Mx5 with bike engine

[matt_long247]

Hi guys.
I've decided I'm going to build my roadster based on the mx5 donor.
But I want to use a bike engine - undecided which.
I Haven't decided whether to use the Saturn or vodou design.

Just wondering if anyone else has used a bike engine in a mx5 based one before as I can't find any.
And which design would everyone recommend to use for the chassis and why?
Any other info would be much appreciated.

Thanks in advance.
Matt.

[wylliezx9r]

I used a zx9r with a sierra donor, cant really see how a mx5 donor would be any different apart from the diff ratio. In fact the Mx5 donor parts are lighter so i guess it's better suited.
Im selling everything you would need to get a zx9r in a haynes chassis if your interested at a cheap price. When I say everything I literally mean that. Engine,all the electrics, full custom built manifold and backbox in stainless, airbox, instruments, reverse box, propshafts, radiator, header tank, engine cradle etc etc. Engine made 140 odd bhp on the rollers. Only selling as managed to pick up an S2000 engine cheap.

[matt_long247]

Pm'd :)
Does anyone know the diff ratios for the mx5? preferably the LSD version? Or what other options are available as its looking hard to find a 'cheap' mx5 with the LSD, such as a standard diff and fit a aftermarket LSD with a better suited ratio?

[robo]

Pm'd :)
Does anyone know the diff ratios for the mx5? preferably the LSD version? Or what other options are available as its looking hard to find a 'cheap' mx5 with the LSD, such as a standard diff and fit a aftermarket LSD with a better suited ratio?

I think you might struggle a bit to find a mazda diff with a 3.1 ratio which is what I am led to believe you will need to run a bike engine. It might pay to mongrel the back end to take the sierra diff.

http://www.ebay.co.uk/itm/sierra-differential-3-14-diff-locost-kit-car-caterham-westfield-bec-7-/160908282341?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item2576e189e5

Bob

[matt_long247]

I think you might struggle a bit to find a mazda diff with a 3.1 ratio which is what I am led to believe you will need to run a bike engine. It might pay to mongrel the back end to take the sierra diff.

http://www.ebay.co.uk/itm/sierra-differential-3-14-diff-locost-kit-car-caterham-westfield-bec-7-/160908282341?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item2576e189e5

Bob

yeah thats what i was thinking, although i wasn't keen on the idea as it may cause more problems if i ever decided to put a car engine in, which is why i was wondering if such as quaife make a suitable LSD i could fit?

matt.

[ozzy1]

Why the obsession with LSD? Unless u are racing it seems a bit pointless.

[wylliezx9r]

Hi Matt,

PM'd back.
I'm running a 3.64 LSD in my car at the moment, car tops out about 120 which is near perfect really.

Cheers Dan

[matt_long247]

Why the obsession with LSD? Unless u are racing it seems a bit pointless.

Yeah sorry i forgot to mention that in the original post.
i intend to race it in the 750mc RGB series when i get it finished and on the road :)

[ozzy1]

3.62 is a good ratio for less than 1000cc bike engine.
3.32(?) or 3.14 (i think it is) is suited to the big stuff like R1,Hayabusa etc.
I found that a 3.62 ratio with a zx9 motor was a nice drive,good acceleration and good top end.The 3.92 was manic acceleration but sod all speed in each gear.From memory on the motorway it was screaming its tits off at about 95 mph as was bloody annoying.

[matt_long247]

Its mainly going to be used on the track with occasional road use. So shouldnt hopefully be on the motorway very much.
I've bin doing abit of research and it sounds like 2001-2005 mx5 sports have a 3.6 ratio. If this is correct and the same fitment, then it should be spot on.

[snapper]

If your going to race avoid start would be to find what speed others are getting on the straight.
No point topping out at 110 if others fly past you
Get a gear ratio program then you can find your speed in gears with available diff ratio and tyre size

[matt_long247]

That's a good point I'd not really thought about tbh. Il have to do some more research on the 750 forum on that and try find what ratios others are using for theirs. Im new to the whole kitcar/ racing thing so I'm sure there many other things I may have over looked. Can you think of any other key ones?

[snapper]

Weight
If your running 500Kg and others are 450Kg you've got a lot to make up
Initially though you want to be near enough in weight power and gearing to be in with a chance.
Andy Bates at AB Performance is a great bloke to talk to and will give you some pointers

[matt_long247]

Ill be trying to reduce weight through out the build as much as possible. Luckily I'm only small anyway. Haha. Thanks iv just had a look at his website. Il Definatley give him a ring an see what tips he can share with me.

[PorkChop]

The longest MX5 diff you will find is a 3.6:1.

Your chosen bike engine will play a huge part in if your diff is long enough. I did consider a BEC using MX5 running gear and if you're using a fairly modern bike engine, then a 3.6:1 diff would be long enough (based on the gear ratio calculator I have).

[matt_long247]

i dont suppose you can confirm which models have the 3.6:1 diff?
and its going to be dans zx9r setup i think :)