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

Hi!
I'm asking a very open question here, obviously - but...
I have in mind a conversion for a 60s car (the Hillman Imp).
The kerb weight for the car is quoted at around 750kg (100 more than an Austin Mini, but a prettier car IMO) - plus is also rear engined/rwd which suits my driving style better :D
Several Imp owners have converted their cars to bike engined high-revved speed-machines (keeping the Imp's transaxle) - but I would like to get a vehicle that is designed primarily for efficiency whilst keeping the old-school looks intact (though this may hurt the aerodynamics).
Imp engine - 37.0 bhp @4800 rpm. Torque. 67.0Nm(49 lbft) @2600 rpm

Thinking:
BMW R850 Boxer engine - produces 57 lbft , 70 bhp
Oilhead/air cooling could cause problems, but Imp has rad in back, air drawn from under car (messy). Would keep Imp's diff/ section of transaxle casting (or equivalent).
Interested in how difficult it would be to 'de-tune' for lower BHP, remapped for good MPG.
I have a gut feeling that a low-slung torquey boxer engine has plenty of potential for good thermal efficiency, plus breathing is not hurt so bad.

Or for really ambitious build
R1200GS - with 85 lbft 100bhp
- converted cam lobes for Atkinson cycle with Mild hybrid e-motor/batteries combo.

Has anyone any experience using these motors for economy? Is it a good starting unit?
Note - being all Ally the Imp's engine/tranaxle comes in at around 70Kg as standard. I can's see the point in replacing it with anything heavier without a very good reason.

Most bike engines are biased towards ultimate output (higher rpm hp rather than lower rpm torque) than economy and it seems they return econo not as good as we'd hope for when repurposed. Still, they can be made to work and I'm sure some are better than others. So after all my blather I guess I don't have direct experience with the options you listed... whichever one is more of a "torque" engine will probably give better fe.

Not sure why you would not just use a Geo Metro/Suzuki Swift 1.0L and its transaxle. The 3-cyl G10 motor is all-aluminum and very light, and the transaxle is also very light, I believe its only 45lbs. Motor is designed for MPG.

There is another bike engine I ran across that looked promising, 650cc V2-cyl water cooled, shaft drive, here it is,
Honda CX series - Wikipedia, the free encyclopedia
saw one for sale for $100 a while back, but was sold before I can get there with my trailer.

If money is no object. I had a friend who rode a 2000 Triump 955 ST. Claimed it got 65 MPG before the performance mods.

PERFORMANCE

Maximum Power
110PS (108bhp) at 9,200 rpm

Maximum Torque
97Nm (72ft-lb) at 6,200 rpm



2000 Triumph Sprint ST

I have seen a used 955 sell for under $3K.

I can vouch for this engine. I had a Honda CX650C, and it's a great motor (674cc). Built-in 5-speed/clutch, with a splined shaft output. Lots of power from a reasonable rpm, water cooling for flexibility, good power (65hp IIRC), good economy, at least in the bike (50-60 mpg basically rodding the piss out of it with 200+ pounds of knucklehead on the seat, and no fairings).

For a small front-engine/rear drive, I'd think it'd be perfect. Get a driveshaft from a motorcycle, cut off the u-joint, and have a shop weld it onto your existing driveshaft, and you're in business! Hook up a set of paddle shifters (1/2 travel to lighten the clutch, 1/2 travel to switch gears) for sequential shifting and you're off to the races! Rear engine/rear drive, I'm not sure how the drivetrain would work, but still an excellent, tough, tractable motor. Probably small enough to set up as a mid-engine/rear drive motor.

Charging system works (a little bit of a weak spot, but fixable), and has thermoswitch-controlled radiator fan, and water temp sender and oil pressure switch for instrumentation.

If you don't need quite that much power, the same basic engine was built in huge numbers as a ~500cc, and they're much easier to find.

I could see an engine like the Honda Goldwing's working ok, 1,100cc to 1,800cc depending on the year, it's a flat 4 boxer set up for shaft drive and water cooling and is from a motorcycle that is designed to be able to be loaded down and towing a trailer where alot of motorcycle engines are designed for low load high revs.

I was going to mention the Gold Wing.. but my 1100 and I guess most all of them don't return very good fe, usually in the 30's and I don't think I've seen anyone claim any better than 40. In fact I'm deciding if my bike would run better and more economically if I ditch the 4-carb setup and put a single automotive carb on there...

I also have a GL500, which has the same drivetrain as the CX500. It got 45-55 mpg, driven gently and slowly. I'm not real impressed with that and always felt it should be better.

The Suzuki 650 twin (SV650 , DL650) is also rather efficient - at least in a bike.

Why the attachment to the motorcycle engine? find an engine out of a smart car that's been crashed or out of a Geo Metro.

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.

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.

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 :thumbup:

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

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.

Thanks all!

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 :)

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.

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.

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.

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.

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.

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.

Question - are you looking for lightest weight or best FE ? Or are you just wanting a bike engined Imp (deep respect :D) with some FE ?

The best FE would be the ForTwo diesel or the 1.2 Polo TDi. Good luck on the latter one. And If you do those then either go mid-engined or line yourself up with a load of work to get a suitable gearbox and gearing unless you can get the gearbox from the Smart to fit.

Reasonable FE would be a more modern car engine, say a K-Series maybe a 1.1i with FI to take advantage of EOC etc. But then you have to connect it to your transaxle but this has been done.

The Imp is of course a small cottage for Aero unless you work on it quite hard. There are a few Clans about which you could use for this type of conversion which have less frontal area but may need Aero work.

Hillman Imp (god, what did Chrysler think when they bought Rootes ?)
http://www.visionmotorservices.co.uk...+near+side.jpg

Slightly more sporty Imp Coupe
http://farm4.static.flickr.com/3621/...e7ae1be6a7.jpg

Clan Coupe (Imp oily bits)
http://upload.wikimedia.org/wikipedi..._at_Woburn.JPG

Note the best car ever in the background... :D

Maybe shaft drive isn't the be-all and end-all. One of these chain-drive differentials with integrated disc brake might make it practical to use (and swap between) any number of sprocket-drive motors.

Chain drive vs. a drive shaft now there is a world of difference, the drive shaft you are going to have more of a loss at the differential but it is durable and doesn't need adjusting with a chain drive be prepared to adjust the chain tension from time to time especially on a home built project and there is that unknown if the chain can handle your design and stress...

Chains are very efficient (non o-ring ones), and very strong chains are available (similar differential to the one at the link was used on a racecar running 230hp through a chain), but adjustment could be an issue.

I wonder, in an automotive setting, if it would be practical to have the chain run inside a housing so it could be continuously lubricated and kept clean. Timing chains seem to last practically forever, for instance. They have nice continuous tensioners, too (oily chain slides on long curved spring-loaded poly blocks).

Interesting issue. Size/shape of the space available might be the determining factor.

And then there's belt drive...

I'm going to say +1 on the Suzuki SV series V-twin engine. A couple of my friends in a social riding group get the best economy of the bunch riding SV-1000's, and they are very torquey...perfect for a small car imo.

why don't you just use and modify the engine it came with?

For the Imp you should get a 1+L automotive engine that has the best choice of gearing. BSFC isn't going to vary a whole lot between engine families built within the last decade or so, but gearing can, and that's where you are going to make or break it in terms of mpg. A 750kg car should be able to get great mileage with low enough gearing.

Why not go w/ a used set of ITBs, a wide band O2 sensor, and something like megasquirt? It would be a bit pricey at ~$200+, but you could go as lean as you wanted to.

Because it is a bit pricey! Don't forget adding an ECU, pressurized fuel system, etc. And I can go as lean as I want via cheap lil ol skool jets.

One reason fe is poor on my Wing is a suspected rich-running carb. They're kinda a bugger to remove and service, and parts are rape-me expensive. :mad: Remember, Honda hates their customers.

Besides the shaft drive being less efficient than chain or belt and gearing not as tall as it could be, I don't think there's a fundamental (architectural) reason for the 1100 to be so inefficient. The carburetion is poor on mine but the ignition and exhaust systems should be good for effient fe. I think it's probable that a cam profile more biased to lower rpm operations would help along with intake system resizing (smaller, longer tubes).

The megasquirt ECU kit is very expensive at ~$140, but everything else isn't too bad. You should be able to get everything else used for about (fuel pump for ~$30, the TBI setup for ~$40, both used, and the wideband sensor for ~$60 new) $130, or less if you shop around. I dunno if it's economically worthwhile paying $200+ more to be able to tune for all the different engine speeds/loads, but it could be if you put enough mileage on the bike. Even if the difference is only 55mpg versus 45mpg w/ the auto carb, it would still pay itself off in ~20k miles.

It would probably be best to see what you could get w/ a cheap auto carb first, then maybe go for the TBI setup if your results aren't as good as you hoped for. Everyone hates their customers these days. I called after my door lock went out and Toyota was asking $800+ for it. Over $1000 for the door card. :(

In answer:
As you you have implied, if ultimate FE was the only driver I wouldn't even be starting with an Imp :rolleyes:
I would say, as the standard car can do 50+ mpg (UK) on run, -even with a progressive choke- I would have a hard time to get more than 20% better. It does suffer round town though, and this is where I think modern wizardry could play a part (ECU's, etc).

As is commonly known, (by those who care!) the Coventry Climax engine was pretty advanced at the time & it has been common to bolt-on injection & other improvements to the std block for quite some time. That said I do think, the money cost of 'modernising' is now greater than replacing with an modern equivalent. The trouble is that, even low-displacement car engines today are at least as heavy (+ have more grunt than is needed) than the original (A Toyota 1KR-FE 2007 onwards would be great but I can't afford one yet).

It's for these reasons that I have reckoned that a torqued Bike engine (of 750+ from the early 2000s) would be the best compromise. And I just like the concept of using Boxer and perhaps experimenting with it (ECU maps, cam-mods, etc) down the line.

Whoah! Very cool. Had I known about this one when I started my project, it may look very different now. Bookmark saved!

However, you aren't limited to shaft driven bike engines if you have a car with a driveshaft either. For my race car I'm using an adapter intended for Dwarf Cars or Legends Cars that use a sportbike engine/tranny coupled to a driveshaft.
http://ecomodder.com/forum/attachmen...p;d=1294471591
If the original poster needs one, they are made by Hawk Machine. Small company, but really good product and customer service. Link: Hawk Products Page

Mike