The subject of this paper is quenching effects in the piston top land crevice of a SI engine. The influence of this crevice geometry on HC-emissions and on flame propagation phenomena into this area is examined using the multi optical-fiber measurement technique.Examinations of HC-emission and flame propagations into the piston top land crevice have been carried out during transient engine operation as well as warm steady state running conditions. These results will be presented and the observed phenomena will be discussed in detail. The possibility to reduce raw emissions by varying the piston crown geometry will be proved. An estimation of the potential for a reduction of hydrocarbon raw emissions will be given in order to enable development engineers to reduce the pollutant emissions of SI engines with higher efficiency.