This is an example taken from from a draft coppy of the new IVA manual.
Probably the same requirements as SVA.
Application:Vehicles subject to Basic requirements Method of Inspection
This inspection applies to the exhaust system fitted to the engine which provides the motive power for the vehicle. In the case of a motor caravan, ambulance or hearse with a base vehicle approval, modification to the exhaust system length after the rear silencer not exceeding 2m in length are permissible without further test In the case of a motor caravan, ambulance or hearse the requirements according to the category of the base or incomplete vehicle based on maximum mass may apply. Using sound level meter to the manufacturer’s instructions, carry out a stationary noise check.
Position the vehicle within the authorised test area. With the sound meter horizontal, set the microphone height so that it is at the height of the exhaust outlet or 200mm from the ground, whichever is higher.
a. At an angle of 45 degrees to the exhaust outlet in the direction which gives the greatest distance between it and the vehicle contour
b. At a distance of 500mm from the exhaust outlet. With the vehicle at normal operating temperature, run the engine at ¾ of its ‘maximum power’ speed, and note the sound level reading obtained. Note 1: Manufacturers drain holes are permitted in silencers
must be securely mounted.
must have all componentssecure.
must not leak. See note 1
must be fitted with a silencer.
must have a measured sound level not exceeding 99dbA.
I hope this is of some help.