I was in the same situation - including considering BMW 4.4 V8
But I want something that won't ruin my future budget like my last project... (I couldn't afford to drive my beast so I had to sell it and it wasn't "nice experience"). That's why I choose BEC way
For me - bike engines pro's are:
MOT, TAX, insurance etc should be cheaper if displacement is the main factor (like in Poland). Not sure how it works in UK or wherever you are
I think it's easier to fit bike engine then BMW R6/V8(
) or Volvo T5 or any big lump... (but you have to install electric reverse or something similiar)
I like bikes - and high rev bike sound in my toy car will be sweet addition.
They are con's of course:
Bike engine kit is usually more expensive than car engine (but it depends what car engine you compare to)
You will need specific BEC parts like sprocket adapter, baffle plate, electric reverse etc.
It's harder to IVA/SVA BEC - bike engines aren't "eco-friendly".