In the existing consequence bio-diesels have established a lot of consideration as an alternate fuel for internal combustion engines. Though properties of bio-diesels aren't alike conventional CI engine fuels predominantly their higher value of viscosity and lower volatility. In accumulation the bio-diesels have poor atomization individualities due to diminished CA at the time of fuel injection. This paper emphasizes the adaptation of internal burning engine combustion chamber structure, for promoting whirl to get better the burning of mixture. An assessment of works indicates that investigational studies haven't accompanied on a specially modified piston for appraising at a persistent speed of 1500 revolutions per minute and compression ratio (CR) of 17.50 at 250 bar injection pressure (IP) and advance injection timing too. The performance considerations viz... Specific fuel consumption (SFC), brake thermal eff. (BTH), carbon monoxide (CO), oxides of nitrogen (NOx) and unburnt hydro carbons have been studied. The aim of this effort is to analyse the effect of cylinder structure on burning and exhaust gas emissions of a bio-diesel (Simorouba) fuelled specially modified piston conventional diesel engine. It is observed that for the IC engine with personalised piston contributes optimal performance. This exertion is to overview the effect of specially modified piston on burning, performance parameters and engine exhaust emissions of a bio-diesel (Simorouba) fuelled specially modified piston conventional diesel engine. It is being observed that for the internal combustion engine under contemplation with specially modified piston gives optimal performance.