APR recently released a low cost open intake for the Mk7 GTI. A previous post addressed how this intake flows compared to other intakes that I have flow tested. (Briefly, it performs well when connected to other aftermarket intake parts.)
The APR PEX “open” intake falls into the category of “hot air” intakes as a result of the open design, but is such a characterization as hot air justified?
Prior testing with several open design intakes has shown that the main knock against the open design, ingesting hot air from the engine compartment, can be substantially mitigated by a well designed partition. This test will be to evaluate the air temperature going into the turbocharger when using the APR PEX open intake and compare with a stock airbox, which is a closed design.
The temperature of interest is the air as it exits the intake and prior to entering the turbocharger. Once air enters the turbocharger it is heated significantly, even when out of boost. Measuring air temperature anywhere after the turbocharger makes useful evaluation of the intake affect on pre-turbo air temperature very hard to assess.
An RTD temperature probe is installed in the turbo inlet elbow to record the air temperature as it exits the airbox.
Note: The picture shows the RTD probe installed in a stock GTI turbo inlet elbow, for this test the probe is installed in a “generic” aftermarket turbo inlet elbow.
The GTI will be driven along a route that is regularly used for recording data so the readings from the APR PEX intake can be compared with a closed intake.
The stock GTI airbox will be used for comparison. The GTI airbox is fitted with an aftermarket air filter and the grate in the lower half of the airbox is removed. The duct is opened on the driver’s side and the passenger side rear is blocked where the duct is normally open to the engine compartment. This duct is in place during both test runs, so this configuration applies to both the stock airbox and APR intake.
The conditions and time along the route will be similar, but not exactly the same, between test runs. With the goal of identifying differences that would be large enough to affect overall vehicle performance if there are small differences in the test conditions the Pre-Turbo air temperature should not be significantly effected.
A series of third gear full-throttle pulls will be conducted midway through the drive to record air temperature during a situation that will draw a high volume of intake air. If the partition is not performing well then the air filter will be drawing in a higher fraction of air from the engine compartment with an accompanying rise in the pre-turbo air temperature.
The full-throttle condition is of more interest than partial-throttle since full-throttle is when maximizing engine power output is desirable.
The entire drive using the stock airbox:
The entire drive with the APR PEX intake:
Next shown is the post-pulls, return home, portion of the drive. This phase encounters lower speeds and less intake air demand.
Stock airbox measurements:
APR PEX intake measurements:
The stock airbox turbo inlet air temperature over ambient (delta) varies between 9-10 degrees Fahrenheit (F).
The APR intake delta varies from 14-15 degrees F.
Temperatures recorded during the final pulls with the stock airbox are next:
Pre-turbo inlet air temperature over the ambient air temperature is approximately 7 degF during the full throttle pull.
The APR intake measurements are:
Pre-turbo inlet air temperature over ambient during the pulls is approximately 13 degF.
A cursory look at the turbocharger WGDC shows that there might be a small difference. I estimate possibly around 1%, but this does not account for differences in Outside Air Temperature which were present and would affect Intercooler Efficiency, which in turn affects the work required from the turbocharger.
Pre-turbocharger air temperatures were recorded during full throttle third gear pulls using an APR PEX open intake and a modified stock GTI airbox. The air temperature “delta” over ambient was measured at approximately 7 degF with the stock airbox and 13 degF with the APR PEX open intake.
During the final portion of the test when the GTI was operated in a “normal” manner the stock airbox temperature delta was approximately 9-10 degF and the APR open intake delta was approximately 14-15 degF.
The closed airbox provides cooler air to the turbocharger, but the difference between the stock closed design and APR open design, with an effective enclosure/partition, is not likely to affect vehicle performance to an extent that a driver would notice.
Measurement of turbocharger wastegate duty cycle is inconclusive, supporting the conclusion that differences between the Modified Stock Airbox and APR PEX intake affect on pre-turbo air temperatures are small.