Mk7 GTI Inlet Duct Test

Intake Duct Block Off Plate Test


A while ago I was asked if blocking off the back of the intake duct on the passenger side would change the conditions of the air entering the airbox.

Mk7 GTI Inlet Duct Test
Mk7 GTI Inlet Duct Test

The Test:

Finally I’ve got around to assessing the before and after temperatures going into the airbox with the duct opening to the engine open and covered.

Note: I’ve gone cheap with this test using a 12″ long piece of tape to cover the opening.

For this test I have an air temperature probe installed at the outlet from the stock airbox.

Mk7 GTI Airbox Temperature Probe
Airbox Temperature Probe

The driver side inlet has been opened, this is the area behind the red scoop – in the bottom right corner of the above photo.

The GTI was operated at steady state driving and also for a pair of third gear, high boost, pulls.

The Results:

With the air duct in the stock Mk7 GTI configuration, open to the engine compartment, the air temperature measurement is shown below:

Mk7 GTI Inlet Channel Duct Open
Mk7 GTI Inlet Channel Duct Open

Air temperature exiting the airbox remains no less than 5 to 7 degrees Fahrenheit above the outside air temperature and during the two high boost pulls there is no significant change in the temperature exiting the airbox.

The next chart shows the air temperature at the same location with the duct opening covered.

Mk7 GTI Inlet Channel Duct Covered
Mk7 GTI Inlet Channel Duct Covered

The air temperature exiting the airbox is approximately the same under steady-state operating conditions, approximately 5-6 degrees F above ambient.

A difference is measured during the third gear acceleration under boost with the covered duct arrangement showing a drop in the air temperature to the outside air temperature reading.

Note: During the first data collection the vehicle turned off the road and turned around.  This led to a longer time between acceleration events and also resulted in momentarily higher airbox temperatures due to the low vehicle speed.  In the second data collect the car continued travelling between pulls at a higher rate of speed and the pulls were conducted at a shorter time interval.


During steady state driving having the intake duct covered or open did not produce any difference in temperature at the airbox exit.

Under heavy acceleration the covered duct produced lower temperatures at the airbox exit compared to the open duct.

35 thoughts on “Intake Duct Block Off Plate Test”

  1. But won’t that cause the engine to get less air to cool itself?

    1. I’ve wondered that myself. I have a block-off plate installed. I didn’t “feel” a difference. VW engineers are pretty smart. I imagine they opened that inlet for a reason. I’d love to know that reason. 🙂

    2. I don’t believe it – the engine is primarily cooled through teh radiator in front that gets plenty of airflow. I believe this opening to prevent jam-up when driving in the snow. Interestingly enough, my Atlas has a v. similar air duct configuration BUT has a “flapper” door covering that opening. When driving at slower speeds, it will be closed allowing cooler air in/reducing engine bay air to enter and at highway speeds it will open by way of the higher air flow.

    3. I don’t think that’s a main source of cooling air for the engine. I’ve not tried looking at underhood temps with the opening blocked, but I’ve recorded underhood temps quite a bit and they get warm no matter what I do.

      1. I’ve heard folks say that duct it’s to cool the oil filter…

          1. Interesting! I have noted no discernable change in oil temps since blocking it off.

  2. Chuck Raspa

    Nice work Jeff, I kind of thought you would get those results. I have a question about heat under the hood. When I had my MK6 GTI there was a guy named Modshack, who made intakes for both the MK6 and Audi TT’s. He said that if you remove the rear seal at the back of the engine bay, in front of the cowl, and replace it with edgetrim (something like this it would help with eliminating some of the heat under the hood. I have done this on my MK7, not all the way across, but on both sides, for about 10 inches to the original seal, where the first connector is to hold down the cowl. When he did his GTI he said it really lowered under hood temps with the airflow from the front to exiting in the rear. Let me know your thoughts. Thanks, Chuck

    1. Hi Chuck, I tried that a month or two ago. I removed the rear seal completely for a few drives. I haven’t written up the results yet, I think that means there wasn’t much of a difference, lol. I need to go back through my files and see what the recordings showed.

  3. For this matter, do you think that the turbo blanket is going to lower the temperature under the hood.

    1. I doubt it. I have a turbo blanket that I’ve not installed. Eventually I will get around to seeing what affect it has.

  4. Hi Jeff,
    I’m guessing the front end of the driver side of the duct is also opened? (I’m referring to the part in the first picture, but on the driver’s side)

    1. Also like we discussed before this temperature difference will translate to minimal performance difference? Considering the turbo will heat them up to similar temperature. Is this the correct understanding?

      1. I’m guessing any change would be undetectable by the driver. There might be a very slight improvement in boost onset, but that’s probably it.

  5. Before and after turbo blanket test would be great! Measure intake temp, EGT temp and possibly coolant/oil temps.

    1. I usually have an Accessport recording when I make any hardware changes and all of those are variables that are logged.

  6. I think I read somewhere that someone had a bump in oil temps (+2 degrees) by blocking it off. Did you experience this?

    1. I don’t see how this can accurately measure this wihtout a ton of data.

    2. I wouldn’t notice a 2 degree change in oil temps. I can check the data logs but I doubt they will show anything conclusive.

  7. I had the genuine block off plate on my mk7 R, but it seems to cause some sort of faint ticking noise which is just barely audible from the cabin during light acceleration with the windows up. I initially thought it was from the DI injectors or a solenoid causing the tick, but removing the block off plate seems to stop the noise.

  8. Was this test done with the driver’s side (with the red scoop) remaining open or did you seal that off?

    Background: My stock Mk7 has no opening whatsoever on the driver’s side so all intake air comes from the passenger side and I assume that, with a higher flow intake at slow speeds air will be drawn from both directions. I plan to open up my driver’s side as well (suggestions on how? I was planning to purchase the Mk7.5 grill piece but I like your scoop) but wanted to know the details for this test.

    I guess there are four intake duct configurations to consider: 1) stock, passenger side only, 2) passenger side only with block off plate, 3) and 4) same as (1) and (2) but with driver’s side grill opened up.

    I think this is a very interesting problem with some cool fluid dynamics here. I too would be curious to see the engineers reasoning. As mentioned above, I expect it has to do with snow/rain, but I also think noise might be a large factor in design (often the reason such restrictive intakes are built in the first place so I’m told).


    1. The driver side was unchanged, blocking of the rear duct opening was all that was changed on the intake. I’ve not found the scoop to cause any change to the intake conditions. The plate on the passenger side into the engine compartment helps to keep the air going into the airbox slightly cooler at high airflow rates. It has a negligible affect on airflow quantity. The opening on the driver side helps a little to improve airflow through the duct, I don’t know if opening it affects the air temperature going into the airbox.

  9. Chuck Raspa

    Jeff, I know I asked you the other day about the rear seal taken off. I would tend to think under hood temps may be a little lower than with it on, plus, having the passenger side opened and not flowing to the drivers side. I believe I read that was left open to cool the engine.

    1. I have some results with the seal on and off that I’ve put into a couple of charts, I just haven’t got around to posting them up. It was done with the Eventuri intake so the passenger side is open.

  10. Chuck Raspa

    Thanks, just looking to see if there is a difference of under hood temps with and without the seal.

  11. Clarence Tripp

    The different ambient temperatures might be confusing the steady state results but given that the right side is open so ambient air is entering there as well the fact that under load the air box temp drops to ambient must be a win for using this blocking plate.

    If the right side was closed would there perhaps be an even bigger difference, even for the steady state loads.

    Love your work BTW.

    1. Thanks! If the back was covered and the front right not opened I’d be concerned about reducing some of the airflow potential.

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