Intake Air Study

Summer is finally here together and higher temperatures. This also creates a problem with intake air temperatures. What comes to power output, high temperature is not good. If you want to save fuel, high intake air temperatures are not that bad. Since I’m interested to get most for my money, I want to get most out from the fuel I burn in my engine as well, so in my case low intake temperatures are good. This produces the most amount of power as well. Motivation to this test came from this picture:

So, after 70C intake air temps engine is starting to loose power.

From the factory, S14 is fitted with massive aluminium airbox. Reason for this is most likely the price, it is easy to manufacture and it provides a good method to reduce the intake noise.  Aluminium box is also very good in collecting the heat and preserving it. Preserving the heat is a good thing to have in cold climates and also saves some fuel since engine heats up faster.
See attached picture how plenum preserves the heat. Temps are measured immediately after shutting of the car. Sensor is located in the plenum.

Typically ECU’s retard the ignition and reduce the amount of fuel when intake air is hot. This is because hot air has less air molecules and less fuel is needed. Typical formula is that every 25 degrees, fuel is reduced by 8%.
Also, ignition is retarded in order to reduce knocking. In my setup Autronic, I have set it so that ignition is retarded 1 degree after intake air is above 50C, 2 degrees after 75C when load is above 20%.  Following graph shows the intake temps in the morning and in the afternoon. This shows that my ignition is retarded most of the time in the afternoon.

So, this is the story with stock intake. I’m in process of purchasing a Carbon Fiber intake and it is interesting to see the difference between the stock one and the carbon fiber one.  In theory it should be able to keep the air cooler.

Carbon fiber intake arrived and is installed. Results are here: Normal.dotm 0 0 1 58 336 Nokia 2 1 412 12.0 0 false 18 pt 18 pt 0 0 false false false /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin-top:0in; mso-para-margin-right:0in; mso-para-margin-bottom:10.0pt; mso-para-margin-left:0in; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman"; mso-ascii-font-family:Cambria; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Cambria; mso-hansi-theme-font:minor-latin;}

 

 

1. Intake air temperature is significantly lower. This was the main reason why I purchased the unit.

See the next picture, while driving

2. Heatsoak is reduced a lot since the old, massive piece of aluminium is missing. Temperature rises similarly, but cools immediatelly after start

See the picture, stationary part

 

See also  Carbon fiber intake installation notes 

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