I have an mx5 mk2.5 2005 1.8 vvt . I got a 0.4.3 (not VR Conditioner yet ) and test it with ardu-stim look that working fine. I am planning to turbocharge my car and I was thinking to do a piggyback setup the reason is I want most of the stock stuff to work "alternator control, fuel pump , radiator fan" without big drama. I ask in a FB group but they were very negative I don't really understand why. So my plan was to leave the stock ECU in place and give the speeduino all inputs from the sensors plus what needs extra and allow speeduino to control injectors and Ignition.
Any thoughts what can be a problem, what can't work as expected?