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Subaru’s New SI-Drive: “Intelligent” Mode Can Boost Fuel Efficiency by 10%

The SI-Drive selector

Subaru has introduced a new drive system—the SI-Drive—that allows the driver to maximize engine performance, control and efficiency by choosing from among three selectable modes—“Intelligent”, “Sport” and “Sport Sharp”—using a rotary dial on the center console.

The SI-Drive controls the electronic throttle system’s response and fuel and ignition curves to modify engine torque characteristics, changing the performance character of the car in each mode.

Subaru introduced the system along with the new 2.5 GT spec.B Legacy at the New York International Auto Show. The SI-Drive will be available on 2007 turbo Legacy and Outback models.

With “Intelligent” mode selected, the system reduces engine torque and maximum power and switches to a more relaxed throttle response curve. Intelligent mode is an ideal choice for smoother response while commuting in traffic, for example, where it can also help boost fuel efficiency by up to 10%, according to Subaru.

Intelligent mode’s more relaxed responses and lower torque output complement the low-traction surface driving safety provided by the Subaru Symmetrical All-Wheel Drive System.

When “Intelligent” mode is selected in vehicles with a manual transmission, a shift-up indicator blinks to signal the optimal shift point for maximum fuel efficiency.

In “Sport” mode, the performance of the 2.5 GT spec.B (and other 2007 turbo Legacy and Outback models) is similar to the 2006 model, with quick throttle responses and powerful, linear acceleration. The linear acceleration characteristic of this versatile mode makes it ideal for driving on freeways and suburban streets or for climbing mountain roads.

In “Sport Sharp” mode, SI-Drive modifies the engine’s electronic throttle mapping to deliver lightning quick throttle response and more power sooner.

The on-tachometer display indicates mode and shows the active torque curve.

On 2007 Legacy and Outback models equipped with the 5-speed automatic transmission (not available on Legacy 2.5 GT spec.B), SI-Drive also changes the transmission’s shift patterns. It will hold each gear longer through the rpm range and downshift more quickly under hard acceleration, depending on the mode selected.

The SI-Drive system includes instrument panel displays that allow the driver to monitor performance. The multi-information display located in the tachometer face—in addition to providing trip computer functions—denotes the selected SI-Drive mode and provides an active torque curve display.



This is an excellent idea. I hope Toyota comes out with something similar for its hybrids. The software could be programmed to provide a wide variety of performance/economy configurations.

I like that they chose the term "intelligent" in lieu of economy. Quite apropos.

Lance Funston

What does changing a nob really do that hammering the gas pedal doesn't? My undersanding of engines like VTEC is they are constantly looking at engine parameters and adjusting on the fly to deliver the right torque curve, power, and efficiency. The automatic transmission is trying to do help with this as well.

The thing about the turbo is the way the power comes on very suddenly when you hammer it. Perhaps this intelligent mode is really looking out for that to smooth it out. And if someone starts to cut you off as you come off the on-ramp in economy mode, am I losing something when I step on it to merge?

What am I missing here people?


It adjusts the basic map by which the engine control unit makes its decisions based on the inputs you describe. So the same action taken in a different mode may have a different result.

Mike GR

I wrote something about "software presets in future hybrids" a while ago: here.


Lance- VTEC does not constantly adjust anything. VTEC simply allows a low cam profile with short overlap for better low end performance and a high cam profile with long overlap for high rpm performance to be used at the same time.

Variable valve timing systems do have some leeway in adjustment but only of the valve opening and closing events which still doesn't affect the throttle response, ignition timing and fuel curves (which are all optimized for a set of conditions determined by the engineers...except throttle response which is only really changed when you have a by-wire throttle). Automobiles are not constantly adjusting the values for optimum fuel at times and then optimum power at other times as the "dumb" machine would not know when to employ the proper mode. You can have several sets of fuel and ignition timing parameters for different uses but how will the engine know which to employ?

If you need the power you simply dial up the sport mode. You probably would not need it in most cases anyways unless you are trying to pass someone on a 2-lane highway.

tom deplume

Couldn't the same result come from adjusting the software between the driver's ears?


The driver only has one input.
The throttle position and rate of change of such.

ECU can adjust boost pressure, timing, injector duty cycle, egr % opening (if present) etc

BWM's valvetronic system elininates the throttle buterfly, engine speed is controlled by wire by adjusting the valve lift.

GM's 4.2L i6 uses a cam phaser to adjust when the exhaust valves open/close relative to the intake.
They can set up low overlap (time when intake and exhaust valves are both open) for low speed, low end torque and more overlap for more airflow /hp at higher engine speeds

James may

I think it's a great feature. Most drivers, myself included, don't have spare thinking time to modulate accelerator pedal for best fuel economy. It's a good thing, I think, to be able to give the dirver the chance of an upfront decision on whether to drive more efficiently on a journey. Also, if they have 'over sized' their engine on car purchase, gives them a chance to use it as if it were a more efficient, smaller engine without loss of street cred. Good practical real world improvement I think.


What would be great is if a manufacturer could design a system that switches between the Otto and Atkinson (Miller) cycle. You hit the gas to accelerate - Otto. You lay off the gas and cruise - Atkinson. I don't know how you could do this other then using individual actuators on each poppet valve, but I'm no expert, so I could easily be overlooking something. Anyway, this concept seems to more or less replicate that general concept. What I don't understand is why control electronics can't be devised with an input feedback loop that does this automatically based on what input (how hard the driver steps on the pedal) to the system is.

Errant rambling,


To switch from Otto to Atkinson without lowering your compression ration (and efficiency), you'd need to make the piston come closer to the head at TDC.  There are ways to do this, but none of them appear to be simple or cheap enough yet.


I have a 05 subaru legacy gt wagon. You can reflash the ecu with an ecomony map which limits turbo boost and other engine paremeters for distance driving. This is really works well with an increase to 31mph. This can also be used to create more power/torc for performace driving . search (cobb accessport)

Robert Shafer

For the Intelligent mode with a manual transmission, the shift speed has to be correlated to the engine speed and RPM to match the optimum point on the BSFC (brake specific fuel consumption) map to obtain maximum fuel economy. It has to be more than a light on the instrument panel, so the driver can pay attention to road conditions. I get 38 -39 mpg in my 2003 Subaru Forester 2.5 liter M5 by keeping the engine speed under 2000 RPM in the city. I do this passively by listening to the engine speed or transmission gear whirring pitch, not by looking at the tach.

Scooby Doo

As a happy owner of a 2008 Subaru Legacy GT Limited, I find that this feature is a definate plus in my car. For my daily commute I keep the car in "Intelligent" mode so that I can get better gas mileage in the high-traffic drive through metropolitan New York. When I am out for an exciting ride using the Subaru's great grip and handling AWD system, I switch into "Sport". When I pull up at a stop-light next to a young guy revving their Mustang or Maxima's engine, I switch it into "Sport Sharp" and surprise them by showing them my tail lights. I don't waste the gas to race Honda's because after test driving and considering a Civic SI, and an Accord Coupe V6, I know that I'd trade a little gasoline for a car that can make me smile without driving it like I hate it.

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