Does anyone know how many amps the engine draws minus the starter eg ecu, sensors, bcm injectors cuz I wanna fit a large relay to turn it on and off

What exactly are you trying to add a relay to? What circuit?

I'm using the rx8 ecu for the electronic power steering, abs and lights and cab stuff, ones I've put the key in and turned to power irl find a live feed that will switch the relay on to power the gm ecu and all engine functions

What ever you are powering through the relay you just need to add up each circuits current load to determine what amp relay to use.

Yes that'* wat I'm asking I need the information

I'd suggest looking at a fuse block diagram for the donor car. Take the current ratings for the fuses of each circuit that you want to include and add them up.

That'* a huge load for a single relay. You will have to divide the load across 2 or more relays.

OK that'* no problem I have bought a 200a relay, pluss a 170a and lots of 40a should be able to spread load evenly does anyone know of free flashing or remapping software I can get pluss the leads to rewrite ecu

No such thing as free software. You will need HPTuners to do what you want. $500. There is no work around with this. Period. I wouldn't trust EFIlive as far as I could throw it.

You would need to make your own OBD2 16 pin connector. You will only need 4 wires I believe. CAN high, CAN low, BATT, GRND.

Free???? Let us know how that works.