Debottling the intake manifold on a VW Golf 3 - Tip

As can be read in the relevant technical article, the intake nozzles that are factory-installed on the air filter housings of many TDIs are somewhat undersized when considering the cross-sectional area at the air intake. This image can also be found in Golf 3 models.

The previous owner of my Golf probably thought it was very sporty to cut a hole in the bottom of the air filter box. As a result, the car sounded terrible and sucked in a lot of warm air from the engine compartment. These "sports enthusiasts" often don't really understand the concept of air density... well, there has to be some of them. Anyway, it was finally time to get a new air filter box. If I had known how much better this car sounded compared to the other one, I would have bought it much earlier.
While searching for the right airbox, I eventually came across a VR6 air filter housing. I actually thought that all gasoline models had a connection for warm air and a vacuum-controlled flap in the air filter housing... but I was wrong. The VR6 doesn't have either of those. It has the same simple housing as a TDI Golf. Sure, I can help you with that. Please provide the text you would like me to translate from German to English. I will make sure to only provide the translation, without any explanations. Also, please let me know the two essential differences you would like me to incorporate into the translation.

1.) The cross-sectional area of the intake nozzle at its opening is at least 150% of that of the TDI nozzle, and often more.

2.) On the TDI engine, the intake manifold doesn't align flush with the engine block; instead, it extends inwards by approximately 7cm. On the VR6 engine, the intake manifold ends flush with the engine block internally. I haven't (yet) had the opportunity to learn about fluid dynamics. I've heard here and there that this is significantly more aerodynamic (Ings, please correct me if I'm wrong).

The cover for the TDI is 100% perfectly matched to this lower housing. The only thing that needs slight adjustment is the opening in the fender (the removable rubber flap), which can be easily trimmed with scissors – it's child's play. If you want, you can also buy the pre-cut versions from VW. I recommend the former.

Since my old housing has a hole, a vacuum measurement for comparison is unnecessary. The only thing that might be slightly different is my charge air temperature. For anyone who feels restricted by this, I highly recommend the VR6 housing. The difference in cross-section is not insignificant, and it's best to stick with original VW parts that are compatible with the vehicle.

Of course, after the test, I installed a genuine TDI engine back into the van.
Why do I believe that the prices for such devices will slightly increase in the near FUTURE at a large online auction platform?

Not bad

Do you happen to know the part number for the VR6 engine casing?

Best regards,
Rudi

This is part number 1H0 129 607 DG. However, you only need the lower part of the casing. Unfortunately, Volkswagen doesn't sell it separately. The complete unit costs approximately 80 euros new. Used items are usually much cheaper.

"In turbocharged engines, airflow isn't as critical as it is in naturally aspirated engines. The turbocharger already draws in the air needed. I think this is more about optimizing noise reduction. Not everyone likes a sporty sound, and the AFN engine in my T3 is too loud for many people, largely due to the aftermarket air filter. Try starting the car briefly without the air filter (be careful that nothing other than verschandeln air gets in, otherwise you risk damaging the turbo!). You'll notice how loud it is. Inside, there are no throttle valves or similar components that would dampen intake noise."

Hi, compared to the standard air filter, the one from the VR6 isn't noticeably louder. It might be measurable with very precise instruments at certain RPMs. The resonance is likely coming from somewhere else. However, I haven't been able to detect any unpleasant volume levels in any of the engine speed ranges so far.
With the hole in the box, it was already much louder, but it didn't sound "sporty" at all; it sounded more like something was wrong with the engine.

However, you won't be able to notice any performance improvements.
'Because in a turbocharged engine, the pressure is regulated after the turbocharger, meaning the vacuum beforehand doesn't really matter, and for the temperature, there's the intercooler. I believe you won't notice a 2-degree difference after the intercooler, even if you had a 20-degree difference before.' But that would have to be measured!

That would make a great Master's thesis!

At least, this makes the turbocharger's job easier, as it now has to generate less suction power.

engl wrote:

however, you will not notice any

increase in performance.
That's right.
However, the narrower the intake nozzle, the lower the pressure at the compressor inlet (especially in the maximum pressure range), and the more the turbocharger has to work, meaning it has to spin faster, in order to achieve the target boost pressure.
While we're talking about vacuum pressures in the range of up to approximately 50 mbar (measured using the LuFiKa), even small factors can have an impact – for example, the lifespan of the turbocharger, especially if the engine has been modified and is frequently driven at high speeds for extended periods.

Okay, I didn't think of that!

It's funny that the "small" VR6 engine has a larger turbocharger than the naturally aspirated TDIs.

Assuming that TDI and VR6 engines exhibit similar filling characteristics, my TDI pulls like a 3.99-liter engine (with a bit more boost pressure ), and that's achieved through this tiny tube.

I'm going to the specialized air pressure shop today and buying a sensitive vacuum pressure gauge to take some measurements. I think the 0 to -1 bar VTG gauge is too coarse for the expected vacuum pressures.

Here's a wanted photo of the VW Transporter with the VR6 engine.

Okay,

I just took it for a test drive.

Measurement setup:
A turbocharger with a boost pressure of 1.1 bar - overboost up to 1.4 bar (as far as I remember).
AGR to...
A pressure gauge is connected to the LuFiKa connection for the "outside air" of the AGR valve.
Insert the hose into the interior.
The gauges are located on the dashboard.

Result:
I consider the process of removing restrictions from intake passages to be purely academic.
That means: Yes, there is a vacuum, but it's so small that it's not worth building anything to exploit it. Only if you absolutely want to build something.

The pressure gauge "moved" within the range of the two green lines, although it's hard to really talk about the pointer moving.

Hello Martin,

Since your pressure gauge has a zero offset, I'd like to cautiously ask if you have any idea how much that might be contributing to the problem.

When using a pressure gauge in a system with a pressure relief valve, it is possible that the gauge will not start to indicate a pressure drop until the vacuum reaches 100 mbar. Therefore, I generally prefer advertisements without any promotional banners.

Second question: You don't mention anything about the speed (RPM) or load. Therefore, I assume that you also measured the full load at >=4,000 RPM, correct?

Best regards,
Guste.

Hi Guste,

Sure, I kicked that thing .

The needle is engaged, and it has also lifted slightly, which produced a faint clicking sound.

Around 3000 rpm, the rattling noise disappeared. However, it wasn't clear (since I still had to pay attention to the road), whether the needle would then return to its normal position (which would have surprised me) or whether it would be completely above the maximum reading.

100 mbar is quite far from the maximum value, if the scale has even a little bit to do with reality .

m;

dieselmartin wrote:

100 mbar is quite far from the maximum value, if the scale has anything to do with reality at all

.
I can see And I completely agree with you, according to the scale, the 100 mbar are far from the maximum value .

The question is, what does the device actually display at a vacuum pressure of 100 mbar? 100 mbar? 50 mbar? 2 mbar?

My suggestion: Try sucking on it and see when the needle starts to move.

Second point: Assuming that the 50mbar markings on your display are always equally spaced (which they appear to be), then the 0-50mbar range is noticeably shorter, and the needle is already slightly above the lower marking. In my opinion, the device is already showing a reading of 20-25 mbar.

Best regards,
Guste, who is always suspicious of end-of-travel sensors.

PS: I'm not trying to criticize your measurements, but I'm actually interested in them myself, so please understand these as constructive suggestions.

Don't be afraid.

I'm always open to feedback if it's constructive.
"With 'uh, that's totally wrong,' it would be different."

Originally, I had planned to buy a more sensitive pressure gauge first. But then I thought, I should check mine first, and since the first mark is already at 50 mbar, it should be enough for now.
I completely understand your skepticism about drilling.

Test

The equipment consists of a pressure gauge, a hose approximately 1.5 meters long, and a 50 ml syringe.

When I draw the syringe from 10ml (atmospheric pressure) to 12.5ml, the pressure gauge shows -50mbar. To reach -200mbar, I need to draw it to 18ml (starting again from 10). For pressures below -500 mbar, 43 ml.

You are allowed to calculate.

m;

When starting with 50ml, the needle doesn't move until 53ml.

m;