CVT can be more efficient than manual because:
1. The engine can always be revving at the most efficient speed, while for fixed ratio gearboxes the engine typically doesn't stay in the efficient powerband a lot of the time.
2. There is no interruption while accelerating. Even the fastest manual shifters will still have a spilt second when the engine is not driving the wheels between shifts.
3. If you drive a manual properly, you would rev match a lot. Pressing the throttle in neutral or with the clutch disengaged is just wasting fuel.
There are some points for manual driving:
- When accelerating, if you are too slow you waste fuel by not covering ground fast enough, too fast and you also waste fuel by spraying an unnecessarily rich mixture which does not translate into acceleration. I believe there are two different ways which people feel the throttle, first is press to a fixed point immediately and wait for the revs to catch up, the second is to gently ease up the revs while pressing the pedal. The latter is definitely more efficient. Change up when you feel the engine has reached its sweet spot.
- When to shift up? I personally don't think there's a fixed point such as 2,000 RPM. It depends on the traffic situation and road condition. For example if traffic is moving slowly then I shift up really early, by 40 km/h I'm already in 4th gear (gentle acceleration) (bear in mind your Getrag has taller ratios than my Aichi Pockai). If it's an open road ahead then I tend to drag gears a little longer, because if I shift too early, the engine will be well below the efficient torque band, which brings us to the next point...
- Use the correct gear for the correct condition. Ever ridden a multi-speed bicycle? Your car engine feels exactly the same as when you're pedaling a bike. I think people who have spent a lot of time cycling are more efficient manual drivers as they understand the principles of gearing. The first thing to know is that lower RPM does not necessarily mean better efficiency. The low RPM = efficient rule only applies if you're cruising at a constant speed or accelerating *very* gently on flat ground or going downhill. For going uphill, you probably already know that you need to rev higher by using a lower ratio. For example, climbing up a moderate slope at 40 km/h in 4th gear which on my gearbox will give me about 2,000 RPM. With that ratio, you probably have to open the throttle quite a bit to maintain that speed, so a lot of fuel is pumped into the engine but the ratio is too high and you may feel the engine struggle to maintain that speed. However if you climb the same slope at 40 km/h but in 3rd gear, your revs will be closer to 3,000 RPM and you don't have to open the throttle as much as you did in 4th gear, so it's actually more efficient even though your engine revs are higher.
Also other points regardless of gearbox:
- Anticipate the traffic in front of you. Look beyond the car directly in front and observe the traffic flow. My favourite way to measure how well you do this is to watch the brake lights of the car in front and count how many times they brake compared to how many times you brake. I find that generally, for every 5 or 6 times the car in front brakes, I only brake once. Remember that braking converts your car kinetic energy into heat and every time you brake, you have to accelerate and burn fuel to regain your speed. Therefore a driver who brakes minimally is an efficient driver. You must use your brakes when necessary, such as coming to a stop but generally, drive in a manner which minimises braking. In heavy traffic, accelerate gently. Don't attempt to block vehicles cutting in front of you. If you see a red light in front, lift off the throttle and coast.
- The most efficient cruising speed is around 80-90 km/h. Any faster and your engine will be wasting power unnecessarily on overcoming drag from air resistance. Following this rule I managed to hit 546 km on about 34L,
gogoman86 who has done 600+ km on a tank will probably tell you the same too.
- If your time is flexible, avoid traffic jams. It's a 20 km drive to office for me every day. In the mornings if I leave at 7 or 8 am, it takes an hour to get to office. However after 9 am the time is reduced to less than half an hour. As for coming home, the earliest time I leave office is 7 pm, because before that various places will be congested. I can leave at about 6+, but I choose to stay to 7+ just to beat the jam.
- Watch the air cond thermostat. The colder your setting, the more often the compressor has to run and more fuel will be burnt. For me, the warmest temperature and blower speed 1 will suffice at night and early morning, during mid-day blower speed 2 and thermostat somewhere in the middle. Also I wait for the engine to warm up first by driving a few kilometres before turning the air-cond. The engine is thirsty when cold and there's no need to add additional load then.
- Generally engine oil has negligible difference on consumption. Been on 15w50 from new until 50,000 km, then switched to 10w30 but I don't think that has improved my consumption. My previous 546 km on a tank and also 20 km/L achieved on a midnight run with
davidke20 were on 15w50.
- There's only a certain amount you can do to improve your consumption. When I lived in PJ I could consistently hit below 8L/100 km and get 400-450 km a tank (sometimes more, especially with trips to KLIA), however here in Penang I normally get about 8-8.5L/100km due traffic lights every few hundred metres. I've tried really hard, following all the points mentioned above and going as far as switching off the engine at traffic lights (manual stop-start) but it's still very hard to get below 8L/100 km on this Island. The Campro engine is thirsty by nature and initially available only with poor gearbox choices, but now with the CVT and Getrag manual you guys are better off than us stuck with the older gearbox. So don't feel overly frustrated if your figures are not looking good, apply all the points above and if you're really fed up, sell the Gaga and buy a BiBa / Mirage / secondhand Sawi.
- If you haven't already done so, go sign up for an account at www.fuelly.com so that you can log and analyse your consumption over time.
Nov 7 2013, 10:22 PM
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