The ROUSH CleanTech Propane Autogas Engine is certified to California Air Resources Board's optional low oxides of nitrogen emissions standard for heavy duty engines with 0.02 grams per brake horsepower-hour. The engine is 90 percent cleaner than the current EPA's most stringent 0.2 g/bhp-hr heavy duty engine standard, according to the company. This certification covers all of the company's 6.8L V10 3V propane engines for Class 4 to 7 vehicles.