70 mm Throttle Body Test

Background:

After finishing the tune for the Mabotech M520 turbocharger, I decided to see if there would be any benefit from replacing the stock GTI throttle body (TB) with a larger one.

A search on eBay turned up an Audi A5 throttle body for $36 – a low enough cost for an experiment with a low likelihood of providing a benefit.

Audi 70 mm Throttle Body and Hose
Audi 70 mm Throttle Body and Silicone Hose

Installation:

Due to the larger size of the Audi TB I also needed to use a different silicone hose for joining the throttle body to the cold side charge pipe.

Audi 70 mm vs. Stock GTI Throttle Bodies
Audi 70 mm vs. Stock GTI Throttle Bodies

The larger throttle body also required different length bolts for attaching it to the intake manifold.

70 mm Throttle Body Bolt and Stock TB Bolt
70 mm Throttle Body Bolt and Stock TB Bolt

After some work, all of the new pieces were in place.

70 mm Throttle Body Installed
70 mm Throttle Body Installed

Test drive:

I then took the car for a test drive to log the data and compare it with the stock GTI throttle body.

70 mm Throttle Body Test Drive
70 mm Throttle Body Test Drive

The GTI features the Mabotech M520 turbocharger, which enables the engine to produce around 500 whp. Consequently, acceleration is typically done in fourth gear, as there is insufficient traction in third gear.

A single-gear full-throttle pull from around 2,000 RPM to 6,500 RPM is made.

Test Results:

The outside air temperature during collection with the 70 mm throttle body is similar to that of other logs recorded recently, which were made when the outside temperature was 5 degrees Fahrenheit cooler.

70 mm Throttle Body Test - OAT
70 mm Throttle Body Test – OAT

Intake air temperature is also similar to the baseline stock throttle body data.

70 mm Throttle Body Test - IAT
70 mm Throttle Body Test – IAT

Boost pressure is the same as with the GTI throttle body.

70 mm Throttle Body Test - Boost Pressure
70 mm Throttle Body Test – Boost Pressure

The turbocharger wastegate duty cycle (WGDC) is also unchanged with the 70 mm throttle body.

70 mm Throttle Body Test - WGDC
70 mm Throttle Body Test – WGDC

The calculated airflow is unchanged, and the fuel flow is also unchanged.

70 mm Throttle Body Test - Airflow & Fuel Flow
70 mm Throttle Body Test – Airflow & Fuel Flow

Finally, there’s no significant change in estimated peak wheel horsepower.

70 mm Throttle Body Test
70 mm Throttle Body Test

Conclusion:

A 70 mm throttle body was fit to a Mk7 GTI to see if the larger throttle body would provide any performance improvements.

There is no indication that the 70 mm throttle body provides any advantage over the stock GTI throttle body on a car operating with a hybrid turbocharger that holds 34 psi of boost, tapering to 32 psi.