A 270cc engine in a car! Surely we jest?
Well first let’s see what the engine is required to do. Remember the car is a light, range extended plug-in electric car with everything minimalised to save weight. Even the electric range is cut back to 25 miles to halve the usual battery pack; half the weight and half the cost. In normal use the car would do the school run or a shopping trip on battery power alone but with no range anxiety thanks to petrol back up. Most electric cars boast longer range but for the majority of journeys they have carried around a heavy stack of surplus batteries. It follows that for most of our short journeys we are also lugging round the petrol engine so weight is going to be a major consideration.
The main use for the petrol engine might come from a weekend run in the country with some fast roads thrown in. With the 20-40bhp electric motor for brisk acceleration and overtaking the 12bhp petrol motor is really just for cruising at up to 50mph. Bear in mind that the engine is charging the batteries when the car is stationary, at the lights say, so the available, combined power when on the move is higher than one might imagine.
The Honda GX engine range actually gives us the choice to go for a bit more power but with weight penalties. Thanks to the go-kart scene they can all be tuned for more revs and more power. The rev limiter is always removed and a stronger flywheel added.
The GX200 only weighs 35lbs and can produce a useful 9bhp. The Loncin Chinese clone version only costs around £250 and makes a good starting point.
Next up is the GX270. Weighing in at 55lbs this might turn out to be the sweet spot between power and weight. With the usual modifications and the bigger carburettor from the GX390 this engine will give a good 12bhp.
The GX390 is good for up to 20 bhp but weighs a back straining 69lbs. Only testing will tell if that is departing too much from the light and minimalist idea but it would certainly be good for breaking the speed limit on the motorway. One should bear in mind that the engine and the electric motor are mounted just ahead of the rear wheel and the aim is to keep the overall weight distribution just slightly front heavy.
The engine mounting plate on the Original Twist hybrid 3-wheeler will be pre-drilled to mount all 3 engines so the choice is there. We can also consider the Briggs and Stratton racing engine with all the right bits built in at the factory – it’s called the ‘Animal’.
No doubt some inveterate tinkerers will have a spare engine for tuning experiments and, who knows, in time there might even be a racing series.
It is the intention that the engine will be pretty much clipped on and able to be changed in a couple of minutes so concepts like service exchange engines, rented engines etc are feasible. With that in mind the little 35lb GX200 that fits in a shopping bag looks attractive.
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