• Bernoulli pressure drop calculations

On the intake side of the engine, airflow velocities are calculated using a modified bernoulli equation. Once the velocities are known, the pressure drop across each restriction point in the intake system is calculated and contributed towards the final horsepower figure.

• Cylinder filling index

Peak power is optimally found at the perfect balance between pressure drop and flow velocity (cylinder filling). A cylinder filling index is calculated based on the flow velocities previously calculated in the Bernoulli pressure drop stage. Correcting for cylinder filling prevents the typical ‘bigger is better’ mentality and shows the power differences between optimally sized and oversized engine parts in the lower rpm ranges.

• Tuned pipe length resonance tuning

Exhaust header primary pipes are analyzed using a resonant pipe equations. The equation corrects for the effect of exhaust gas temperatures on both acoustic velocity and on air density. EGT’s are calculated internally based on engine demand and how aggressive the build up is and the final temperature used in the calculation takes into account the header pipe length and the average temperature drop acorss that length of pipe.

• 2 spring , 2 mass damper modeling

Intake manifold 1st and 2nd order resonant peaks are modeled using a 2 spring & 2 mass system factoring in all air masses and volumes associated with the cylinder, manifold runners, manifold plenum, and intake system or charge pipe.

• Dynamic compression modeling

The piston position is calculated in the bore based on the angularity of the internals (the rod length to stroke ratio). This position in conjunction with the cam duration is used to calculate the effective dynamic compression ratio of the engine which provides a real world balance between increasing flow (with a longer duration camshaft) and a reduced dynamic compression ratio (from shortening the compression stroke due to the longer duartion). This allows the simulation to give a realistic illustration of the tradeoff between flow capacity and compression pressure.

• Compressor & Intercooler thermal efficiency

Based on the compressor type (turbo, centrifugal, roots, screw) and based on the spool rpm, an rpm by rpm boost curve is created inside the model. A 2nd efficiency curve is created factoring into account the compressor efficiency at peak torque and at peak power and extrapolating between those two. A 3rd efficiency curve is created based on the intercooler dimensions and how it compares to an ideal intercooler. All three curves are then combined to create a final rpm by rpm density ratio curve that affects the engine’s final output. Through this process the Virtual Dyno corrects for boost pressure, compressor efficiencies, intercooler efficiencies and spool characteristics giving an ideal result.

• Flow restriction modeling & backpressure

On the exhaust side of the engine a flow restriction model is used to calculate the flow velocity and the associated pressure drop of every part in the system (header pipes, collector outlet, primary & secondary catalytic converters and primary and secondary mufflers as well as the cat-back exhaust piping). The associated pressure drops all contribute towards the final power figure.

• Combustion Duration & Optimal Ignition timing advance

Total combustion duration is calculated based on bore size, dynamic compression pressure, and engine rpm. Ideal timing advance and the power stroke duration (from ignition event to exhaust valve opening) can then be calculated based on the combustion duration. Power delivery is then calculated based on the total amount of power delivered from the combustion chamber force due to combustion pressure over the combustion duration.