Previously I’ve made posts on the topics of a Bicooler compared with the stock GTI intercooler and also a Bicooler compared with a pair of aftermarket stock location intercoolers.
It’s been two years since I made those posts and since then I have had the chance to use a couple more Bicooler setups. Coming across a discussion of Bicooler versus Stock location prompted me to pull together current data for a selection of intercoolers and compare the cooling performance trends of the two designs.
Four brands from each type of intercooler will be compared.
The bicoolers are all paired with a stock Mk7 GTI intercooler. This isn’t a setup I operate with very often so I have less data for this pairing.
For the stock location aftermarket ICs, I selected four models that would all be mentioned in response to the question “What stock location intercooler should I get?“.
For this comparison, only the Intake Air Temperature (IAT) above the Outside Air Temperature (OAT) will be used. These values are compared at an engine speed of 6,000 RPM while in full boost during a wide-open throttle third-gear pull.
Data is collected using a Mk7 GTI equipped with an IS38+ turbocharger.
Note: Other conditions could result in different outcomes. For instance, an IS20 turbocharger or a hybrid turbocharger would likely have different temperature readings. Also, driving at a drag strip or on a road course would likely produce different results. The operating conditions chosen for gathering data are relevant to my typical use of the vehicle.
Pulls are repeated after a short period during which the vehicle slows and the intercooler has some time to cool. There is no set time for this down period which will introduce undesirable variation to the data.
The chart below shows the data points and average values for the intercoolers being compared:
Shown next is a comparison of the summed IC data by type along with confidence intervals for the values.
A t-Test is used to compare the sample means and evaluate the hypothesis that there is no difference in the group means.
This hypothesis is rejected, the sample difference of the groups, 1.8 degrees Fahrenheit, is large enough to likely not be a random result at a 5% significance level:
As shown above the green arrow, the effect size is relatively small, which means that even though there is a statistically significant difference in the sample means, the test might not have enough power to detect this size difference.
A power analysis confirms that the number of data points (69 and 28) is not adequate for the effect size, with a desired probability of 0.8 for detecting the effect.
The number of data points should be increased to 99 and 41.
Intake air temperature measurements from four bicooler configurations using a stock GTI intercooler were compared with four aftermarket stock location intercoolers.
The average Intake Air Temperature above Ambient at 6,000 RPM during a full-throttle third-gear pull is the value that was compared.
On average the stock location intercooler temperature was 1.8 degrees Fahrenheit less than the bicooler & stock GTI IC configuration.
The difference in the sample means is significant at the 5% level but not enough data was compared to have confidence that a 1.8 degree difference can be detected with 80% confidence.
Whether the estimated difference is accurate or not, in a practical context under the conditions and manner of this test it is unlikely that the difference would make a difference that an operator would notice.