All manufacturers of diesel vehicles (4-wheelers or higher) claim that the engine of theirvehicle would work at better efficiency if the owners follow the recommendations given intheir instruction manuals. There remains different mileage figure for the same capacity ofvehicle engine designed by different manufacturers. They would also not part with theirknow-how in order to prevent others from working on it. An alternative which can be thoughtof as a means to increase the engine efficiency is to preheat the fuel before it goes to engine.Though this contributes to the purpose, but needs inputs of extra energy. As this does notincrease efficiency to an appreciable extent, this is not a viable proposition. However, as perthis present invention, it has been found that a lot of scope still exists for further improvingthe engine efficiency. Herein new designs have been worked out in order to further increasevehicle diesel engine efficiency. There have been considered two modes of increasing theefficiency of vehicle diesel engines- viz. (i) by internal recovery/conserving of heat byredesign of silencer in order to utilise it back in the engine and (ii) by designing the optimumadvance of fuel injection; these two together leading to 11-15 % increase in engineefficiency.