Fuel consumption in a Brabus (Sorry for the lame question, but it's killing me!)

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Permalink Reply by Guy El on August 27, 2009 at 10:40am

Ian,

I just read your post on , that answered a lot of my questions.

I know that the gearbox is a sequential 'box, and that the car performs the clutch functions, but I hadn't realised that it's ok to let it downshift for you in manual mode. That would make it so much easier to drive in manual..

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Permalink Reply by Ian Pellant on August 27, 2009 at 6:25pm

Guy,
In manual (softip) mode the smart will automatically downshift when the revs drop too low... touching the brake pedal will signal it that you are intentionally slowing down, so it will quickly decide to downshift then. The only exception is when I'm in the suburbs and know I'm going to do a 90 degree left hand turn at 10 kph then accelerate up a grade to 30 kph.. the smart will downshift semi-automatically, but it hasn't learnt that corner yet, so will not downshift two gears. A quick double tap on the left paddle just as I start to turn left and voila!
There is over-rev protection and the smart will upshift automatically in any stick mode if revs exceed about 6350.
The Auto program (softouch) adds the touch button on the side of the shift lever and it tries to fully automate the shifts. It really has a hard time with first gear and standing starts. Hold the pedal down too far and the turbo kicks in and everything sticks in first until over-rev pursuades it to upshift... a bit of a scream when it happens because you didn't really intend to be a hoon, but the smart decided to have a blast from the traffic lights. Flip the right paddle to spank it.
To see how quick and smooth the shifts can be, flip the paddles to go through 3 - 4 -5.. 5 -4 -3 when doing 60 kph. Up and down. The shifting is quick and smooth. It is the nose up, nose down body plunge under acceleration that gives the shift a bad name. Treat the gear shifts as you would in a traditional manual shift, dry plate clutched car and the whole process becomes a lot smoother.

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Permalink Reply by Guy El on August 27, 2009 at 7:06pm

Thanks for your time all the help Ian! Much appreciated.

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Permalink Reply by Timothy Cain on August 28, 2009 at 9:12am

My '09 fortwo PURE is now getting 49.6 UK MPG. That's with about 2400 kilometres on the odometer. My overall mileage for the 2 months I've had the car is over 45 UK MPG. This has been with air-conditioning on 75-90% of the time and a mix of highway and city. Different car, but just as a guide. I've explained each of my fill-ups here. (http://fuelthesmart.blogspot.com/)

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Permalink Reply by Guy El on August 28, 2009 at 12:46pm

Here's my summary, if you're interested:

A/C pretty much on all the time, usually only one person in the car (me), only I drive the car, Using Auto Mode. Average air temps are between 28 degrees (night) to 35-40 in the days. Mostly driven during the day. Mix of in-town and highway driving about 50/50.


27.53 liters (98 Oct)
319.3 km
8.6 l/100km
Notes: First fill ever, definitely Zero Boost, totally babied it, varied revs really gently, never went past 1/4 throttle.

28.89 liters (98 Octane)
312.1 km
9.3 l/100km
Notes: Breaking in the engine


30.29 liters (filled it with 100oct)
274.5 km
11 l/100km
Notes: Driving up to 4,000rpm no full throttle, but was going on boost


25.44 liters (100 oct)
222.8 km
11.4 l/100km
Notes: Driving up to 4,000rpm no full throttle, but was going on boost


31.45 liters (100 oct)
368.0 km
8.5 l/100
Notes: Mostly highway driving. I drove some 70km on about 5 liters of fuel, no A/C, keeping the revs really low as an experiment on the highway. Those are unrealistic driving conditions. This is probably the best efficiency this car will ever do.


20.38 liters (100 oct)
182.7 km
11.2 l/100
Notes: Some more "normal" driving now that it's past the babying stage


19 AUG 2009
28.89 liters (100 oct)
274.0 km
10.5 l/100
Notes: Usual, mix of highway and in-town

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Permalink Reply by Ian Pellant on August 28, 2009 at 6:39pm

Guy,
One thing that stands out is a fill of 31.45 litres. The smarts have a maximum tank capacity of 33 litres (5 of which shows up as reserve / finer scale fuel gauge readout).
You seem to have been fillig up at a variety of pumps. That is an unpreidcatble variable. I know my local service stations well and at one I know that one pump will deliver precise quantities (according to ScanGauage), whil another pump on a different aisle will deliver about 2 litres more than expected. Pump one is less sun exposed to pump two. The cross fall on the hardstand is different. Pumps are a much bigger variable than we may expect.
Always use the same pump at the same time of day - preferably early morning when the fuel is coolest and densest, when trying to get consumption figures.
How do you do know the turbo boost? Xclusive has a gauge?
I'm using the ScanGauge to monitor MAP in kpa. Anything over 100 kpa is obvious boost. Don't see it much in normal cruising.
Have to lead foot around town to get worse than 6.5 lhk. Your figures really are too high a consumption.
I'm off for an 800 km round trip with a dicky CKP sensor... my lhk figures may be a bit abnormal for this trip due to drifting ignition timing and mix... an adventure beckons.

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Permalink Reply by Guy El on August 29, 2009 at 10:38pm

Ian,

100% of all my fills were made at the same station, at the same pump (there aren't many 100octane pumps here). It's the same place that I fill my other cars.

The 31.45 was me coming back from a long trip on literally fumes. The fuel gauge in the car read 0.5 liters!! It was that I really wanted to go to that pump specifically. I left another town 70kms away and the car flashed low fuel and said 5 liters left just as I turned onto the highway.. I risked it, babied it with A/C off for most of the trip. I was really curious to see what kind of mileage it would get.

I would probably trust the pump more than the car's gauge. The car's gauge shows 8 bars when full, and stays on the first bar for at least 60kms, about 40-50kms on the second bar and then races through the last 6 bars. It is somewhat accurate at below 5 liters when it gets into the details.

By a boost gauge, I meant finding an aftermarket gauge that resembles the colors of the Brabus clock, and replacing the clock with a boost gauge, just for fun.

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Permalink Reply by Ian Pellant on August 30, 2009 at 4:38am

Hi Guy,
I did the round trip ok... just a bit of a worry getting the smart to cold start on both mornings.
Managed to attain 5.5 lhk driving south, then 6.1 lhk coming back. Really inexplicable differences in fuel consumption that I'm hoping is caused by the crankshaft positioning sensor being flaky. The ScanGauge shows varying fuel consumption (second by second) when steady cruising at 100 kph. MAP (Manifold Absolute Pressure) stays constant, but the mixture is obviously changing from around 5 lhk to almost 7 lhk at the same speed and load.
Turbo boost (MAP) seems to be greater in 5th gear than in 4th at 100 kph... maybe the turbo is producing more torque at the lower rpm in 5th. In 4th the rpm are higher and the power is more in the brake horse curve. (?)
The only way I reproduce your heavy consumption would be by sustained uphill drives... with no fuel saving by returning downhill.
I hope the replacement sensor arrives this week...
One reason for the fist bar on the fuel gauge lingering is that the gauge measures the level in the fuel tank.. it does not try to guess how much is in the filler pipe so until that is used and the tank starts to drain, the gauge stays on full.

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Permalink Reply by Guy El on August 30, 2009 at 4:53pm

Hi Ian,

Good to know it all went ok!

The higher boost pressure could sound like "boost creep" to me. It occurs on some turbo cars when you get into in longer gears.. It's usually when the wastegate can't bypass enough exhaust gases and the turbo's boost pressure increases.

Cars are usually tuned from the factory to understand small rises in boost pressure a little bit beyond the norm, in case things like this happen.

On the other hand, if the boost pressure is electronically controlled with a solenoid or something, it could be that the car's ECU gives some more boost in 5th to keep the car accelerating at a healthy pace..

I've been driving the car in manual mode, and it's pretty cool (only "quirk" is that it can get caught off guard on corners, but now i just blip it down right before entering the corner).
I can also get the shifts super smooth now, with a quick lift off the gas pedal and a smooth stepping back on.

Unfortunately I did a lot of highway driving and that will affect my mileage figures, but as of the next refill, I will see if there are any noticeable improvements.

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Permalink Reply by Ian Pellant on August 30, 2009 at 7:32pm

Hi Guy,
The wastegate is discussed on Evilution. One the things to remember is the small size of the engine and turbo... the wastegate generally is not an issue on the smart.
If you check the power and torque figures for the turbos vs the na the biggest difference is in the torque, not the power. Max torque for the na is 92 Nm @ 4,500 rpm. My turbo is rated 120 Nm @ 3,250. Your Xclusive is: 140 Nm @ 3,500. To me this indicates that the turbos boost torque and move it down the rpm scall compared to the non-turbos. This should mean we have more grunt in 5th than the na and this is where the turbo is working a bit more. Start doing over 4,000 rpm in 4th and the turbo phases out (?)
Yep.. the quirk in manual shifting is to flick the paddle down one or two gears before pulling hard on the steering wheel on a 90 degree residential corner... or suffer the "where the heck is that paddle" syndrome.

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Permalink Reply by Ian Pellant on September 7, 2009 at 8:22pm

Hi Guy,
The crankshaft positioning sensor was replaced last Friday.
Did the Cairns to Townsville round trip yesterday - 707 km total. Average speed 74 kph, max legal speed 100 kph... it's not a good highway!

Fuel consumption with Shell Premium 95 RON was 5.8 lhk, both ways. That's a lot more stable than previous trips that bounced up to 6.5 lhk. I'll switch back to Shell V-Power 98 RON and perhaps see the consumption drop to 5.5 lhk.

The car is now sticking in 5th in Auto, more than it used to. At 100 kph, it's doing about 3,000 rpm - just under the max torque output. Turbo around 80 kpa. That's a bit sluggish on downchange for hills, so I still prefer manual shifts. Turbo boost drops when in 4th doing 100 kph.

Hypothesis: if the crankshaft positioning sensor is not quite right, the whole fuel mix is affected and fuel consumption can be high.

On a road dominated by Toyota Prados, it takes a while before they give up trying to push me as we leave each town / slow section of the road. I need a rear facing camera to catch some of the expressions.

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Permalink Reply by Guy El on September 8, 2009 at 9:23am

Hi Ian,

Most interesting. The ECU definitely has a funny way of downshifting and I am definitely using manual mode much more these days for super smooth driving including taking turns and speeding up the downshifting so that I have more control coming out of the turn (instead of the gearbox hunting for the best gear to be in).

Maybe as time goes by and ECUs become more intelligent, they'll take into consideration steering angle, and predict that you are turning, or even better it will be ready to downshift if you use your indicators and start to turn the wheel in that direction :)

I think I'm going to have the guys at the dealership take a look at the excessive consumption thing, it could be a faulty sensor on my side too, although no other symptoms are displayed.

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