HKS 2021 Subaru WRX LEGAMAX Sport Exhaust

By changing the pipe diameter from 74.7mm to 60.5mm x 2 to 45mm x 4, the straight structure achieves low exhaust pressure while reducing unpleasant exhaust note, thus improving both performance and sound quality.
Symmetrically arranging the 4 silencers and the beautiful 98mm titanium tail creates a muffler that is not only powerful in the rear view but also visually appealing when the vehicle is lifted up.
This exhaust system produces a pleasant bass sound at normal revs and a sporty sound when the accelerator is depressed.

Configuration

Product specifications and sound quality
By changing the pipe diameter from 74.7mm to 60.5mm x 2 to 45mm x 4, both low exhaust pressure and sound deadening effects are achieved.
In addition to the pipe diameter, the expansion pipe, resonance pipe and muffler have been adjusted appropriately to bring out the boxer engine's character, emphasizing the unique low sound while creating the image of a sound quality with a dry high sound when the driver steps on the engine.

Exhaust resistance test results 

The graph above illustrates the relationship between flow rate and exhaust resistance as measured on a flow bench. Lower resistance relative to flow rate indicates reduced exhaust resistance.
When comparing this product with the stock muffler, approximately a 70% reduction in exhaust resistance was observed. This reduction is attributed to the pipe diameter, layout, and straight structure without apertures, which collectively achieve significantly lower exhaust pressure.
The table below displays the pipe diameter and number of pipes for each part, as well as the equivalence of multiple pipes to a single diameter.

Power check (Exhaust replacement only)

The graph above illustrates the power and torque results measured on a chassis dyno. A significant increase in torque of 14.5 Nm (1.5 kgf-m) at 3500 rpm is observed when comparing this product to the stock muffler.

Power check (with HKS Power Editor)

The graph above displays the power and torque results obtained from the chassis dynamometer. Even when paired with the Power Editor, a maximum torque increase of 12.9 Nm (1.3 kgf-m) at 3200 rpm was verified compared to the stock muffler.

Product refinement and precision
Development began with the concept of an exhaust system that prioritizes three key aspects: performance, sound quality, and appearance.
By incorporating a longer pipe length, a departure from the conventional design, we successfully minimized muffled sounds and accentuated a sporty high-frequency tone around 500 Hz. Additionally, utilizing four 45 mm pipes enhances the cross-sectional area, thereby improving both performance and sound quality.
Attention to detail was paramount in the design of the rear view. A symmetrical four-pipe cannon configuration, strategically positioned hook and bracket protrusions, and an intermediate pipe layout engineered to maximize floor space utilization were implemented. This meticulous design ensures minimal ground clearance while delivering a striking quad-tip appearance.

TIG welding is extensively employed in crafting the main silencer, ensuring precision and durability. Furthermore, the titanium tail undergoes a meticulous baking process to achieve a stunning gradation effect. These intricate designs are meticulously executed by skilled craftsmen, all done by hand, ensuring each product meets the highest standards of quality and aesthetics.

HKS has dedicated ourselves to perfecting even the smallest details, ensuring that you can enjoy our LEGAMAX Sports muffler for years to come, no matter the situation. We sincerely hope you derive immense satisfaction from your experience with our product.