Last issue we developed a very sophisticated lean cruise mode for the Insight, and added two driver-adjustable knobs. Now it’s time to wrap-up the first stage of the Insight project – did we meet our stated fuel economy and performance goals?
The goals of the first stage of our Insight project were a 0-100 km/h time somewhere in the seven second bracket, and open road fuel economy in the Threes (in litres/100km).
I wish now I’d added another criterion: driveability better than the factory car without electric assist working – but more on this in a moment.
So those were the goals – now, were they met?
No they weren’t!
But I got close….
Measuring a good 0-100 km/h time proved quite difficult. Give the car too many revs on launch and the little 165 tyres just spun. Give the engine too few revs and it would bog down before coming onto boost. The best, consistent result came with just the right amount of wheel-spin.
This approach resulted in a 0-100 km/h time of 8.2 seconds.
To do any better than this would require increasing peak turbo boost, or holding it at a higher level for longer – neither of which I want to do. My reluctance to go higher in boost from its current peak of 80 kPa (11.6 psi) is based on:
Putting this another way, I reckon the car’s quite happy on this much boost; I don’t think it would stay happy on anything much higher. In addition, the injectors, despite being 63 per cent bigger than standard, are right on their limit. Going higher in boost would need another injector upgrade.
So the 0-100 km/h time is 8.2 seconds – a time that does not meet the goal of being in the Sevens.
So what about fuel economy? Did we meet the goal? It depends so much on how you measure it!
Driven with an eye towards economy, on the open road the car will easily turn in fuel economy in the Threes (litres/100km).
Note that this does not mean the use of 'hypermiler' techniques like pulse-and-glide, or coasting down hills in neutral – or even crawling away from traffic lights. Instead I am talking about early gear up-changes, using low amounts of boost, and reading traffic a long way ahead so that throttle lifts can occur early. It also involves dropping (say) 10 km/h on open-road hills – so from 110 km/h to 100, for example.
However, unless you are chasing max fuel economy, driving in this way isn’t so much fun.
Driven with a bit of verve, fuel economy will worsen to being in the Fours. Indicatively, this approach uses a burst of boost every now and again, perhaps redlining occasionally, and pushing a bit through traffic.
Driven hard – full boost, lots of throttle, lots of acceleration – and fuel economy will turn into low Fives.
Note: the same economy – Fives - will also be achieved with more gentle driving but if the air conditioning is run all the time. The air con worsens fuel economy by about 15 – 20 per cent.
Driven really, really hard, the car will deliver low Sixes. I am talking redlining every gear, top speed, almost all driving done at either full throttle or zero throttle.
My judgement is that this does meet the stated fuel economy goal of 'Threes' on the open road. However, I don’t think I will be seeing this much – but that’s because I want to be able to sprint up hills at speed and whoosh past trucks!
So the open-road fuel economy goal of being in the 'Threes' is met.
Driveability should have been one of my initial criteria of success.
Having never mapped programmable management before, let alone from a blank slate, I wasn’t aware of how incredibly finicky and precise the tune needed to be if driveability was to be better than the factory Insight (and similar to how most unmodified cars are).
Getting the required degree of driveability (ie what I was happy with) took infinitely longer than tuning the basics of fuel, ignition, boost, EGR – and so on.
And there’s another very interesting point to keep in mind about driveability.
Decisions made in the tuning to improve driveability have made a large difference to the fuel economy outcome. For example, I deliberately forsook best fuel economy for better driveability in three key tuning areas:
In each of these areas I started off with strategies that gave better fuel economy, but then changed them in order to improve driveability. So I pour in the fuel on throttle transitions, run richer than stoichiometric on any boost, and delay my transition into lean cruise - and then don’t go quite as lean as is possible.
The change to greater throttle enrichment gave these improvements:
The use of richer air/fuel ratios on any boost gave the following advantages:
The use of a less extreme lean cruise mode gave the following advantages:
So to retrospectively add another criterion to list: the need for excellent driveability was met.
So that’s the end of Stage 1. Stage II will involve a new electric motor controller, new High Voltage battery pack and a new Battery Management System.
The new system should be able to over-rate the 10kW standard electric motor for short periods, and with all that torque available just off idle rpm, the engine (and so turbo) should be able to be brought up to speed very quickly.
Estimates suggest that the torque at 2000 rpm should be able to be doubled. If that’s the case, the torque curve should then be flat from around 2000 – 5500 rpm… something that should give incredibly good driveability.
The original aims for this next stage were 0-100 km/h performance in the Sixes, and fuel economy on the open road in the Twos (litres/100km) – I now doubt that I’ll achieve the latter but I think it’s possible I’ll scrape in the performance figure.
That’s the plan, anyway…