back to article BMW i8 plug-in hybrid: It's a supercar, Jim, but not as we know it

I almost felt sorry for the BMW press team last November at the i3 press launch. The questions hacks kept returning to were: “When is the i8 going on sale?” and “When can we drive it?”. Fair play to the BMW staffers, who didn't stop telling us how groundbreaking and generally fantastic the i3 was. As indeed it is. BMW i8 Plug- …

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Pushing close to £100k is a lot of notes to be treated like a leper at every junction, albeit in a motor with (arguably shaky) green credentials.

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@returnmyjedi

I would love a car that enabled me to be treated like a leper at every junction (people getting out of the way).

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Re: @returnmyjedi

"I would love a car that enabled me to be treated like a leper at every junction (people getting out of the way)."

An old faded blue Ford Escort 1.6L will do that for you. A couple of strategically placed dents will increase the distance between you and shiny Merc. driver - just don't mess with the lorries.

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Re: @returnmyjedi

Having driven a big army Foden recovery truck I can safely say it is the biggest leper on the roads, even trucks would get out of the way.

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I'll throw my hand in as well, on that sentiment

Words, words.

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Re: @returnmyjedi

Foden recovery truck? Where I live it's tank transporters, and the odd learner Warrior driver.

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231BHP from 1.5l

I'm a fan of the 3-cylinder engine - short crankshaft, good balance and there is no point at which all the pistons reverse direction at the same time - but this is extraordinary. For comparison, the Mercedes turbodiesel OM639, which was also a 3 cylinder 1.5l, produced about 94HP. Given that electric motors, carbon fibre and aluminium are relatively mature technologies, to get so much out of such a small road engine with good fuel economy is pretty awe inspiring and perhaps the most impressive bit of the car.

It does show, though, that the big advantage of the electric motor is that, by handling the high torque and low speed requirements, it allows race technology to be used in a production vehicle.

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Anonymous Coward

Re: 231BHP from 1.5l

I wonder how BMW have managed the stresses of loading up a small engine to put out that sort of power. I assume in racing they tend to either go through a lot of engines or rebuild them a lot, but that's not going to be popular in a car costing north of £90k. However, it's BMW, they must have thought of that before putting it into production.

If I had the dosh I'd be interested..

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Re: 231BHP from 1.5l

It's not that high really. Though still impressive.

BMW has been doing 100hp per litre for 20 years with the M series. My 2000 M Roadster has 324hp or so from 3.2 litres (the 3 series gets an extra 20hp from the same engine with a longer exhaust).

Bolt a massive turbo on, and an extra 80hp ain't asking that much.

And it's a beemer - it'll be solid and reliable. though I may be biased, but I have 2 of em - the other one is a 4.4 V8 X5 from 2001 - it's done 130,000 miles and looks and drives like it came out the factory yesterday.

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Re: 231BHP from 1.5l

Basically, Diesel engine technology to cope with the pressures. If the engine is being electronically managed rather than foot pedal actuated, you can design the operating envelope to avoid oil starvation. Also remember, most of the time it's going to be putting out a few tens of horsepower. Design for hundreds, get reliability for tens.

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Re: 231BHP from 1.5l

Strength wouldn't be an issue when you are designing the engine for this kind of output.

The main issues of high boost petrol engines of old were:

1. Lag ( or LAAAAAAAAAAAAAAAAAAAAAG, whoosh, gear)

2. Pinking, or pre-ignition.

Variable geometry turbos and other variations along the same theme, along with electronic boost control solve 1.

Direct petrol injection solves 2.

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Re: 231BHP from 1.5l

A 3-cyl engine has rather poor balance (rocking couple) and needs balance shafts. VW didn't bother with the little 1 litre engine in the Citigo, which is why it feels as if it's going to shake itself apart (and why I didn't buy one after test driving it). Ford economised on their EcoBoost 3-cyl engine by using an unbalanced flywheel to compensate, whcih is a bodge first tried years ago.

I suspect BMW did it properly and used balance shafts in this one, especially as the capacity is too large just to try and ignore the problem, as is tempting with a 1 litre or smaller.

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Re: 231BHP from 1.5l

An inline 3 has good rotational balance but an end-to-end rocking couple. Even with a balance shaft, the parts count is reduced and it is more compact than an equivalent inline 4. The OM639 has a balance shaft and I'm sure BMW can spring for one, especially as they can be used to run auxiliaries.

Given the increasing number of 3 cylinder engines in city cars, VW and Ford really don't seem to have been trying.

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MJI
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Re: 231BHP from 1.5l (is nothing)

1100bhp from 1.5l is.

See the M12 based on the M10, 1100bhp in qualifying.

Another BMW 1.5 turbo

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MJI
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Re: 231BHP from 1.5l

BMW are good at high power reliable engines, It will last.

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Rear

Since a friend told me that from the back the i8 looked like it was 'pooing' a Porsche 911 I alas now cannot unsee it.

I do like how it echoes the old M1 however, and the mpg returned under hard driving is astounding.

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Christmas Prezzie sorted

Top of my list.

{Drums fingers impatiently}

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Anonymous Coward

Please compare to Tesla?

Because the Model S can carry world+dog, has more ponies (416HP on the top version), can push to 60mph one second slower, and almost the same range (okay, way less), for almost the same price (yes, more expensive), while generating zero CO2. A number-by-number comparison would be very, very interesting. And the S has no sporty pretensions, it's a freaking *sedan*.

A round-up of electric and hybrids is in the order. I'm asking dedicated magazines as well.

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Anonymous Coward

Re: Please compare to Tesla?

Not a hybrid, so less need to plan ahead or carry a VERY long extension lead and a hotel chain membership card. I am fully aware Tesla is working on a solution (looking forward to that), but the present reality is that having a petrol tank in addition to a power socket seems to be the most practical solution for anything that needs to go further than a few local shops.

Personally, I prefer the hybrid approach because it does regenerate energy from braking, but is not full-on dependent on how many duracells under the bonnet still carry a charge.

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Re: Please compare to Tesla?

compare it to a tesla? Sure. The tesla looks shitter, wont take you round a holiday without spending the day charging, cant realistically hoon it about as you'll drain the battery in no time but at least it costs less so you can buy a focus to drive between cities.

I'd love one of these.

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Devil

Idiot's Solution

I cannot understand why people bother with hybrids. It's the idiot's solution to a problem. You have an internal combustion engine carrying around an electric motor and it's batteries and you have an electric motor carrying around an internal combustion engine and it's fuel tank! To top it all you can even charge the batteries using the internal combustion engine for maximum inefficiency!

As for the idiots that think's a Tesla produces zero CO2...aaargh!!!

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Re: Idiot's Solution

When you grow up and get a driving license you'll find that not all parts of a journey are the same. No one system can be ideally suited to all. Having a composite drive system that can handle the cruise, hard accelerate, stop-start and all the other variations of motion with one or more subsystem seems damned handy to me.

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Mushroom

Re: Idiot's Solution

And the idiot's solution is...make every part of the journey inefficient! Well done, you should get a job as a climate change expert!

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Re: Idiot's Solution

Let's spell this out for the hard of thinking.

To get the best efficiency out of a Diesel engine, which on its own is the most economical IC design, you need a multispeed gearbox, a stop/start system so fuel is not wasted when stationary, and as human beings aren't that good at knowing when to change gear, preferably an automated gearbox. The Diesel engine also needs a particulate filter.

The stop/start system needs a heavy duty battery and starter motor, and an updated alternator.

So, starting with the optimised Diesel, we use a bigger battery, a bigger electric motor and alternator(we now don't need the starter motor as well), we throw away the complicated gearbox, we replace the gearbox control system with the electronics to control the electric motor, and now because the IC engine can always run under optimal conditions we scrap the expensive Diesel engine and its particulate filter and replace it with a cheaper petrol engine. The petrol engine is lighter, so that counteracts the additional weight of the batteries.

The batteries can be charged during the overrun descending hills and while braking, by using the electric motor in reverse, so we actually save energy that was otherwise wasted in heat in the brakes.

Back in the 1990s, clever people at Toyota decided that the problems of pollution from Diesel were probably insoluble, at least in densely populated Japan, and invented the Prius. They were mocked. It's now 2014, Diesel particulates are recognised as a major health hazard, air quality in cities is declining, and those Toyota engineers look very prescient indeed.

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Re: Idiot's Solution

To top it all you can even charge the batteries using the internal combustion engine for maximum inefficiency!

As opposed to using your brakes to generate useless heat? You have to look a bit further than your nose to solve complex problems. E.g, band energy and peak energy don't have the same worth.

You think all the taxis are switching to hybrids because it looks cool? They looked at the average consumption of a Prius, and they know how much they are saving.

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Facepalm

Re: Idiot's Solution

"I cannot understand why people bother with hybrids."

That much is clear. I suggest you write to those idiots at BMW and point out the error of their ways. Maybe they'll make you head of engineering.

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Boffin

Re: Idiot's Solution

Oh no! Let's start with a crap solution, make it less crap and convince the buyer that you have the best solution. Honestly you should be a car salesman. Let's just continue with your methodology...now that we've got a light engine, a heavy battery and a heavy DC motor, let's swap the heavy battery for a light one to drive a light starter which will get rid of the heavy DC motor and we'll add a light and simple gearbox (not one of those complex one's you previously specified). Voila! I'm a better car salesman than you!

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Stop

Re: Idiot's Solution

I think you will find that BMWs products are based on a sales strategy and not an engineering one. They're not really very well known for radical ideas, just small changes every few years so as not to scare off their middle management customers. And what have their brilliant engineers come up with as a solution? A hybrid! How novel.

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Re: Idiot's Solution

Yeah, sorry, if taxi drivers are buying them they must be the best solution.

Normally I use my brakes to stop the car but from now on I'll use my gears, I'd hate for my brakes to contribute to global warming.

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Facepalm

Re: Idiot's Solution

Should I be a car salesman?

Again, let's spell this out for the hard of thinking. A gearbox has to transmit torque over a range of loads and speeds. It has to deal with shock loading (dropped clutch, for instance) and, if it isn't automated, fluffed gearchanges which give the synchromesh a hard time - unless you've removed the synchromesh on grounds of lightness and simplicity, in which case it has to resist shock loading of the engagement dogs. Have you ever dismantled a gearbox?

Now, IC engines can be designed to operate over a wide range of rpm with more or less constant torque, but it turns out if you do that they also have a low BMEP and aren't to efficient. Engines with a high specific output tend to have a narrow torque band. This means plenty of gears to keep the pot boiling. Have you ever ridden or driven something with a racing engine?

Your light and simple gearbox is going to be weak, easily broken, and won't have enough ratios for modern road use with modern engines.

It's easy being an armchair engineer; to every problem there is an obvious solution. Which is almost invariably wrong.

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Boffin

Re: Idiot's Solution

Yes you should.

Yes, I managed it from reading a Haynes manual, that's how complex a gearbox is. Describing the everyday life of almost every gearbox in the world isn't an argument for your preferred solution.

Is the solution to these inefficiencies to bolt on a completely different drive mechanism? Really?

"In 2004, the Honda Racing F1 Team produced what they considered a “jewel in the crown” in race car design...a light weight composite gear box..."

Yes indeed, I suspect the BMW engineers never even left their armchair when they came up with the solution of a (Toyota) hybrid in an impractical car with a ridiculous price tag. They should clearly be awarded some sort of prize in recognition of their engineering brilliance. A golden armchair perhaps?

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Re: Idiot's Solution

I give up, I really cannot compete with someone who has reached the level of reading a Haynes Manual.

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Facepalm

Re: Idiot's Solution

You make me laugh professor Arnaut! What kind of idiot would refer to a Haynes manual before dismantling and refurbishing something as complex as a gear box! I don't know, I really should have got a degree in gearboxology before even attempting it!

Well at least you didn't run off after dropping a lone comment, for that at least, I salute you.

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Re: Idiot's Solution

You need to read this.

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32.9mpg? For a hybrid?

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"32.9mpg? For a hybrid?"

Or rather

32.9mpg? For a freaking super-sportscar?

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Anonymous Coward

32mpg is excellent

Judging by the pictures, those roads are similar to the ones I drive in my Mk5 Golf GTI (2.0 turbo) and when I drive them hard like the author, I get 23-25mpg. My car doesn't do 0-60 in 4.4 seconds...

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32.9mpg?

Double what Top Gear managed taking a Mk2 Prius on their test track.

I can't think of another petrol-powered "performance car" that would achieve 33mpg in traditional "performance car" style road testing. Can you?

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Anonymous Coward

"32.9mpg? For a freaking super-sportscar?"

Exactly!! To put it into perspective my M5 can JUST hit 30Mpg under granny driving conditions. On a 200Mile drive on the motorway I will average about 25Mpg over the whole journey....If I add in a couple of "Boot it away from the tailgaiting Audi when the traffic in front clears" moves that will be in the teens...On a recent jaunt to the countryside (similar driving roads that the test of the i8 was on, and I am guessing similarly aggressive driving ;) ) I returned home with an average of 8 MPG (and a mahooosive grin on my face).

33Mpg whilst being tested by a couple of yobbos with lead feet on empty country roads is a damn find achievement...especially considering the darling child of the eco world (the prius) would have struggled to keep the MPG in the 30s under the same conditions, and that is no where close to being a sports car.

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Anonymous Coward

"Boot it away from the tailgaiting Audi when the traffic in front clears"

Is that done for safety or ego reasons? Surely it would be better to simply pull in a lane and let the tailgating idiot go off and wrap themselves round something elsewhere?

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Anonymous Coward

Re: "Boot it away from the tailgaiting Audi when the traffic in front clears"

"Is that done for safety or ego reasons?"

Neither...I do it for fun.

"Surely it would be better to simply pull in a lane and let the tailgating idiot go off and wrap themselves round something elsewhere?"

If I had 450Bhp less then that is what I would do, but yea, it's much more fun my way.

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"(the prius) would have struggled to keep the MPG in the 30s "

Thermodynamics, don't you love it?

The i8 weighs around 1.5t, the Prius weighs around 1.4t. On the other hand it probably has less wind resistance than the Prius, so let's start from the basis that they actually have about the same energy consumption on identical journeys, with a mixture of traffic through to fast road work.

The Prius has a normally aspirated 1.8 litre engine with a compression ratio around 13 to 1, if I recall (I'm not fact checking, this is a blog post). The i8 is producing a maximum of around 160BHP/litre and so its turbo boost is going to be several atmospheres. That means that its effective CR is going to be higher than that on the Prius. What's more, since it has a bigger battery, it will spend more time with the engine running under load, since the limited battery on the Prius means that in traffic the engine often has to run at low load to recharge the battery. Spark ignition engines are less efficient on part load because the effective CR is less, so the i8 should be running with a higher effective CR all the time, which means higher achievable efficiency.

The point about the i8 engine is that it is very small, and having only 3 cylinders reduces friction compared to a similar engine with more cylinders (the swept area for rubbing surfaces is lower). That's why 3 cylinder, or even 2 (TwinAir) is becoming a popular design. Therefore, its high CR isn't wasted by pushing around lots of rubbing surface.

What governs fuel efficiency, as well as CR, is the expansion before pressure is released by the exhaust valve (i.e. useful work being done by the hot gas). We're talking basic Otto cycle here. For a turbo engine, some of the expansion energy is recovered by the turbine and used to push the cylinder down during the inlet cycle. This is why turbo engines can be more efficient than N/A engines, whereas superchargers are less efficient because they require shaft power to drive them.

So overall we have two cars with similar energy demands to achieve a given level of performance, and two IC engines of which we expect that of the i8 to be if anything a little more efficient.

tl;dr: on normal roads and driven in a similar way, a simple consideration of IC engine thermodynamics and the advantage of a bigger battery lead us to believe that the i8 should have lower fuel consumption than a Prius. And for so much money, it really ought to.

Under unlimited conditions, of course, the i8 will go a lot faster and so friction and wind resistance will increase the fuel consumed per kilometre.

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Anonymous Coward

Not sure why anyone thinks 32MPG is a good figure for a hybrid. I bought a Petrol SL350 V6 last year and under my mixed bag of commuting and generally being a dick on the M4 its still returning me between 33 and 38 MPG. intact I just drove my daughter 8 miles up the road to her school and came back to 30.8 for local traffic...

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32.9MPG out of a 362HP supercar.

It's pretty damn good.

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Re: "(the prius) would have struggled to keep the MPG in the 30s "

The Prius engines are also Atkinson cycle - which is something I can't remember to do with the valve timing. It is supposed to improve efficiency at the cost of peak power

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Re: "(the prius) would have struggled to keep the MPG in the 30s "

It was a review car. I suspect the pedal was fully to the floor for most of the rides (regardless of gear). I very much doubt your SL350 would perform as well given to the same reviewer.

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The advert

A great write-up and I love the car, but the advert for it that I saw on the telly was so mind-numbingly pretentiously wanky that I almost threw my remote at the screen!

"I am the impossible. I am the blank page" *vomit*

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Re: The advert

could not agree more. unfortunately today's breed of corporate marketing drone will never risk anything remotely creative. it's incredibly frustrating for ad agencies and incredibly boring for viewers.

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Re: The advert

As someone rarely subject to the indignity of televisual advertising*, thanks for the heads up. They must have hired the same polo-necked pricksters as Mazda.

*Grey market torrents, adblockers, making a habit of ad skipping on catchup boxes, coughing up a donation, etc.

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Super car?

While a very interesting car, not sure I would compare it to a supercar like a 458 or MP-12C. Looks more like competition for grand tourers than out and out supercars

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