So I've been trying to figure out a few things. How do you figure out how much an engine can theoretically put out for torque, horse power and RPM. What is it that gives it those numbers? Stroke? Displacement? Through my reading I did discover that the Octane you should use is regulated by the compression ratio, that's pretty neat.
I've been trying to look it up but all I can really find is HP=RPMxTorque/5252. Ok, so how do you find torque?
Well torque=HPx5252/RPM.
I do performance research & development on diesel engines as a MechE.
Torque is best measured by a steady state dyno. The engine spins, the dyno resists that torque (water brake, eddy current, electric motor, etc). That resistance pushes against a load cell (which is calibrated regularly using traceable standards.) The load cell puts out an electric signal is recorded by a computer.
Torque = Force x Lever arm distance
Force is measured by the load cell - electric signal.
Lever arm distance is a measured constant.
Power = Torque x Rotational velocity
Torque is calculated from the above.
Rotation velocity is engine speed converted to proper units. This is also measured.
Now you have the measure of engine power.
The next question is much more difficult. The power of an engine is dependent on 1 - how much fuel it can consume, 2 - the energy content of the fuel, and 3 - how efficiently is converts that chemical/heat energy into mechanical energy.
1 - depends on what kind of engine. Gasoline runs close to stoichimetric, diesel runs very lean. In either case, these engines are generally limited by available air for combustion.
So for the same displacement, a diesel will run less fuel. A turbo can increase the airflow. Displacement increases the airflow. Improved head, port, and manifold flows will improve volumetric efficiency and thus a little bit of air and decrease pumping losses. Increased engine speed will increase airflow (but has the side affect of increased friction power).
2 - Except for multi-fuel engines this is pretty consistent. Be careful that energy by mass and energy by volume can be very different. Hydrogen has best energy/mass and worst energy/volume. Diesel has very good energy/volume but lower energy/mass.
3 - Injection timing, ignition timing, compression ratio, pumping losses, engine friction, heat rejection characteristics, etc interact to affect this last and essential parameter. Typical high speed diesel thermal efficiency peaks at ~42%. Gasoline peaks ~38%. Gas turbines peak ~35%. Of course it all depends on engine size and design details. For all engines, the thermal efficiency goes to 0% as it goes to idle.