40 CFR § 86.508-78 - Dynamometer.

---
identifier: "/us/cfr/t40/s86.508-78"
source: "ecfr"
legal_status: "authoritative_unofficial"
title: "40 CFR § 86.508-78 - Dynamometer."
title_number: 40
title_name: "Protection of Environment"
section_number: "86.508-78"
section_name: "Dynamometer."
chapter_name: "ENVIRONMENTAL PROTECTION AGENCY"
subchapter_number: "C"
subchapter_name: "AIR PROGRAMS"
part_number: "86"
part_name: "CONTROL OF EMISSIONS FROM NEW AND IN-USE HIGHWAY VEHICLES AND ENGINES"
positive_law: false
currency: "2026-03-24"
last_updated: "2026-03-24"
format_version: "1.1.0"
generator: "[email protected]"
authority: "42 U.S.C. 7401-7671q."
cfr_part: "86"
---


# 86.508-78 Dynamometer.

(a) The dynamometer shall have a single roll with a diameter of at least 0.400 metre.

(b) The dynamometer shall be equipped with a roll revolution counter for measuring actual distance traveled.

(c) Flywheels or other means shall be used to stimulate the inertia specified in § 86.529.

(d) A variable speed cooling blower shall direct air to the vehicle. The blower outlet shall be at least 0.40 m 
<sup>2</sup> (4.31 ft 
<sup>2</sup>) and shall be squarely positioned between 0.3 m (0.98 ft) and 0.45 m (1.48 ft) in front of the vehicle's front wheel. The velocity of the air at the blower outlet shall be within the following limits (as a function of roll speed):

| Actual roll speed | Allowable cooling air speed |
| --- | --- |
| 0 km/h to 5 km/h | 0 km/h to 10 km/h. |
| 5 km/h to 10 km/h | 0 km/h to roll speed + 5 km/h. |
| 10 km/h to 50 km/h | Roll speed ±5 km/h. |
| 50 km/h to 70 km/h | Roll speed ±10 pct. |
| Above 70 km/h | At least 63 km/h. |

(e) The dynamometer shall comply with the tolerances in § 86.529.

[42 FR 1137, Jan. 5, 1977, as amended at 42 FR 56738, Oct. 28, 1977]