GrimmSpeed 15-17 Subaru STi (w/ OEM Sound Generator Tube) Post MAF Hose Kit - Black

GrimmSpeed
SKU: grm125013

Quick Overview

Some OE parts look passable and others miss the mark. In the case of the factory post MAF hose, the quicker you can get it out of your bay, the better. We’ve now got you covered with The GrimmSpeed Post MAF Hose Kit that not only looks better but fixes...
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Some OE parts look passable and others miss the mark. In the case of the factory post MAF hose, the quicker you can get it out of your bay, the better. We’ve now got you covered with The GrimmSpeed Post MAF Hose Kit that not only looks better but fixes the flaws of its OE counterpart.

GrimmSpeed's hose construction improves flow with 2 main features:

The first is the smooth inner surface, removing the pockets from the OE corrugated folds. These folds are necessary for the factory rubber design for flexibility during installation and structural integrity. The Grimmspeed hose is made with reinforced silicone, which is flexible but has strong structural properties that enable us to have a hose that is very easy to install without worrying about collapsing under a vacuum.

The second feature is a tapered center portion, making sure the inner diameter matches the OEM air box and turbo inlet. A mismatched diameter creates steps, which will interrupt the airflow trajectories and create small vortexes in the post-MAF hose. The Grimmspeed hose was designed specifically to prevent these issues:

postmafhose-tapertapered-portions.jpg

Coupled with The GrimmSpeed DRY-CON Panel Air Filter, this will be the best way to maximize your factory intake system until it’s time to upgrade into a full GrimmSpeed Intake.

Note: If you’ve got a 2015-21 STI with the factory sound generator tube and want to delete that piece, you can either purchase the 15-21 post-MAF hose and GrimmSpeed Sound Plug Delete or opt for the 18-21 STI MAF hose.


Testing

The first step in improving on an existing part is to find its shortcomings. The OEM rubber hose, designed with corrugated folds, requires a straight section in the middle, which means sharper curves on both ends. This contributes to uneven airflow through the hose with high and low-pressure spots. The GrimmSpeed hose design can support a minimal curve transition, maximizing airflow. The plot below shows the pressure through the length of the hose, the GrimmSpeed design resulting in a smoother transition from the airbox into the turbo inlet:

postmafhose-slidesoem-vs-grimmspeed.jpg

The removal of the corrugated folds also adds a significant reduction in vorticity (a calculation used for flow disruption, with blue representing the consistent flow and red more turbulent) between the two designs. The smoother flow will give us a more consistent air supply to the turbo:

postmafhose-slidesoem-vs-grimmspeed-flow-rate.jpg

The tapered center portion is also an important design choice for contributing to even flow through the hose. A plot comparison showing vorticity between a non-tapered version and Grimmspeed’s tapered hose shows an additional reduction in turbulence through the center of the hose where a majority of airflow will occur:

postmafhose-slidesoem-vs-grimmspeed-flow-rate-copy.jpg

Quick Specs

  • 4-Ply Reinforced Silicone- Extremely durable avail. in red or black
  • OEM fitment- Easy install, no modification or tuning required
  • Seamless Flow- CAD optimized design
  • High-Quality Breeze Hose Clamps Included
  • GrimmSpeed Logo to Represent your Favorite Brand!

Fitments

  • 15-21 STI (With factory-integrated sound tube)
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