I can see from your reply that you studies really hard for your exams and I wish you best of luck for results.
Dear ab maza aayay ga koi to mila bahass karnay wala.
Now coming to the point. I do know that its the gears that determine how fast a car goes and almost everybody with some knowledge of cars knows that. The tires getting in contact with road surface is also a sort of gear system. As you have seen as soon as we change the tire size the averages change drastically.
Saying that it is the gear ratios that determine how fast a car can go but what is the limiting factor here. To take it as a simple thing what if you put reborn manual gear in an idsi will it also reach 220 as its top speed and 110 in 2nd gear. I know that you might have though about that sometime as you are also car enthusiast like me.
Coming to the point yes the gear ratios do determine how fast and at what speed a car goes but the most important thing is the torque and bhp figures at a given rpm for a certain car. That is why the bigger the car engine is it can achieve high speeds at lower rpms. Imagine if you put a manual accord gearbox in an idsi will it achieve the same speeds in all the gear. Answer is yes the top speed will be the same in lower gear but the time the car will take to gain speed will be too much given the fact that the car has too low bhp to move at a certain speed.
Let me explain you by an example. Suppose idsi reaches 50km/h in 1st, 90km/h in 2nd, 130km/hr in 3rd, 165km/hr in 4th and 200km/hr in 5th at 6000 rpms. Say if you put the gear box of car that reaches 60km/h in 1st, 110km/h in 2nd, 155km/hr in 3rd, 195km/h in 4th and 230 km/h in 5th at 6000 rpm in an idsi. Now what will happen
The simple effect would be that idsi will have faster and higher top speeds in lower gears up till mid range of 4th gear like say 180-185km/hr because at that speed idsi will run out of bhp's to counter air and road resistance. But another thing will happen. Lets take 2nd gear with stock gear box the car will be at 45km/hr at 3000rpms now with gear box of a faster car it will be running at 55km/hr at 3000rpms. Here the most important thing is how much bhp and torque the car has at 3000 rpms to achieve this much speed. If the has the torque and bhps to move it from 40-45 in 1 second than it will take around 1.5 second to move from 50-55 in 2nd gear at same rpms i.e 3000. I know I am being too complex here but I believe you can understand what I meant to say
Let me sum up the example. Yes the main thing that determines how much speed a car achieves at a certain rpms is its gear ratios but the thing that leads engineers to define those gear ratios is the torque and bhps of the car at certain rpms. Before the advent of computers they used to do it manually by large sheets and huge numbers but now they do it by the means of a computer. There is always a best setting or you can say a perfect combo between the engine and gearbox. If you deviate from that perfect combo you might have higher top speeds in all the gears but the pick up of the car will fall similarly you can reduce the top speeds of the car in a certain gear the pick of the car will be very good.
To understand this thing there is a game called EA sports F1 2004 where you can go to workshop and modify your cars gear by changing the ratios.
Yes it is possible to have a car with a single gear no problem in that but that will require a lot of force to move in first gear and that force will not be provided by the engine but by the clutch plate, in that case we may have to change clutch plate everyday. Remember riding a bicycle if you have to move it from a standstill you know how much force is required, that bicycle only has 1 gear.
About the compression ratios yes they effect how much power the car produce and I have learned that higher the compression ratio the more power the car will produce but you have to keep in mind that there is no detonation or pre ignition.
About the efficiency of engines dear you stated it way to low the petrol engines have efficiency of 55-60% and diesels have an efficiency of 70-75%.
BTW this discussion was meant to be a healthy and no offence meant to anyone
Regards