There are a few things to consider when jump-starting a car with a different engine size. The most important factor is the battery voltage. A 4 cylinder engine typically has a lower battery voltage than a V8 engine, so it may not have enough power to start the V8. Another thing to consider is the amperage output of the alternator. A 4 cylinder engine will have a lower amperage output than a V8, so it may not be able to charge the battery as quickly. Finally, you need to make sure that the jumper cables are long enough to reach from one battery to the other. If they are too short, they will not be able to transfer enough power to jump-start the car.