If you want my honest opinion Paz here it is
If you are gonna go with bike engine then get the Hayabusa engine kit car such as westfields Megabusa, or same engine fitted to other type of kit car.
Reason being they are by far the strongest bike engine on the market and if correctly built and baffled properly can produce huge power with reliability. If your a complete and utter loon then bolt a 3071r on one and make well over 450bhp in a car weighing around 450kg with your arse scraping nearly on the floor its scary scary stuff unless of course you don't care about an early appointment with the grim reaper
I loved my one on the track, nearest thing youll get to the thrills a bike will give you and you7 feel pain at end of day with neck ache and general aches & pains as you need to work the car hard but get it right and corner speed you can carry is Amazing with slicks fitted but get it wrong in one of these coffins and you run the risk of serious injury as they fold up like a pack of playing cards.
I had to get rid of mine as I was simply too big (fat) for it and pit marshalls refused to let me out in it at Brands hatch as my head was around 10'' higher than the roll hoop and as im a bit broad in the shoulder department my upper body was actually over the edge of the main cockpit which they deemed as a real risk should I have crashed lol. Height of hoop I could have sorted but nothing I could do regarding the width unless I took an axe to my upper body.
So before you buy anything make sure you will actually fit in it
freeze your nuts off in the winter
nightmare in the wet as slide all over the place
feel very vunerable on normal road driving as even a new shape Mini looks like an arctic as your so low down
if you wear a helmet driving round town or open roads with one of these cars then you will feel like a right cock as people point at you and you get comments such as think your the stig, what a #anker
but drive without a lid on and get your face pasted in bug flesh and can tell you first hand it fooking hurts when a bee spanks you in the gob or car in front flicks up a stone and smacks you in the face
so choice of 2 evils really.
very very juicy with bike engine screaming at 13k off the limiter, I was forever putting fuel in it and worked out i was getting around 4mpg on track bouncing it off limiter
depending on rear diff fitted will top out at around 125mph as many use freelander diffs and on a track with long straights the big boys will eat you up and spit you out, but youll have last laugh soon as you hit the twistys
So overall.........Brilliant fun on a dry trackday or drifting in the wet but anything other than that they are just not practical in any way shape or form which is why i flogged it.
If the bike engine with sequential shift isn't your scene then go for something car engine based such as vaushall redtop or fords 1.7 crossflow with twin 45s which will be more manageable and easy to live with and save your ears from bleeding into your lid HaHa
Good luck with your search, heres a couple pics of my old one (do miss it if im honest)