[erichyung]

I read in the mpg and dccd thread that the gas mileage will generally improve when running full open (dial all the way down) on highway.
My questions are:

1. Is it okay to change the dccd from auto to manual while driving on highway as long as I'm not making any turns?

2. By running dccd to full open at all times, even on city driving, would it increase the mpg even more?

Thanks


edit: please move this thread if necesary.

[La Mer]

Real simply, there are two limited slip, center differentials. One is mechanical (center dif), one is electromagnetic (driver's controlled center dif.). The mechanical dif is 'on' all the time. The dccd is variable.

The only thing the dccd does is 'open' or 'lock' the electromagnetic dif. with a few settings in between the two. With it open, I am thinking that by reducing the dccd's control over the center dif, you are reducing power loss.

That's the way I've always understood it.

[lackskill]

I think the DCCD is only an electromagnetic clutch. IMO there is no real benefit to running in full rear. the center diff doesnt lock up until you slip as I understand it.

[fullerton]

It is not worth changing the DCCD for mileage reasons. If there is a difference, it is so small that one fast acceleration would destroy any gains.

You may change the settings on the fly at any time save when the wheels are moving at different rates (turns, slipping, sliding...)

[youknowimwhoa]

For your first question

The manual says you can change it any time as long as no slip is occurring.

For your second question

It wouldn't matter. You are not going to occur much slip at highway speeds.

[erichyung]

Originally Posted by youknowimwhoa

For your first question

The manual says you can change it any time as long as no slip is occurring.

For your second question

It wouldn't matter. You are not going to occur much slip at highway speeds.

thank you for the reply!

[RizzuH]

I drive on the freeway frequently and there is a noticeable mileage gain when I have the car cruising w/ the DCCD to full rear as opposed to Auto. I switch back to Auto when it comes to city driving and such, but when it comes to straight highway driving, putting the DCCD to full rear does improve my MPG.

[JPWEraser]

I've not noticed a mileage increase at all with DCCD open, but I do think that it is easier to drive the car smoothly.

[BlueGold]

Originally Posted by RizzuH

I drive on the freeway frequently and there is a noticeable mileage gain when I have the car cruising w/ the DCCD to full rear as opposed to Auto. I switch back to Auto when it comes to city driving and such, but when it comes to straight highway driving, putting the DCCD to full rear does improve my MPG.

Where is your data?? I call BS.

All the DCCD does is "control" slip. When in open you will slip more easily. When locked...you will slip less easily. Otherwise the HP/TQ split remains the same (cannot change that). On the highway you will experience no slip in normal conditions.

[Tortfeasor STi]

My view has always been that there is not magic pill for MPG savings. You just have to give it less gas and deal with not having fun driving the car. But since I can't financially justify buying a 30g car and then not enjoy its power and handling (a waste of the 25g it costs over the price of a used beater car) I choose not to care about it. I just fill it up when I get near E.

[gregsachs]

Originally Posted by BlueGold

Where is your data?? I call BS.

All the DCCD does is "control" slip. When in open you will slip more easily. When locked...you will slip less easily. Otherwise the HP/TQ split remains the same (cannot change that). On the highway you will experience no slip in normal conditions.

Also, mechanically the diff is open unless there is slip.

[Loubaru]

Originally Posted by Tortfeasor STi

My view has always been that there is not magic pill for MPG savings. You just have to give it less gas and deal with not having fun driving the car. But since I can't financially justify buying a 30g car and then not enjoy its power and handling (a waste of the 25g it costs over the price of a used beater car) I choose not to care about it. I just fill it up when I get near E.

+1. If you can't afford gas you shouldn't have bought a STi. I haven't really seen a difference between auto and DCCD open.

[Gondy]

Originally Posted by Tortfeasor STi

My view has always been that there is not magic pill for MPG savings. You just have to give it less gas and deal with not having fun driving the car. But since I can't financially justify buying a 30g car and then not enjoy its power and handling (a waste of the 25g it costs over the price of a used beater car) I choose not to care about it. I just fill it up when I get near E.

Pretty much my philosphy also! If you are all about getting the most bang out of your buck at the pump, and drive like a sally everywhere you go in the STI... you got to stop and think that you just wasted $35 g's on a car that you don't fully use!

Would you buy an Iphone just to use it to talk on the phone (and not use it to its full potential)?? I know I wouldn't, that would be a huge waste of $$$

[fullerton]

besides, the cost difference between having fun int he car and being bored is what, $500-$750 per year? I don't think that is a lot of money for fun.

[MaSTi04]

I agree with the "there's no difference" group. Believe me I've tried (for fun). My commute is about 150 miles round trip so I dedicated a full tank onboth open vs. auto. There was no difference that was noticable other than handeling.

I may be wrong, but my theory <------ read that again!!.....is that there's no difference because no matter if it's open or in auto there's just as much drivetrain lag no matter what mode it's in. Obviously how hard and how much gas you give it will change MPG, but give a control/constant there can't be a difference if you aren't changing the load. ie. Giving or reducing the more gas you use is the only variable.