t will be very difficult to build without engine maps, because you need to know the characteristics of each node, the temperature in each section. Some of the information can of course be found on the internet at the engine manufacturer's website.

The performance simulation of an aero-engine model requires design and off-design points. For the design point (DP) calculation, the component maps are not used but scale factors are calculated instead for scaling of the maps during subsequent off-design (OD) calculations. The DP is necessary before the steady-state or transient OD simulation because it is used as the reference point for the OD calculation. In conclusion, to precisely estimate the gas turbine engine performance, the component maps containing the performance characteristics must be used.

There are different approaches that can be followed to model the performance of a turbojet. Mostly, it depends on the application. This paper can help you understand the different modeling schemes that are available in the literature and some of the particular applications where they out stand: Article Experimental Evaluation of Different Microturbojet EGT Model...

Moreover, if you have further questions on the regard of physics-based modeling or data-based modeling just send me a message and I will help you solve your doubts.