The phrase "steel exhaust" refers to the part of a vehicle's system that releases gases produced during combustion. It means that the exhaust is made using steel material. Full definition
The new stainless steel exhaust system is less restrictive, which allows exhaust gases to flow out with less pressure. (articles.orlandosentinel.com)
On stainless steel exhaust systems: What makes of car typically have that, at least as a common option? (mechanics.stackexchange.com)
Design details like chrome accents and dual stainless steel exhaust tips add a confident flair while the newly designed headlamps and tail lamps leave a lasting impression, coming and going. (bakermotorcompany.com)