Previously, an initial investigation examined the effect of the catalytic substrate on the gas dynamics of the blowdown pulse on the QUB single shot rig. This initial investigation measured the resulting waves from the catalytic converter in the exhaust pipe. In this early study the substrate was at ambient temperature but it is recognised that after light-off higher reaction temperatures will result from the exothermic nature of exhaust gas oxidation and reduction. Therefore substantially different results will occur.This paper details a series of experiments which investigate the influence of an operating catalyst on the unsteady gas dynamics in an exhaust system using the QUB single shot rig. In addition to measuring the effect of temperature on the gas dynamics previous work is reviewed with emphasis now on specifically measuring the features present rather than having to decipher superimposed pressure traces. As an aid to those involved with implementing catalytic devices, several substrates are evaluated with respect to their physical and geometrical properties. The results of pressure pulses passing through a substrate at various temperature regimes were investigated to establish the transmission and reflection coefficients.