This can vary from car to car and product to product. Modern ECU’s are incredibly advanced and make the necessary adjustments automatically for proper drivability. As a rule of thumb, none of our catback exhaust systems require an ECU tune, and none of our exhaust products that include our HJS 200 cell catalytic converters require an ECU tune. It is only when you delete the catalytic converters (for competition use only of course…) that you enter a scenario where you could consider an ECU tune “required” though it could be for different things. When running catless, an ECU tune is required to conclusively prevent a check engine light from coming on. Some people choose to try oxygen sensor spacers to turn off this check engine light, but results vary with this method. Running catless without an ECU tune on most modern cars has shown to still maintain proper drivability. An exception to this that we have found is the 718 generation Boxster/Cayman and McLarens, which running catless on requires a tune to prevent boost spiking/surging under hard acceleration.
That said, an ECU tune is required to maximize the performance potential of any given vehicle and exhaust combination. Most cars are detuned (restricted via software) or tuned conservatively from factory. There is always room left on the table with the factory software (especially when freeing up the exhaust flow) that an ECU tune can take advantage of. If you would like to review ECU tuning for your specific vehicle and upgrades, please give us a call and we will ensure you make an educated decision.