Bike engine, car gearbox. Hypothetically.

[Lefty]

For a really light kit car l, say 500kg. Could you mate a big inline 4 bike engine with a gear pre-selected into a car gearbox?

I'd imagine you'd need to somehow sort a flywheel/clutch. Has this ever been done?

I just watched a video of a z-cars Hayabusa Elise. The bike gearbox just looks a massive pain in the ass and the clutch probably a real weakness.

[Lefty]

I know the Morgan 3 wheeler has an mx5 box but the v-twin would have had a separate transmission in a bike anyway, right?

[Huff]

As a BEC-owner - no, the sequential dog box is one of the great joys of the whole arrangement!
And clutch changes - easy and cheap/quick to arrange if required, because its tucked under one easy-to-access end cover; but mine's now over 24K miles on the original, only £100 in parts and 30mins work if needed; hardly a problem.

The thing you are probably overlooking is that from bike crank to bike gearbox input is a reduction gear anyway. (c.1.5 - 1.6:1 is usual) so, if you wanted to feed the bike engine into a conventional car 'box, you'd likely need a ridiculously short final drive instead to make it all worthwhile, else you'll end up with too high gearing to get the thing into its useful power range at useful speeds, and wonder why it wont 'pull'. Conventional car gearing will have rather higher losses than thr bike garbox too: helical gearsets of large dimater and greater inertia, and cirtically - too-wide-range gearing/gaps betwen gears, very poor match overall for a high-revving/powerful modern bike engine that makes peak power in the top third, if that, of the rev range; typical sports bike boxes are only about 2:1 difference between 1st and 6th gear in ratio spread.

This is also where the bike-engined formats fall down in trying to apply the idea to 'heavy' cars; and by heavy, I mean >500kG. Huyabuse Minis are fairly daft at 650kg; for Elises and similar even heavier things, MX5s even, better options exist. Just becasue you can derive 180hp from a 'Busa doesnt mean it wouldnt be better-off/better to drive, with 200hp from something more conventional. So much inertia inherent on the chassis that ultralightwight powerplant is of no benefit.

Summary: gear low enough to get it moving, no top end; gear for top end, can't get it moving easily. Silly.

Anyway - that V-twin is a low-revving lumpen thing anyway, so direct bolt-up makes sense. The Harley-derived 45deg V-twin genesis has more in common with agricultural implements than bike engines IMO.

Edited by Huff on Wednesday 11th May 23:54

[annodomini2]

The box itself is fine (usually), the real issue for most is the lack of reverse gear which is needed for the IVA.

So you need some other mechanism, reverser box or electric.

I'd want to go less than 500kg if you can.

You need to increase the final drive so that you increase the wheel torque due to the weight.

[Tango13]

Reversing is not a problem...

http://www.novaracing.co.uk/ProductHondaReversingG...

Don't forget that the circumference of a car tyre is a bit smaller which will help the gearing too.

All the gear ratios for pretty much any bike can be found here...

http://www.gearingcommander.com/

[dom9]

http://www.miatabusa.com/

[George111]

Lefty said:

I just watched a video of a z-cars Hayabusa Elise. The bike gearbox just looks a massive pain in the ass and the clutch probably a real weakness.

As mentioned above the gearbox is a delight, even the Hayabusa in my car has hand operated paddles which give a very quick change. The clutch is reliable and very strong, many turbo and and supercharged cars and bikes operate using the standard gearbox and clutch. In a bike you might need a stronger output shaft. Stronger springs are available as are several new clutch centres to stop them grabbing.

You can buy a hayabusa engine for about £1500 plus a basic turbo kit and ancillaries for another £5k (inc ECU and calibration - varies from supplier to supplier but it WILL cost you at least £5k whatever they say) and maybe £800 fitting bits and bobs. That gives you a sequential gearbox and 300+bhp for less than 100Kg - where else can you get that ?

The clutch can be changed in 40mins once you're used to it, as it's on the front (in a car) of the engine under one cover.

Have a chat with Steve Broughton at SBD about ECU and options.

Mine has carillo rods, JE pistons and pins, heavy duty output shaft and modified gearset, reprofiled cams, Nova starter gear and clutch, Rotrex C94 supercharger and MBE ECU and makes about 340ish bhp with sequential gearbox. Fuel consumption is a bit shyte though.

The only thing to watch with bike engined cars, as alluded to above, is the reduction ratio so you need a high ratio diff. Mine is a Sierra 3.14 with ZF LSD but you can't get away with the most common 3.9 or so unless you want to limit your top speed to 110. There are other options these days, mine was built in 2004.