This paper presents an experimental analysis on the effect of thermal insulation of engine internal walls on the performance and emissions of a heavy-duty diesel engine. Some parts of the engine, like pistons, cylinder head and exhaust manifold were thermally insulated from gas contact side in order to reduce heat losses through the walls. Each component has been analyzed, independently, and in combination with others. The results have been compared with that of the original engine configuration. The analysis focuses on NOx and, smoke emissions along with brake specific fuel consumption. In order to take advantage of the engine insulation, an optimization of the air management and injection settings was finally performed, which provided the best combination for each engine configuration. The results showed that, on the one hand maintaining the same level of NOx, soot emissions is reduced using insulated cylinder head and insulated pistons, but these configurations increase the fuel consumption. On the other hand the specific fuel consumption is reduced using insulated exhaust manifolds, being this the only configuration that improves both NOx-Soot and NOx-BSFC tradeoff.