Technical Understanding: Intakes: Stock vs. Drop In vs. Aftermarket

Its been quite a while since I’ve posted a Technical Understanding thread with some hard data and calculations to further feed our minds. Since most of the conceptual basis of the earlier threads were…..for the least bit…..theorhetical and quite possibly boring, I decided to do a little experimenting (with help from NS01GTI) to collaborate data to compare stock intake with drop ins and aftermarket intakes.

Test Requirements
– APR K04 93OCT Runs (~366hp ~380tq)
– APR IC (will affect IATs but will remain consistent)
– 3rd and 4th Gear Runs (Data was collaborated in 4th gear due to sample size and output.)
– Consistent Ambient Runs (Or at least within a +/- 5*F Tolerance from our Nominal)
– Stock Intake is a CBFA Intake with no modifications
– VWR Drop in incorporated the deletion of the baffle at the bottom of the air box
– Carbonio was done in two stages: Stage 1 only and Stage 1+2 (PENDING DATA COLLECTION)
– Same stretch of roadway was used
– Variation in Starting RPM Ranged from 200-300RPM in 4th (~2200) and 200RPM in 3rd (2700).
– Redline will be assumed as the normal redline but some logs will be shown past 6600RPM due to the DSG Stage 2 flash (7100RPM Redline) that was added mid testing (DSG Tuning added Post VWR Drop in, Pre Carbonio Stage 1)

Stock Intake

(C) Grambles423

3rd Gear Run:

(c) Grambles423

4th Gear Run:

(c) Grambles423


Immediately you can see that the stock box will not hold boost properly throughout the entire rev band. Sort of a “dying effect” much like the stock turbo sees.

Boost control is smooth in the midrange which correlates with the peak condition you see intially. Still, the “butt dyno” registers a loss in the system and takes away a lot of the “raw” manly feeling of the K04. You can see the discrepancy from requested and actual better in the 3rd gear log.

Some thoughts in my build thread about the construction of the stock box:

The filter is not the problem. Its a huge geometrical cluster f$%* from RAM Air vent to the MAF:

– Lets start with the ridiculous tubing that leads from the RAM air all the down, with gravity, into the bottom portion of the air box. We’re already talking about almost 6″ worth of frictional and flow loss.

– Then the air comes at an angle into the box that allows it to sort of bounce around inside without a clear direct path for it, causing turbulent flow into the filter and even more loss at higher RPMS.

– Then the air is pulled, against gravity, into a very restrictive particulate filter then is brick walled by the top of the intake box.

– From here the air has suffered enough, but keeps getting directed into the horizontal port where IMMEDIATELY is greeted by another wall to direct the flow a full 90* into the straight MAF portion. From there….its smooth sailing.

The point of most intakes is to eliminate almost 5-6 different directional changes in the system, where at each point, will create more and more loss as more flow is entering. An aftermarket setup will direction flow into one direction….directly into the MAF.

I stood there looking at this monstrosity as I was installing it and couldnt help but wonder WTF those engineers were thinking in terms of performance. I have a huge appreciation for other designs, but I cant help but wonder that there was an easier way of doing it. Sure, most of it is baffling to minimize sound, but you eliminate cooling factors and flow characteristics.

Takeaway: Stock box is not efficient enough to hold and maintain boost through the rev band an on into the upper RPMS. Also, stock box shows higher IATs up the RPM band even with the APR IC.

VWR Drop In Filter

(c) APR, LLC

4th Gear Run:

(c) Grambles423


(c) Grambles423

So what does this mean? It seems that the drop ins will actually help alleviate some of the down low restriction and allow the turbo to spool quicker, but will not give any added flow up top. Since in fact that two MAF rates look IDENTICAL at redline, I would be safe to say that its simply not worth it. The boost still dies sharply after the “point” has been reached where the flow just cannot keep up with the requested pressure.

Dont mind the lower value for the Drop in filter for boost at the final point. This could be % error in between measurements on different days. The point to take away is that it did not ADD any “breathing” at higher RPM. Ipso Facto……the stock intake box is just too damn restrictive for the boost to keep matching requested values at the last 1/3 of the rev band.

Takeaway: While a drop in allows for some down low flow to spool slightly quicker, up top the car still cannot meet its requested boost. You’re still choking the car at upper RPMs

Carbonio Stage 1

(c) Grambles423

4th Gear Pull

(c) Grambles423

Looking over the logs, the carbonio decreases lag and onset WAY faster than the VWR drop in and Stock filter and flows more in the higher RPMs, thus allowing to hold boost easier (0.29psi discrepancy between Specified and Actual)

More analysis:
Max Variation Between Spec and Actual After Peak (Negative Denotes Higher Actual Reading than SPEC)
Stock Filter: 2.465
VWR Drop In: 2.32
Stage 1 Carbonio: 0.45

From here, we can see that the maximum variation between specified and boost are much much higher in the stock intake compared to the Carbonio. This easily can prove our theory that WITH an aftermarket intake, you can meet and hold requested boost much easier due to the optimum control strategies by the N75 valve and ECU

Variation Between Spec and Actual At Peak (Negative Denotes Higher Actual Reading than SPEC)
Stock Filter: -1.305
VWR Drop In: -1.16
Stage 1 Carbonio: -1.07

This measurement denotes the difference between Actual and Spec at the peak boost moment. Some discrepancies can be chalked up due to the date of runs and ambient temperatures etc. etc., but you can see that each can peak about the same over the specified value.

This proves you cannot boost higher with either intake. No difference in peak readings.

Average Variation Between Spec and Actual After Peak (Negative Denotes Higher Actual Reading than SPEC)
Stock Filter: 0.68
VWR Drop In: 0.38
Stage 1 Carbonio: -0.15

This measurement denotes the average variation between spec and actual across the RPM band after the peak. you can see that you’re actually making a little more boost OVER the requested value with an aftermarket intake.

This proves the point of the “dying” effect in the RPM band of the stock intake.

Range of Variation Between Spec and Actual After Peak (Negative Denotes Higher Actual Reading than SPEC)
Stock Filter: 3.77
VWR Drop In: 3.48
Stage 1 Carbonio: 1.3

The measurement shows the range of variation across the rev band. The higher the rev band the harder the engine/turbo is working to meet/hold the requested boost.

The proves to yield more power across the rev band with an aftermarket intake. You’re not really benefitting yourself by running the stock intake on a K04.

Peak MAF Readings
Stock Intake: 236.4
VWR Drop In: 235.8 *******Difference can be error between measurements
Carbonio Full: 258.8

Difference in Peak and Redline Hold
Stock Intake: 5.51psi
VWR Drop In: 5.61psi
Carbonio Full: 3.9psi

Difference in Requested and Actual at Redline
Stock Intake: 2.2psi
VWR Drop In: 2.03psi
Carbonio Full: 0.29psi

Takeaway: Data speaks for itself. An aftermarket intake is definitely worth while. Especially one that is sealed off from the engine bay and only pulls cold air from outside the vehicle.

Carbonio Stage 1 and 2 (***COMING SOON)

(c) Grambles423

Additional Intake Comparison Data (Carbonio vs. Modshack)

Rights Unknown

Thanks to the help of NS01GTI, we were able to get an accurate depiction of the clear differances between the two common intakes seen on this forum. One for Noise control, the other for high performance. Its ultimately the end user’s decision to make a choice and what they would like, but for some fun, we decided to take the same data that we did in the previous setup:

4th Gear Run Carbonio:

(c) Grambles423

4th Gear Run Modshack:

(c) Grambles423

Comparison Graphs:

(c) Grambles423

What I immediately saw was the discrepancy in reuqested boost values and actual values again. It seems that the Modshack, while not having the restriction like the stock box, still shows upper RPM boost loss from requested. MAF vales were also very considerably different in the midrange that we couldnt just say there was “variation in the runs” Almost 50-60g/sec more.

The driver also noted the “butt dyno” difference between the two. At upper RPMs the car just felt out of breath.

A quick thought about the sound differences:

Its considerable enough to say that the spool is actually faster on the Carbonio causing a pressure differential in the actual mechanical structure within the carbon fiber. Since carbon fiber has more movement, it has the capability of better transmitting more frequencies of the incoming pressure waves, THAT is why the carbonio is so loud at lower speeds.

1) Carbonio has more mid range MAF and a quicker spool time.
2) Ambient conditions were different to each run but both IATs got down to the same temperature (~33*C)
3) Modshack has an almost 2psi difference between requested and actual at a higher RPM. The Carbonio seems to hold the boost more.
4) Carbonio log was started at a lower RPM, yet spooled quicker than the Modshack which started almost 200RPM quicker. The Carbonio log was the “hotter” of the two logs in terms of IATs


All in all this was a very fun excersise and it really showed some similarities and differences amongst OEM design, drop ins and aftermarket competitors. While it was VERY hard to keep some variables consistent, we still managed data that can be judged as sufficient for analyzing.

Furthermore, even if the data speaks so much, it helped me (and probably others) understand more of the flow dynamics involved in our little TSI engines. Where’s the performance compromise? Where’s the sound compromise?

Leave a Reply

Your email address will not be published. Required fields are marked *