Saw this on fleabay, anybody got one of these??
I didn’t think the ECU was re-mappable?
I guess if someone has the right gear and knowhow, it wouldn’t be too difficult to re map the prom that holds the fueling map. I would think that gains on a normally aspirated engine would be fairly small though. You have to ask why didn’t Mazda do it from day one, and why aftermarket chippers don’t bother with it?—
I believe that Mines do a remapped ECU for the NA6, but, then again, they will pretty much remap anything 
Ordinarily, the ECU is not re-mappable (AFAIK ECUs of this vintage cannot usually be “flashed” like modern OBD-II ECUs.)
The item listing talks about a raised rev limit and a reduction in fuelling above 4,000RPM. There is a well know mod for these ECUs that involves replacing the oscillator crystal with one of slightly higher frequency. This results in timed events within the ECU appearing shorter than they really are. As a consequence the engine appears to be running slower (causing the rev limiter to take effect at a higher real engine speed) and the injector pulses are shortened (less fuel). Ignition timing is also possibly slightly advanced. Below 4,000RPM the fuelling will be controlled in loopback mode according to the signal sent by the O2 sensor so an adjusted timebase/frequency will have little effect here other than perhaps on phasing of the fuel injector pulses. Small changes in phasing have little or no effect on engine performance where injectors are fired in batch mode (as they are on MX-5s of this vintage).
It is of course possible that the ROM has been replaced with one containing new software and/or fuel and ignition tables, but personally I am inclined to think that this is a crystal mod.
Wow! Niggle, you really know your stuff!
Out of interest, do you know how the ‘cold start’ thermistor works with the ECU? I have head that above 4000rpm it stops interferering with the fuelling? I only ask as I thought I had issues with my ecu Thermistor and thought perhaps above 4000rpm the problem ‘went away’. If you know what I mean?
I don’t know exactly how the Mazda ECU software works, but assuming that it uses widely accepted principles that are commonly used for EFI systems then IMHO it is indeed reasonable to assume that the temperature correction applied by the ECU via readings obtained from the water temperature sensor (thermistor) might not be applied in open loop mode (above 4,000 RPM and/or at Wide Open Throttle).
Cheers niggle.
I do hope you won’t be invoicing me for such valuable knowledge??? 
Certainly not, mate. That’s not what Forums are for, surely?
a company in japan called “grid” remap standard ecus by using a daughterboard and eprom chip
not very common , but i have some links for quite a few site where owners have tinkered with the ign timing maps and fuelling for differnt torque type stuffs.
its all too techie for me in fairness