Intake Temperatures
Admittedly, this information is here mostly to help myself attain my 200hp goal in my 1.8L Impreza. It's always said that cold air explodes better and thus making more power. There's also a point where air gets so hot that hp can actually be docked. This would be caused by exceeding the maximum efficiency of a turbo compressor map. This is where I'll try to document some steps I take to get the intake temperatures down to a near ambient level.
| Where the Probe is | Low Temp in Celsius | High Temp in Celsius | Ambient Air Temp |
| On the air filter, right behind the passenger headlight | 30.7 | 56.7 | 30 |
| On the air filter, right behind the passenger headlight | 25 | 53 | 25 |
| Throttle body, inside the intake tract with 5psi and no intercooler | 25 | 63.7 | 25 |
| Passenger fender, (same place as a ganzflow or where the stock air box gets its air. | 23.6 | 44.9 | 25 |
Results: Well, I'm not quite sure what to think about this. Obviously, according to the temperature readings, the fender is the best place to pull in the air. With the same ambient air temperature the fender managed to stay 8 degrees C cooler than where the filter currently sits behind the light, that's about 20 degrees F. More tests will have to be done to see how much of a difference can be made at the throttle body to see if it's worth reworking the intake.
After installing the intercooler.
| Where the Probe Is | Low Temp in Celsius | High Temp in Celsius | Ambient Air Temp |
| Intake temp with probe in the Intercooler. | 49 | 69.9 | 30 |
Now that I've installed an intercooler, I wonder what the maximum temperature is that I can have and still increase power. Here's a little write up by "Dabbler" from the I-Club.
<< "Assume
that 5psi is gaining you +34% more power, just by virtue of the fact you're
breathing 34% more air molecules:
14.7 + 5 = 19.7
19.7 / 14.7 = 1.34
1.34 - 1 = 34%
But the incoming air is now less dense, since you're heating it up with your
turbocharger. Assume change in density is:
(Original Absolute Temp / Final Absolute Temp) - 1
Temp has to be in Kelvin or Rankin.
So, assuming 25C ambient (298K), and using your measured 65C intake temp (338K),
we get:
298/338 - 1 = -12%
Assume the overall power gain is:
(pressure change) x (density change) - 1
1.34 x 0.88 - 1 = +18%
So this setup should produce (approximately, of course), 18% more power. This is
probably a bit low, because the original (i.e., normally-aspirated) intake temp
was most likely above ambient to begin with.
Working the equations back toward the intake temp that would result in 0% gain,
we get:
126.3C
Beyond this intake temp, the engine would be making less power, even though it's
under boost.
I'm sure there are a number of variables in there not taken into account, but
like I said, first order approximation, right? >>
Not a bad write up, makes sense too. So all that said, the intercooler is "OK" at almost 70 degrees, but the power increase is not really there. If I can get it down closer to ambient temperature, then the power increase will be more dramatic.
In more simple terms, for every 4 degrees C that the temp is dropped, you can expect about a 1% increase in power.
Next on the list of lower intake temperatures is to install my hood scoop.