Fuel Economy Improvements

[AmericanRonin]

So I just bought an '06 Legacy GT and I absolutely love the thing. The only gripe I have is that the fuel economy's a little less than what I'd like it to be. I've already put Pulstar Sparkplugs in it but I'm also looking to add a cold air intake and a performance exhaust. Can anyone recommend any good products with regard to this? Or anything else that would improve fuel economy for that matter? Bear in mind I'm looking more to improve fuel efficiency than to make my car faster. God knows I'll probably get in trouble with this thing being as fast as it is . . .

 

Oh, I'm based out of Charleston, SC too. So if anyone knows any good places in the area that specialize in Legacies, that'd be a big help too.

 

Thanks all.

[ehsnils]

Cleaning of the MAF sensor can help. AutoZone has a MAF cleaner in a spray can. Don't touch the resistor since it may break or get damaged.

 

Unnecessary features on the car that causes drag is also a factor. And of course - unnecessary weight. Don't forget that electrical appliances also adds drag, as does the AC.

 

Add a K&N air filter, that can make the airflow a bit better.

 

Tires creates a lot of drag. Narrower tires have less drag, but unfortunately also less grip in dry conditions. In wet conditions you may get better grip with narrower tires.

 

And for some the fuel efficiency actually gets better when they go Stage 1 or Stage 2 instead of remaining stock. But it also depends on the driver if there is a gain. A session using RomRaider (http://www.romraider.com/Documentation/Documentation) may be of interest, but that requires patience and experience to get something out of it.

 

Personally I think that the electronic throttle is part of the problem with fuel consumption because it's hard to modulate finely at low throttle openings.

 

Personally I prefer NGK plugs. (Had an engine once that only worked well with NGK) But the spark plugs are generally not an issue for fuel consumption unless they are getting really old or are contaminated. Just make sure that the gap is as specified on all plugs. (1.1 mm or 0.8 mm depending on engine type and year) Look here for more about how to "read" the spark plug: http://www.ngksparkplugs.com/tech_support/spark_plugs/faqs/faqread.asp?mode=nml

 

A check and cleaning of the injectors may provide some improvement. Injection cleaner in the tank a few times may help, but sometimes you have to remove the injectors and analyze them externally to determine if they are behaving correctly. Each injector shall provide the same amount of fuel over the whole duty cycle and with an uniform spray. See pictures here: http://www.wai-wetherill.com/ACE_Fuel/ACE_ASNU.cfm. If one injector gives less or more fuel than the others the engine will not run as well as it should and also cause unnecessary wear on the valves. In extreme cases burnt exhaust valves. It also puts unnecessary strain on the cat. So a matched set of injectors is a good thing. There are companies that provide matched sets: http://www.witchhunter.com/subarumod1.php4

[ean611]

To Echo what ehsnils wrote, stage 1, especially a protune, will help.

 

Stage 2 with a protune (Downpipe only, uppipe in 05 only, catback not required), from reports on this board, will add 1-2mpg along with the HP benefit.

 

Then again, if you add the HP, you may have a tendency to hit your gas pedal more, which will result it more burned gas

[f1anatic]

The problem is YOUR RIGHT FOOT !

I personally find Pulstar Plugs to be snake oil. NGK Iridium IX

Cleaning MAF is good as is a better (free flow) filter.

You could try tuning the car - Stage 1 or Stage 2 and yes you increase horsepower and fuel economy. You gotta read up on that but let's just say Subarus run rich from factory.

 

Last but not least you should use cruise control anytime every time. On the hill, down the hill, at 35 mph or at 70 mph. And Coast into gear as you approach a stop, downshifting only when necessary to maintain momentum. Shift gears at 2500 rpm or so and reach the cruising speed and flick the cruise control on. And watch the "rate of acceleration".

 

Finally read the document below.

http://www.everytime.cummins.com/assets/pdf/MPG_Secrets_Whitepaper.pdf

[SLegacy99]

Air filters, do the trick. I have a Weapon-R cone that got me a couple MPGs.

[stanjk3]

From what I've read the stock airbox is fine on the 05+ LGT unless you go stage 3. Changing to a Blitz air filter helped me a little, but it was more likely due to the air filter I had being really dirty.

[terrangama]

i heard TGV deletes will help w ith mpg

[AmericanRonin]

What is a TGV delete?

[mwiener2]

i heard removing the turbo worked the best

[Max Capacity]

Cobb AP stage 1 with a Pro Tuner. A month ago I met up with Mike of Tuning Alliance. He reflashed my version 1 AP and we went for a test ride while he made adjustments.

 

I'm pulling 16.5psi and can get 26-27 mpg without trying to hard.

[mwiener2]

 

I'm pulling 16.5psi and can get 26-27 mpg without trying to hard.

 

 

calculated or as read from the trip computer?

[Scotty]

I had better fuel economy when running the SPT intake. Going stage 1 or 2 doesn't necessarily increase fuel economy. You tend to get on the gas more and decreasing the economy.

[Tracer-X]

I had better fuel economy when running the SPT intake. Going stage 1 or 2 doesn't necessarily increase fuel economy...

 

 

Probably because it was tricking your car into running lean and setting your engine up for potential damage from detonation.

 

No one has specifically said this yet so I will. DO NOT buy an intake. DO buy a panel filter. The intake is more then fine for a stock turbo.

[adidasoutback]

well unfortunately I find subaru did do several very aero and fuel economy poised decisions on our cars, like a recessed wiper cowel so they dont drag as well as hidden sprayers for the wipes that dont make drag. Also on the underside is that plastic cover on the front end, and all the windows and doors have a pretty small gap in them, seems like the air flows over them well.

 

I think these cars just have ancient transmissions, I mean at 75 im doing almost 3300 rpms and in a normal 4 banger id be at 2900 3000. The final drive and well all the gearing in these cars all need to be done, they accell awefull (2.5i and 3.0R) and sit awefull high in the rpms at highways speeds. The higher the rpm the less effiencent to me.

 

But thats IMO, your right foot is the biggest chooser of your millage.

[AmericanRonin]

Thanks everyone for the input. I use the cruise control just about as often as possible and I average around twenty-five to the gallon or so. Again, that's not bad, but I feel like there's room for improvement. I hadn't heard of the panel filter. What exactly is that?

 

Also, I'm a complete and total amateur when it comes to tuning. Could someone clarify what exactly Stage one and Stage two tuning entails?

[f1anatic]

I can easily do 30-31 real mpg on cruise control at 70 mph. Or 32-33 mpg on cruise control at 60 mph. My display reads 1.2 mpg higher than real (old fashioned calculations). Stock turbo but all other major bolt-on upgrades in place. It is all in how you drive and I admit I drive in a rather sedate manner.

[ehsnils]

well unfortunately I find subaru did do several very aero and fuel economy poised decisions on our cars, like a recessed wiper cowel so they dont drag as well as hidden sprayers for the wipes that dont make drag. Also on the underside is that plastic cover on the front end, and all the windows and doors have a pretty small gap in them, seems like the air flows over them well.

 

I think these cars just have ancient transmissions, I mean at 75 im doing almost 3300 rpms and in a normal 4 banger id be at 2900 3000. The final drive and well all the gearing in these cars all need to be done, they accell awefull (2.5i and 3.0R) and sit awefull high in the rpms at highways speeds. The higher the rpm the less effiencent to me.

 

But thats IMO, your right foot is the biggest chooser of your millage.

 

The boxer engines are short-stroke, which means that they have a larger bore than stroke. This in turn means that the optimal rpm range is higher than other engines but that doesn't necessarily mean that it's causing bad economy. There are many other factors involved.

 

And the reason why the stroke is short is because space is limited in the engine compartment.

 

One factor that contributes to fuel consumption is which oil you use. This has a great impact when driving short distances. A 10W30 or 10W40 oil can cause 5 to 10% higher consumption than a 5W30 or 5W40 oil at short distances. Same goes for transmission oil.

[f1anatic]

Thanks everyone for the input. I use the cruise control just about as often as possible and I average around twenty-five to the gallon or so. Again, that's not bad, but I feel like there's room for improvement. I hadn't heard of the panel filter. What exactly is that?

 

Also, I'm a complete and total amateur when it comes to tuning. Could someone clarify what exactly Stage one and Stage two tuning entails?

 

A panel filter is a better, free flow filter. Most popular ones are Perrin or AVO and they are foam rather than cotton (which needs be oiled). I run my Perrin without oil even though it calls for a light coating of oil.

 

Stage 1 - for Subarus it means reflashing the engine to a different calibration. There are 2 ways which have proved most popular: OPEN SOURCE (basically a sort of DYI) and ACCESSPORT (COBB TUNING). The open source is much cheaper 3x cheaper in fact than COBB TUNING but some people (myself included) feel that Cobb acessport is a more establised way of doing things. Partly because it was the only thing available when we got the car; and still is for the newer 08+ WRX and 07+ LGTs (i think, but the info may be dated). However it does the same thing. Exactly the same thing.

 

Stage 2 - here you reflash the engine after replacing your up-pipe (running from engine exhaust manifolds to turbo) and down-pipe (connecting the turbo to the rest of the exhaust piping). These 2 pipes, dealing with the hot turbo side, are usually equipped with catalytic converters which restrict flow big time. Some choose to replace with catless others who are more tree-hugging by nature, replace them with hi-flow cats. The higher the flow...the more horsepower to be found.

 

I do not know what year your car is...but if you have an 05-06 and not looking for major power upgrades, I would just buy a used Accessport (which is year and transmission specific) and play with it. It will allow you to run several settings in your car such as a more powerful mode; a stock mode or even a fuel economy mode. These calibrations are standard and certified by the manufacturers to be uber safe. That should make you happy for a while - but you can also pro-tune and have a custom map made to your request if you so wish.

[f1anatic]

You have a 2006 car. A used Accessport should be your answer.

[adidasoutback]

The boxer engines are short-stroke, which means that they have a larger bore than stroke. This in turn means that the optimal rpm range is higher than other engines but that doesn't necessarily mean that it's causing bad economy. There are many other factors involved.

 

And the reason why the stroke is short is because space is limited in the engine compartment.

 

One factor that contributes to fuel consumption is which oil you use. This has a great impact when driving short distances. A 10W30 or 10W40 oil can cause 5 to 10% higher consumption than a 5W30 or 5W40 oil at short distances. Same goes for transmission oil.

thats very good to know about the boxer, but why on earth would you need the car to sit in the optimum rpm range on the highway? None of my other cars did, and I dont see why this one would, on the highway a 6th gear wouldnt hurt these cars at all, its not like they are hondas with not tq in the low range and even if it dropped 500 rpms to like 2500 to 2800 I personally think you would see way better millage would you not? Id think that was all gearing not really where engine rpm is at highway speed.

 

I guess I just hate my transmission. I think its old and need an extra gear and a syncro in reverse as well as way better gear ratios.

[Max Capacity]

calculated or as read from the trip computer?

 

I know, I've been around here for a while, that's real as long as most of it is highway. For short periods the dash did show just over 30 mpg once.

 

Combined real is 23-24ish. Used to be 22-23. Which is pretty much what my 98' and 00" GT's got.

[ehsnils]

thats very good to know about the boxer, but why on earth would you need the car to sit in the optimum rpm range on the highway?

 

You don't, but it also explains that the engine has a lower torque on lower RPM:s, which means that to obtain a decent torque at normal driving the RPM has to be a bit higher. The low RPM torque of the Subaru boxers is really not remarkable.

[itsme]

i heard TGV deletes will help w ith mpg

yes they do. But not really worth it on stock turbo.

[itsme]

I had better fuel economy when running the SPT intake. Going stage 1 or 2 doesn't necessarily increase fuel economy. You tend to get on the gas more and decreasing the economy.

That's not true. Stage 1 and to improve the gas mileage because the stock tune is richer most stage 1-2. Look at you fueling tables. Stock tune is not the greatest. I helped scale a friends MAF and in the normal driving range it varied from +17% to -14% corrections on a bone stock car. What mileage did you get when you went stage 1 or 2? Plus the SPT intake has been shone to lose power by alot of people. I saw about a 2mpg bump each stage. I was getting @27mpg on stage2.

[AmericanRonin]

How easy is it to install an accessport? Is it recommended that I get a high flow air filter, cold air intake, etc. if I have one?