Tuning for Fuel Economy

[Flinkly]

Here are my two (Stock) AVCS (cruise/non-cruise) and Timing tables. I read them as cruise=emissions optimized and non-cruise=power optimized. find it interesting that both have a 40 AVCS bump for a few cells (but below "normal" cruise speed). I also removed (didn't show in the picture) everything beyond 4k rpm, as the cruise/non-cruise maps are identical (and 4k+ really isn't cruise anymore...)

 

I also cruise at 65mph, so about 2600rpm and .4-.65g/rev

 

I think i'm going to start lowering the cruise map, so first rev will be reducing all 40's to 30's. I'll do some coarse changes like that until my 65mph highway cruising maximizes MPG/minimizes load.

Edited January 8, 2015 by Flinkly

[covertrussian]

Keep your first row at low .20 and zeroed out. It seems to help with breaking (more vacuum due to less reversion and less mixture just floating out).

 

I'm completely stumped on why 07+ LGT's run such aggressive AVCS maps. Maybe emissions went way up, and due to catless uppipe? Your head also flows better then my 05-06 one. My 04 FXT is similar to the LGT with AVCS being fairly low (15 and under cruising).

 

On my 05, when I run AVCS30, I loose major gas mileage. There is a chance, tin foil hat on, that the 07+ get much better gas mileage due to better overall design, and they had to knock it back down to be within EPA standards & Emission standards. In which case, if you run a 10* AVCS max, you might gain some gas mileage.

 

I would love to hear your feedback if you want to test that. I personally test at 70mph because the roads I drive on vary from 60-70mph posted limits. Also since VA put up a lot of 70 posted limits, even going 70mph exactly, you get run off the road like crazy, I can't imaging going 65....

[pnmid]

Regarding tire pressure effect on gas mileage, I got at least a .5 mpg better with 2-3 psi increase, even when running Cobb OTS economy map. I started running 37 front/35 rear in October or November.

This time of year, I could lose 2 psi just taking the car out of a 35 degree (unheated) garage to the 15 degree outside environment. I added 1 psi this morning as the temp is about 5. I could probably increase it to 40 front/38 rear if it stays below 25 degrees.

[covertrussian]

This is the first car that I have that cares this much about tire pressures. Granted I am running 225's instead of 215's. But even with 215's I think it still liked higher tire pressures. For me to gain 2-3mpg just from increasing the tire pressure by 6psi is quite a bump, it also goes in the other direction (loosing 2-3mpg) when colder air sets in.

 

Tire pressures is what kept my tune gas mileage runs inconsistent, ever since I found the happy number 45/43psi warm, I can finally get consistent MPG numbers.

[hadvw]

Generally how much does pressure go up from cold -> warm? How does ambient temp impact this? Any guidelines? Edited January 10, 2015 by hadvw
initial post wasn't very useful..

[Flinkly]

Need to roughly estimate volume available for air in the tire, psi you want, and expected heat while driving.

 

Or just good ol checking. Check pressure before you start (and temp of ambient) then pressure after driving. Do this a few times. Then guesstimate from there!

 

Sent from my XT1028

[covertrussian]

Generally how much does pressure go up from cold -> warm? How does ambient temp impact this? Any guidelines?

 

I'm building a list trying to get a trend. So far it seems like ~40*F ambient temps gives you +4psi. I think 60*F probably gives you +5-6, hence it puts 36psi cold right at 42psi warm, aka in happy zone for mpg.

 

I check and fill up the tires while they are cold, then after driving one way ~65 miles, will measure them, get food, and drive back. When I get back, while filling up I'll measure the tire pressures and note it down as the warm psi (along with ambient temp).

[covertrussian]

Went to City A yesterday, got 29.44mpg, 45-46* Timing @70mph, 38-48F, Tire PSI 42/40@38F, 440lbs additional weight (to the base car weight), similar temp ranges. Two changes, fresh 5w30 synthetic oil (Valvoline) and AVCS set to 10*. Last week I went to that city, I got 26.37mpg, 260lbs, 46* timing, AVCS 0, 38-42F, Tire PSI 42/40@38F, Shell Rotella T6 5w40 (3300miles in).

 

On T6 the best mpg I've gotten to City A was 28.72, 440lbs, AVCS 10*, 36-37F, Tire PSI 42/40@37F, but that was with 41* max IGN timing at 70mph. I have gotten 29.23mpg to City B on T6 and 42* timing. Thus I don't think T6 had as much to do with the gain as just going from AVCS 0* to AVCS 10*.

 

I hate to have multiple variables for testing, but realistically it's very timing consuming, and expensive, to test only one change at a time, plus the weather is never 100% same (who knows about the wind speed differences haha).

 

Overall car seems to like AVCS 10 more then 0 with the downpipe. I'm tempted to try out AVCS 5-7* and see if it likes it more. Luckily gas is cheap and it costs me $10 to go roundtrip...

Edited January 12, 2015 by covertrussian

[covertrussian]

Finally tried out AVCS at 5* to see if car likes less overlap then 10 but more then 0.

http://i160.photobucket.com/albums/t188/covertrussian/Cars/05%20LGT/ECU/AVCS/DPAVCS5.png~original

 

Went to City A and got 26.02mpg, 45* base timing +1* for temps, 440lbs extra weight, 35-40F, warm tire pressures at 45F/44R.

 

Learning view looks normal too (except for A, which has been an issue most of the year).

http://i160.photobucket.com/albums/t188/covertrussian/Cars/05%20LGT/ECU/AVCS/LWAVCS5_IGN45.jpg~original

 

Might try 15* next, previously AVCS15* and 45* timing had an unhappy learning view in warm weather. Plus was lower then with AVSC10*, but that was on a hillfull non roundtrip fillup.

[PCvillain]

Of course! It's a no brainier, it destroys your ring lands and shortens the life of your motor. I was willing to loose MPG just to have a more reliable motor, but as my testing has shown so far, I lost no MPG due to disabled CL to OL delay.

...

The only time I've seen the CL to OL delay help gas mileage was in very aggressive driving, where your in boost very often, the delay reduces your fuel amount and power (plus added extra detonation). But once again, I'm willing to loose 1-2mpg aggressive driving, just to have reliability. Calm driving CL to OL delay being disabled doesn't hurt the mpg, in my testing it seems to help your mpg.

 

I am totally interested in this MPG research on these cars. Too bad Subaru didn't.....GJ and thanks.

Do you all use a COBB for this? I guess I will have to invest in some ECU burning equip.....

 

I have just found out that my 05 LGT has likely burnt valves or maybe rings. I had a 20% lean injector....They are taking it apart this week. $2-5000 depending upon work needed.

I always track my MPG via http://www.fueleconomy.gov and have about 22 overall. About what a 2012 Suburban can get....sad face.

[covertrussian]

Thanks, I personally like the challenge, and paying less since I like to drive far for fun of it. Subaru did pretty good actually, all things considered (most other similar powered awd cars get same if not worse mpg). Though Volvo did beat Subaru with the turbo AWD S60, but it's a European car with it's bag of troubles.

 

I use a Tactrix cable, RomRaider & ECU Flash for tuning. I wish I could do real time tuning like Cobb, but I don't know if I want to pay $700 plus having a locked ECU. Plus attaching a wideband to Cobb for logging is more painful then through Romraider. Plus Cobb is no better for log reviewing, you still have to use excel, seriously guys...

 

Good luck with your LGT, makes sure to ditch the factory tune, it's the culprit!

[covertrussian]

Been working on my Stage 2 expanded map using MickeyD's Stg2 map for reference. I added more timing to low portions of the map (city driving). Little less aggressive then the previous map I've made.

 

Anyway went to City B (one with mountain crossing), 114m hwy 6m city, got 31.35mpg! The temperatures were on the warmer side, I pumped up the tires to 42/40psi @43f, but the temps while driving ranged from 46-58F. Checked the warm tire pressures and they were at 46.5/45.5psi @52F.

 

Sadly this is reaching the 60*F ambient mark where my gas mileage magically goes up. I was hoping to to a under 50*F test, but mother nature had other plans. Either way I'm very happy with the numbers, definitely the best mpg ever for a round trip run.

 

Stock Map:

http://i160.photobucket.com/albums/t188/covertrussian/Cars/05%20LGT/ECU/Timing%20Advance/05LGTBaseTiming.png~original

 

New Map:

http://i160.photobucket.com/albums/t188/covertrussian/Cars/05%20LGT/ECU/Timing%20Advance/05LGT_Stg2_v3002.png~original

 

 

 

Now I need to work on my city MPG. With temps hitting below 30*F daily, my calm driving city MPG has been 16.54mpg at best, and aggressive driving has been at 15.38mpg. My new stage 2 fuel map is much leaner for WOT, staying around 10.8-11.1afr, instead of low 10's. We'll post numbers as I get results (takes at least a week for me to rack up 1/4 tank of city miles, that's what happens when you drive 8 miles daily avg).

[xt2005bonbon]

covertrussian, did you hear about the Btssm android app? A fellow member developed it. It does everything except write to the ECU as of now, although it can reset it. Refresh rate is as fast as romraider. I mention it to you since you like numbers

As for me, I use it ALL THE TIME. It's always on in my car. I can pull LVs, log whenever I want, keep an eye on my fuel trims, FKC, FLKC, etc... It has helped me notice and fix developing vacuum or boost leaks several times. And it also has a knock warning feature based on FKC and FLKC values. Can't live without it!

 

Have a look if you haven't already

 

http://legacygt.com/forums/showthread.php/btssm-bluetooth-adapter-app-229709.html

[covertrussian]

Looks pretty cool, but I don't mind having a laptop hooked up to do that. It's nice that it has graphing though .

[xt2005bonbon]

It's especially practical though. Do you have your laptop in your car at all times? I think that is the main advantage of what he designed--the fact that you can almost always run this thing each time you're in your car, since you would always carry your phone or tablet with you. Anyway, just fyi .

[covertrussian]

Agreed and I don't, but it's always with me when I'm going on long trips. I do have a Scangauge that I have hooked up if my laptop is not, but it really lacks on information it shows compared to SSM protocol.

 

Scangauge is more accurate on MPG readings then the stock gauge does though.

[xt2005bonbon]

I remember a guy on the forum who had an old small laptop running xp, that he left in his trunk at all times. He then output the video signal from it to his nav unit, so he could constantly monitor ecu parameters, log via romraider, etc.. I don't know all the details, but I wanted to do exactly that, until that btssm thing came out. And that was the end of it!

 

Although I still have my laptop ready to write to my ECU in case I need to upload a revised tune.

[Flinkly]

I've got a windows 7 10" laptop in my car at all times. when others are riding with me, it's usually under the seat. otherwise it's my passenger and logging. I use it sometimes to analyze data, but a larger screen and faster graphics processor are sometimes needed for big logs.

[covertrussian]

NSWF did that, pretty nifty setup. I run an old XP laptop too, but it's showing age. What sucks is, newer laptops don't as many pixels so doesn't fit all of the gauges as easily.

[rhino6303]

I used to use my 10" Windows 7 laptop to do that...until I bought the openport 2.0. Now I just use microSD logging all of the time. It is so much easier than anything I've done before.

[covertrussian]

One of these days... sadly getting wideband feed into it might be rather difficult.

[covertrussian]

Little update on my city mileage findings thus far. For me higher tire pressures yield no improvement to fuel economy. I drive 4-6 miles one way, thus the tire pressure only goes up by 2psi tops, usually only 1 right now. Even when I ran 45psi cold, I still got about the same gas mileage.

 

Now my FXT did benefit increasing the tire pressure form stock 29/27psi to 36/34psi, but different tires, sizes and profiles.

 

Here is a list of items that I've noticed for city driving that seems to be hurting the fuel economy more compared to highway driving:

• I noticed with my UEGO, stock LGT fueling tends to linger around 14.6AFR cruising, not 14.7.
  
• It is a lot easier to get past 0psi while city driving, I do see the tune get into 13's AFR, which is fine for safety of the motor. Due to the small nature of the turbo, you will have this issue until you get a bigger turbo.
  
• The car seems to be rich for only a minute after a cold start. I see my wideband at 14.7afr fairly quickly. Which is fairly impressive, I plan on measuring at what CLT closed loop hits on a very cold start. I did notice some of my worse MPG is when temps dip below 25F for the fill up.
  
• My car is running Smurf Blood, the car was serviced by Andrewtech before I bought it, so I'm sure he used his mix (3qt Redline Lightweight Shockproof, 1qt Motul 300). I do think this is increasing drag in the city, not sure I want care to drain it for inferior fluids to find out.
  

Edited January 22, 2015 by covertrussian

[Flinkly]

yeah, for winter or cruising, grill louvres would be nice. keep your engine bay "sealed" up during warmup, and only open when you actually need any cooling, and only enough to get the coolant below 200. otherwise you just have increased warmup time and drag.

 

i'd just put winter grill blocks in, but would be afraid of temps being too high after warmup.

 

and to me, making a homebrew grill louvre mechanical system would be easy. making it respond to coolant temp, and electronically open and close in response to coolant temp - difficult.

[covertrussian]

I don't know if it would really help that much, my Subaru's warm up much faster then my Nissans. Interesting thing that I noticed, even with my radiator fan running always, city MPG was the same as with it being unplugged. I would say Subaru's thermostat design is already efficient.

 

If you do build a group louvre, post up your results .

[covertrussian]

Updated the first post with this information. I'm in process of summarizing my findings so far. Next up is the ECU tuning summarization.

 

Mechanical Modifications for Fuel Economy

 

Before messing with the tune, you want to make sure your car is mechanically sound. This is why I'm listing mechanical tuning/modifications first.

 

This is my personal experience with modifications that improve, or decrease, fuel economy on my two Subaru's:

2005 Legacy GT 5MT ~ 100k miles

2004 Forester XT 5MT ~150k miles

 

Suspension

Tires

Switching the tires to new wider (from 215/45/17 to 225/45/17) tires, did make me loose a negligible .27mpg post tire size correction. There are a ton of variables here though: different tread patterns, different rubber compounds, and new tires will always give you worse MPG because they have more tread flex which increases drag.

 

The reason I say post tire size correction, stock tire size makes your odometer be off by -1.5%, but speedometer reads correctly. With 225/45/17 tires, my speedometer is off by 1mph, but odometer reads on par with my GPS and Google Maps. Odometer is what matters, if you run stock tires, and don't apply the correct tire offset, you will be reading about .40mpg more then you really are getting.

 

Tire Pressures

Tire Pressures does effect gas mileage, more so in the winter then in the summer. This is because colder air doesn't increase the warm tire pressure as much as warmer air does. With my personal experience,the deciding temperature is 50-60F. Below this temperature range, I have to run much higher cold tire pressure to gain back the lost mpg on 225/45/15 tires.

 

I gained ~2mpg highway at 35-44F ambient temps, by simply increasing the cold tire pressure to 42f/40r (warm 45f/43.5r) from 36f/34r (warm 39.5f/38r).

 

My gains were negligible on warmer days though, I believe the warmer days will get 36/34psi closer to 42-45psi warm. Which seems to be the sweet spot for my tires. I do also believe the magic tire pressure number will vary based on your tire width. Wider tires will need more cold tire pressure to have less drag. I highly suggest looking for 50psi max sidewall tires, to give you plenty of playing room.

 

For city driving, higher tire pressures have resulted with non-existing gains. Part of the reason could be due to my short ~5mile trips, where the tires only warm up by 1-2psi tops. Higher tire pressures do make the city NVH (Noise, Vibration, Harshness) much worse.

 

Alignment

To be tested

 

Brakes

Regreasing all of the caliper pins and removing the rubber bushings that expand over time and drag, ~1mpg gain city.

 

http://i160.photobucket.com/albums/t188/covertrussian/Cars/05%20LGT/Suspension/Brakes/Caliper%20Brackets/CIMG1668.jpg~original

 

 

Transmission

Drivetrain Fluids

My LGT is running the Smurf Blood mix (3qt Redline Lightweight Shockproof, .8qt Motul 300). It's thicker then factory fluid or synthetic alternatives. I'm thinking this is one of the reasons my city MPG suffers so much more then highway mpg.

 

Engine

Crank Pulley

GrimmSpeed lightweight crank pulley made no noticeable MPG improvement on my LGT. FXT gained .70mpg gain city though.

 

http://i160.photobucket.com/albums/t188/covertrussian/Cars/05%20LGT/Engine/Pulleys/Crank/CIMG1583.jpg~original

 

Intake

On FXT switching from aftermarket air filter to OEM one, has yielded a .40mpg gain city.

 

Turbo Inlet

No noticeable improvements going to an aftermarket silicon inlet, even with replacing a pretty torn stock inlet.

 

Spark Plugs

Currently I am running Side Gaped plugs, Unfortunately I do not have much useful information for preside gaping. When I replace the spark plugs with new ones I'll have better comparison. On my Nissan's, side gaped plugs usually increase 1-3mpg though.

 

Exhaust

UpPipe

On FXT going from stock catted up pipe to STI Catless uppipe yielded me a negligible .17mpg gain city.

 

Unfortunately I do not have any numbers from the LGT going to an Invidia Uppipe, I broke the O2 sensor during installation, thus needed a brand new one. This negates any gains/loses becaue it's a major variable change.

 

http://i160.photobucket.com/albums/t188/covertrussian/Cars/05%20LGT/Engine/Exhaust/Uppipe/STIvsLGTUppipe.jpg~original

 

Downpipe

Stage 2 Downpipe in it self doesn't seem to help fuel economy. In fact it starts hurting it until you disable AF3 corrections, but I also found I still lost fuel economy even post AF3 disabling, due to tune running too much timing or too much AVCS advance.

 

After a retune a better flowing downpipe should in theory help with fuel economy due to reduction of pumping losses. I am planning on going back to stock downpipe for more testing eventually.

 

 

Fuel

Winter vs Summer Gas

It is easy to blame Winter gas for decreased fuel economy. Since I've been religiously adjusting my tire pressures and logging ambient temperatures. I've noticed that my winter fuel gas mileage has been approximately the same as summer fuel.

 

E10 vs 100% Gas

To be tested, all of my current testing is done on E10 Shell 93 gas.

Edited January 22, 2015 by covertrussian