost you can see how the temps started to become worlds apart. This is due to the physical compression of air, or "adiabatic heating." This is a really good explanation of that concept: http://www.youtube.com/watch?v=z0x-EyL_lcQ
As inlet pressure drops before the turbo temps also drop because of two factors:
1. adiabatic cooling
2. some cooler fresh air being drawn in from the fender area.
As outlet pressure increases temps increase because of two factors:
1. adiabatic heating
2. heat transfer
After a long pull the manifold and turbine housing become very very hot. Therefore, if heat transfer was the primary cause I would assume outlet temps would remain high after the pull as the manifold and housing remain hot. Since most of the heating is cause by the work of the compressor wheel compressing the air charge the temps drop once the work is done.
Another argument would be that coolant keeps the turbo cooler than the manifold or turbine housing because I kept the car running while checking the meter, and that's why outlet temps came down. That's true, coolant does cool the turbo, and that's a very good thing IMO. However, coolant temps after the runs were in the 200*F range. If heating was primary, outlet temps would have reflected that instead of dropping to a touch higher than inlet temps.
This is why I believe some cooler air would drawn in and that inlet temps didn't just drop because of adiabatic cooling causing minimum inlet temp to drop below the starting temp both times. You can get an idea of air filter placement in the first picture. The second shows the cut out I made to sink the filter slightly down into where trans cooler lives. http://i539.photobucket.com/albums/ff356/pwee1882/28.jpghttp://i539.photobucket.com/albums/ff356/p...2/Rearmount.jpg
Sorry for the GINORMOUS post.