A Quest for 35mpg (Subaru Outback Limited Sedan 2.5L auto)

[Zerohour]

So took some time this morning to order a mod that I wanted to do for a while.

Since the skirts and taped wheels are gone, I'm seeing easily a 5-10% drop in FE. But I ordered the lightweight Agency Power pulley for my Subaru. Depending on year/model it drops the Subaru crank pulley weight from 4.5-6lbs down to 1.1lbs. It is noted as one of the best mods for a non-turbo Subaru.

I'm still considering 17" Wheel and tire combo that comes in at 6lbs per corner lighter. Although I'm not sure if I want to speed that much money for wheels and tires. Time will tell.

[spirilis]

Wow this is a huge thread, not sure if anyone mentioned this but wanted to toss it in there. I have a 2008 Subaru Forester (2.5X Premium, non-turbo, 5-speed manual transmission) and recently did an experiment where I replaced my plugs with NGK's V-Power coppers but overgapped them to .050" (stock gap was .043")

Background:
0-60K miles - Commuting ~90 miles a day mostly freeway, tended to get around 26-28mpg consistently. Spark plugs changed at 30K by a reputable dealer though I don't know what they used, but the car worked fine.
60K miles - Got the 60K mile service done by a new dealer (I moved), fuel economy instantly dropped to around 24-26mpg. The dealer said "there is no fuel filter to replace on this so we did a fuel system flush procedure", later on I pulled the plugs and they were NGK Platinum's (OEM recommends Copper, from what I gather). Don't know what the gap was.
90K miles - New job, new commute has me going around 50 miles a day mostly hilly terrain with some flat stretches and some bends. Before doing the 90K mile service (MYSELF this time...) I was getting consistently 24-25mpg. After changing the plugs to NGK V-Power coppers, still 24-25mpg.
Around 94K miles - Decided to tinker with spark plug gaps. Pulled the plugs and checked them--the V-Powers were gapped around .044", close enough to the shop manual's gap (.043"). I overgapped it to .050" and reinstalled. Still running the stock ignition coils and ignition wires, never changed them (might be a good idea soon...)
Instant bump to ~26-27mpg with my same hilly 50 mile/day commute. This is over 4 tank fillups so far, with one datapoint in the upper 25's (that cycle I recall a lot of idling and getting stuck behind school busses...)

[Zerohour]

Some good insight. I think my current plugs have ~15K on them with the engine at ~92K-93K.

With your .50 gap, it is possible that you may be getting a better burn at your freeway cruising rpm. The ideal spark plug would be able to adapt to the conditions inside the cylinder. It may be possible a wider gap is giving you a cleaner, more complete burn when under load.

Since you have three posts, I'm wondering how long have you been accurately tracking fuel mileage? I could put down 24-26mpg winter and 26-28 spring just by temperature changes alone. I also would put down 18-23mpg gallon tanks before I toned down the aggressive driving.

[redpoint5]

Originally Posted by Zerohour

I ordered the lightweight Agency Power pulley for my Subaru. Depending on year/model it drops the Subaru crank pulley weight from 4.5-6lbs down to 1.1lbs. It is noted as one of the best mods for a non-turbo Subaru.

I'm still considering 17" Wheel and tire combo that comes in at 6lbs per corner lighter. Although I'm not sure if I want to speed that much money for wheels and tires. Time will tell.

I would be very interested in your results after the pulley mod.

I am under-driving my Acura with aluminum pulleys that saved a bunch of weight, but I only had the car a couple of months before I did the mod, so my driving style was still evolving. I don't know how much of a FE difference it made. I figure turning the power steering pump, water pump, alternator, and AC at a slower rate should save some power. It will probably take 20yrs to recover the cost of parts alone, assuming a 1% fuel savings.

I still say all of this is lunacy when you can just go MT and outperform the most outrageously modded auto. It may be fun lunacy though.

[spirilis]

Originally Posted by Zerohour

Some good insight. I think my current plugs have ~15K on them with the engine at ~92K-93K.

With your .50 gap, it is possible that you may be getting a better burn at your freeway cruising rpm. The ideal spark plug would be able to adapt to the conditions inside the cylinder. It may be possible a wider gap is giving you a cleaner, more complete burn when under load.

Since you have three posts, I'm wondering how long have you been accurately tracking fuel mileage? I could put down 24-26mpg winter and 26-28 spring just by temperature changes alone. I also would put down 18-23mpg gallon tanks before I toned down the aggressive driving.

Well while I haven't done the full A-B-A and haven't diligently tracked the first 'A' in any kind of journal, I have tested the fuel economy (miles/gallons pumped at the click) after my 60K service very frequently with different gas stations (and sometimes with the same one, with the same pump, same driving style) and it's always been a disappointing 24.something mpg. Since widening the plug gap I have been very diligent about keeping a log (in a memo on my cellphone), and here's the log:
26.4
26.2
25.6
26.5 (latest)

One thing to keep in mind is the temps here have been rising; while I don't personally believe that has a huge amount of influence on my vehicle (I don't recall my FE being better in the summer than in the winter with past experiences) it provides an opportune time to try the last 'A' test, regapping the V-Power's to .043" and seeing how things fare then. I will post an update when I do that.

[Zerohour]

Trust me, there are a big difference in summer to winter fuel economy. Its easily 10% with a Subi.

[Zerohour]

Originally Posted by redpoint5

I would be very interested in your results after the pulley mod.

I am under-driving my Acura with aluminum pulleys that saved a bunch of weight, but I only had the car a couple of months before I did the mod, so my driving style was still evolving. I don't know how much of a FE difference it made. I figure turning the power steering pump, water pump, alternator, and AC at a slower rate should save some power. It will probably take 20yrs to recover the cost of parts alone, assuming a 1% fuel savings.

I still say all of this is lunacy when you can just go MT and outperform the most outrageously modded auto. It may be fun lunacy though.

Sorry, missed your post yesterday!

The pulley is more critical with AWD and an automatic. The Subaru, well mine at least, actually maintains into the 33-38 while at highway speeds, and it its pretty good for around 30-33 range for 40-55. The problem is parasitic loss from the acceleration of all the rotational mass.

I can't pull out reasonable without dipping down to 8-10mpg and staying in an low rpm range. Even then it takes 1/4 of a mile to get up to speed, so for that quarter of a mile i'm using a 1/40th of a gallon for every stop sign, for every slow bum that near stops to make a turn. So I'm probably wasting half a gallon a gas a day just stopping and going. When you're only using 3-3.5 gallons a day, you're talking ~15% loss in FE as waste, this would bump my trips with the Subaru into the 30.x marker.

This is terribly true for any hills as well, the climb rate at 25-30% load to maintain even 35-40mph dips me down to 16-20mpg. All I really need to do is reduce the load the engine is under in these conditions and I would gain full mileage...at this point, look at hybrids. These are exactly how they get a ton a mileage.

Thus the only solution to reduce load is to reduce rotational mass or static mass of the vehicle. Since I kind of like doors and trunks and seats, it is hard to reduce static mass. Rotational mass can be done through pulleys, driveshafts, rotors, tires etc.

[brucey]

Do you feel the pulley actually improved your mileage at all ?

[Zerohour]

Originally Posted by brucey

Do you feel the pulley actually improved your mileage at all ?

Okay boys and gals, you'll need to sit down for this one. I thought I put numbers in wrong, but I haven't!

So here you have it...two day work commute setup with new pulley:
a) wheels open (no tape)
b) no skirts,
c) temps in the 40s-50s,
d) weather is reasonable - no rain, overcast, slight humidity.
e) full tank of gas
f) spare tire and trunk bits re-installed
g) tires inflated to 33psi front, 34psi rear (down from 38 psi all four)
h) 5w-30 Castrol, previously 0w-30 Mobile eco-oil

Result: 136.8 @ 4.753 gal of gas = 28.78 MPG!

Now this was an honest try to get high mpg, I was squeaking the best out of the car. But that matches some of by best results I had using the eco-mod tricks and gadgets.

That being said, this was done because I ordered an unequal length "race" header. The header has definitely been a power adder to the car. and I may have more than made up for the two days of green mileage. I will fill up on my way home Monday night, and stop for gas on Wednesday. We'll see if we can get a good comparison between before and after header.

The sad part is that I needed to remove my front grill block. I had "plowed" someone's recycling bin during winter. The resounding effects have now creeped up and the fiberglass is flaking apart from the impact zone. So off it had to come. It makes me depressed that alot of the hard work has come undone, but thats life! It will make it a huge challenge to see if I can match/near match mileage without grill blocks and the header installed.

For your viewing pleasure, exhaust clip from header install.

http://www.youtube.com/watch?v=UpSzn_3ZFLo

[Zerohour]

So here is a bit of an update!

Pre-header install, with crank pulley and grill block:
136.8 @ 4.753 gal of gas = 28.78 MPG

Me driving moderately spirited with exhaust header and bedding in new brakes:
334.3 Miles @ 12.48 Gallons = 26.79 MPG

Eco-miles, without grill block, with crank pulley, with header installed:
153.8 miles @ 5.542 Gallons = 27.75 MPG

So not quite the 28.78 from pre-header install...but...I also just installed new brakes and the morning commute included 2"/hr rain fall!