Bike engines into cars

It's a pretty massive topic to be honest. Is there anywhere you'd like us to start?

What are your aims with the car?
Do you want to modify it as little as possible, or do you want to get the best performance out of it?
Do you worry how it goes around corners? if so how much?
Are you trying to do it as cheap as possible, or as well as possible?
Do you realise how hopeless to drive on the road a bike engined car will actually be? It's never really going to be a daily unfortunately.

It's a path that will involve a lot of decision making with regards to compromises you'll have to make down the line, so unfortunately none of us can really tell you how you want to do it.


Oh yeah, and welcome to the forum, I do like the idea of a bike engined mk2 breadvan. Any examples of your previous VW's for us to ogle over?

Sounds like a big project! Welcome to the forum and have a video!



The car in the video is a Suzuki SC100 Whizzkid with a CBR1000F engine, which makes a Polo seem huge and heavy by comparison! Might need a Hayabusa engine then!

If you are planning to end up with a bike-engined car, I wouldn't worry too much about doing it up beforehand. There's no point spending money twice by changing things like suspension which will be no good once the engine conversion is done. Obviously, removing the weight of the engine and gearbox from the front, say 150kg or so and then putting 100kg into the rear will change the car's requirements for suspension, not to mention the fact that the rear suspension system will have to be almost completely replaced during the conversion.

When looking at wheels and tyres, don't forget to think about what brakes you're going to use. I would imagine that doubling or tripling the car's power output will require bigger brakes. Personally, I would also say that a full rollcage is a necessity as well for safety, since the car will be moving at such an increased rate of speed and you will probably want to race it as well, or at least go on track days.

If you are going to race, then choose which class you will be racing in and read the rulebook back-to-front to ensure that it will conform to the regulations. The same goes for the road rules if you are planning to register it. Changing the engine, driveline and rear suspension will be a substantial modification and in the UK I believe that will require an inspection for registration, so make sure you know the rules before you do anything.

Last but not least, you have said that you don't have much mechanical skill or experience. If you don't have the ability to do the work yourself, then a conversion like this will cost a substantial amount of money. The easiest way is probably with a kit from someone like Z Cars. As shown in the link below, the chaps at Z Cars have a lot of experience with these types of conversions and can sell you a kit to convert your car to mid-engine, rear-wheel-drive. It's advertised at 6,350 quid, plus VAT, plus the engine and transmission! That kit is designed to take either a bike engine or a FWD car engine, so you could use something like a Honda VTEC engine, which would be much more civilised for road use.

www.zcars.org.uk/univkit.php

If you wanted to stick with a bike engine, it might be better to just buy their drivetrain/rear-end kit and tie it into your own roll cage. They list them for 3 grand including LSD, electric reverse, brakes and suspension. www.ebay.co.uk/itm/ws/eBayISAPI.dll?ViewItem&item=110806002622&clk_rvr_id=311769642221

Having said all this, they do have a 'Cars for Sale' section, which is offering a fully built R1-powered Mini for 10 grand. Not bad value if you ask me! By the time you paid someone to do your own conversion it may cost you a lot more.

How about sticking a beetle engine engine and box in with a turbo ..

If its power then what you say is true . But if its coolness...

I'll try and list some of the main issues you'll encounter in terms of the decision making, so you can get an idea of what will be involved.

Engine:

Mounting, bike engines are typically solid mounted, or mounted on very stiff mounts, this is great in a bike, and no an issue at all if you plan to only use the car for track days or racing, but it will be loud and uncomfortable for normal road use. They tend to use a lot of small mounting points, rather than a couple of big ones like cars do, so you'll need to make a framework to support it.

You need to get air to it somehow, both for the intake, and to keep the temperatures down to a sensible level. Big scoops are great, but not to everyones taste, and they can be pretty curse word-poor aerodynamically.

You need to get the drive to the wheels. The normal method is to use a chain driven differential. This is fine, but needs regular maintenance, you're moving a lot more weight than the chain was designed for initially, so they tend to wear out relatively fast, and need regular re-tensioning, even with high quality chains.

As someone's already mentioned, bike clutches aren't meant for shifting ~700kg of car, so you'll either be killing them regularly, uprating it (I don't know what the options are for upgrades myself), or you'll be looking to loose a lot of weight from the car.

Controls, throttle cable's easy enough, although chances are you'll need to do something about the amount of cable it pulls. The gear linkage is quite strait forward on bike engines, as being sequential you only need it to move in one plane. I'm not sure about R1's, but you might need to adapt the clutch to hydraulic.

Oil, bikes are designed around the idea that they'll lean in corners, this means the oil only sloshe's around a little side to side, the engines aren't designed around heavy cornering when mounted level. For normal road use you may be fine, but if you want to do much playing on circuits, then you may find you need to do something to stop oil starvation in the bends. Either dry-sump if you're feeling flush, or baffling and maybe a accumulator could sort it.

Rear Suspension:

You can't use the Polos rear suspension, so you'll need to work out what you do want to use. If you want the minimum work/modification, then a trailing arm set-up like the z-cars use would work well, as the shell's already got the strength in the right place, and you could probably even use the standard shock turrets. If you want the best handling possible, then the technically best set-up would be to go double wishbone, but this will involve a fair bit of design work, and will need a framework building to carry the wishbones. Another option would be to use a Mcphearson strut, which would only need lower wishbone mounts, and a bit of bracing at the strut-tops. Keeping things in a subframe type structure tied into a roll cage for strength should keep you from needing to add any real metal to the shell, like the z-cars do.

Front suspension:

There's nothing physically stopping you just using the standard front suspension if you want to keep things simple, and aren't too bothered about handling. If you are worried about handling, then to be honest, it's not very good on this age Polos, and the cars requirements from the front suspension are now completely different, you've changed the weight distribution, the driven wheels, and more than likely the rear roll centre height, spring rates and anti-roll bar rate, so if you want it to handle well, the front will at a minimum need different springs, shocks and a different ARB.

Legalities:

There's not really any way you could do this without cutting up the floorpan, which is modifying a monocoque, so the vehicle will loose it's identity. By this I mean the VIN number and number-plate wont apply to it anymore, so it'll need re-registering as a drastically modified vehicle. To do this, you'll need to get it IVA tested, this costs about £470 iirc, and you'll need to make sure the build meats the regulations to pass it. Probably best to allow another ~£100 (I think) for a re-test, as it's not likely to pass first try.


I'm sure there's more I've not mentioned, and sorry if you know most of this already. Any questions just ask, we'll try our best to answer them.

I can sell you a very good abf to mount up front ...

After reading this I might stick to pretty and not a bit insane lol

This kind of info is perfect an everything I asked for before jumping into something a big for me, I think I'm gonna stick to corrados and vr's

Bike engines in small cars seem like a fun thing but I've heard they're not nice to use on the road....It would be a huge conversion, as already stated it would involve chopping the back end around, the headache of suspension, braking, strenghtening etc etc etc. Couldn't you try fitting a Polo GT engine or something similar? Not too up on watercooled VW stuff but if memory serves the 1.3 MK3 Polo GT engine can fit. Having said that there's been bigger engines fitted to Polo's. Have tou tried posting on Club Polo? Quite a few been converted on there so you could get some pointers. Knowing the options/work needed for each option would help you decide which is feasible in terms of budget and skill level (not putting down your skill level as I've no idea what it might be ). I looked at a bike engine conversion when I had my Fiat Cinq and it was in the thousands to do, I could buy a car as fast & a dam sight more user friendly for less money.

You could just use the Polo as a daily & buy an R1 for sunny day fun.