GrimmSpeed EFR7163 Twinscroll Turbo Kit Development

The time has finally come to let the cat out of the bag on GrimmSpeed EFR7163 Twinscroll Turbo Kit development! We’ve been developing this system alongside our top mount intercooler since late last summer. The initial purpose was to build a single car that would produce big turbo power, but with responsiveness that’s similar to factory. This car would be an excellent test bed to prove that our TMIC would support big power with killer responsiveness, without sacrifice. We selected the Borg Warner 7163 Twinscroll Turbo for this project and immediately got to work with the design of a truly equal length header.


We quickly realized why nobody else is doing this. The configuration of the twinscroll ports on an aftermarket turbo is rotated 90 degrees from the factory turbo, making the routing of an equal length manifold below the car extremely difficult. We had to leverage all of the engineering tools and technology that we have access to in order to design a manifold that would fit the turbo that we selected without losing usable ground clearance and veering from our equal length requirement. The firing order of the motor dictates the runners that need to be paired for the twinscroll turbo to function properly, but it’s not even that simple. It’s not our style to hack something together that fits and works – we optimize. Finally, in such tight quarters, it’s also critical to figure out if a given manifold design can be fully welded and if there is adequate room for bolts/studs/nuts and tools needed for installation.

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FARO arm 3D scans of the underside of the car and of the factory manifold and turbo gave us a very good idea of the space that we had to work with. We experimented with three different collector designs and five different runner concepts before settling in on the one below. We were able to design a collector and runners in Solidworks that offered truly equal length (variance between runners is only 2.3%). Because we were concerned with ground clearance, we removed the EFRs IWG (internal wastegate) and used a pair of external wastegates. Knowing what we know now, our plan will be to utilize the EFR’s IWG on production kits if/when the project reaches that stage.

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For this design, we knew that we needed a perfectly symmetrical collector to help us achieve the performance that we’re targeting and utilize the full potential of the twinscroll EFR turbo. The way that the runners pair up and enter the turbo is critically important, so despite the tight space constraints that we’re working with, we made no sacrifice in the general collector design.

The best that we could fit is still a bit steeper than we’d have preferred, but we’re working with hard limits here. This collector has a 45 degree merge angle. Being that the turbo that we’ve selected uses a divided T4 turbine housing, that’s the size flange that we’ll use. Of course, it’s helpful that GrimmSpeed also manufactures the highest quality T4 gaskets around!

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Our engineering team and fabrication team worked together to prototype the kit with great accuracy. We were able to use a very slightly modified GrimmSpeed StealthBox Intake and a very slightly modified GrimmSpeed J-Pipe. For charge air cooling, we used a GrimmSpeed prototype charge pipe and prototype TMIC. The charge pipe is quite simple, as the EFR7163 has a bypass valve built into its compressor housing. After welding was finished and the pipes became cool, what we ended up with was a thing of beauty:

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Getting coolant and oil through the turbo just took some clever routing of hoses, since the factory turbo already uses both in the same location. For the turbo oil pan, we were able to simply reuse the factory oil pan, mounted directly to the turbo. Production kits will very likely include a smaller, custom pan, but that’s yet to be determined.

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We need to start with a shout out to DB Performance in Rogers, MN. We really enjoy the opportunity to bring our cars to a third party shop for dyno testing and tuning. We think that it helps us maintain a level of transparency in a world where closed-door dyno testing is so common and we love having a second set of expert eyes on the work that we’re doing. Shane, Danny and the rest of the crew run a top-notch operation and if you’re in the area, we highly suggest that you check in with them regarding maintenance, modification and tuning. These guys build some serious cars.

With the kit finally on the car, we knew a few things. We knew that fueling would limit our ability to make power. Our intention is to run the car on E85, so we’ll need a supplementary fuel system to deliver the volume of fuel that we’ll need to push this kit. We also knew that the kit would produce power and torque in excess of the limits of the factory motor. A phone call to our friends at IAG Performance for their Stage 3 shortblock and 14mm head studs solves that problem with ease. At the same time, we’ll have the heads gone through before putting it all back into the car. Other supporting modifications will be made at the same time (clutch, mounts, etc).

Step one, though, was to get the car to the dyno for some shakedown pulls and to build confidence in the kit before pulling the car apart for motor/heads/fueling. We pumped the 93oct out of the tank and replaced it with MS109. The thought was that this would help us safely and repeatably push the kit a little bit farther on the dyno than 93oct and E85 would allow with the factory fuel system. Our goal here was to determine that the cooling and oiling of the turbo was working flawlessly and to prove that the complexity of the manifold was justified by the increased performance offered in terms of spool and power production. The car was tuned by Shane at DB Performance (Rogers, MN) with the COBB Accessport.

2015 Subaru WRX, 6MT, 9000mi

  • GrimmSpeed EFR 7163 Turbo Kit
    • Borg Warner EFR 7163 Twinscroll Turbo
    • GrimmSpeed EL Manifold
    • Turbosmart Compgate 40 EWGs (pair)
    • GrimmSpeed J-Pipe (modified)
    • GrimmSpeed Stealthbox Intake (modified)
    • GrimmSpeed Big Turbo EBCS
    • GrimmSpeed Charge Pipe
    • GrimmSpeed Top Mount Intercooler w/ splitter
  • STOCK Catback Exhaust
  • STOCK Fuel System

Dyno: Dyno Dynamics
Stock 2015 WRX Baseline: 166whp/181wtq
Fuel: MS109

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Our first dyno session with this kit went even better than we had hoped. We kept very conservative, as the goal wasn’t to make power, but to prove that the setup functions properly. The coolant and oil feed and return for the turbo worked flawlessly on the dyno for 7hrs, which was one of our primary concerns, given the compact space.

Our primary goal for this kit was to provide a driving experience that isn’t unlike a stock turbo car, but with a power curve that leaves nothing to be desired. To achieve that, we knew we needed a turbo that could spool extremely fast but with the potential to produce really healthy power. This preliminary test was to prove the first part, as we’re quite confident in our ability to achieve the second. As the chart below shows, the GrimmSpeed EFR7163 Twinscroll kit spools just 200rpm slower than a ‘stage 2’ stock turbo car, hitting 15.5psi@3000rpm and 19.5psi@3500rpm as it approaches its target boost. With E85 and higher boost targets, we expect even faster spool, but these results alone are more than enough to demonstrate the capability of this beautifully designed turbo manifold paired with a killer EFR twinscroll turbo.

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Although making power wasn’t part of the goal, we know it’s on everybody’s minds, so we’ll share anyway. As you can see this car, in 100% stock form, produced 166whp on the dyno at DB Performance (known for reading very low). With the EFR7163 kit at only 20-21psi and relatively conservative tuning, the car was making 320-330whp and 300-310wtq. On our local dynojet, that equates to a ballpark 400whp/390wtq. The strange behavior at the top of the chart can likely be attributed to the fact that the car isn’t setup to make power (stock catback, for example) and some fuel/spark issues that we’ll sort out when we come back ready to turn it up.

What’s next?

We’re waiting for the weather to get into the 40s next week so that we can run the car on the road and do some logging and 2015 TMIC testing before we pull it apart for the following:

  • IAG Performance Stage III Short Block w/ 14mm head studs
  • Headwork/valvetrain
  • Supplemental fueling so that we can run E85
  • Water-meth
  • Capable clutch
  • Catback exhaust
  • TGV delete
  • Data acquisition hardware/sensors

Then we’ll be back to the dyno to push the car and find its limits. That’s all we’ve got for now! As many of you know, this project is also a way for us to push our 2015+ WRX TMIC pre-production units to their limits (maybe?). We’ll keep you updated on that front as well, but all we’ll say for now is that they’re keeping up with this kit very nicely so far.