Duct 9 – Eventuri and Stock Accordion


Previous experiments were performed to collect information about how the intake duct configuration affects the air temperature going into the turbocharger.

At this point, some other factors are being investigated, specifically if the design of the turbo inlet hose can affect the air temperature.

I have occasionally come across claims that a silicone intake hose is beneficial compared to the stock accordion hose by having better insulative properties that help to keep the air temperature going into the turbocharger lower. (See my fact check of the HPS claims.)

Stock Mk7 Accordion Hose
Stock Mk7 Accordion Hose

Although the GTI is equipped with an intercooler, the air temperature entering the turbocharger is important to determining the power required by the compressor to increase the pressure of the air. Warmer air is less dense and this raises the power requirement for compression.

The Duct 8 experiment was conducted using an MST Silicone hose. For this experiment, I am swapping back to the stock accordion hose to see what if any, effect there is on the air temperature going into the turbocharger.

In this post, I discuss using an Eventuri closed intake with a stock GTI accordion hose and recording pre-turbocharger air temperature during full-throttle acceleration to compare with the other tested configurations.

Test Procedure:

The Eventuri intake with stock turbo inlet hose is installed in my GTI. The car is driven for several minutes to bring the engine oil up to normal operating temperature and then a series of third-gear full-throttle pulls are made to record the pre-turbo air temperature at an increased airflow rate.

During this session, a total of four (4) full-throttle pulls in third gear from approximately 2000-6300 RPM are made to support averaging the air temperature data.

Data recorded during the pulls will be evaluated. It is assumed that operating out of boost, whereby the engine is producing low power, is a condition of lesser concern for the effect of the hose on pre-turbo air temperature.

Stock Accordion Test Results:

An overview of the data collection session including the turbocharger inlet air temperature (TIT) is shown below.

D9 Overall View
D9 Overall View

A close-up of the data during the third gear pulls is shown next.

D9 Data Collection Closeup
D9 Data Collection Closeup

Configurations being compared in the remaining charts are:

Duct Configuration LabelDuct Configuration
D1CTS Intake / Stock Air Duct
D2CTS Intake / Stock Duct w/ Open Driver’s Side
D3CTS Intake / Stock Duct w/ Open Drv. Side and Covered Rear Pax Side
D4CTS Intake w/ Foam Around Heat Shield / D3 Configured Air Duct
D5CTS Intake Without Heat Shield / D3 Configured Air Duct
IE V2 (D6)IE v2 Intake / IE v2 Air Duct
APR PEX (D7)APR PEX / D3 Configured Air Duct
EV (MST) (D8)Eventuri Intake / MST Hose
EV (Stk) (D9)Eventuri intake / Stock accordion hose

The first chart shows the Turbo inlet air temperature versus the outside air temperature at the start of the pull.

The gray circles are the individual data points. The square symbol is the mean temperature difference value. All temperature measurements are in degrees Fahrenheit.

D9 Starting over OAT
D9 Starting over OAT

On average, the stock accordion pre-turbo air temperature is lower than with the MST silicone hose.

The next chart shows the pre-turbo air temperature rise, or fall (if below zero), during the pulls:

D9 Temperature Rise or Fall
D9 Temperature Rise or Fall

The stock accordion hose and MST silicone hose produce similar drops in air temperature.

The final chart shows how high the pre-turbo air temperature is above the outside air temperature at the end of the pull.

D9 Final Temperature above Ambient
D9 Final Temperature above Ambient

The stock accordion hose produces a lower temperature difference at the end of the pull compared with the MST silicone hose, or any other configuration tested thus far.

This outcome is logical since the amount of drop was equivalent to that of the MST hose, but the stock accordion showed a lower start temperature.


Pre-turbocharger intake air temperature was measured during full-throttle pulls on a Mk7 GTI equipped with a stock accordion hose.

Air temperature versus the ambient air temperature was compared with results recorded using an MST silicone hose and found to be slightly lower with the stock accordion hose.

This result contradicts claims that a silicone hose provides better insulative properties, thereby producing lower air temperature entering the turbocharger.


Leave a Reply