hi all
I have long contemplated a Mazda rx8 and doing an engine swap , probably 2.3 ecoboost
the other option was an LS3 in a porche boxster , and yes they do fit.

? to all

1) apart from insurance do I have to tell inform any one
2) do I need an sva test
3) if the new engine has a lower emission's than the standard engine does this cut the road tax

any help would help my pondering.

No expert, but I think the rules regarding testing and inspection of the vehicle are governed by whether any structural modifications have been made to the chassis. Both the RX8 and Boxster being monocoque this may be a slightly grey area.

There's a chap on here fitting an Audi 1.8T into an RX8 - forget his username, but he may well know the legalities better than I do.

Think this is the user...

john-t5

thanks for that

So long as there are no changes to the body structure ie cutting bulkheads etc then you are unlikely to need an IVA.
You will need to inform the DVLA and provide proof of the engine change and that you rightfully own the engine you have fitted.
Your insurance will probably want an engineers report.
The replacement engine will need to meet the same exhaust emissions requirements as the original RX8 engine. As for tax it will remain as for the RX8 unless you want to go the HUGE expense of full emissions certification.
HTH