Deep dive: Throttle Response Model

First introduced with Update 2.0 on selected car classes, and then further expanded with Update 2.0.0.2, Project Motor Racing took a significant step forward in how throttle response and engine behaviour are simulated. This isn’t just a technical improvement; it’s a fundamental shift in how the car communicates with the driver.

From Input to Output: A More Realistic Model

To achieve this, we analysed real-world data measuring how engines produce torque and power relative to throttle input. From that, we developed an approximation model that closely matches these behaviours across the full RPM range.

Real Engines Are Not Linear

Real engines are inherently non-linear. At partial throttle, power delivery does not scale directly with input, and this behaviour changes depending on RPM. Previously, engines could continue to rev towards redline even under light throttle — something that does not reflect real-world behaviour.

Real-world throttle vs power curve—note the non-linear relationship between input and output.

What’s Changed in Update 2.0

The updated system introduces a more accurate mapping between throttle input and torque output. This allows for sharper response at lower RPM and a more progressive, controlled delivery as revs rise.

Old throttle response. Our old system gave something like this when tested at around 60% rpm.

New throttle response: changes with starting RPM.

With update 2.0, we got more like this. You can see that 50% throttle output already gives you over 70% of the power you're going to get at that specific rpm. At higher RPM it gets somewhat more towards linear, but overall, you tend to get more percentage of power than percentage of throttle still. This all means that as you step on the throttle, you get power earlier, sharper, through the travel.

Bringing Engine Character to Life

This system moves beyond a one-size-fits-all model. Each engine can now express its own mechanical identity, from the lazy throttle behaviour of the BMW 320 Turbo Group 5 small inline 4 engine with a turbo bigger than a house, to the instant reactions of the naturally aspirated rotary engine of the Mazda RX-7 GTO and the modern delivery of a car in the GT500 EVO class.

Turbo response example: How torque and power grow as the turbo spools up, compared to steady state.

Throttle response example: how power builds progressively with throttle input.

This graph shows how throttle response changes with starting RPM. The orange line is at 2500 rpm, and you can see that 25% throttle already gives almost 60% of the total power available at that low RPM. At higher RPM, the behaviour trends somewhat closer to linear, but overall, the engine still tends to deliver a greater percentage of power than the percentage of throttle input. In practice, this means that when you step on the throttle, power arrives earlier and more sharply through the pedal travel. The high RPM results go below the 0% power line because of curve smoothing on the graph but also tell you that you'd be getting engine braking at low throttle and high rpm.

What You’ll Feel On Track

On track, this translates into stronger response at lower RPM, a more intuitive connection between throttle and acceleration, and greater control when managing traction. It becomes easier to balance the car, particularly on corner exit.

Try It Yourself

Even when stationary, the difference is clear. Rev the engine and notice how quickly it responds and how precisely you can now hold a specific RPM. That same control carries directly into driving situations.

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