While doing some research on possible performance differences between Diverter Valves (DV) and Blow Off Valves (BOV) I had an exchange that highlights a problem caused by lack of data when trying to get questions answered.
A statement was made about one performance difference between a DV and BOV possibly being due to the BOV venting the charge air to the atmosphere. The theory goes that when air is dumped into the atmosphere that the engine will run rich momentarily because less air is being supplied to the engine and the ECU cannot adjust fast enough to the reduced airflow.
The exchange below is not uncommon, where a reasonable theory has no data to support it.
Because I am in the process of evaluating data that I have logged on my GTI with a stock DV and a Forge BOV making a comparison to evaluate the validity of the claim that the AFR becomes rich with the BOV is easy to make.
The chart below shows data logged with the stock DV in the lightly shaded colors, and the Forge BOV with the darker colors.
The accelerator pedal is released going to 0%, momentarily thereafter the throttle plate begins to close, and in both cases the AFR does NOT move to a RICH reading.
Lacking any data to compare with these results there is no basis for believing the claim that the BOV causes the engine to run in a rich condition following the charge air being bypassed to the atmosphere.