What bike engine should be used in a Mini-sized ecomodded car?

[Vekke]

I would use some 600 cc bike engine and built a supercahrger system there if you want to use bike engines. If you already choose engine with most torque on the lower revs it will be more reliable in daily usage.

Propably cheapest and the most best FE would come from VW lupo 3L engine which is 1.2 TDI. That smart engine would be also nice but it might be more expensive.

[nimblemotors]

well, heck just buy a Smart Car, but my Prius gets better mileage and can hold 4 people, and a trunk big enough to haul home the Honda 500CX engine I bought yesterday for $100

The issue with motorcyle engines are they have no reverse.

I think one would want to use them for a hybrid, that is what I'm thinking
of using it with the boxster.

The problem

Originally Posted by mnmarcus

I'd vote for the smart fortwo's 799cc diesel. I think its around 50 hp but would have a lot of torque a gas engine wouldn't. I don't think we can get them in the US, lucky europeans... Nothings going to beat a diesels efficiency. I've been dreaming of a micro ecomodder car with a ~20 hp v twin diesel.

[NHRABill]

Have to agree with tq over HP in this scenario. You can't go by what MPG the motor will get in a bike cause the weight of the car will be 3x and then some you also have to add in the loss of power and efficiency through the drive line. By the time you are done you will be dissapointed. Someone mentioned a gullwing that would be your best bet they are designed for the heavier load and many of them did come with reverse.

[Air-Hybrid]

Thanks all!

Originally Posted by nimblemotors

The issue with motorcyle engines are they have no reverse.

Ooops! I hadn't thought of that!
Perhaps an electric reverse would suffice.


I am drawn to 2-cylinder boxer engines because they have a low profile (height). Width is not a problem in this car, but the original engine had to be tipped by around 30degrees to fit under the parcel shelf. With a low enough boxer engine there may even be room for some (well insulated) boot (trunk) space in the rear.

The best configuration I can think of is where the front steering setup (remember engine & drive are rear) is replaced with a lightweight fwd diff. and CV'd driveshafts - that connect in an electric motor (for mild hybrid + reverse 'gear').

Ideally the car would pull-off on electric, then bump-start the gas-engine. Deleting the need for a start motor and dynamo in the back. The biggest problem here would be the battery pack could only charge when the cars moving but it would be somewhat bigger than normal

[bikepilot]

The BMW boxers aren't terribly efficient. Also note that they build up a lot of heat and need excellent airflow. They will overheat and suffer in really bad traffic and you can't leave them idling for very long. Also, it might be taller than you think - the cylinders are flat, but the crankcase design is actually fairly tall.

Bike engines in general aren't very efficient at all. Also think about the drivetrain and how you'll connect the engine to the wheels. The BMW engine is sort of like a cage engine - it has a big flywheel and dry clutch off the back and separate transmission.

The most efficient bike engine I've used I think is the suzuki Banidt 1250 motor. It also has loads of torque. It returned a consistent 50-60mpg pushing the heavily loaded bandit around with vigor. Being liquid cooled it'll be easy to keep cool in the cage configuration. It uses an integrated transmission with the engine and has a very large-diameter wet clutch that I think would hold up to getting a cage rolling more easily than most dry clutch systems. Its also a 10-minute job to replace the clutch plates rather than a 10+ hour job like on the BMW.

[roosterk0031]

I'd lean towards honda v-twins out of the cruiser bikes, more power down low, made from 500cc to 1800cc, start with a 1100cc, liquid cooled shaft drive. If it's too much or not enough can go bigger or smaller later.

[fjasper]

Originally Posted by bikepilot

Bike engines in general aren't very efficient at all.

Something to take into account is that maintaing speed with a 800lb loaded motorcycle at 70 mph may require more power than a 3,000lb car at the same speed. I haven't found much data for motorcycle Cd (rider position, custom windshield, highway pegs, etc. make a big difference, for instance), but the limited data I've seen is in the Cd>1.0 range, so a Goldwing probably requires more power to cruise at 70mph than does an Accord, let alone civic.

The Hex head BMWs (R1200 not in cruiser body) seem to be able to get 50 mpg, but I definitely agree on maintenance difficulty and cost, although replacing a clutch in a car application might be more like any other replacement depending on how it's mounted. Wet clutch=good, though. Cooling can be managed, as there are provisions for a thermostatically-controlled oil cooler. A fan to provide airflow over the air-cooled parts when slow or stopped, probably of similar capacity to a radiator fan, should manage that, but water-cooled would be easier, I think.

I have an older BMW, 1997 R1100RT, it has modern engine-control systems, and gets 40-45 mpg while pushing around my oversized windshield, big upper fairing and generally terrible aerodynamics. Bike + me + gadgets = ~900lbs.

I can reduce drag noticeably by lowering the windshield a couple inches. I've done it with a throttle lock engaged, lowered the windshield, pick up 5mph, raise the windshield, lose 5mph on a flat road. I suppose if I did the math, I could figure out something from that data, but I'm too lazy to do it.

It'd be interesting to see BSFC numbers for these motors, but I'm guessing that's not going to happen.

[Air-Hybrid]

This site seems a good resource for comparing bike MPGs.
Of course, the figures are for engines pulling bikes and are often rider logged, so not any kind of 'bible', still...

Motorcycle Fuel Economy Guide

Using a bike with a shaft drive seems a good option.
Boxers should also have a lower CoG if they can be made to fit!

I realise that bike engines are usually skewed towards performance rather than economy, I just think the getting hold of a modern efficient & light, small-displacement car engine (in the UK) is going to be a greater battle.

[Air-Hybrid]

Regarding weight comparison I reckon the car can be reasonable easily dieted down to under 1200lbs. The CD is no likely to be good, but again some 'tricks' can probably be employed to better it. - One advantage is no radiator opening at the front (although air is drawn from underneath in factory spec).
Wrt the BMW boxters having a largish flywheel, this I would think is an advantage when moving (and maintaining) the extra mass of a car.

[fjasper]

I don't want to start a "my brand of motorcycle is inherently superior to your brand of motorcycle" argument, but I've heard good things about the newer Harley motors for fuel consumption, and there are lots of people around who know how to customize them. The low-rpm performance and wide-ratio transmissions (low gears for getting a heavier vehicle moving, while still having a reasonable rpm for highway cruising) might make them suitable.

I'm more of a metric-bike guy, but my friends with the HDs speak highly of the build quality and fuel economy.