DV vs BOV AFR readings

DV vs BOV Research: No Data Required


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.

Data Analysis:

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.

6 thoughts on “DV vs BOV Research: No Data Required”

  1. I like you do a lot of testing of various things/urban legends w/r to the MK7 and as you say, folks often take what they hear/read is gosphel without critically thinking or evaluating data. I’ve been in back/forths like above with folks that won’t believe the contractictory data even if you show them. Great work. Looking forward to the full study on this and de-bunking the mysteries of the BOV vs. DV argument!

    1. Thanks! There are probably more theories floating around about what differences there are than I’ll have the appetite to tackle. Some of the statements I’ve read are a real stretch. Hopefully the comparison data will help confirm or refute a number of them.

    1. “But bro, if you don’t recir that air the engine won’t know what to do and run rich/lean/blow up.” – MK7 people on the internet

      1. L’ecu détermine la quantité d’air admise en fonction de la température et de la pression. Il n’y a pas de débitmètre donc que tu relâche l’air dans l’atmosphère ou juste avant le turbo ça ne change rien, il n’est pas rentré dans le moteur et la pression dans la tubulure est nul.

        1. Google Translate – “The ECU determines the amount of air admitted based on temperature and pressure. There is no flowmeter so whether you release the air into the atmosphere or just before the turbo doesn’t change anything, it hasn’t entered the engine and the pressure in the manifold is zero.”

          I agree. One thing I’ve observed is that the Re-circulation Valve (DV/BOV) is commanded to close before the Boost pressure drops to zero. Around 0.5 psi is the lowest I’ve seen the reading when the DV/BOV is closed.

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