Modifying the stock intake is an alternative to purchasing a dedicated aftermarket intake.
On a couple of occasions, I have encountered enthusiasts who have stated that they changed from a modified stock intake to an aftermarket intake when their car was being dyno’d and the aftermarket intakes showed a significant improvement versus their modified stock intake. Unfortunately, they did not have any evidence to support their conclusions.
While I agree that an aftermarket intake possibly can outperform a modified stock GTI intake, I’m skeptical that the difference is enough to qualify as being significant.
Flow bench testing of airflow rates of the stock intake, a modified stock intake, and the Eventuri intake is something I have performed in the past.
I have also logged acceleration times with each of these intakes using my IS38-equipped Mk7 GTI.
What follows are the results that I have recorded.
Modifying the stock intake increases airflow by approximately 14% compared to an unmodified stock GTI intake.
The Eventuri intake increases airflow by approximately 17% compared to the unmodified stock intake.
During a series of third gear full-throttle street pulls the Eventuri-equipped GTI is estimated to be making a peak of approximately 3 whp more on average than the GTI equipped with the modified stock intake:
When accounting for the variance of the multiple (7) Eventuri pulls and multiple (10) stock intake pulls there is no significant difference between the horsepower estimates.
Flow bench measurements and street pull horsepower estimates show small differences between a modified stock GTI intake and an aftermarket intake.
The highest flowing intake that has been tested is within 10 CFM of the Eventuri intake. It is unlikely that an aftermarket intake is going to produce horsepower results significantly greater than the modified stock GTI intake at airflow levels supported by the stock IS20 and IS38 turbochargers.
Note: The highest flowing intakes are open filter designs that will raise the pre-turbocharger air temperature slightly more than the closed Eventruri design. This result will likely offset some of the power improvement these aftermarket intakes should be allowing.