A Stirling engine cycle combined with a SI engine cycle to recover the SI engine exhaust gas waste heat. One dimensional combustion simulation code is prepared for Spark Ignition type engine (M355G) simulation. The accuracy of numerical simulated results has been validated with M355G experimentally. The experimental generated power and exhaust gas temperature vary in the range of 84.1- 176.7 kW and 610-710 , respectively. The 1D code estimates the generated power with maximum 5.9% error and average exhaust gas temperature with 3.8% error in the operating range of the engine. The thermal analysis is done, and the results show that about 25% the part of input energy transfers by the exhaust gas as a waste. The results indicate that by installing a Stirling engine heater on the exhaust pipe of the SI engine can recover about 8.4kW of the waste heat at the best condition. The simulation of Alpha-type Stirling engine is done by GT-Suit program and the Solo V161 experimental results is used for the validation. According to 9% error in generated power calculation for validation, the new Stirling engine is suggested for installing in exhaust pipe. The generated power and thermal efficiency is estimated for Stirling engine in various exhaust gas temperature which occurred in various SI engine working condition. The coupled engines heat balance showed that the thermal efficiency is about 2-3% more than the ordinary one.