STONE’s Valvetronic Cat-Back Exhaust Explained

Published in

Stone Exhaust USA

5 min readDec 17, 2021

This write-up is a deep dive into STONE’s valvetronic cat-back systems. We will be exploring each process and component in the fabrication of each STONE exhaust system.

STONE valvetronic cat-back systems replace the stock exhaust all the way from the catalytic converters to the tailpipes. The overall benefits of the valvetronic cat-back is to maximize airflow and performance whilst creating an exhaust that looks and sounds best in class.

What Material Do We Use? Stainless steel vs. Titanium

A quick search would tell you there are an array of materials exhaust manufacturers can choose from when building their exhaust systems.

For us, longevity is a factor largely weighed in when fabricating our systems.

For our exhausts, STONE uses premium quality T304 Stainless Steel. This stainless steel is an iron-based alloy containing 18% chromium and 8% nickel. The element of chromium added to the composition enhances the metal’s oxidation resistance levels by a steep notch. This metal is utilized in our exhausts as it endures turbulence, high temperature, prevents corrosion, and resists rust. Apart from that, it absorbs harmful micro particles to improve both flow and inhibit premature aging of the exhaust.

Comparisons show that titanium is perceived as the stronger of the two materials. However, it is not what we see fit for our exhausts. Titanium is susceptible to corrosion and carries an impending maintenance cost. It is common to see cracks appearing in titanium exhausts. There are several reasons for this; one potential reason is the rapid cooling and heating of the material during fabrication or the result of poor welding processes in the factory, causing an internal injury that later manifested as visible cracks in the external surface of the exhaust system.

However, there are many who appreciate the idea of the titanium element in their exhaust. Hence for those who love titanium, STONE offers tailpipe options like titanium blue, gloss and matt carbon fiber, chrome black, and more to accommodate individual preferences.

Production Process — Reverse Engineering & 3D Scanning

Take a step back. Before an exhaust is manufactured, our engineers scan OEM car parts to make sense of the parts and analyze factors like the pipe diameter, route, and degrees of the bending angles. We basically reverse engineer and 3D scan, to lay the foundations in our exhausts’ development cycle.

During prototyping, we tap into 3D simulation software to simulate the exhaust gas flow, thermal and pressure rise zone. This insight aids in discovering solutions to potential weak points and to implement changes in the design until we find an optimal build. This helps rectify any margin of error and ensure the exhaust is 100% OEM fitment.

During prototyping, we tap into 3D simulation software to simulate the exhaust gas flow movement and thermal and pressure rise zone. This insight aids in discovering solutions to potential weak points and to implement changes in the design until we find an optimal build. This helps rectify any margin of error and ensure the exhaust is 100% OEM fitment.

Mechanical Welding Arm

Among our most important features in our production process is our mechanical welding arm.

Mechanical welding arms are a notable investment because of their capacity to successfully establish precision and penetration compared to manual welding. Our engineers monitor direct spot welding using the mechanical welding arm for the exhausts’ durability. We take careful measures to ensure every exhaust component is mechanically welded by the arm to avoid cracks and to increase the life span of the exhaust.

Crisscross and Overlapping Welding Technique

Besides that, the flange between the turbo and the downpipes reaches extreme temperatures (800℃ to 1100℃) which creates stress on the connection point. By utilizing crisscross and overlapping welding techniques to increase the width and penetration of welds, we vamp up the endurance and tolerance of these connection points.

7-Axis CNC Bending Machine

Have you heard of the 7-axis CNC Bending Machine?

It is the prized machine in the aerospace and defense industries to achieve levels of precision. STONE uses this because it is powerful in its operational abilities and potential to achieve a desired geometric form in the exhaust.

Incorporating this machine into our production process has helped prohibit airflow obstruction and welding fracture issues. Moreover, this machine has enabled us to surpass the industry’s standard to a 98% roundness with an accuracy error of under 0.025mm as well as to maintain the wear of the outer bore at only 25% at 180°.

Valvetronic System

Our in-house valvetronic system forgoes the conventional design of complicated wiring and rubber inside the valve which is prone to aging.

This valvetronic cat-back system is easily installed by connecting it to the vehicle’s OBD-2 port.

If you opt for the valvetronic system, the remote control comes with three modes: ON, OFF, and AUTO. The ON and OFF buttons allow users to switch modes instantly while the AUTO mode has a predefined RPM based on on-road tests which allows users to customize the valves to open and close automatically based on the RPM they set. For example, you can set the AUTO to 4000 rpm. The valves will open when it reaches 4000 rpm but once it drops below 4000rpm, the valves will automatically close.