Code of Colorado Regulations
1000 - Department of Public Health and Environment
1001 - Air Quality Control Commission
5 CCR 1001-13 - REGULATION NUMBER 11 MOTOR VEHICLE EMISSIONS INSPECTION PROGRAM
Part C - Inspection Procedures and Requirements for Exhaust Emissions, Fuel Evaporation Control, Visible Smoke Emissions, Emissions Control Systems, On-Board Diagnostics (OBD); and Practices to Ensure Proper Emissions Related Adjustments and Repairs
Section 5 CCR 1001-13-C-XI - ENGINE CHANGES

XI.A. Pursuant to § 42-4-307, a replacement engine or powertrain, and the required emissions control equipment, computer management systems and vehicle test types shall be determined by the Division's Emissions Technical Center personnel based upon the vintage of the vehicle engine and compliance with tampering statutes § 42-4-314 and § 25-7-144. An affidavit (Vehicle Evaluation Form DR2365), shall be issued by the Emissions Technical Center personnel specifying the year of the engine and associated emissions control system requirements. Note: An engine built from a new replacement block that otherwise resembles or is built to original specifications is considered to be the year the engine resembles, and therefore does not require an engine change verification form DR2365 to be tested by the contractor.

XI.B. For those OBD II vehicles in which the original engine type has been changed, the emissions limits and applicable emissions control equipment for the certification level of the new engine test group package apply. Only an equal or tighter certification test group can be installed.

XI.C. For those vehicles which have been converted to operate on fuel(s) other than the original fuel type; the applicable emissions control equipment for the test group of the new fuel type powered engine equivalent as originally manufactured, for the vehicle body/chassis, per the registration or replacement engine configuration, will be determined by Emissions Technical Center personnel.

XI.D. For those vehicles registered as model year 1975 and newer, that were assembled by other than a licensed manufacturer such as kit-cars, registered according to section § 42-6-117, and assigned a special State identification number, the applicable emissions control equipment and limits will be based upon a determination by Emissions Technical Center personnel of the vintage of the vehicle engine. An affidavit (DR2365) shall be issued by the Emissions Technical Center personnel (ETC Technician) specifying the year of the engine and shall be presumed to be that stated by the vehicle owner unless it is determined by state Emissions Technical Center personnel or designee, after physical inspection of the vehicle engine, that the year of the engine/fuel system is other than stated by the owner.