Tuning for Fuel Economy

[covertrussian]

The reason I asked was because that means your timing is actually ~6° earlier than that table (for most of your map), correct?

 

Ah good point, let me clarify that with a screenshot

http://i160.photobucket.com/albums/t188/covertrussian/Cars/05%20LGT/ECU/Timing/Base%20Timing/Stage%202%20KCA%20Max.png~original

 

As you can see most of the cruising ranges is not IAM dependent. I also keep an eye on the real time Total Timing through my Scan Gauge as I'm driving (it's all it's really good for, so useless for actually keeping track of MPG since it has worse accuracy then the dash gauge ).

[covertrussian]

I can't do as many highway only tests anymore, due to kid and budgets , thus for now I did some city tests. City tests are much harder to keep consistent (due to weather and traffic changes over the couple days it takes to rack up enough miles), so do consider that when reviewing the data.

 

Anyway, to the data, I kept a log of locations I went to, how many cold starts and tried to keep it very similar between the two. The first two tests had about 30 miles with rear left tire being at 25psi, third test had a patched tire and kept 39psi no problem.

 

Headlights Off (No DLR): 20.68mpg

Headlights On: 19.43mpg

Headlights On 2: 20.06mpg

 

On third test I did avoid one store, which has a lot of stop and go traffic to get to, that coupled with not having a deflated tire is the reason why I think got it higher mpg then the second test.

 

As you can see headlights cost me 1.25mpg on a bad day and 0.62mpg even when environment was more favorable to it. If I compare the two A-B-A highway trips 100% day (no headlights) vs 1/2 evening 1/2night (at least 50% headlights) I have a 1.69mpg difference. Perhaps my 65w OSRAM bulbs are to blame after all .

 

If I get a chance I will try to do a day A-B-A Highway trip with headlights on later in the future.

[covertrussian]

A couple weeks back I found that my Engine was not happy with 45* of timing highway on a bigger turbo. Two weeks ago I did a more controlled A-B-A test and got 30.85mpg during the day, this is the 3rd highest MPG to this city to date.

 

While on that trip I noticed that I was still hitting ~40*, turns out I missed some spots were KCA table kicks in, this led me to updating the timing map. Using NSFW's Timing Editor, which lets you combine base and KCA tables and see the total timing easily, I was able to remove those hills. While I was at it I got tired of looking at the jagged 2d graphs and smoothed the whole thing out.

 

Before:

http://legacygt.com/forums/attachment.php?attachmentid=239286&stc=1&d=1476586821

 

After:

http://legacygt.com/forums/attachment.php?attachmentid=239287&stc=1&d=1476586821

 

Thanks NSFW, you made an awesome tool! Maybe you can add the ability to multiply values instead of just adding by sub 1* increments?

 

Anyway, since most of the highway portion stayed about the same, aka 38*, I didn't want to waste an A-B-A highway test to get fairly similar numbers as two weeks ago. I figured I would venture out into testing AVCS again, perhaps with a freer flowing turbo higher intake cam advance would yield good MPG's again.

 

Higher AVCS advance equals to earlier intake valve closing, which decreases how much air and fuel mixture escapes back into the intake track during the compression stroke. Because the amount of bleed off is decreased your dynamic compression ratio increases. The main downside to early intake valve closing is the intake valves open earlier too, increasing the amount of overlap. Wikipedia has a pretty good quote on EIVC:

 

Early intake valve closing (EIVC) Another way to decrease the pumping losses associated with low engine speed, high vacuum conditions is by closing the intake valve earlier than normal. This involves closing the intake valve midway through the intake stroke. Air/fuel demands are so low at low-load conditions and the work required to fill the cylinder is relatively high, so Early intake valve closing greatly reduces pumping losses.[2] Studies have shown early intake valve closing reduces pumping losses by 40%, and increases fuel economy by 7%. It also reduced nitric oxide emissions by 24% at partial load conditions. A possible downside to early intake valve closing is that it significantly lowers the temperature of the combustion chamber, which can increase hydrocarbon emissions.

 

I quickly built a 15* Highway AVCS map, Update: I recently discovered that on 05-06 this means overlap would be at only 5*, due to exhaust cam closing before intake cam opening at 0* AVCS. Take AVCS value and subtract 10* and you will get the total overlap.

http://legacygt.com/forums/attachment.php?attachmentid=239288&stc=1&d=1476586821

 

Results: This trip got me 29.14mpg during the day with 67-72*F temps, this is down 1.71mpg from two weeks ago. Looks like 10* of AVCS is still the champ, perhaps I should try 5-7* instead?

 

Conclusion:

It looks like the car wasn't happy with the added overlap. Usually with more overlap your EGR increases too, that slows down the burn time, which means you need more timing, but because the earlier intake valve closing increases dynamic compression less timing would be needed. I've tested AVCS being at 15* with 38-45* of ignition advance and always got less MPG and more knock then AVCS being at 10* and similar ignition timing. Perhaps much less timing is needed at this cam angle.

 

This also makes me wonder about 07+ LGT's, which run 40*of AVCS and a lot of timing, maybe that's why their MPG's are no better then 05's? Perhaps running much less AVCS would be beneficial to 07's (who wants to test this out?)

Edited November 6, 2016 by covertrussian

[Flinkly]

Are you offering to do some tuning work?

[covertrussian]

Are you offering to do some tuning work?

 

Yesir, I plan on eventually owning an 07+ Spec B and would like to know if those engines/ECU's can get closer to what I get on my 05. Your just gotta be willing to do some highway tests with as few variables as possible .

 

Everything is in favor of gas mileage for 07+, you have higher compression, better flowing heads, TGV's tumble the air for better atomization while cruising, with 6 speed much lower RPM's. I just don't understand why, from mechanical stand points 07+ still only gets 26mpg highway.

 

On AVCS front, I'm building a hypothesis on this, It finally clicked in my head last night after reading some hot rod cam articles.

[Flinkly]

I'd offer my mostly stock car as a test vehicle, but my 850cc DW injectors (or something) have been causing me no end of fueling... oddities.

 

After we move (2 weeks!) I hope to give her some time to fix it.

[covertrussian]

Stock one would be a little easier to play with (less variables). I personally haven't tuned these cars for bigger injectors (I'm really trying not to go bigger then stock 520cc if I can avoid it ). I've tuned my Nissan for bigger injectors (actually running the STI 520cc yellows on her), concept should be about the same, but Subaru ECU do find a way to make it more complicated

[solidxsnake]

I'd love to help you, but I'm not sure my tune is all up-to-snuff to test AVCS stuff (the MAF scaling/fuel trims aren't nearly as close as I'd like). I noticed quite a bit of difference in cruising with dropping my AVCS down from 40° to 15° or so.

 

For what it's worth, I'm running a JmP VF46 custom, Cobb intake and downpipe, SPT catback, and stage2+ tune (originally by Mike at TA, with very minor/insignificant changes on my part); still on stock fueling, with TGVs intact, etc. I'm currently looking to replace my intake with a stocker, because I don't feel like trying to tune for the Cobb since the MAF seems to be quite inconsistent. I'm also just lazy

[covertrussian]

What kind of differences did you see going from 40* to 15*?

 

I would ditch the intake if your not able to get a consistent tune on it. I've learned to not trust a lot of intakes on the market, lots of crappy designs and MAF placements.

[covertrussian]

Even though last week's AVCS test was a flop, it helped me better understand cam phasing and the whole overalap vs timing picture.

 

One of the eye opening articles that I came across is this one: Secrets Of Camshaft Power

 

Specifically this exert:

Overlap

....

Less overlap increases efficiency by reducing the amount of raw fuel that escapes through the exhaust, while improving low-end response due to less reversion of the exhaust gases back up the intake port; the result is better idle, a stronger vacuum signal, and improved fuel economy.

 

After reading over that part it finally hit me like a hammer. As I reduce exhaust restrictions, I need to reduce overlap because it becomes easier for the exhaust to escape the cylinders, ie increased scavenging effect. Scavenging is actually a good thing and increases power for NA and big turbo guys, because the vacuum behind the exhaust stream sucks in the fresh air and fuel mixture. In our low rpm cruising the valves stay open much longer then they would be at redline, which means the scavenging effect will suck out our precious fuel into exhaust stream where it's simply wasted (hello high EGT's).

 

All the sudden it made sense on why I could run 20* of Intake AVCS with a stock turbo and downpipe and still get up to 30mpg: the exhaust was so backed up that the pressure differential wasn't great enough to vacuum out all of the fresh air and fuel. When I went stage 2, I would get knock running 15* of AVCS and 45* of timing, but reducing it to 10* (0* overlap on 05-06) of AVCS made the engine happy and delivered plenty of 30mpg results.

 

 

Since my city timing is not finalized, for this highway trip I left the city portion with 10* of AVCS but set the highway portion to be 5*, I also set reduced the timing by 2*, to make sure I wasn't over MBT.

http://legacygt.com/forums/attachment.php?attachmentid=239678&stc=1&d=1477363983

 

Testing Results:

I went to the same city as last week (the AVCS 15* one) for the A-B-A test, even though the temps were identical it was much windier (7-9mph winds, while last week was 4mph winds). Even with the extra wind resistance the car got 30.50mpg. Sure I got 30.85mpg couple weeks back with AVCS being at 10* and cruise timing at 38*, but I couldn't reduce the cruise timing any more without loosing gas mileage, basically I hit the roof of what the car can do with AVCS being at 10*.

 

I think the next step is to try more cruise timing, but I might start messing with more mechanical mods to increase efficiency. I want to port and polish my headers (would love some Equal lengths, but it's hard to justify), and I think it's time to to move to a new intake.

 

Update: This is continued in Mapping AVCS Cam Angles and Overlap post.

Edited November 6, 2016 by covertrussian

[covertrussian]

Update to this, remeasured my toe today at lunch, and I have 5/32" toe in up front and 7/32" in the back. All this time I thought I was at 0" toe front/back, guess that's what I get for measuring and adjusting toe right after having the it hang. Not used to factory springs compressing so much after a day of sitting (my other car has nice and stiff coilovers).

 

Not sure how much resistance toe in really creates, but probably no more then .5mpg loss at best in this case, still though, another point to address and test.

[covertrussian]

This is a continuation of AVCS 5 Testing post.

 

UPDATE: I believe there is a typo in the 2005 Legacy Manual giving us wrong exhaust valve closings. All other EJ255/7 motors with the same exact cam have 5* ATDC closing, while Legacy manual says 5* BTDC. This makes a lot of this post's information incorrect.

 

Here are the cam angles according to the 05 LGT manual:

http://legacygt.com/forums/attachment.php?attachmentid=239734&stc=1&d=1477486376

 

I'm a visual person, lets graph this, blue dots are the intake cam durations and red dot is the exhaust. I tried to find some software that would do this for me, sadly had to resort to a basic image.

http://legacygt.com/forums/attachment.php?attachmentid=239743&stc=1&d=1477488132

 

According to the FSM the max AVCS advance we can get is 20*, which seems odd since I believe people said 05's can do 30* of avcs (I've done it myself too)? At 20* of AVCS advance we would be at 15* BTDC, which equals to be 10* of overlap since exhaust cam closes at 5* BTDC.

 

Now this is where it gets interesting since I was always under the impression that AVCS advance of 10 would be 10* of overlap (and that's the case with 07+ LGT's). At 10* of AVCS advance we are actually at 0* of overlap already and at 5* the exhaust valve has been closed for 5*. So in this case we are not playing with overlap, we are instead playing with intake valve closing timing.

 

This is where I'll refer to another part of the camshaft article mentioned in the previous post:

Camshaft: Intake Closing

The intake closing point has more effect on engine-operating characteristics than any of the other three opening and closing points. The earlier it occurs the greater the cranking pressure. Early intake closing is critical for low-end torque and responsiveness and provides a broad power curve. It also reduces exhaust emissions while enhancing fuel economy.

 

As rpm increase, intake charge momentum increases. This results in the intake charge continuing to flow into the combustion chamber against the rising piston far past BDC. The higher the engine’s operating rpm, the later the intake closing should be to ensure all the charge possible makes it into the combustion chamber. Of course, closing the valve too late will create significant reversion. It’s a fine balancing act.

 

In a perfect world, the optimum intake closing point would occur just as the air stops flowing into the chamber; would get the valve seated quickly and not waste time in the low lift regions where airflow is minimal and there is no compression building in the cylinder; wouldn’t be so fast that the valve bounces as it closes, allowing the charge to escape back into the intake port and disturb the next charge; and, in hydraulic street cam applications, would ensure the closing ramps are not so fast that they result in noisy operation.

 

If we go by that and assuming our FSM numbers are all correct, reducing the AVCS to be 5* means we didn't reduce overlap, instead we kept the intake valves open longer into the power stroke and are pushing the air and fuel mixture out of the combustion chamber back into the intake track.

 

What I'm not sure about, is why it's so much more sensitive about ignition timing, I'm getting 5-10* of pulled timing due to feedback knock in the city with AVCS at 5*, while at AVCS 10* it was fine and dandy. EDIT: I reverted the city portion back to 10* and still saw knock, this knock and FBKC is related to something else.

Edited May 5, 2017 by covertrussian
Correcting the degree wheel

[covertrussian]

After doing a lot of digging it seems like 07-09's are running a lot more overlap then 05-06's. I didn't want to clutter this thread with non MPG related cam valve timing numbers, so I made a new thread here: AVCS Timing And Overlap (2005-06 vs 2007-09)

 

Cliff notes from that is, with 07-09, what ever value you see in the AVCS map that's how much overlap you are running. While with 05-06's you have to subtract 10* from the AVCS map to see your overlap numbers.

 

This still doesn't explain how or why 07+ run so much AVCS advance and overlap and are not detonating to hell. Though their timing maps are milder for the highway areas.

 

And I still want to play with someone's 07+ .

[hadvw]

Interesting aside: the nav bar tells me there's a page 5 (for my settings) with posts 161-163. But clicking on the page 5 link brings me back here (to page 4).. First bug like that I've ever with the forum software. Edit: Interesting, my post came up as #161. Not sure why it thought there were more before. Were some deleted?

 

All I can say is: I wish I had your understanding of the tuning process, and your time and dedication for it. Stock, I got around 18/25 as claimed, sometimes 26-27 on longer trips. Stage 2 (gutted pipes) wasn't too bad either with the VF40. Stage 3 (bnr16g, DW650s), and I'm lucky to get 15/22.

 

Mind you, I've been chasing some other issues lately (bad coil, I think). If I REALLY baby it on the freeway, I can sometimes see 25 mpg for portions of a trip (that's with the tune adjusted to show pretty much correct mpg for my injectors as measured by 5-10 tanks). 30 mpg?? In my '05? Maybe coasting downhill all the way.. I know, MT is probably +1-2 MPG anyway over my 5EAT, and I almost never take it easy, and a lot of my driving is stop-and-go with lots of sudden acceleration. I can accept 15-16 mpg for that. I'd just love to see 26-28 on the freeway sometimes when cruising at 70-75 mph. Maybe CA91 gas is partly to blame for that too.. And I guess most of my longer trips involve some significant elevations.. But still.

[Flinkly]

Well, and Subaru tunes more for mpg than any tuner would.

[covertrussian]

@hadvw I've seen that bug recently too, weird.

 

As for time and dedication, it's about the challenge of doing something most people don't care or want to do. I've been told plenty of times to just buy a Prius, where is the fun in that, plus it's boring to drive. It's really a numbers game for me, since money savings are actually fairly minor.

 

The goal here is to have a high MPG and good HP car without having to switch to a dumbed down Eco tune that's impossible to accelerate on. Having cruise and non cruise maps would be the best way to go (but more complex to tune).

[covertrussian]

With the success of reducing AVCS to 5*, wanted to test going back to 0* intake AVCS, which is what the stock tune calls for on these cars.

 

Since I got pretty good results with AVCS 5* and reduced timing I decided to pull 4* from highway portion of the map too. (In hypothesis I will explain why this was a mistake).

http://legacygt.com/forums/attachment.php?attachmentid=240346&stc=1&d=1478400423

 

 

Results: This got me 28.60mpg with very similar conditions as last 3 MPG tests, a quite a bit less then before. One thing that did change is gas was 5 cents cheaper then last 2 time, first thought was that Shell switched to winter fuel, but looking at my logs and it was the same price in beginning of October when I got 30.85mpg with AVCS at 10*. According to most sites gas stations switch to Winter fuel around mid September, thus I don't think gas was the issue here.

 

I did also remove the driver side head heatshield (passenger side has been off for couple weeks) and the cross over pipe's heatshield. I don't think it should effect gas mileage all that much if at all at low RPM's and loads that we are on the highway.

 

Hypothesis:

Reducing AVCS and reducing timing hurt the gas mileage by quite a bit. I was scratching my head on why, but while writing this post I reread a few things and updated the AVCS 15* test. I realized that I was thinking about this wrong (this is why I do these posts, before I started writing this post I couldn't think of a single thing to improve. ).

 

First lets analyze what happens when you increase AVCS:

Advancing the AVCS closes the intake valves sooner. When intake valves close sooner, less of the air/fuel mixture bleeds out thus increasing the dynamic compression, this translates to higher burn efficiency and requiring less timing. The caveat here is with early closing comes early opening, which increases overlap (if above 10* of AVCS on 05-06's). Overlap causes the cylinders to fill with already burned gasses, aka internal EGR effect. Since these gasses are cooler and displace fresh mixture, burn efficiency is reduced requiring more timing. You basically have to find a sweet spot between needing less timing for increased compression and needing more timing due EGR. I've tested AVCS being at 15* with 38-45* of ignition advance and always got less MPG then AVCS being at 10* and similar ignition timing. Perhaps much less timing is needed as you increase AVCS.

 

In this test we are on the other side of the spectrum, reducing AVCS to 0* also closes the intake valves later, which under partial throttle causes the rising piston to bleed some of the air and fuel mixture back into the intake runners which can be a good thing:

 

Late intake valve closing (LIVC) The first variation of continuous variable valve timing involves holding the intake valve open slightly longer than a traditional engine. This results in the piston actually pushing air out of the cylinder and back into the intake manifold during the compression stroke. The air which is expelled fills the manifold with higher pressure, and on subsequent intake strokes the air which is taken in is at a higher pressure. Late intake valve closing has been shown to reduce pumping losses by 40% during partial load conditions, and to decrease nitric oxide (NOx) emissions by 24%. Peak engine torque showed only a 1% decline, and hydrocarbon emissions were unchanged.

 

Source

 

Since we are pushing air and fuel mixture out, we are reducing the potential of the mixture at lower loads, this reduces the dynamic compression ratio and burn efficiency. As burn efficiency goes down more ignition timing is needed to make sure all of the air and fuel gets burned up. This is where I made the mistake of reducing the timing, I should have been increasing it!

 

Why bother with AVCS 0* or even 5*? The part about subsequent intake strokes having higher intake pressures is what's intriguing me about late valve closing, it would help reduce the throttling pumping losses. I think it's a game of finding the perfect ignition timing with those two AVCS angles to get good gas mileage.

Edited November 7, 2016 by covertrussian

[dabearsjoe420]

What can I change on my 97 legacy outback

 

Sent from my SM-G935P using Tapatalk

[covertrussian]

What can I change on my 97 legacy outback

 

Sent from my SM-G935P using Tapatalk

 

Sorry can't help with older cars, not even sure how much is tuneable on those cars. But I will say that the items that I'm testing should apply to all internal combustion gas engines.

 

Just remember that what applies to full throttle doesn't really apply to part throttle. Like say with timing, at full throttle you tune for MBT, while at part throttle MBT timing wont necessarily give you the best gas mileage.

[covertrussian]

Last week I mentioned that I was worried that winter fuel and lack of heat shields might be the reason why my MPG might have been lower with AVCS 0*. I really hate to waste a trip to retest an old tune (my old jagged timing map just wont die!), but I needed to set a base heat shieldless Winter MPG on last good fuel economy tune.

 

When I'm retesting an old tune, I usually try to sneak in another variable that is for the better, especially when it comes to tire life. I redid my alignment and brought the front from 5/32" toe in to 0" toe in and rear toe in from 7/32" to 1/8".

 

AVCS is back to being 10* and here is the ugly unsmooth timing map... I will say though, this map did have a much torquer feel while passing cars then my last couple maps.

http://legacygt.com/forums/attachment.php?attachmentid=239286&stc=1&d=1476586821

 

This timing map, minus a passenger (marginal help), minus heat shields (should hurt mpg due to exhaust being cooled), plus better alignment (should marginally help) got me 31.33mpg and some knock!

 

Traffic was lighter today both city and highway, lower city traffic will help, but lower highway traffic would make it worse since unintentional drafting is not there. Having less weight helps in the city, but on highway it can hurt (objects in motion want to stay in motion, heavier objects don't get swayed by wind as much).

 

About the knock, my IAM got lowered to 0.85 on the way back, sadly I wasn't logging IAM so don't know when it happened. But this further tells me that that timing map is too aggressive above 0.90g/rev. Maybe next week I can test my newer timing map.

 

Finally something for fun, here is a map trace of how many times I was in each cell while one the first leg of the trip.

http://legacygt.com/forums/attachment.php?attachmentid=240704&stc=1&d=1479100844

Edited November 14, 2016 by covertrussian

[covertrussian]

I've been wanting to do a daytime (no headlights) cooler weather highway MPG test and have went last couple weekends but each time I would run into other variables (heavy winds, holiday traffic, etc.)

 

Got a chance to run out today, with the same tune as the 31.3mpg run. Today Temperatures were 39-46F (62-65f in 31mpg run), traffic was about the same, but it was completely overcast while the 31mpg run was sunny. This time I got 28.21mpg, quite a big drop. Last weekend with a slightly different tune, I got 29.77mpg, with some stopped traffic, Sunny, temps were at 47-55F.

 

According to this I'm loosing 1.5mpg for every ~10F temperature drop. I think I'm seeing a trend with cloudy weather bringing worse MPG's too. Perhaps the sun being out is warming up the temps in the engine bay and gas tank?

[Gigs]

this thread makes me wish I didn't do like 60% city driving my combined has been around 21mpg.

[covertrussian]

I drive about 8 miles a day, 19mph average, doing only 4 miles between cold starts is not good for the car . I purposefully go on highway trips to other cities, for one it lets me test gas mileage, but it's also helps evaporate all the moisture in the oil and helps melt the sludge.

[Gigs]

Well did a 70/30 split of highway / city driving for 98 miles with my 5at bone stock LGT Wagon and got 20.4mpg which is not half bad considering the stock tune is geared towards emissions.

 

Dam VF40 was making boost at every hill with cruise control on.

 

Route of attack is a Topfeed conversion while doing all intake gaskets , Downpipe / uppipe then tuning to increase VE like you have done.

[covertrussian]

That's really low, I think with that kind of a split I would get 25ish, but ambient temperature does have a lot to do with it.

 

VF40 is actually good, I got plenty of 30mpg trips out of it, though I did retard my boost tables to make sure she was not boosting at highway speeds at part throttle:

http://i160.photobucket.com/albums/t188/covertrussian/Cars/05%20LGT/ECU/MPG%20Tuning/MPG_WGDC_001.png~original