1) First question is the same as that i asked from @storm bhai. If turbos can increase performance, why a turbo charged 1800cc Honda motor lacks in torque compared to Toyota V8 engine? Or am i again missing a lot of factors? If I am, please consider them same for both engines (if thatās possible). And whatās the story behind the replacement for displacement statement if you CAN get more torque and hp from lesser displacement engine by modifying it accordingly.
A1) Well, letās consider Toyotaās legendary 1UZ-FE engine. The fully developed versions of this 4 liter V8 engine with VVT-i had approximately 300 bhp @6000 rpm and about 300 lb-ft @ 4,000 rpm. Please note that I am not using exact figures here.
Now, how would this compare with a small turbocharged engine, developing 433 lb-ft of torque and 812 bhp? You should then consider that the torque and horsepower peaks for this engine are at 9,750 rpm. Can you guess the capacity? Only 1.5 liters. Can you guess the engine? This is nearly a quarter century old design by BMW that was used in the 1986 Formula F1 racing cars. Later versions went on to develop over 1200 bhp for races.
Similarly, an 1800 cc Honda motor can be developed to produce even higher levels of torque and horsepower. What you are missing are three things: cost, durability, and reliability. It will cost much more to develop a smaller motor to develop high levels of output. Then, the engine will likely have a short life span, typically no more than a race or two, including qualifying, may be less than 1,000 miles only. Even to get that kind of mileage, you will have to service it after every run with a partial strip down.
That obviously will be painful on many levels in real life out on the road.
Therefore, the story behind the āno replacement for displacementā saying is this: it is the least expensive way to get big, reliable and durable output from an engine. Sure, you can develop a smaller engine to do the same job, but these issues have to be kept in mind.
Now you can begin to see why Storm likes his engines big and slow and torquey.
2) So as far as Iāve understood at the moment is that torque is what once pushes your car and hp is what supports that PUSH. Everything else considered same, a faster car on a track will be the one with proper mix of hp and torque. A car with more hp but less torque might accelerate faster after its in motion but will be slow on the launch, and a car with more torque and lesser hp will be quicker on launch but will get slow after sometime. But there are factors like where does the peak torque comes in for both cars and how much revs the engine is doing etc. etc..... correct? Somewhat?
A2) You are thinking along the correct lines, but there are things like power to weight ratio, traction, type of transmission, gear ratios in each gear used, type of shifting between gears that will effect the outcome greatly. Assuming everything else is the same between cars, your concept is basically correct.
3) If I let you drive a car, you donāt know which engine it has, petrol or diesel, how many hp how much torque etc etc. You are just allowed to drive and test the car. Is there any way you can determine that the car has more torque or more hp? Or is there anything you can anticipate about the specs of the engine just by driving it? Is there any way to FEEL the power?
A3) I would do the following:
In a legal and safe way, make a little test run area. Mark out exactly one quarter of a mile (1320 feet). Weigh the car with a full load of fuel and driver (you can do this at a commercial place that weighs trucks, or place four weight scales under each tire simultaneously, or just use a published figure and add the weight of the driver for an estimate). Start an acceleration run through this distance. When you are crossing the end line, note your speed at that point.
Now use this formula to get an estimate of bhp at the wheels:
Horsepower = Weight x [(speed/234)^3]
For example, for a car that weighs 3200 lbs, and is travelling at 111 mph at the end of the quarter mile run:
Horsepower = 3200 x [(111/234)^3] = 341 bhp approximately.
Now consider the type of transmission and estimate the drivetrain losses at about 15% for a manual and 20% for an automatic gearbox. Correct for an additional 5% loss if the vehicle is four wheel drive.
Thus for the example, with a rear wheel drive manual car, the peak output of the engine is about 392 bhp. Now one can easily calculate peak torque as well, using the redline as the assumed point of peak output for both.
For the shape of the horsepower and torque curves, you can try different runs with shifts at a selected rpm point and repeat the calculations to get output at that point.
Lastly, the best way to feel the power is through a carefully calibrated human butt dynamometer, but this is a highly specialized instrument. 
