Thanks for that additional info - I will do another search for a 2.0 engine and if one appears in reasonable condition and it can run ok on the 1.8 ecu he might go for it- I’m happy to fit it but don’t fancy potential ECU hassles as modern electrics are not my area of expertise - I’m more okd school points and plugs
You could do some more research on miata.net about running a 2.0 on a 1,8 ECU, there are more topics about it. And you can’t do anything related to the ECU that I described before, you need someone for it 
At least, if you want to reuse a stock ECU. Shouldn’t be too expensive. I paid about 100 for an ECU, instrument and keys and another 50 to get a dealer to link my original 1.8 keys and instruments to the 2.0 ECU. In the end I didn’t use the new keys and instrument cluster. Haven’t really done anything besides fitting the ecu (nuts/bolts and 1 plug 
).
Also, when it comes to replacing the engine, I have read that if you have the opportunity, swapping it by dropping it from the underside of the car should be easier than getting it out from the top. Probably has something to do with how far the engine sits back.
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Hey, late to the conversation,
I may be in a similar situation needing to replace 1.8l engine. Going for 2L.
My car is currently 1.8l 5 speed nc 2007, if Im swapping in a 2L does it need 6 speed trans swapping too?
Or can I keep in the 5 speed?
Thanks
Gearbox fits, drop your wiring loom, ECU and diff off at the scrapyard though.
If you think it’s cheap and easy think again.
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Bit late to the party. It costed me about 200-300 extra compared to the 1.8. I needed the 2.0 ECU and best would be to use your own dials as that has the original mileage displayed. Perhaps change the background of the RPM dial as the 2.0 has a slightly higher rev limit. Then you need to program the new ECU to work with the immoboliser circuit contained in your instruments. You will need a garage that is capable of doing that, that won’t be just any universal garage. Probably will be either a Mazda specialised universal garage or an official Mazda garage but then it’s a question of wether the mechanic knows what needs to be done and wether they’re willing. In my 1.8 the wiring for VVT was there anyway.
If you know where you can take the car (I assume the UK has some places where it can be done) then it’s really not that difficult. Even better, the 2.0 runs with the 1.8 ECU so even with stock ECU there’s profit to be had. I don’t know where anymore, I think miata.net, but someone compared the mapping for the 1.8 and 2.0 ECU and the only thing that differed was the controlling of VVT. My 2.0 ran fine for several months on my 1.8 ECU. From the start.
Another option would be to get something like Versatuner or so, replacing the stock software of the ECU with after market and having the option to deactivate the immobiliser.
Edit: if going down the Versatuner route, be sure to check out what a 2.5 conversion costs where you live.
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