19 December 2025

 

^{This article is based on an exclusive MoveTheNeedle.news interview with Marelli executives, who explained how LeanExhaust was engineered, why it matters in today’s mixed-powertrain market, and where OEMs are likely to adopt it first.}

As the automotive industry accelerates its push toward lower emissions, higher efficiency and sustainable mobility, even long-established vehicle systems are being re-examined. Automotive exhaust systems, often viewed as mature technologies, are now under renewed pressure to deliver weight reduction, compactness and emissions performance—without compromising durability, noise control or regulatory compliance.

This pressure is intensifying as the industry navigates a prolonged transition period. While internal combustion engines and hybrids will remain in production for years to come, the global shift toward electrification is already reshaping investment priorities, regulatory frameworks and supplier economics. Against that backdrop, exhaust systems are expected to become fewer in number over the long term, while simultaneously becoming more technically complex in the short to medium term.

Marelli’s LeanExhaust system, recently recognised with the Innovations in Lightweighting Award from the Society of Automotive Analysts (SAA), reflects this shift. The award, presented during the 9th Annual Materials Innovation Summit in Auburn Hills, Michigan, highlights supplier technologies that deliver meaningful mass savings in support of the industry’s sustainability goals.

LeanExhaust stood out for achieving significant exhaust lightweighting while maintaining exhaust emissions performance, acoustic behaviour and long-term reliability. According to Marelli, the system reduces exhaust system weight by up to 16 kilograms, contributing to substantial CO₂ reduction across the vehicle lifecycle.

The technology was developed within Marelli’s Green Technologies business, which focuses on solutions that support lower emissions across internal combustion, hybrid and electrified vehicles. That positioning reflects the reality that, even as fully electric vehicles gain share, hybrid architectures are expected to play a central role in many markets—keeping exhaust systems relevant, but under growing scrutiny.

Lightweighting automotive exhaust systems without sacrificing performance

For Masaaki Ashida, Product Management Department Director within Marelli’s Green Technologies business, LeanExhaust’s significance lies in how weight reduction was achieved.

“The key point lies in the fact that, by utilizing proven design and manufacturing technologies that Marelli has cultivated over the years, we have achieved weight reduction without sacrificing exhaust emission performance, noise performance, or durability and reliability.”

That balance is difficult to achieve in automotive exhaust systems, which operate under extreme thermal and mechanical stress while remaining subject to increasingly stringent emissions and noise regulations. As standards tighten globally, exhaust systems must deliver higher performance with less material, leaving little margin for error.

Engineering decisions behind a 16-kilogram exhaust weight reduction

The headline weight saving is the result of multiple engineering decisions rather than a single breakthrough. According to Tadashi Nakasuji, Senior Manager of Engineering in Marelli’s Green Technologies business, material optimisation and system integration were central.

“In addition to using thinner materials and eliminating glass wool, the lightweighting achievements in this solution also include integrating two separate catalytic converters into one and achieving a more compact double-tube structure. And overcoming challenges in the manufacturing process has greatly contributed to making the materials even thinner than before. Of course, tackling these kinds of challenges is also key to realizing new ideas, such as unique dual-layer structure and micro-hole pipes.”

These kinds of changes also reflect broader industry pressures. Rising raw material costs—particularly for metals and catalyst-related materials—are forcing suppliers to reduce material usage while maintaining performance. At the same time, OEMs expect cost competitiveness even as regulatory demands increase, placing additional strain on exhaust system design.

Meeting exhaust noise and emissions regulations in a compact design

Despite its reduced size and weight, LeanExhaust still meets or exceeds applicable emissions and noise standards. Nakasuji emphasises that compliance and durability were core design requirements.

“LeanExhaust was developed precisely with the aim of achieving significant weight reduction, without sacrificing performance, durability and reliability required of exhaust products. Both the unique dual-layer structure installed in Hot end and the micro-hole pipe adopted in Cold end contribute to improved environmental performance by reducing emissions and exhaust noise.”

This focus reflects a broader challenge for the exhaust sector: regulatory thresholds continue to tighten, while the room to add mass, volume or cost continues to shrink.

How LeanExhaust delivers a 52% CO₂ reduction

Marelli states that LeanExhaust contributes to a 52% reduction in carbon emissions compared with exhaust systems currently in production. Nakasuji explains:

“The 52% weight reduction was calculated by comparing the new solution with exhaust systems currently in production.”

The calculation reflects component-level savings and system layout changes.

“For reference, the weight reduction related to the Hot end is 45% and for the main muffler is 27%.”

Such gains are increasingly important as OEMs look for CO₂ reductions not only at the vehicle level, but across individual systems—especially in hybrid vehicles, where incremental efficiency improvements still have a measurable impact.

Designed for hybrid vehicles and electrification-driven packaging constraints

While exhaust innovation is often associated with traditional ICE vehicles, LeanExhaust was developed primarily for hybrid powertrains, including PHEVs (Plug-in Hybrid Electric Vehicles) and HEVs (Hybrid Electric Vehicles). As such, Marelli’s key priorities included weight, compactness and environmental performance—factors increasingly shaped by electrification.

Hybrid vehicles often face tighter packaging constraints as batteries, power electronics and additional cooling systems compete for space. In that context, more compact exhaust systems are becoming a necessity rather than an optimisation.

From an OEM perspective, LeanExhaust delivers advantages in terms of improved energy efficiency, cost effectiveness and sustainability. Reduced material usage supports both cost and sustainability goals, while improved thermal management contributes to fuel efficiency.

The company emphasised that LeanExhaust was developed internally at Marelli, with OEM dialogue guiding technical targets—an approach that reflects the growing need for close supplier–OEM collaboration as system complexity increases.

Ensuring reliability was the primary technical challenge. The company relied heavily on Model-Based Development (MBD) to identify and resolve risks early, particularly as thinner materials and new structures were introduced.

According to Takashi Honjo, Senior Director of Engineering in Marelli’s Green Technologies business, LeanExhaust is already moving toward series production, with Marelli collaborating with several OEMs to bring the technology to market. Initial rollout will focus on C-segment passenger cars, with broader applicability across vehicle segments.

Ashida believes that LeanExhaust will provide Marelli with a strong competitive advantage in the future exhaust business—a market expected to become more challenging. The global transition toward electric vehicles threatens long-term demand for traditional exhaust systems, since battery-electric vehicles do not require them at all. While hybrids and internal combustion engines will persist for years, the overall trajectory points toward shrinking volumes, heightened competition and increased pressure to justify continued investment.

In that environment, innovations such as LeanExhaust illustrate how exhaust suppliers are responding: by making systems lighter, more compact and more efficient, while aligning closely with OEM electrification strategies. For Marelli, the message is clear—exhaust technology may be a mature field, but standing still is no longer an option.