Category Archives: Engine Bay

Introduction: 2015 Subaru WRX 3-Port Boost Control Solenoid

If you’ve been in the Subaru game for long, you’re probably well aware that a 3-port Boost Control Solenoid (BCS) is considered my most to be a ‘must have’ improvement before having your car tuned. GrimmSpeed has become the trusted brand in the BCS market, with tens of thousands of solenoids in operation today across the globe.

The 2015 WRX offers a unique change of pace, as the factory 2-port solenoid is mounted directly to the plastic turbo inlet and interfaces with an o-ringed feature, rather than a vacuum hose. With expertise in designing machined parts and a tried and true boost control solenoid, we were excited to dig in and create a solution with an already proven pedigree of high performance and quality.

GrimmSpeed 2015 WRX BCS

GrimmSpeed 3-port BCS 2015 WRX

GrimmSpeed 2015 WRX Solenoid

Enter the GrimmSpeed 2015 Subaru WRX 3-Port Boost Control Solenoid, the first and only of it’s kind.

We began by recreating the factory turbo inlet and solenoid in CAD to ensure a perfectly fitting system. From there, we designed a beautifully fitting machined adapter that would recreate the o-ring sealing feature that the factory solenoid uses. This bracket features 1/8 NPT threads so that both barbed fittings (included) and AN fittings can be used interchangeably, for use with the GrimmSpeed BCS, Manual Boost Controller, or other boost control solutions.

A small mounting bracket secures the solenoid to the machined adapter, to create a compact system, while still allowing those interested in running other boost control solutions the flexibility to do so. Mounting the solenoid directly in place of the stock solenoid allows for vacuum hoses of similar length and a shorter wiring harness. We contemplated the option to make a fully integrated solenoid, but decided that creating an adapter and mounting solution allowed people to use a solenoid that’s already been heavily tested and that tuners are familiar with. One possible change between now and production is to integrate the BCS mounting feature into the adapter. Cost and complexity will determine if that’s feasible shortly.

GrimmSpeed 2015 WRX BCS

2015 Subaru WRX Boost Control Solenoid

2015 wrx boost controller

Lastly, we worked to identify the exact electrical connector used on the stock solenoid so that the GrimmSpeed solution would be a true plug and play (differs slightly from the connector pictured). After that, we went ahead and built prototype and pre-production units.

2015 wrx boost control solenoid

As a brief overview of the advantages of a 3-port boost control system vs. the factory 2-port system, the 3-port systems works by interrupting the boost signal traveling from the turbo to the wastegate. That boost is redirected back into the turbo inlet (post-MAF sensor) and re-ingested by the turbo. The factory configuration simply ‘bleeds’ the signal from between the turbo and wastegate which creates a system that is a bit less complex, but reacts more slowly and with less precision.

We’re currently finalizing the detailed design and moving into production. As soon as we have an estimated release date (expected 2-3wks), we’ll begin accepting pre-orders at a discounted group buy price. We’ll start a different thread for that when the times comes, so for now, let’s keep this discussion technical.

The next step is to get a small initial batch of solenoids into the hands of your favorite local tuners. If you’re a tuner yourself or you’d like to nominate a tuner for receipt of a prototype unit, please comment below and we’ll add you to the list. From this list, we’ll select testers based on experience and geographic location.

Casting Intercooler End Tanks – A Day at the Pattern Shop!

Pattern Shop Newsletter 1_630

The photo above shows the machining of the TMIC outlet end tank master. The Bottom received a finishing pass and then the part was flipped so that the top could be roughed out. When all is done, this will be a flawless part. Now that the master parts for both end tanks have been completed, we’ll make a cast iron match plate from each of them. You probably noticed that it looks a lot like they’re being machined from wood and that’s because they are! These master parts will only be used a single time – to cast the real molds from, so a heavier duty material only costs more and takes longer, with no added value.

Interesting Note: The master that you see here is not dimensionally identical to our final part – it’s actually larger. Based on the foundry’s preferences, standard shrink allowances and the geometry of the model, the pattern makers job is to determine how much the cast aluminum part will shrink/contract during solidification. An easy way to cut cost, especially if you’re casting overseas, is to skip this step. Ever had an application-specific intercooler that didn’t fit quite right? There’s a decent chance that uncontrolled shrinkage was at least partially to blame.

For those unfamiliar with high end casting processes, creating the tooling and molds is the giant hurdle standing between your design in CAD and real parts. With properly designed and manufactured tooling, casting and machining the parts is relatively straight forward. One of the many benefits of casting right here in Minnesota is that we’re able to sit down with everybody involved and work through potential issues to mitigate the risk of trouble during production almost entirely. That means lower production cost for us and lower pricing for you!

GrimmSpeed Downpipe – Frequently Asked Questions

grimmspeed wrx downpipe

There’s are certain questions that we typically get from customers, regardless of the product being discussed. Instead of making you call or email for an answer, we thought we’d address a few of the heavy hitters right here so that the information is available to you 24/7.

Question: I’m planning on going Stage 2 with my car, do I really need an aftermarket downpipe to run higher boost and make more power?

Answer: Yes! The purpose of an aftermarket subaru downpipe is to remove restriction from your exhaust system. In the stock downpipe, that restriction comes in a three different forms. The first and most important is that the factory downpipe contains highly restrictive catalytic converters. Aftermarket downpipes generally either remove the catalytic converter all together or replace it with a much higher flowing unit. GrimmSpeed offers options for both. The second restriction is a result of the design of the turbine outlet flange. The OEM flange is a flat plate, obstructing exhaust flow from the IWG and forcing it to merge with exhaust from the turbine immediately. As soon as you’ve seen one, you’ll know what I mean. The third is in diameter. Stock downpipes use a smaller diameter tubing than most aftermarket downpipes. If the purpose is to remove restriction, the reason for larger tubing is clear. Even a small increase in internal diameter has a large impact on the total flow area of the tube.

grimmspeed subaru downpipe engineering

Question: Ok, so I know I need an aftermarket downpipe. There are a bunch of different styles. Do I want bellmouth or divorced?

Answer: This is where things get a little bit tricky, because you’ll get different answers depending on a person’s personal opinion regarding the proper design of a subaru downpipe. It’s important that you understand the pros and cons of each and make an educated decision for yourself. To be clear, both will do what you want, which is to unlock some serious power potential, but there are differences that can facilitate more efficient tuning and better boost control that are equally important. The reason that we’ve gone with the divorced design, despite the increased cost and complexity, is that we believe that it’s the best, plain and simple.

Imagine that your downpipe is a freeway, your turbo is a tunnel and your internal wastegate is traffic trying to enter the freeway. On a typical freeway, a car would use an on-ramp to get up to a proper speed and direction before merging with traffic in a controlled manner. That is exactly what a divorced subaru downpipe, like the GrimmSpeed unit, facilitates. Our divorced tube is the perfect length for the exhaust gases from your IWG to merge with the rest of your exhaust with minimal turbulence. Any shorter, and the exhaust from your turbine is still recovering from leaving the turbo, expanding into a larger tube and making a turn down towards the ground. Any longer and you’re simply adding unnecessary cost, material, weight and complexity to the assembly. Now, imagine that the traffic entering the freeway simply enters from a stop sign. We’ve all had to make that nasty right-hand turn during rush hour, don’t make your exhaust do the same. Good, predictable exhaust flow for your internal wastegate will ensure that you are also able to create good, predictable boost control.

grimmspeed sti downpipe faro arm

Question: I have X downpipe right now and i didn’t have any trouble installing it, but I just can’t get rid of my exhaust leaks now.

Answer: This is something that we hear very often. Persistent exhaust leaks of this kind often come from flanges that are severely warped or from parts that don’t fit properly. Creating exhaust components that fit perfectly is more complex than most people (and other manufacturers, it seems) realize. Designing a part that installs easily is one thing. Engineering a part that installs easily, has appropriate clearances from other components and has nice, relatively flat flanges that are are at exactly the right angle to create a perfect seal is a bit more difficult.

Here’s where GrimmSpeed’s engineering process emerges miles ahead. Other manufacturers create their welding fixtures from an OEM downpipe to match it exactly. Sounds great, right? Wrong. We’ve been engineering top of the line exhaust components for a while now and we’re going to let you in on a little secret – Subaru isn’t perfect. In the design of this downpipe, we used our FARO Arm to 3D scan a handful of OEM downpipes and saw that from pipe to pipe, there was a significant amount of variation. We bring all of this data in CAD, overlay the scans, and then find the average of each flange location. We then design our pipe and build our fixtures to that average, instead of a single downpipe. This ensures that our tolerance range is at least as tight as the OEM, with no GrimmSpeed downpipe ever fitting worse than an OEM part. On top of that, we also use our FARO Arm to 3D scan the areas of each test vehicle affected by the downpipe. This ensures that we have proper clearances for the firewall, O2 sensors, transmission bracket, subframe and so on.

Question: So what sets the GrimmSpeed Subaru Downpipe apart from other downpipes that get decent reviews but are a little bit less expensive?

Answer: This is where you’ll have to use the information that we’ve shared to make an educated decision for yourself! If you’ve made it this far, you already understand the care that we take in our design and manufacturing processes. Now, we’ll overlook fitment and design and consider just build quality. All of our materials are top-quality, Made in the USA stuff. Aside from the obvious benefits of supporting local and domestic business, this means that we know exactly what we’re using to build these downpipes. All “Stainless Steel” downpipes are not created equal. Our 3″, 16ga tubing is beefy and our 1/2″ 304 stainless flanges are the thickest and flattest around. Thick flanges help us avoid warping during the welding process and ensure a fantastic seal to your turbo.

We periodically check our fixtures for accuracy using our 3D scanning equipment, to ensure that over time, it hasn’t pushed or pulled from the heat cycling. Each downpipe is welded by hand just feet (literally) from where they were designed and developed. Robotic welding looks great, but in an application like this, nothing can replace the skilled hand of a true craftsman. This type of welding requires that changes be made on the fly to ensure not only a cosmetically excellent weld, but more importantly, a structurally flawless one.

grimmspeed exhaust welding tig

The bottom line is that we’re all Subaru enthusiasts here. We get it. We’ve all had the ‘budget’ downpipes at some point and while some of us have had fine experiences with them, others of us have not. We take pride in developing and manufacturing products that we know won’t let you down in 5 days, 5 months or 5 years from now. A GrimmSpeed downpipe will outlast your car and we stand behind each one that leaves the shop 100%.

Need help with which GrimmSpeed Subaru Downpipe will work best for you? Check out the links below for more information on each fitment.

Restriction in the Stock BRZ/FR-S Intake – Introduction

grimmspeed intake testing brz frs
This photo shows placement of one of the fittings for pressure sensing.

When we began thinking about designing an intake for the twins, we first wanted to evaluate the claim that “the stock intake is good enough.” Its general knowledge that in the last ten years or so, that factory OEM intakes have become very good in design, and are often difficult to improve upon. There are several ways to evaluate this claim, and we wanted to start out with looking at the design of the entire intake as both an overall system, as well as the sum of all of it’s parts.


A visual inspection doesn’t tell an absolute truth about the system, but it does give you a place to start evaluating. The first source of restriction you’d look for is sharp or abrupt entry points. Air entering a pipe without a flared entry (think velocity stack, or a funnel shape) produces a restriction, compared to one that does have a flared entrance or transition. Just the same, when air has to traverse a larger and larger angle bend, there is an increase in restriction. The same can be said for when air has to pass over surfaces that are not smooth, etc. All of these situations add restriction, which can be measured as a drop in pressure. The ideal case to move air from point A to point B would be a perfectly smooth, straight length of pipe, and even that will have a pressure drop as the length of the pipe increases.

So from a visual standpoint, lets break apart the sections of the intake: There is a snorkel, front of airbox, air filter, rear of airbox, MAF housing, intake elbow, and throttle body. The entire system can be looked at as being the area before the snorkel (behind the bumper cover) to just passed the intake elbow (right at the throttle body). Measuring the difference in pressure between these two points will give you the overall restriction of the system. But in order to identify where the weaknesses in the system are, one would be more interested to measure the difference in pressure between components in the system. For example, to measure the restriction the air filter has on the system, you would measure the pressure before and after the filter. And if you add up the pressure differences between all parts of the system, it should equal the overall restriction.

Back to the visual inspection of the system, what do we see as a potential problem area, and why do we want to choose these locations to test? The first part of the system that air sees as it enters is the snorkel. The inlet of the snorkel looks good; there is a well formed velocity stack that has minimal extra material from being molded. It’s a slight oval shape, roughly 2.25in x2.5in. About 10 inches down the air’s path, the snorkel starts to make an approximate 90 degree bend to it’s exit. The bend is very smooth, and all the while the shape is transitioning to a flatter oval, while at the same time increasing in overall cross sectional area. At the point where the snorkel transitions into the air box, it is roughly 2in x 5.7in. The snorkel contains two resonators along the first section, in two different sizes, each containing a small drain hole at their lowest point. The snorkel is sealed to the air box with a strip of foam that interfaces the outlet of the snorkel to the inlet of the front airbox.

The front face of the airbox is angled at the bottom, and contains a circular emboss. Both features are in place to maximize area before the filter, while still clearing the radiator and fan. There is also a large resonator to the left of the entrance. The front airbox has a hole at it’s lowest point just right of the entrance, as does the large resonator, both for drainage purposes. The inside of the front of the airbox is very smooth across all surfaces. The only noteworthy point from a flow standpoint is at the entrance. The half of the entrance below the snorkel has a smooth radius flowing towards the filter. However, the half above the entrance is abrupt, and looks different than you would expect from viewing it from outside the box. Outside the box, just above the exit of the snorkel there is a hump which looks to exist as an area to smooth airflow going towards the filter, but just the opposite appears to be true as there is a void here. One can only assume this is for strength, or some phenomenon that is hard to explain.

The air then flows through the filter, which is not your typical paper filter, and has only 14 large ribs. I am unsure of the media of the filter, but it is similar to a fabric like cotton. The ribs on the front side are longer than those on the back to increase filter surface area.

After the filter is the rear of the airbox, which contains mostly smooth transitions, with a taper at the opposite side to the exit that should promote flow towards the MAF housing. The only noticeable source of restriction in this piece are several protruding ribs that run lengthwise in the rear of the airbox, however small. The exit of the airbox is technically the mass air flow, or MAF, housing. The entrance to the MAF housing appears to have been optimized, as it is one of the most important parts of the entire engine. The rear face of the airbox has a section “dug out” to smooth the transition into the MAF, and the opposite side of that feature has a molded plastic velocity stack. Immediately at the entrance is a plastic matrix that is commonly referred to as an “air straightener.” This is specifically put in place to help the MAF provide the most accurate reading as possible by modifying the flow of air before it. The thickness of the pieces of this matrix is 2mm, and the diameter of the entrance here is roughly 68.5mm. The entire MAF housing is only about 70mms long, and places the MAF sensor about 25mm, or about 1in after the air straightener. The inner diameter at the MAF sensor is 70mm, and the diameter at the outlet of the MAF housing is about 72mm. So there is a taper through the entire section, albeit minimal.

At the exit of the MAF housing is the entrance of the intake elbow. The entrance to the elbow is just under 3in in diameter, and has an immediate 90 degree bend. This bend is very tight, and has a centerline radius significantly under 3in. This most likely means that the diameter of the cross section does not stay a constant 3in as the bend progresses. There are ribs on the outside of the part for strength, but they do not exist on the internal surface of the elbow. There is a tube exiting the elbow for the sound tube, just opposite of the intake elbow’s entrance, and a resonator toward the bottom of the engine bay, both located directly on the bend. Immediately after the bend is a roughly 2.25in long flex section. This section contains 5 smooth ridges that exist on the inside of the tube, and extend outwards of the tube less than .125in. After this flex section is a 5in long straight section, smooth on the inside, with ridges on the outside. This terminates at the entrance of the throttle body.

Based on this visual assessment there isn’t much to expect in the way of restriction. From the entrance of the system to the exit, we expect to see a restriction from: 90 degree bend of the snorkel, air filter, decreased size (in comparison to the air box volume) of the MAF housing, the tight 90 degree bend on the entrance of the intake elbow, and the flex section located right after the previous bend.

See Part 2: The Equipment to Continue

Product Release – GrimmSpeed Alternator Cover

We’ve done it again! We know that there are a lot of options out there for Subaru alternator covers, so when we decided that it would be fun to put the GrimmSpeed spin on it, we knew that we needed to come up with something that had all the characteristics of a great GrimmSpeed products (quality, craftsmanship, fitment, style) but that also had a unique look. For this, we looked to the Subaru engine bay for inspiration.

grimmspeed alternator cover

Drawing from the asymmetrical features in the engine bay, the horizontal lines on the Top Mount Intercooler and the design of the GrimmSpeed Tool Tray Radiator Shroud, we created something pretty neat. It all started with the use of our FARO Arm, to 3D scan the OEM alternator covers as well as the factory engine bays.

grimmspeed alternator cover engineering faro armWhat we ended up with was a unique shape that provided protection from the accessory belts as well as added a bit of style to what is typically an ugly, cluttered are of the engine bay. Machined and anodized mounting hardware provide a clean, safe and secure method of keeping the cover in place and brushed stainless steel, red, black and silver powdercoated finishes provide options for just about everyone, whether you want sleek and subtle or a splash of color.

grimmspeed alternator coverAs always, feel free to contact us with any questions or to order your own!

– Matt