Tuning for Fuel Economy

[Gigs]

That alone is probably worth some serious economy as i can constantly feel it going partial throttle

[quick4dr]

Ive been averaging 17 with a 60 mile mostly highway commute, very hilly. usually use 3rd and 4th in manual mode otherwise she dives into 5th and lugs along.

 

19psi tune by Mikey, blouch 1.5xtr

 

likely going to have Tuning Alliance build me a fuel saver map

[covertrussian]

Are you going back downhill too? Some of my best highway MPG has been on a hilly highway stretch (the main city I go to actually). As long as you get downhill in the same fillup it equals out.

[bhazard]

Has anyone ever managed to safely tune for 87 or even 89 octane? I'm not sure exactly when it started happening but all the stations out here cranked their prices on premium to 50 cents or more higher than regular. Is it even possible or just not worth the risk?

 

Kinda sucks going from a 45+ mpg TDI to a 20-25 mpg sube especially when the fuel is more expensive.

[solidxsnake]

Has anyone ever managed to safely tune for 87 or even 89 octane? I'm not sure exactly when it started happening but all the stations out here cranked their prices on premium to 50 cents or more higher than regular. Is it even possible or just not worth the risk?

 

Kinda sucks going from a 45+ mpg TDI to a 20-25 mpg sube especially when the fuel is more expensive.

 

I'm sure it's possible... at first pass you can pull a bunch of timing and add some fuel to the tables (also lower boost). The car will lose quite a bit of pep, but I suppose that's expected.

[covertrussian]

It's possible, but you will quickly run out of timing to pull before you start to really pull back the boost.

 

It's just not worth it in the end, might even lose gas mileage.

[bhazard]

Yeah I would expect to lose some pep for sure. It just sucks cause I remember some stations charging only 5 or 10 cents more for 93 and now it's 50 cents more minimum. Some are as much as a dollar higher per gallon. Really bones you if you DD your sube like I'm going to.

[covertrussian]

It's been 50 some cents difference for a while here, though I've had 93 only cars for almost a decade. That's why I bought the NA Outback, needless to say I was fairly annoyed to see it knock with 87 so I've been running it on 93 up until recently where I started retuning it to work with 87.

 

Anyway, I finally got my Legacy's clutch replaced with a single mass flywheel setup, I'm hoping to do some MPG testing this week, hoping that the ~5lb lighter flywheel/clutch setup doesn't cost me highway mpg.

[covertrussian]

Finally got to test the single mass flywheel on a highway gas mileage test. Got 29.41mpg today with 49-55F temps with ~5-7mph winds. I did do a few more stops then last couple times, so that probably attributed the slight gas mileage hit.

 

It seems like the lighter flywheel setup didn't hurt gas mileage much if at all, wont know for sure unless I get another 60-70F sunny non windy day... yeah wont be for a while...

[Smithcraft]

Just to comment about the headlight/power usage having an effect on fuel economy.

 

While I always drive with the headlights on, while I was burping the new radiator, I figured I'm mess with the lights, while I was monitoring the temp on the Access Port.

 

While cycling through the assorted light settings, I watched the boost values since that should relate to economy. From the lights off, to lights on, lights on/fogs on, hi-beams on, there was a steady change in the boost value.

 

So power drain is definitely a thing with fuel economy.

 

SC

[covertrussian]

Where you watching the boost gauge? If so you probably would see a slight reduction in vacuum. My manual gauge is harder to pay attention to on that level, but it makes complete sense.

 

Fuel Economy Update

It's been balls cold still, that's why I haven't been updating this thread. I don't even bother wasting my time and gas money doing fuel efficiency testing if it's below 55F or if it's too windy (above 10mph).

 

With that said I did sneak in a highway trip couple weeks ago on a warm day. I just installed the new tires, Falken FK450 215/50/17 (22.8lbs each). On a 60-75*F day, after tire size correction, I got 30.20mpg.

 

That's is 1mpg down from the best I got last November at 31.33mpg with Cooper RS3-A's 225/45/17 (24lbs each). It could be because Falkens are less efficient, or most likely it's because they are brand new and have too much tire flex still (coopers were 3/32's in last test ).

[Smithcraft]

Yes, I was watching the boost gauge.

 

I tried it again today, and it's close to a 0.1 drop for lows, and a 0.2 drop for highs, so flashing highs gets close to 0.3 drop in vacuum.

 

SC

[Smithcraft]

Yes, I was watching the boost gauge.

 

I tried it again today, and it's close to a 0.1 drop for lows, and a 0.2 drop for highs, so flashing highs gets close to 0.3 drop in vacuum.

 

SC

[zero260]

I tried out your AVCS table and changed upped my base timing a few degrees in the cruising areas. I managed 27mpg around 55-60, but that dropped to 24 at 70-75. how are you getting 31mpg?

 

05 OBXT manual, rebuilt 4k miles ago. full exhaust, 18g, sti manifold, 3mm spacers, tgv deletes, 06 wrx flywheel clutch combo, tuned with romraider.

[covertrussian]

I tried out your AVCS table and changed upped my base timing a few degrees in the cruising areas. I managed 27mpg around 55-60, but that dropped to 24 at 70-75. how are you getting 31mpg?

 

05 OBXT manual, rebuilt 4k miles ago. full exhaust, 18g, sti manifold, 3mm spacers, tgv deletes, 06 wrx flywheel clutch combo, tuned with romraider.

 

I've actually been getting 30mpg at best lately with new tires (215/50/17, seem less efficient in rolling resistence) and WRX clutch. But it's been really windy here too, the times I got 31mpg it was sub 5mph winds. I also go 70mph but I do a few 75mph accelerations to pass trucks usually, when going form 75mph to 70 it does involuntarily do pulse gliding too. I also fill up before every highway trip, if I fill up the night before the next day's cold start will set me back about 1-1.5mpg.

 

Anyway with that aside here is my input on what could be going on and suggestions on fixing it. The Outback has a few disadvantages over the Legacy...

 

Aerodynamics:

- The higher stance increases drag

- It's a Wagon, which also increases drag due to bigger wake field behind it

- Roof rails and cross bars increase drag too.

- Front bumper seems to be less aerodynamic with big fog lights.

- According to specs Outback is 1.6" wider, this increases the frontal area

 

At the end of the day 05 Legacy GT has a very slick 0.29 Cd, 22.3' Front areal, and 6.46 CdA.

While the 05 Outback has 0.34 Cd, (most places say 0.31 but I found subaru.ca tech pdf that says 0.34, for comparison Legacy Wagon is 0.32). 05 Outback XT has 25.3' frontal area and finally a much higher 8.60 CdA.

 

With that in mind, the only one that you can control is ride height, are you at stock height? Every inch reduction should reduce Cd by 0.01 points. I'm thinking of lowering my LGT for this reason now...

 

What's interesting is, my 2012 2.5i Outback is even worse aerodynamically, but I haven gotten 33mpg on it (even though it's rated at 28mpg epa). But Subaru did something in 2010+, because pre 2010 2.5i outbacks were rated at 26ish.

 

Gearing

Outback has the same 5th gear but 4.444 final gear. Now if you run the stock sized 26.7" tall tires you will rev slightly lower then stock LGT. But if you put Legacy sized tires on your Outback your RPM's are going to go way up. Here is some math to show this:

 

Stock LGT: FG 4.111 - 215/45/17 (24.6") - 70mph = 2,902rpm

My Tires: FG 4.111 - 225/45/17 (25.0") - 70mph = 2,855rpm

Stock OBX: FG 4.444 - 225/55/17 (26.7") - 70mph = 2,890rpm

OBX on my Tires: FG 4.444 - 225/45/17 (25.0") - 70mph = 3,087rpm

 

What size tires are you running? Running taller tires helps reduce your RPM's, but this is where you can't have your cake and eat it, because taller tires are heavier. What's worse is they move the weight to the outside of the wheel where it is harder to rotate. This is why 17" rims over 15" hurt gas mileage very minimally.

 

 

Now onto your actual mods and tunes

How much timing are you running at the 70mph RPM before 1.00 g/s? With your mods,18g specifically, you might be running too much timing.

 

Are you going into open loop a bunch?

 

With aftermarket exhaust/DP, Are your AF3 adjustments disabled?

[bhazard]

In my experience, outbacks just suck at mpg. I typically manage 18-20 mpg with my 5eat XT. That's a mix of city and highway. Not beating on it.

 

Even my 97 5 speed would never do better than 24.

[Flinkly]

until recently, and with no tuning or mods, i can get 26mpg average. meaning i get as high as 28 in the summer and drops to 25 in the winter.

 

i've been stuck at 25 recently, but have had some intake leaks and other issues that i believe are the culprit.

 

08 obxt 5mt

[covertrussian]

In my experience, outbacks just suck at mpg. I typically manage 18-20 mpg with my 5eat XT. That's a mix of city and highway. Not beating on it.

 

Even my 97 5 speed would never do better than 24.

 

This is why I'm curious on my 2012 gets such good gas mileage. At worst I've gotten 27 highway and at best is 33.66mpg. I just weighed the car and it's at 3,400lbs, which is almost 50lbs less then my 05 LGT .

 

Maybe it's because of the 6th gear, I'm at around 2,600rpm highway. At first I thought it was due to longer gears, but turns out it's actually all due to tall tires. If I were to put my legacy tires on the outback, it would bet at 2,850rpm too basically.

[bhazard]

until recently, and with no tuning or mods, i can get 26mpg average. meaning i get as high as 28 in the summer and drops to 25 in the winter.

 

i've been stuck at 25 recently, but have had some intake leaks and other issues that i believe are the culprit.

 

08 obxt 5mt

Imo a manual will always do better than a conventional auto. The 08 also got higher 4.11 diff gears than an 05.

[zero260]

What's interesting is, my 2012 2.5i Outback is even worse aerodynamically, but I haven gotten 33mpg on it (even though it's rated at 28mpg epa). But Subaru did something in 2010+, because pre 2010 2.5i outbacks were rated at 26ish.

 

in 2010 the biggest change was the CVT transmissions on Outback and legacy models. I have a '11 legacy 2.5i and I get 34.5 mpg on the highway.

 

What size tires are you running? Running taller tires helps reduce your RPM's, but this is where you can't have your cake and eat it, because taller tires are heavier. What's worse is they move the weight to the outside of the wheel where it is harder to rotate. This is why 17" rims over 15" hurt gas mileage very minimally.

 

cheap aftermarket 17s with factory sized tires for 17" rims

 

Now onto your actual mods and tunes

How much timing are you running at the 70mph RPM before 1.00 g/s? With your mods,18g specifically, you might be running too much timing.

 

Are you going into open loop a bunch?

 

With aftermarket exhaust/DP, Are your AF3 adjustments disabled?

 

Base timing @ 2800rpm

0.25 0.40 0.60 0.75 0..90

40.11 40.11 43.28 43.28 40.11

 

I only go into open loop when accelerating to speed

I have disabled AF3 adjustments

 

I'm currently running wastegate boost(12 psi) until I have my full maf scaling locked in(I'm close)

[Flinkly]

ever thought or tried to run lean at idle and/or really low load? just pondering it on the way home.

 

my stock rom has 14.4-ish as a target at idle (rich) rather than leaner...

[covertrussian]

in 2010 the biggest change was the CVT transmissions on Outback and legacy models. I have a '11 legacy 2.5i and I get 34.5 mpg on the highway.

 

Mine's actually a 6 speed, so CVT stuff doesn't apply. Now mine revs around 2650rpm at 70mph in 6th gear, but after doing the math it's geared exactly like my 05 LGT, it's just the tires that make it rev that low. Also it has absolutely no power at that low of RPM, requiring me to downshift to 5th on steeper hills around here.

 

cheap aftermarket 17s with factory sized tires for 17" rims

 

In that case you should be around 2,900rpm at 70mph, which is on par with the GT's.

 

Base timing @ 2800rpm

0.25 0.40 0.60 0.75 0..90

40.11 40.11 43.28 43.28 40.11

 

Aha! I think your running too much timing for how efficient your turbo and rest of the setup is. I'm running 38* in all of those ranges.

 

I only go into open loop when accelerating to speed

I have disabled AF3 adjustments

 

I'm currently running wastegate boost(12 psi) until I have my full maf scaling locked in(I'm close)

 

When accelerating I try to avoid going above 0psi. Which is around 1.00 g/s, which is still in closed loop for me.

 

I'm at similar setup with wastegate boost only and around 13psi. Stock MAF scaling (because stock intake/filter). Though the time I tried out my DIY WAI I got almost 1mpg increase in gas mileage highway and negligible city.

 

ever thought or tried to run lean at idle and/or really low load? just pondering it on the way home.

 

my stock rom has 14.4-ish as a target at idle (rich) rather than leaner...

 

I slightly leaned out my idle, from the 14.4ish to 14.7-14.9. I am trying to avoid those kind of tricks, at least for now. The goal is to get as much MPG as I can with cat friendly AFR's and no hypermiling driving tactics.

[covertrussian]

I installed the Tomei Equal Length header a few weeks back. I've been waiting for a less windy day to do a proper gas mileage test, but that's not happening anytime soon.

 

http://legacygt.com/forums/attachment.php?attachmentid=248186&stc=1&d=1493058453

 

Since I installed new tires this year, it's hard to really compare to previous years logs (different rolling resistance between tires). So here is some data from new tires:

 

02/20/2017: 30.25mpg - 60-75F - Sunny - Winds 0-5mph

04/16/2017: 29.61mpg - 74-88F - Sunny - Winds 15mph (22mph Gusts)

04/21/2017: 26.04mpg - 82-91F - Sunny/Overcast - Winds 14mph - Last UEL run and I think this one is fluke, gas pump was disabled when I got back.

 

 

EL Header, same tune, without undertray:

04/30/2017: 28.36mpg - 84-88F - Sunny - Winds 21mph (31mph gusts)

 

Not looking too promising for header helping gas mileage. I started looking for another causes, prime suspects were spark plugs, air filter, dragging brakes. Air filter did have debris in it, I cleaned it up and vacuumed it.

 

Next were spark plugs, I last replaced them 37k miles ago with LFR6AIX and 0.040" side gap. Yesterday the gap measured at 0.059", that's a lot of wear!

http://i160.photobucket.com/albums/t188/covertrussian/Cars/05%20LGT/Engine/Sparkplugs/20170502_123238.jpg

 

Installed LFR7AIX's, which I had chilling in the garage, side gapped them to 0.035". I probably should have went with 7's a long time ago anyway, but since I do a lot of 4 mile drives, I'm worried about fouling.

 

Installed the undertray too (they are far enough from the header that I don't think it will melt now), this should help with aerodynamics a little bit more.

 

Went on a highway trip, I was 200lbs less then usual (no passengers). Here is what I got:

05/03/2017: 30.27mpg - 64-75F - Sunny - Winds 12mph (18mph gusts)

 

Now last year, on this same tune, about same occupant weight, the best MPG that I've gotten to this city was 31.33, with 5mph winds. I think with similar winds I would have gotten 31mpg at best.

 

Now it's time to figure out what the header likes timing and AVCS wise. Maybe it will finally like 15* of avcs? Pointers on which direction to modify the tune for the header? For full throttle I needed to add 2* of timing to regain power that was lost and then some ontop, but that's at full throttle where you rarely hit MBT on pump gas. Under vacuum it's really easy to go over MBT, did my MBT go up in cruising areas too now? Efficiency mods usually lower MBT though, maybe the big tubes (Tomei is on bigger side of EL headers) reduced the efficiency of the exhaust flow?

Edited May 4, 2017 by covertrussian

[covertrussian]

I am now pretty convinced that 2005 Legacy GT FSM has a typo on when the exhaust valves close. I spent the morning searching manuals and part numbers and everything I found says all 2005 EJ255/7 cams are the same. Heck even 2006 LGT manual shows the correct exhaust closing timing. Basically instead of saying 5* ATDC, it says 5* BTDC, easy one to fat finger.More details can be found here.

 

Why is this a big deal? Well as of late last year I was operating under the assumption that AVCS 10* was 0* of overlap, for fuel economy and power tuning. Everything I would read online says that ALL engines (even turbo) like at least some overlap. But tuning the legacy I would always loose power or gas mileage when going away from 10* of AVCS, aka going away from 0* overlap. This also eliminates the funky "negative overlap" zone, where everything under 10* of AVCS was not in overlap regions. Now that I know (99% sure) that it's a typo, I now know that I was running around with 10* of overlap all this time.

 

This also un-nullified my last year's testing with less AVCS (because too much AVCS will let the fuel escape into the exhaust). Which possibly means that with a much better flowing EL Header it's now even more crucial to reduce my overlap.

 

I did make another possible mistake in that AVCS 5* test, I reduced timing, instead I should have increased it. Reason is, advancing the AVCS increases the compression ratio, thus less timing is needed, this means reducing AVCS requires a timing increase. So far I'm finding that 5* AVCS change needs 2* timing change in opposite direction to keep it at MBT (based on my power testing).

Edited May 5, 2017 by covertrussian

[covertrussian]

Since it's been so windy lately I started considering aero mods. I got under the car and started seeing where it can be improved.

 

Rear Bumper: Subaru did a real good job here, not much to improve on.

http://legacygt.com/forums/attachment.php?attachmentid=255210&stc=1&d=1505151387

 

For comparison's sake here is how bad my Infiniti G20 is, which actually has a very low Cd of 0.30 too.

http://legacygt.com/forums/attachment.php?attachmentid=255211&stc=1&d=1505151387

 

Front is mostly good too, but could use some help between the tire and the undertray.

http://legacygt.com/forums/attachment.php?attachmentid=255209&stc=1&d=1505151387

 

I installed the S204 lip mainly for looks but also with hopes that it at least doesn't hurt the fuel economy.

http://legacygt.com/forums/attachment.php?attachmentid=255215&stc=1&d=1505151387

 

Before the lip and without undertray, you can see how the header sticks out past the bumper = bad for aero, this might actually be why I got only 28.3mpg without the tray.

http://legacygt.com/forums/attachment.php?attachmentid=255212&stc=1&d=1505151387

 

This lip covers up the header and suspension parts perfectly.

http://legacygt.com/forums/attachment.php?attachmentid=255213&stc=1&d=1505151387

 

Here is how it looks with the under tray before and after lip.

http://legacygt.com/forums/attachment.php?attachmentid=255214&stc=1&d=1505151387

 

You want the air dam (lip in this case), to sit just low enough to cover all turbulent spots, but not lower then that because it increases your frontal area (read: bigger fridge against the wind ). In this case the undertray is now sitting below the lip, so it might be time to get rid of it/replace it with something smaller.

 

Tune Updates

I started installing the lip because I was drawing blanks on what else to do on the tune. Right after I installed the lip, I actually got an idea to test, since I found out that AVCS @ 10* = 10* of overlap, with a better flowing header the chances of blowing fuel straight out the exhaust during overlap were higher.

 

I made AVCS be at 5* at highway RPM's and loads, but kept the timing the same as AVCS 10 map, which is 38*. It drove fine, not too different, so then knowing that less AVCS means less compression, I added 2* of timing where AVCS was at 5*. It made the motor operate much smoother, like it wasn't struggling as much.

 

I know I'm bad for testing two variables at once, I was just too eager to see if less overlap would help too. Finally it stopped raining and got a sunny day to test these changes, but it was really windy (10-18mph winds and up to 27mph gusts). Now usually if your highway driving wind can help you or hurt you the whole trip. But this particular city involves going south, then east, coming back you go west then north. Which means while going one direction wind will help, 1/4 of the trip in it will start hurting you.

 

On this trip I got 31.25mpg, while last time it was 30.27 with tamer winds. Thus both of these changes helped, since I was bad and tested to variables I'm not sure which one helped and how much , I might retest wit usual AVCS 10 map later.

 

I think the lip helped the front end downforce a good bit, even with such high winds I didn't have to fight with the steering wheel nearly as much. But I can't give all the credit to the lip, since less overlap and smoother engine probably helped just as much too.

Edited September 11, 2017 by covertrussian