B Stead

The BMW i8 is now available in the USA.

It has a three-cylinder turbo engine at 228HP and 236 pounds torque for the rear wheels. And it has a 129 HP electric motor at 184 pounds torque for the front wheels.

Now there is a very reasonable hybrid system that could be used on any car. Basically, electric motors power the front wheels just for pulling from a stop when driving normally or probably the hybrid system hangs-on longer when high RPM's are used. This type of hybrid system uses a small battery pack and braking re-charges the battery. The system makes both a hybrid system and a four-wheel drive system. It's a hybrid system that is reasonable in scope and not too heavy.

But the BMW i8 only works that way in one of its modes. Also, since it is a plug-in hybrid then the battery pack tends to be larger. So there is an all-electric mode, a mode that automatically combines the electric motor with the internal combustion engine, a mode that uses both the electric motor and the internal combustion engine, and who knows what else...probably a mode that uses only the internal combustion engine.

Now the BMW i8 mitigates the system weight with a carbon fiber chassis tub. Then the carbon fiber tub holds aluminum subframes for front and rear suspension. And so the car weight is 3274 pounds.

And what about that mode that combines both electric motor and internal combustion engine ? That's 357 horsepower and 420 pounds of torque.

Problems ? Well, as I already suggested the plug-in aspect, along with the all-electric mode, calls for a larger battery pack than a simpler system. Another problem is that while four-cylinder engines don't have great balance then three-cylinder engines are worst balance.

The price of the i8 two-seat sports car is about $140,000.

http://www.bmwusa.com/Standard/Conte...ighlights.aspx
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B Stead

The BMW i8 appears to have the internal combustion engine in a rear mid-engine location and the electric motor in a front-engine position.

A simpler hybrid system, like I was relating, just has a small electric motor for each front wheel and then a small battery pack for those motors.

I see one note that says the i8 battery pack weighs about 207 pounds. Well, see, if the all-electric mode were eliminated than how much smaller could the battery pack be ? Also, most high-performance buyers would give up 1 mpg in highway driving in exchange for keeping the hybrid-system battery charged since the hybrid system is used for acceleration but also used to improve city-driving MPG.

Finally, while it would be disappointing for the turbocharged internal combustion engine to be a 2.0 inline four instead of a 2.0 inline six, it's very surprising that it is a three-cylinder engine and actually 1.5 in size.

The bottom line is that the weight-saving carbon fiber tub makes the car possible and then the car can be very easily improved
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B Stead

The internal combustion engine of the i8 is transverse at the rear of the car but it looks like the crankshaft is on the rear axle line. That's rear-engine but only slightly rear-engine. Then the i8 actually is a 2+2.

Now with the front motor on the front axle line and the rear engine on the rear axle line, that's a flywheel effect. Except that the battery pack and the fuel tank are mid-ship.

For the engine to be a four-cylinder, the rear track would have to be wider.

This link includes some cut-away views:

http://www.leftlanenews.com/new-car-buying/bmw/i8/#
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