A Tuner Is Working On A ‘Velocity Stack’ Mod For Modern BMWs And Lots Of People Are Pumped

One of the pillars of internal combustion engine tuning is improving flow on both sides of the valvetrain. Whether it’s getting more cool air in or pushing exhaust out as effectively as possible, both boost efficiency, and more efficiency means more horsepower. 

When it comes to intake modification, not much beats individual throttle bodies (ITBs) on a naturally aspirated engine to get more air in as efficiently as possible and to boost overall theatrics—who can deny this design’s deeper and more pronounced intake sound? However, these are a typically costly aftermarket modification, and then tuning the engine’s ECU to work with them takes a lot of effort.

However, modern BMWs that are equipped with Valvetronic intake technology play by a different rulebook. In fact, thanks to Washington-based aftermarket tuning company 22RPD, taking advantage of this induction system that doesn’t rely on a throttle body means Valvetronic owners can achieve a setup that should offer many of the advantages of ITBs (a smaller air path into each cylinder), yet for far less money and in a much more convenient way. Let’s dive into exactly how.

What is Valvetronic?

Many BMWs produced since 2006 sport this fascinating technology: In a quick sentence, air flow is regulated by the valves themselves, not the throttle body—though, a single throttle body for all cylinders is still there in case the Valvetronic system malfunctions. This means there’s a lot more going on under the valve cover, which Jason Fenske of Engineering Explained does a great job at laying out in this video.

The BMW N52 is a naturally aspirated 3.0-liter inline-six that sports Valvetronic, which lives under the hood of my beloved 2011 BMW 128i. Thomas Hundal’s also got it under the hood of his E90 325i, too; we’ve nerded out over this aluminum-magnesium lump of German excellence quite a bit over the years.

It’s a torquey, rev-happy six that produces around 230 horsepower and 200 pound-feet of torque from the factory. In fact, its rev-happiness is thanks in part to Valvetronic: Instead of waiting for air to enter the intake ports when the throttle body opens up, it’s already there, rarin’ to get sucked in.

How This Offers Many Advantages Associated With ITBs

So, because Valvetronic doesn’t need a throttle body, it can theoretically be completely deleted from the equation via aftermarket tune. Not only that, but it’s possible to delete the mass airflow (MAF) sensor as well, and run it like factory BMWs do in Europe. As Thomas Hundal explains in solid detail, “Euro-spec N52s measure air density using the differential between manifold pressure and atmospheric pressure. The intake air temperature (IAT) sensor is one component the ECU uses for fueling, but much of the heavy lifting is done via differential pressure (with a MAP sensor in the manifold) and closed-loop oxygen sensor operation.”

Thus, fewer components between the intake ports and the outside world.

Which is similar to an ITB setup, except there are no throttle body valves at all. Enter 22RPD,out of Renton, WA — a shop that has designed an intake manifold consisting of open intake runners—dubbed velocity stacks in this instance—for each cylinder that resemble ITB trumpets. Check it out:

Before you take off down to the comments and condemn this design for lacking a filtration element and being bathed in engine heat, don’t fret, the pictured setup is just a prototype—the company says the final product will include a filter and proper housing to draw in cool air.

Its design is more than just throwing some tubes over the intake ports, too. The runners have been optimized for flow, and actually looks quite similar to a turbocharged BMW N54 engine’s intake runners. That’s another modification that the N52 crowd’s taken a shine to: Modifying and fitting the intake manifold from the N54 for its shorter runners, which gives the naturally aspirated fare a decent bump in peak horsepower, though reduces output low in the rev band.

The Upsides and Downsides

Depending on aftermarket ECU (er, DME because its a BMW) tuning, 22RPD’s trumpets could result in a very healthy power increase, especially when combined with aftermarket exhaust headers and MILVs (modified intake lift Valvetronic support), which increase intake lift and duration like an aftermarket camshaft. Since 22RPD specializes in remapping stock MSV70 and MSV80 DMEs, running this assortment of hardware won’t require aftermarket engine management hardware, saving interested owners some serious coin.

With just this selection of mods, 261 wheel-horsepower and 231 wheel-torque is allegedly possible. Not bad, not bad at all.

This intake arrangement boosts throttle response, the engine’s ability to rev up even quicker, as well as make for an excellent intake soundtrack. Who doesn’t love a deep-breathing NA engine, especially of the inline-six BMW variety?

There could certainly be some downsides of this throttle body-less intake (which has been discussed for years; see e90post forum post above). Remember: The engine still has a throttle body there from the factory in case the Valvetronic system malfunctions … so what happens if it malfunctions and there’s no backup? Once again, N52 technical wizard Thomas Hundal points out that “if the eccentric shaft locks at full lift without the throttle body in place, the engine will just bounce off the rev limiter until the ignition’s switched off. While there is some possibility of sudden unintended acceleration, most people who are in deep enough to consider this mod will have the skills to diffuse a situation like that.” We reached out to 22RPD, and the tuning company responded that “the fail safe is now controlled by the Valvetronic sensor,” meaning that the Valvetronic system’s own monitoring equipment should act as a failsafe.

 

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[Ed Note: This actually sounds potentially dangerous, though I’m curious what mitigation strategy 22RPD has in mind; I’ve sent an email asking, and will update this article if I hear back. In the meantime, here’s a look at the company’s Feb 17, 2024 blog post titled “THE FUTURE OF NA N52 : NO THROTTLE BODY [BONUS: BETA TESTING SIGN-UP]“:

The BMW N51 and N52 engines, renowned for their reliability and perhaps weight but lets be honest, have long been overlooked among enthusiasts and professionals alike. However, every engine has untapped potential waiting to be discovered. It is with great excitement that we introduce this untapped potential, this new new intake and tune from 22RPD. A product that not only redefines performance capabilities, but also ushers in a new era of N5X performance.

Innovation is at the heart of the 22RPD, and it’s what sets us apart from everyone else on the market. The choice to develop this package to operate without a throttle body, is substantially innovative. This innovative design leverages the full potential of BMW’s Valvetronic system in a new way, using it exclusively to manage engine breathing. Without the throttle body, we have removed a significant restriction in the intake tract. The result? Substantial gains.

This design doesn’t stop at just removing restrictions. It introduces a meticulously engineered trumpet design that surpasses the popular N54 intake and three-stage (3IM) intake in both average and peak power output. Through comprehensive engineering and testing we have developed an improved runner shape and optimized length. Thus enhancing the engine’s ability to breathe effortlessly at higher RPMs while optimizing resonance for midrange power improvements. This design not only optimizes performance but also eradicates common failure points associated with the 3IM intakes and DISA’s, ensuring reliability and longevity. Also, as a small bonus the trumpets save 30lbs or so off the nose of the car, optimally.

Unleashing N51/N52 Power: Dyno-Tested Performance Gains

The revolutionary design behind the 22RPD intake owes its genesis to the extensive groundwork laid with the recent S65 and S85 intakes design by 22RPD prior, combined with sophisticated flow modeling (CFD) techniques. These runners are the culmination of all our efforts across various platforms, representing an evolution in our approach to intake design. We began with fundamental calculations for resonance and runner length. This was followed by 3D scanning the OEM N52 intakes to serve as our baseline reference. With this foundation, we determined an optimal taper figure and initiated modeling of the base geometry. Through several iterations, guided by both modeling insights and CFD analyses, we refined our design before advancing to real-world testing and iterative design on multiple cars.

The proof, as they say, is in the pudding-or, in this case, the dyno tests. Rigorous testing has demonstrated that the 22RPD package delivers significant performance gains everywhere that counts. These gains are not just numbers on a chart; they translate to real-world enhancements in acceleration, throttle response, sound, and overall engine efficiency. For BMW N51 and N52 engine owners, this means experiencing a new level of performance and sound that was previously thought to be unattainable by the little brother of the n54. See the dyno graph below showing the gains with the Bavautoparts 330i.

 

Unfortunately, our other test vehicle had a failing catalytic converter which raised its ugly head part way through testing.

The 22RPD custom intake and tune package represents more than just an increase in horsepower and torque. It embodies a philosophy of innovation, reliability, and performance. By removing the throttle body and optimizing the Valvetronic system, 22RPD not only enhances power but also reduces complexity and potential failure points within the engine. This approach ensures that your BMW’s heart is not only more powerful but also more robust and dependable.

For the discerning BMW enthusiast looking to extract the maximum potential of sound and performance from their N51 or N52 engine, the 22RPD custom intake and tune package offers an unrivaled solution. Its innovative design, backed by solid engineering and real-world testing, sets a new benchmark in N52/N51 performance tuning.

What is Party Mode? Why do you keep saying it?

The “Party Mode” Intake by 22RPD where we throw caution to the wind, filters out the window, and let your engine run wild and free, just as nature (or the automotive gods) intended. Picture this: an intake so raw, so untamed, it scoffs at the mere thought of air filtration and laughs in the face of safeties, all in the noble pursuit of substantial gains. But, dear thrill-seeker, let’s not forget that with great power comes great responsibility. While embarking on this euphoric journey of unfiltered performance, remember that every party has its end, and not all engines enjoy the hangover. So, consider this your cool yet cautionary tale: embrace the exhilaration of “Party Mode,” but be mindful of the morning after. Here’s to living fast, but maintaining enough sense to ensure your ride can keep up with the pace. And let’s remember, 22RPD is not responsible for the aftermath; you take full risk, stepping into the party with both eyes open to the wild ride ahead.

What’s on the Horizon? Upcoming Milestones:

• PARTY MODE Beta test Phase: March 1 – April 1
• Cold Air Feed/Filter Design Period: February 21 – March 14
• Public Release of PARTY MODE INTAKE: April 1
• Testing of Fitment on Filter Design: March 14 – April 14
• Anticipated Release of Filter and CAI Design: May 1

Anticipated pricing for BETA trumpets and tune is $995. If we make any changes for a final product, exchange towards the final product will be allowed. Exchange towards a filtered unit will be allowed.

Ready to join the Evolution? Sign up for our beta program below and be the first to experience the raw, unfiltered bliss of 22RPD’s “Party Mode” intake. It’s not just about making your engine louder; it’s about making your heart race faster. So, strap in, turn up the volume, and let’s make some noise.

The short of that blog post: The setup promises to reduce weight, improve reliability, and increase engine response thanks to reduced restriction and optimized runner design (optimized, specifically, for mid-range RPM (read this to learn more about how velocity stack length affects performance at different RPMs). I myself have concerns about pulling hot underhood air into the engine, and I wonder about that loss of a throttle body failsafe, but maybe there are plans for those. -DT]. 

[Editor’s note: 22RPD responded to our inquiry on intake air temperature with its findings, and the open trumpets reportedly make less of a difference than you’d expect. As per 22RPD: “not that we have seen, both Dyno and street testing has shown similar AIT and even slightly lower due to the lack of an airbox that the “cold/fresh” air needs to travel through, and we are using the N54 ducts to get that air to the stacks.” — TH]

I’m quite excited to see what 22RPD comes up with for a finished project, and it’s clear a lot of you are, too:

It’s so cool that one can exploit the well-flowing N52 like this, and hopefully the bump in horsepower—and overall soundtrack—will be substantial and awesome.