FR-S / BRZ / GT86 Cold Air Intake

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What does it take to build a functional air intake for the Scion FR-S / Subaru BRZ / Toyota GT86?

First you have to define the problem, so what is the problem with the OEM air intake system for the vehicle? The OEM air intake actually functions quite well and even better with a simple drop in filter, but after 20 prototypes and plenty of testing we started to realize that we should redefine our approach and go after the fundamental flaw with the platform. The torque dip!! Sure, gains up top are great and just about every intake on the market makes it in one form or another. We have seen gains from various products ranging from 5 to 12 whp, but very few actually pick up horsepower and torque in the DIP.

The goal at Racer X Fabrication was to create a functional air intake that would address this paradigm. From just past 3000 RPM to 4500 RPM you will see typical torque losses of almost 20 FT/LBS. That is unacceptable. Considering most enthusiasts will spend more time in this RPM range than any other.

OEM base line graph

OEM baseline dyno graph

Click graph to enlarge.

We started with our first prototype, a 60 degree bend utilizing a velocity stack that tapered down to the OEM MAF housing diameter. This prototype would use the OEM filter or a drop in filter. The downside to this prototype was that the 60 degree bend made it difficult to package the appropriate tube before entering the throttle body. This concept would become the key factor later in our designs.

Prototype 1

OEM base line graph v. RXF box with OE filter

OEM air intake vs RXF air intake

Click graph to enlarge.

Decent results were provided from the first prototype, we picked up a few HP and Torque but really fell short of our goal. The results from the same box using a KN drop in filter looked much more promising however the AFR numbers were completely unacceptable.

OEM base line graph v. RXF box with KN filter

OEM air intake vs RXF with K&N filter

Click graph to enlarge.

Next we started looking at larger panel filters. Prototypes 2 and 3 would utilize MX-6 air filters. Both air box assemblies would use KN filters, the major difference between them was the tube bend and air box shape. These prototypes would also stop using the straight section before the throttle inlet.

Prototype 2 and 3

Prototype 2 would again fall short of our expectations but would provide a symphony of acoustical sound and provide more than enough clearance for any oil cooler kit.

OEM BASE LINE GRAPH V. RXF BOX WITH MX6 FILTER (DESIGN 1)

OEM air intake vs short bus MX6 K&N filter

Click graph to enlarge.

Prototype 3 initially looked like it may be promising, it provided clearance for oil cooler kits and had safe AFR. We road tested this unit for 500 miles and then dyno tested again only to see that we had met failure. We also ran another base line of the OEM air box. The interesting thing about the second base line was that it was almost 6 wheel horsepower down from the original base line dyno. We would end up doing several base lines through out all of the testing. All would fall within the the range of the original and second base line.

2ND OEM BASE LINE GRAPH V. RXF BOX WITH MX6 FILTER (DESIGN 2)

Click graph to enlarge.

After Prototypes 2 and 3, we went to even a larger filter. We would look at the RX-7 air filter after some initial testing with our popular MR2 air box that utilized the same air filter. Initial data from the MR2 air box showed the best results yet and we thought were onto a successful design. However, we ended up getting stuck on stupid and tested this design to no end with a total number of 4 prototypes all with similar designs and slight changes between them.

For this air box design we would keep the 60 degree bend and use an OEM style RX-7 air filter. This design still used the same velocity stack that we had been using since the first prototype. This air box and its small design tweaks would all be road tested. All of them would fall short, and still not meet the initial criteria that we set out to achieve.

2ND OEM BASE LINE GRAPH V. RXF BOX WITH RX-7 FILTER

OEM air intake vs RX7 filter

Click graph to enlarge.

  • Prototype 7
  • Prototype 7
  • Prototype 7
  • Prototype 7

Prototype 7 was a new unique approach to the previous prototype air boxes of 4, 5, and 6. It allowed us to do several things. First we could alter the velocity stack shape, second we could change the opening size of the MAF straightener. Third it would let us modify the pipe length before the throttle body inlet. This would also be the final testing of this air box design before being scrapped.

2ND OEM BASE LINE GRAPH V. RXF BOX WITH RX-7 FILTER MAF STRAIGHTENER

OEM air intake vs RX7

Click graph to enlarge.

2ND OEM BASE LINE GRAPH V. RXF BOX W/ RX-7 FILTER SMALL MAF STRAIGHTENER

OEM air intake vs RX7

Click graph to enlarge.

2nd OEM base line graph v. RXF box with RX-7 Filter No MAF straightener

OEM air intake vs RX7

Click graph to enlarge.

Prototype 8, we would eliminate the 60 degree bend and move toward the true solution but not without a few more failed attempts. This design allowed us to check the necessary tube length, and to determine if extra volume was good or bad or if it was truly designed for acoustics. We would test tube lengths up to 30 inches in total length (3.0" and 2.5" diameter) with the whole air box assembly outside of the vehicle. We would also move the position of the MAF sensor and check to see how it affected performance.

Prototype 8

Prototype 8

2ND OEM BASE LINE GRAPH V. STRAIGHT RX7 BOX

OEM air intake vs RX7

Click graph to enlarge.

2ND OEM BASE LINE GRAPH V. STRAIGHT RX7 BOX LONG TUBE 2.5”

OEM air intake vs RX7

Click graph to enlarge.

2nd OEM base line graph v. Straight RX7 box long tube 3.0”

OEM air intake vs RX7

Click graph to enlarge.

Prototype 9, start from scratch again. We went in the opposite direction, we calculated the OEM air filter frontal area and found an appropriately sized filter. This air filter would also be an OEM paper filter. This design would almost match the OEM air box completely, so after 9 attempts we had finally found something that was the same as OEM.

Prototype 9

2ND OEM BASE LINE GRAPH V. SMALL PANEL AIR BOX

OEM air intake vs small panel shroud

Click graph to enlarge.

After 9 failures it's pretty hard to conceive an idea for another prototype. Let alone continue to believe that the best air intake system is still achievable, that it's possible to improve on the OEM system and make it better.

So what did we learn from our 9 prototypes:

  • The OEM air duct is a must! We saw consistent gains around 2 whp when using it
  • A large velocity stack was helpful and mandatory for seeing decent performance results
  • Tube sizing that matched the OEM MAF diameter was more important than the use of the air divider
  • Tube size and length made the most difference in any single prototype
  • An appropriately sized straight section before the throttle body inlet is KEY!!


Prototype 10, we would stop using the panel filter, as it was difficult to package in the engine bay and did not yield the performance we were after. We would make new tooling and dies to create a formed velocity stack that would allow us to clamp a conical filter onto the velocity stack. The velocity stack is slightly larger, 4.5” at the total outside diameter and taper down to the OEM MAF housing diameter. We would create 3 different tapered tubes for testing to find optimal airflow without being constrictive before entering the throttle body.

Prototype 10

OEM BASE LINE GRAPH V. RACER X AIR BOX, CONE GRN

OEM air intake vs Green filter

Click graph to enlarge.

OEM BASE LINE GRAPH V. RACER X AIR BOX, CONE KN

OEM air intake vs K&N filter

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OEM BASE LINE GRAPH V. RACER X AIR BOX, CONE FINAL GRN

OEM air intake vs Green filter

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OEM BASE LINE GRAPH V. RACER X AIR BOX, CONE FINAL GRN, 1000 MILES

OEM air intake vs Green filter

Click graph to enlarge.

While we have shown you an over view of our testing and development for the air intake box, we did not show all designs. Here is a picture of most of them, some we did not even test. Others were tested but did not show the results here.

Prototype air intakes

These are the air filter variations we tried through out the development.

Filters

We know that you have plenty of options when it comes to the air intake system for your FR-S / BRZ / GT86. We also know that you will be extremely pleased with the difference our air intake kit can provide. After 1000 miles of driving and performing dyno testing we picked up 7 whp and 9 ft/lbs of torque in the torque dip!! The intake also has great gains throughout the entire RPM band, all of this while playing nice with the OEM ECU.

Final Racer X air intake box

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