modding for MPG

[dusterbd13]

so, with my ever deepening research into the new, wonderful world of subaru, im looking at power/mpg mods. cart is an 02lgt wagon, auto

my car is currently averaging 23 mixed, with mixed drivers (city highway, short/long trips, my driving and my wifes.)

currently, the car has fresh plugs and wires, new air filter, fresh synthetic ohe oil, and tires at 36PSI. just put seafoam through the tank. need to do the motor as well with seafoam. unknown milage on fuel filter.

my thoughts are that this is a little low. if this is about right, ill skip straight to modding. if it is low, where do i check next?

mod ideas:
1. seal up intake tract to make it truly cold air. my plan is to use bicycle inner tubes tut to slide over the male parts of the plasti tubing, rubber cemented in place. then clamp. also remove the little baffle on the hood for the ram air efect.

2. K&N dropin filter. usually gets about 2 MPG and a little power on dakotas and mazdas, so it should work on a subie, right?

3. Group A throttle body spacer. according to my research, on a stock vehicle it will typically pick up 1-4 MPG. seems a little too good to be tru, but ive seen enough forum posts to be willing to try it. anr fitmrnt issues or anything since i have an auto?

4. Group A crank pulley. lighter rotating mass should free up a little power and mpg, at least in theory.

5. headers. id leave the stock exhaust, as i like it being quiet. i havent seen any reference anywhere to milage increases or decreases due to headers. lot of bickering about sound, though. i dont care as much about the power as much as i do MPG and low noise. anyone done the stock exhaust, header route? much louder than stock? also,what kind of gains in mpg should i see from an EL vs. UEL?

6. syenthetic drivetrain fludis. tranny, diffs, etc.

7. anything im missing? like aero mods, etc?

just let me know your thoughts and experiences. i know that making power, assuming being gentle with the throttle, will increase MPG. but i want to do this in a systematic approach, not making this any less suitable of a traviling car for my family, or less omfortable for my commute.

thansk

michael

[anothernord]

so, with my ever deepening research into the new, wonderful world of subaru, im looking at power/mpg mods. cart is an 02lgt wagon, auto

my car is currently averaging 23 mixed, with mixed drivers (city highway, short/long trips, my driving and my wifes.)

currently, the car has fresh plugs and wires, new air filter, fresh synthetic ohe oil, and tires at 36PSI. just put seafoam through the tank. need to do the motor as well with seafoam. unknown milage on fuel filter.

my thoughts are that this is a little low. if this is about right, ill skip straight to modding. if it is low, where do i check next?

mod ideas:
1. seal up intake tract to make it truly cold air. my plan is to use bicycle inner tubes tut to slide over the male parts of the plasti tubing, rubber cemented in place. then clamp. also remove the little baffle on the hood for the ram air efect.

2. K&N dropin filter. usually gets about 2 MPG and a little power on dakotas and mazdas, so it should work on a subie, right?

3. Group A throttle body spacer. according to my research, on a stock vehicle it will typically pick up 1-4 MPG. seems a little too good to be tru, but ive seen enough forum posts to be willing to try it. anr fitmrnt issues or anything since i have an auto?

4. Group A crank pulley. lighter rotating mass should free up a little power and mpg, at least in theory.

5. headers. id leave the stock exhaust, as i like it being quiet. i havent seen any reference anywhere to milage increases or decreases due to headers. lot of bickering about sound, though. i dont care as much about the power as much as i do MPG and low noise. anyone done the stock exhaust, header route? much louder than stock? also,what kind of gains in mpg should i see from an EL vs. UEL?

6. syenthetic drivetrain fludis. tranny, diffs, etc.

7. anything im missing? like aero mods, etc?

just let me know your thoughts and experiences. i know that making power, assuming being gentle with the throttle, will increase MPG. but i want to do this in a systematic approach, not making this any less suitable of a traviling car for my family, or less omfortable for my commute.



thansk

michael


A drop in filter won't do a whole lot to improve mileage; not as much as a true aftermarket intake. The idea with an intake is smooth, laminar flow in a large tube. And as always, colder air is better for preventing knock, and thus loosing timing advance.

A better alternative to the TB spacer would be phenolic manifold spacers. They keep the intake manifold from heating up the intake air.

A more free-flowing exhaust with a larger diameter will increase MPG, but only up to a point. Anything larger than 2.25" piping is just causing lost velocity of the exhaust. I personally noticed a small increase in mileage with only headers on the stock exhaust. EL headers are more efficient that UEL, but most people enjoy the rumble of the UEL over the EL, which sounds more like a Honda.

On the freeway is the only place that aero mods will net you any gains. Basically anything you can do to make the car as smooth as possible will decrease your drag CE and make it easier for your engine to push the car through air.

[Huffer]

Take out all the sound deadening. Remove all your seats and install a lightweight drivers race seat.
Remove your fuel tank and install a smaller 10gal fuel cell in the middle of the car
Run 14" lightweight alloy wheels with skinny tires
Take out all your glass and replace with perspex

Oh dammit:
not making this any less suitable of a traviling car for my family, or less omfortable for my commute.

[dusterbd13]

yeah, extreme weight reduction isnt exactly DD friendly for my infant.

as far as the aftermarket intakes, what kind of MPG increases are you seeing? i know that guys are reporting fairly good power gains, but thats not what im after. which is why i was looking at maximising my stock setup.

any MPG data on the manifold spacers? seems like it would boost low end torque due to the longer effectlive runner length, and the heat soak would be an issue, but doesnt increase plenum volume.....

anyway, and numbers?

thansk for the help so far
Michael

[anothernord]

yeah, extreme weight reduction isnt exactly DD friendly for my infant.

as far as the aftermarket intakes, what kind of MPG increases are you seeing? i know that guys are reporting fairly good power gains, but thats not what im after. which is why i was looking at maximising my stock setup.

any MPG data on the manifold spacers? seems like it would boost low end torque due to the longer effectlive runner length, and the heat soak would be an issue, but doesnt increase plenum volume.....

anyway, and numbers?

thansk for the help so far
Michael

I think it comes down to having more power overall, so less throttle deflection is required for a given RPM. I don't know the physics on this one though.

It's not the plenum you're after, its the fact that they are phenolic, meaning they don't conduct heat very well. This basically means that you get better low end because the air moving through the manifold at low velocities doesn't get as much heat transferred to it.

[Huffer]

Rallitek PP6 engine management. Get a tune to lean out the rich Subaru factory map while still providing detonation protection & power.

[anothernord]

Rallitek PP6 engine management. Get a tune to lean out the rich Subaru factory map while still providing detonation protection & power.


This. Since I got my wideband and started tuning, I've been appalled at how rich the stock map is under open loop. Like 9-10:1 at WOT.

[jey]

23 is normal.

The best mpg mods have to do with your driving behaviour. Avoid using the brake - every time you use it you waste energy. Time you driving so you hit green lights, don't rapidly accelerate only to nail the brakes 2 seconds later.

[dusterbd13]

yeah, im still getting used to driving an automatic. that torque converter thing is still screwing with me. ive always driven a stick, so the 500 RPM difference between off throttle and on throttle is leading me to over gas it, and waste more.

thanks for the confirmation that 23 is normal. it just seemed low to me.

and the aftermarket engine management appeals to me. i got into burning custom chips for OBD1 GM TBI stuff with my s10. managed to get it to 26 mixed, driving it hard all the time. also one of the quickest mostly stock 2.8 trucks ive ever driven. some of the throttle transitions still need some remapping....

anyway, can someone gove me a link to to this so i can research it further.

the air density thing and heat soak make sense as far as the fuel economy go. doesnt sem like it would be that drastic.

and what intakes are guys having the best luck with? seems like theres a million different ones for the subarus. hell, ive even seen one thats like a grand.

any other suggestions?
michael

[chuckthefuk]

-Remove your a/c compressor or remove/cut the a/c belt. The compressor clutch usually drags and end result usually is lower MPG.
--> unless you like cold air :razz: ..
-Get an SAFC tune by a professional. This wont yield crazy MPG gains but it will level off your air/fuel ratio and prevent your motor from running too rich.
-Drive with the windows up! More aerodynamics!.
-Remove your GT scoop. More aerodynamics!
-If your going with the lightweight rotational mass then a light weight flywheel will help.. In theory
-Lighter wheels (they don't have to be track rims.. a set of 01' RS wheels are much lighter then the GT snowflakes)
---> Steelies are more aerodynamic then spokes. In fact hubcaps help with aerodynamic (Toyota Prius use lightweight 6-8 spoke rims with the ugliest flat hubcaps in order to improve MPG)
-Remove your hitch if you have one :-p

Just some ideas.
-Chuck

[Huffer]

-Remove your GT scoop. More aerodynamics!

correction - swap hoods with a non-GT vehicle. Removing the scoop isn't possible. :)

[j_saffron]

not sure if it helps, but with an automatic, i throw it in neutral at stop lights.
mainly to get my exhaust shields to shut up, LOL. but it might save gas because theres no engine/brake resistance going on.

[chuckthefuk]

-Remove your GT scoop. More aerodynamics!

correction - swap hoods with a non-GT vehicle. Removing the scoop isn't possible. :)

Mr. Literal....

[HeresMyMind]

new tires, with an alignment. EVEN if u have no codes, replace BOTH 02 sensors. i average 24mpg in my 4eatgt wagon before i swapped o2 sensors i was at 21. and before the alignment i was at 19-20

-B

[dusterbd13]

i never even thought about the alignment. good call on that. im figuring factory specs, unless these cars like something differnt. but thats a different thread.

i did just swap the fuel filter, as that was due as well. also, started looking at the intake spacers, throttle body spacer, etc for prices.
ill probably order the group a stuff, unless someone knows something cheaper.

michael

[ouch1011]

If you want to get serious with mods towards MPG, I'd swap the trans and rear diff for something with a numerically lower gear ratio. The LGT is geared more for getting acceleration and better performance from a fairly low power engine in a fairly heavy car. Not a good combo for MPG. I believe the stock ratio is 4.11 on the GT, 3.9 is pretty readily available from the Imprezas since they use smaller tires. Or you could go a long ways down to a WRX trans/diff, thats like a 3.5 or something like that. That may be too far though, since these cars with the 4EAT already struggle to hold a cruising speed up hill without downshifting or at least unlocking the tcc. But, the lower RPM you can get for cruising, the better (to a point), since lower RPM with the same power requirement means moreengine load, lower intake vacuum, less pumping losses.

Also, be careful with what you are hearing about the whole tuning thing, because 95% of the tuning stuff out there is really for WOT fuel and ignition only. Unless the system completely replaces the stock PCM, the stock PCM is still handling and automatically adjusting the part throttle/closed loop driving stuff. Like pretty much every gas powered car out there, it adjusts the fuel trims to average 14.7:1 air/fuel ratio undur crusing and light throttle. The car only runs rich under heavy/full throttle, and any tuning you do at that load will have basically no effect on you MPG, and only a very modest effect if you drive pretty hard.

[anothernord]

If you want to get serious with mods towards MPG, I'd swap the trans and rear diff for something with a numerically lower gear ratio. The LGT is geared more for getting acceleration and better performance from a fairly low power engine in a fairly heavy car. Not a good combo for MPG. I believe the stock ratio is 4.11 on the GT, 3.9 is pretty readily available from the Imprezas since they use smaller tires. Or you could go a long ways down to a WRX trans/diff, thats like a 3.5 or something like that. That may be too far though, since these cars with the 4EAT already struggle to hold a cruising speed up hill without downshifting or at least unlocking the tcc. But, the lower RPM you can get for cruising, the better (to a point), since lower RPM with the same power requirement means moreengine load, lower intake vacuum, less pumping losses.

Also, be careful with what you are hearing about the whole tuning thing, because 95% of the tuning stuff out there is really for WOT fuel and ignition only. Unless the system completely replaces the stock PCM, the stock PCM is still handling and automatically adjusting the part throttle/closed loop driving stuff. Like pretty much every gas powered car out there, it adjusts the fuel trims to average 14.7:1 air/fuel ratio undur crusing and light throttle. The car only runs rich under heavy/full throttle, and any tuning you do at that load will have basically no effect on you MPG, and only a very modest effect if you drive pretty hard.

Right, once the ECU hits open loop, which is above ~4000 rpm and ~70% throttle, the car does not reference the oxygen sensor to run at 14.7 AFR. It is this threshold that is tunable. Actually I find that under normal driving conditions, I go into open loop fairly often, and I do not romp it all the time. I know this because I watch my wideband and see when it jumps from stoic to rich as it enters open loop.

So tuning this area does have real benefits. When I was running N/A with my PP6 piggyback, I was able to pull a lot of fuel up top while still remaining in safe AFR ranges. Not only did the car pull harder in those ranges, but I recorded about 1-2 mpg better on average.

[ouch1011]

That is suprising and interesting to me, but you are contradicting yourself a little. You say that tuning is only really available when the car is open loop, about 70% throttle or 4000rpm. That's pretty typical for most "older" cars. But, tuning for those conditions yields better MPG? I just don't see how that happens, since the time spent under these conditions is so minimal. What AFR were you seeing under light to moderate load above 4000rpm but less than 70% throttle?

BTW, I don't want this to sound like I'm arguing or anything, I want to know about this, since I've done a bit of tuning on another car, and I'm really trying to learn more. Plus I certainly plan on doing a lot of tuning on the Legacy in the future, even though it will likely be with something lie the Accessport or something designed more for the newer Subies.

[anothernord]

That is suprising and interesting to me, but you are contradicting yourself a little. You say that tuning is only really available when the car is open loop, about 70% throttle or 4000rpm. That's pretty typical for most "older" cars. But, tuning for those conditions yields better MPG? I just don't see how that happens, since the time spent under these conditions is so minimal. What AFR were you seeing under light to moderate load above 4000rpm but less than 70% throttle?

BTW, I don't want this to sound like I'm arguing or anything, I want to know about this, since I've done a bit of tuning on another car, and I'm really trying to learn more. Plus I certainly plan on doing a lot of tuning on the Legacy in the future, even though it will likely be with something lie the Accessport or something designed more for the newer Subies.

No offense taken, :smile:

Yes, its true that less time spent in open loop will yield better MPG, but what I should have explained more is that my particular driving style, means that sometimes I go into open loop. The air is a lot thinner here and since my second gear is difficult and takes longer to engage, I have to rev up higher in first gear to stay with traffic from a stop light. So in my situation, I get better MPG by tuning than I would otherwise. Now, if I were to fix that gear and change driving habits, I would get better mileage anyway. In any case, the more efficient you can make the engine, the better.

My AFR's before the Supercharger were around 13 under light load and 12 under full load. No knock and the car ran great. Now with the Supercharger, I stay at 12 all the way up.

[dusterbd13]

full engine management will have ti wait, unless there is an opensource tuning software like tunerproRT for the subies. cant afford to drop that kind of money.

milage gains also come down to how many miles ill have to drive before the modification pays for itself. thats one thing that my wife mentioned, and made sense. if you only pick up 1-2 MPG for 500 bucks, its gonna take a LOOOOOONG time to pay for itself.

regardless, im still gonna do it. my car, my allowance, my choice. i just want to see how far i can go.


also, ive been looking into true CAI kits. unfortunately, i dont see a lot of options listed for the legacy. what are you guys getting them for?

lastly, im first trying a few other options before actual bolt ons. im optimizing the stock stuff and trying a few tricks to see where i can take it.

tricks:
1. opened plug gap by .05 for a little fuller burn. result: better throttle response, feels like more torque
2. 89 octane for reduced knock count. seemed to smooth the car out a bit.
3. all synthetic fluids. up next are tranny and diffs. should be done by next week
4. tire pressure. i set it like i do with my autocross toys. chalk line and a parking lot. currently at 38 cold.
5. removed roof rack crossbars
6. new fuel filter
7. made sure belts are properly tensioned


my wife has been driving it all week, so we'll see what the numbers are when i fill it up over the weekend. im hoping that this thing will crack the 24 barrier.

on a complete side note, has anyone noticed any difference in MPG or cooling with the plastic under engone shrouding removed? mines haning down and broken. has been since i bought it. im thinking of just removing it if theres no real downside other than a dirtier engine bay.

michael

[Huffer]

if you only pick up 1-2 MPG for 500 bucks, its gonna take a LOOOOOONG time to pay for itself.

This is the case with many of the mods we see around here. The AWD is a poor platform to start with MPG modding.

You will seriously get more bang for buck out of a good tune than you will some semi-random CAI pipes and a hi flow filter or a titanium exhaust.
If you stand behind your car on a cool morning and fire it up, it is a LOT richer than some comparable makes like an Accord or Camry.

In terms of aerodrag, removing the undertray is fine, but replacing it with a full-body plate will create far less uplift and air turbulence under the car. This will actually suck the car to the road more but this creates rolling resistance which isn't something you want I suppose...

You could swap the wing mirrors for those "F1" style ones for less drag...go with an internal FM antenna instead of the power retractable one, ditch the wing spoiler...

[dusterbd13]

ive actually thought about doing a full bellypan under the truck for just that reason. and it would be cool.

anyone have any experience with the neon coil mod? i keep seeoing that and the MSD coil referenced, and some initial impressions, but never any MPG differences, etc.

also, anyone have a reputable shop in NC that does subie tuning? im really thinking, and want to see what it would run to have a "Pro" do it.

Michael

[ScaryFatKidGT]

This is the case with many of the mods we see around here. The AWD is a poor platform to start with MPG modding.

In terms of aerodrag, removing the undertray is fine, but replacing it with a full-body plate will create far less uplift and air turbulence under the car. This will actually suck the car to the road more but this creates rolling resistance which isn't something you want I suppose...
they make these for legacy's?

[Huffer]

"They" make bellypans for all vehicles. They're usually custom items.

[d1giPhux]

Your best mod for MPG with a suby.. is to sell it and get a honda. These cars don't get good MPG.. period. Unless you want to do something really extreme and expensive.

[dusterbd13]

i am not expecting astronomical MPG fogures form a subie. im hoping to break into the high 20's, low 30's highway, and middle to upper 20's around town. if i wanted something in the 40's, id get a CRX HF.

thanks for the suggestions so far. please, keep them coming.
Michael

[Huffer]

Forgot to add that you'll want to lower the car. A lower center of gravity helps with cornering, meaning you use less energy to get the car to go around a corner. It also helps with braking and acceleration, which as we all know rob a vehicle of momentum (and hence, overall MPG).

[green97gt]

be careful with the synthetic fluids depending on the vehicle mileage. synthetic fluids have a habit of making fluid leaks very well known.