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 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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Permalink Reply by Ian Pellant on September 8, 2009 at 6:21pm

Hi Guy,

The smart has a steering wheel position sensor for the ABS and ESP. Evilution mention it on: http://www.evilution.co.uk/index.php?id=521

It would be nice if the transmission was linked to the steering wheel position to better control downshifts... maybe the ESP already has that input for braking control but is not it using for applying power, just limiting it.

Manual shifting with the paddles is so much more fun than using full Auto. Using full pedal down to force a downshift causes a delay and lurch on my car... a flick of the left paddle is a lot quicker and smoother.

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