Best way to calculate engine RPM based on RPM, not speed ?

so im trying to make a racing game using unreal engine 5. I managed to get pretty far in an abandoned ue4 project and in it, the vehicles were capable of getting an accurate RPM from Get RPM node. But when i do this in ue5 the RPM seems to be based on the foreword speed.

What’s the best way to calculate an accurate RPM based on the actual engine rpm not the wheel rpm?

Thanks in advance-