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Old 03-11-2008, 03:28 AM   #1
Czum
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Default Brutal cold-weather mileage, 02WRX - suggestions?

Hi all,

Okay, I have an 02WRX 4EAT wagon with a TurboXS TBE, GFB BOV vented to atmosphere, gutted UP and stock intake, turbo and injectors. It's currently tuned to Cobb's stage 2 91 octane MAP. LOVE the power in the car, but the mileage has been brutal - about 13 mpg last tank, all city with fairly conservative driving (well, maybe a little boosting, but not much). It's been very cold here, typically about -30C or below, so I know that mileage will suffer as the car runs very rich, even when warmed up.

I'm not trying to turn the car into an econobox, but I would like to try to improve the mileage somewhat. So my questions for you all are:

- it's easy to get unadulterated 91 octane fuel here, but the 93/94 is all 10% ethanol - which one am I better off using? I know that ethanol gives poorer mileage due to lower energy content, but is that offset by the higher octane rating? In the summer, which one will give me more power?

- will the Cobb economy MAP give me any joy? Yes, I know I'm inviting flamage asking this, since I'll lose power - but when there's snow and ice all over the roads, I don't really need the extra HP right now. I'm willing to trade off for better mileage now, then will go back to the stage 2 MAP when it warms up and I can actually appreciate the added power (too much power now quickly turns into oversteer with all the ice around).

- does anyone know if Cobb has ever tried to make a cold weather MAP? Nothing on their website, but you never know...

- will putting the BOV into recirculation mode improve mileage? I'm not completely sold on the BOV, so would it maybe be better to go back to the stock CBV?

Again, I'm not trying to turn this car into a Prius/Fit/etc - I know what I signed on for when I bought it. But I was expecting something closer to 18/19 mpg city, not 13, and its a little painful paying $65 to go 200 miles each week. I know the mileage will improve as it warms up here, I'm just wondering if there's anything I can do now (that is non-permanent).

Thanks for any suggestions.
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Old 03-11-2008, 04:18 AM   #2
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Do you have the gas leak problem?

Oh yeah, pray for warmer weather.
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Old 03-11-2008, 10:21 AM   #3
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Quote:
Originally Posted by Czum View Post
- it's easy to get unadulterated 91 octane fuel here, but the 93/94 is all 10% ethanol - which one am I better off using? I know that ethanol gives poorer mileage due to lower energy content, but is that offset by the higher octane rating? In the summer, which one will give me more power?

Try it and see, and it also depends if the 93/94 is cheaper. I personally run 91 octane with 35% E85 or so mixed in. it does knock a couple MPG off, but because E85 is $1.50 cheaper, it is worth it. (btw, mixing e85 WILL give you more power if tuned for it, 93/94 e10 should do the same)

Quote:
Originally Posted by Czum View Post
- will putting the BOV into recirculation mode improve mileage? I'm not completely sold on the BOV, so would it maybe be better to go back to the stock CBV?
Yes... Read around on here for the general opinion of a BOV. In short you are tossing raw fuel out the exhaust. Yes technically it might be for a very short time, but it still isn't helping economy.

but... as the poster above me mentioned, have you had the fix for the leaking gasoline? You probably are dripping half the gas out the engine bay, although you SHOULD be smelling it by now. (and anyone within 20 feet should be able to smell your gas fume encrusted clothing)
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Old 03-11-2008, 10:32 AM   #4
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I'm getting 15 MPG on my stock WRX with overinflated tires with similar weather, just bite the dust. When its that cold all the fluid in the differential and tranny are thick as molasse and I'm sure you can feel the car braking on its on between shift when you pull out of your driveway. So its not just the fuel map that's a factor here.

Your best bet would be getting a block heater so you can significantly reduce the cold start cycle and heating pads around your tranny and under your oil pan.

Also, removing the intake tract (the peice going from the box to the front grill) will make your intake suck warmer air, which results in better MPG. The ideal solution would make a real "warm air intake" (yes there is such things) that heat up intake air to give more more "summer style MPG".
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Old 03-11-2008, 11:54 AM   #5
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Good Synthetic Oil in your entire driveline.... block heater... make sure it isn't pulling any timing on you- that will kill your economy!! tire pressures need to be the same (regardless of temp) the vented BOV isn't going to hurt your mileage much under easy driving because it should hardly be opening when you let off- not to mention you have an auto, so it doesn't open between shifts
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Old 03-11-2008, 11:57 AM   #6
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ouch i live in -10 and get 28mpg on the highway... seriously
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Old 03-11-2008, 12:05 PM   #7
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Thanks for the quick replies so far.

Yes, I had the fuel leak problem (started as soon as the weather got really cold (below -20C)) - just replaced the rail and all the rubber hoses a couple of weeks ago. Disappointed that Subaru hasn't made this a recall item. Still no joy, although the heavy leakage that had been occurring is gone. Don't smell gas anymore, except when first starting up on cold days and the car runs really rich. Also put in a block heater. I'll try the suggestion about removing the intake scoop, although it may be moot now (getting up above freezing today!). I should have mentioned that I have a drop-in K&N filter, so incoming air may get in quicker and experience less heating in the engine bay.

Still wondering about the Cobb economy MAP and if anyone was happy with it. I might ask Cobb to consider a cold weather custom MAP - the car is REALLY rich when its cold, maybe too much so. Have to wonder if I couldn't lean it out somewhat and still have reasonable starting. Also have to wonder if the stock air temp sensor gives accurate values when it's -30/-45 outside, and whether the ECU is properly programmed to handle it.

Rayme, how much did you overinflate the tires? I've heard that some people recommend taking the max PSI and dropping it by 10% (so if the max is 40 PSI, then fill to 36, versus the stock recommendation of 30-ish). Do you lose much traction on ice, since the contact patch is smaller? I'll also look into the warm air intake - wasn't aware of these. Of course, there's always the trick of putting a piece of cardboard behind the grill - it's almost standard equipment in Canada
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Old 03-11-2008, 12:10 PM   #8
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Oh, and to answer GeneralTJI, I have full synthetic in the motor (Mobil 1), tranny, diffs and steering. Will have to check the timing - thanks.

Yeah, I seldom hear the BOV (usually just when showing off), so I don't think that it will make much difference, but I'll probably get rid of it anyway.
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Old 03-11-2008, 12:11 PM   #9
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I'm in Regina which is very close to you and I've been getting 14-15 mpg city driving as well. My Green turbo helps to keep me out of boost in the city but thats barely over 300km per tank!! Just know that you're not alone. In the better weather I get 19mpg city driving.
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Old 03-11-2008, 01:44 PM   #10
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I was in the same boat here is ND -30 for weeks and crappy gas milage, its the oxygnated fuel and the more dense cold air that make it happen, just have to deal with it. I'm running the same cobb state 2 map also.
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Old 03-11-2008, 01:47 PM   #11
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There isn't (at least in my ROM) a fuel compensation table for air temp. There is one for coolant temp. Unless you are not able to keep your coolant at operating temperatures you shouldn't be running any richer when it is cold (once you reach operating temps that is). Your fueling is based on how much air (mass of air) is getting into your engine at any time. More air means more fuel being burned. Colder air is easier to compress (as it is already more dense than hotter air) to a given pressure (easier for you to hit your target boost quickly). When it is cold I find that I have a hard time staying out of boost with my current map much less back when I was running cobb maps. The cobb maps target a pretty high boost and wgdc at partial throttle. This makes it hard to stay out of boost especially when cold.

If you want my advice on how to increase mileage without hurting performance, reduce your target boost at part throttle (and also change the corresponding WGDC tables). Mine is set for about wastegate pressure at 50% throttle and full boost only at WOT. This got me a couple MPG in the summer while still allowing me to use the power when I want it.

Also you could lean out your fueling table but unless you have a WBO2 you really shouldn't do this yourself.

CN: Get a tune, don't ask the car for full boost at 50% throttle.
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Old 03-11-2008, 02:27 PM   #12
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Even if there is not "warm temp fuel map", when the engine is operating in closed loop and uses the O2 sensor to get a good ratio, if the engine is actually breathing warm air versus cold air (summer/winter) the engine will send less fuel to reach that ratio since cold air contains more oxygen.

That being said, I dont know if EM and tune disregard the o2 sensor's closed loop function but that's how an engine normaly works.

Quote:
Originally Posted by brettm View Post
There isn't (at least in my ROM) a fuel compensation table for air temp. There is one for coolant temp. Unless you are not able to keep your coolant at operating temperatures you shouldn't be running any richer when it is cold (once you reach operating temps that is). Your fueling is based on how much air (mass of air) is getting into your engine at any time. More air means more fuel being burned. Colder air is easier to compress (as it is already more dense than hotter air) to a given pressure (easier for you to hit your target boost quickly). When it is cold I find that I have a hard time staying out of boost with my current map much less back when I was running cobb maps. The cobb maps target a pretty high boost and wgdc at partial throttle. This makes it hard to stay out of boost especially when cold.

If you want my advice on how to increase mileage without hurting performance, reduce your target boost at part throttle (and also change the corresponding WGDC tables). Mine is set for about wastegate pressure at 50% throttle and full boost only at WOT. This got me a couple MPG in the summer while still allowing me to use the power when I want it.

Also you could lean out your fueling table but unless you have a WBO2 you really shouldn't do this yourself.

CN: Get a tune, don't ask the car for full boost at 50% throttle.
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Old 03-11-2008, 03:17 PM   #13
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Quote:
Originally Posted by Rayme View Post
Even if there is not "warm temp fuel map", when the engine is operating in closed loop and uses the O2 sensor to get a good ratio, if the engine is actually breathing warm air versus cold air (summer/winter) the engine will send less fuel to reach that ratio since cold air contains more oxygen.

That being said, I dont know if EM and tune disregard the o2 sensor's closed loop function but that's how an engine normaly works.
you are missing the point... Yes you are consuming more fuel but that doesn't mean you are running any richer than in warmer temps. The AFR "should" be the same no matter what the exterior temp.
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Old 03-11-2008, 03:23 PM   #14
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I inflated my tires at 36 Psi, which is not that much over the recommended pressure. And the car will always run rich until its at normal temperature, the colder it is the richer it will be until you reach operating temp, it's just physics, and that why a block heater is your friend.

Quote:
Originally Posted by Czum View Post
Thanks for the quick replies so far.

Yes, I had the fuel leak problem (started as soon as the weather got really cold (below -20C)) - just replaced the rail and all the rubber hoses a couple of weeks ago. Disappointed that Subaru hasn't made this a recall item. Still no joy, although the heavy leakage that had been occurring is gone. Don't smell gas anymore, except when first starting up on cold days and the car runs really rich. Also put in a block heater. I'll try the suggestion about removing the intake scoop, although it may be moot now (getting up above freezing today!). I should have mentioned that I have a drop-in K&N filter, so incoming air may get in quicker and experience less heating in the engine bay.

Still wondering about the Cobb economy MAP and if anyone was happy with it. I might ask Cobb to consider a cold weather custom MAP - the car is REALLY rich when its cold, maybe too much so. Have to wonder if I couldn't lean it out somewhat and still have reasonable starting. Also have to wonder if the stock air temp sensor gives accurate values when it's -30/-45 outside, and whether the ECU is properly programmed to handle it.

Rayme, how much did you overinflate the tires? I've heard that some people recommend taking the max PSI and dropping it by 10% (so if the max is 40 PSI, then fill to 36, versus the stock recommendation of 30-ish). Do you lose much traction on ice, since the contact patch is smaller? I'll also look into the warm air intake - wasn't aware of these. Of course, there's always the trick of putting a piece of cardboard behind the grill - it's almost standard equipment in Canada
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Old 03-11-2008, 04:34 PM   #15
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Originally Posted by brettm View Post
you are missing the point... Yes you are consuming more fuel but that doesn't mean you are running any richer than in warmer temps. The AFR "should" be the same no matter what the exterior temp.
yes, but... if he does alot of city driving, he isn't getting up to full temp nearly as fast as you would in warmer climates. So the majority of the driving might be in the rich condition.
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Old 03-11-2008, 04:53 PM   #16
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yes, but... if he does alot of city driving, he isn't getting up to full temp nearly as fast as you would in warmer climates. So the majority of the driving might be in the rich condition.
That is true, the assumption about fueling is that you are at operating temp. The point in my rom where there is no compensation for coolant temp is 158.

However the statement that colder air makes you run richer because the air is more dense is still not correct. You are using more fuel because more air is going through your engine (when as stated you are at full operating temp)

Also the compensation table is for open loop, not closed loop (at least the table is labeled as such). On my car my AFR's quickly (1-2 minutes at idle tops) stabilize at stoich even on the coldest days.

FWIW, I get 18-20 MPG in the coldest part of the winter and 21-24 in the summer with a 60/40 mix of city/highway driving (local 2 lanes, not expressway)
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Old 03-11-2008, 05:54 PM   #17
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how long are your trips daily? when it's that cold, it takes forever for the car to warm up, and it cools down real quick when it isn't running.

I think it has more to do with the frequency of cold start than city driving. I was losing about 15-20% mpg, even here in L.A., during the colder part of the year (btw, that's like 40-50F)
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Old 03-11-2008, 06:00 PM   #18
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Originally Posted by hella_sti View Post
I was in the same boat here is ND -30 for weeks and crappy gas milage, its the oxygnated fuel and the more dense cold air that make it happen, just have to deal with it. I'm running the same cobb state 2 map also.
I can vouch for that. Fargo has been pretty frigid up until lately.

Remember that winter gas is a different blend too (different vaporization points) so that also affects fuel economy.
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Old 03-11-2008, 07:59 PM   #19
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Well this winter in Chicago temps have reached to 5-7F and my car is also a 4eat Stage 2 Protuned (Cobb catted DP, STI UP + catback, Prodrive Solenoid) and I've been averaging anywhere from 13-15 mpg consistently even driving like a grandma didn't help mileage much. Good to know I'm not the only one getting such low mileage.

Edit: And my Kumho ASX 205/55/16 tires are usually inflated to 38psi.
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Old 03-11-2008, 08:33 PM   #20
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I can vouch for that. Fargo has been pretty frigid up until lately.

Remember that winter gas is a different blend too (different vaporization points) so that also affects fuel economy.
I'm in Bismarck, not quite as cold, but I quite checking my mpg when we were down to -20 and colder. I really didn't want to know. Subaru's are by far the worst vehicle I've owned for cold weather mpg, pretty much every else I've owned takes a small hit in winter, maybe 2 mpg overall.
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Old 03-12-2008, 07:24 AM   #21
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Damn you people are crazy! How the heck can you live somewhere so cold?

Anyways, here's what you need to do:
Step 1: Get an engine block heater. I see you've already done thing, but for everyone else reading, what it does is help you car warm up much quicker. While in the cold 'warm up' state it burns about .4 to .5 gallons of fuel per hour at idle. Once the engine is warm it burns only .3 gallons per hour at idle.

Step 2: Inflate those tires to what it says on the side of the tires. Steel belted tires don't poke out in the middle if you put more air in them. The tires were designed to be able to handle whatever the max sidewall rating is safely. But I don't know jack sheet about driving in snow so maybe hold off on this one till the snowy weather is gone.

Step 3: Shutoff the car at stop lights after it's warmed up. Yep, 0.3 gallons of fuel per hour when the engine is idling. Doesn't sound like much, but what if you spend 3 minutes stopped at a stop light, and you get stuck at 5 lights on the way to work and 5 lights on the way back? Thats 30 minutes a day just sitting there doing nothing. For a 5 day work week, thats 2.5 hours, or 0.75 gallons of gas wasted. Go 300 miles a week and use 10 gallons of gas, thats 30.0mpg. Use 10.75 gallons of gas and its just 27.9mpg.

Step 4: Drive like you're brakes are broken. I never drove in snow before but I guess you probably already do this anyway? Anyways, any time you hit the brakes or downshift to slow down, kinetic energy is being turned into heat energy. Heat energy is lost energy. So if you see a light you know you're going to get stuck at, go ahead and take your foot off the gas asap. Also leave more space in between you and other cars. That way you don't have to slow down as much if one of them decides to slow down and turn off the road.

I've heard that the BOV makes the car run rich at idle. Has something to do with letting the air out of the system before it gets into the engine or something? Really don't remember, but yeah, put it in recirculate mode and you should see the mpg's go up.

But overall, the best suggestion I have is this. Move to Texas you stupid Canadian! I just got 32mpg in my car, 20mpg better than what you got, and I don't have to wear a jacket tomorrow either. Plus people don't talk funny here.

Haha, my bad attempt at humor. I know Canadians aren't stupid.
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Old 03-12-2008, 10:01 AM   #22
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Great tips, I already try most of these. And btw, I did get 32 MPG once around when it was around -5c (23F) on the highway.

My 15 MPG is in fact, due to my 20 minutes (10 min morning, 10 evening) to work, the car only start blowing somewhat warm air after 5 minutes, so about 50 minute per week I'm driving my car with a cold engine in warmup/choke mode, which results in that 15 MPG mess.

I would benefit from a block heater, but the winter's almost over and I just bought an old toyota paseo to get me though the next winter, 1.5 of fuel sipping power! It should pay by itself in insurance and fuel cost alone lol...

I know it's cold, but when you're raised digging up snow tunnels and snow sledding, it doesn't feel that bad

Quote:
Originally Posted by bomber991 View Post
Damn you people are crazy! How the heck can you live somewhere so cold?

Anyways, here's what you need to do:
Step 1: Get an engine block heater. I see you've already done thing, but for everyone else reading, what it does is help you car warm up much quicker. While in the cold 'warm up' state it burns about .4 to .5 gallons of fuel per hour at idle. Once the engine is warm it burns only .3 gallons per hour at idle.

Step 2: Inflate those tires to what it says on the side of the tires. Steel belted tires don't poke out in the middle if you put more air in them. The tires were designed to be able to handle whatever the max sidewall rating is safely. But I don't know jack sheet about driving in snow so maybe hold off on this one till the snowy weather is gone.

Step 3: Shutoff the car at stop lights after it's warmed up. Yep, 0.3 gallons of fuel per hour when the engine is idling. Doesn't sound like much, but what if you spend 3 minutes stopped at a stop light, and you get stuck at 5 lights on the way to work and 5 lights on the way back? Thats 30 minutes a day just sitting there doing nothing. For a 5 day work week, thats 2.5 hours, or 0.75 gallons of gas wasted. Go 300 miles a week and use 10 gallons of gas, thats 30.0mpg. Use 10.75 gallons of gas and its just 27.9mpg.

Step 4: Drive like you're brakes are broken. I never drove in snow before but I guess you probably already do this anyway? Anyways, any time you hit the brakes or downshift to slow down, kinetic energy is being turned into heat energy. Heat energy is lost energy. So if you see a light you know you're going to get stuck at, go ahead and take your foot off the gas asap. Also leave more space in between you and other cars. That way you don't have to slow down as much if one of them decides to slow down and turn off the road.

I've heard that the BOV makes the car run rich at idle. Has something to do with letting the air out of the system before it gets into the engine or something? Really don't remember, but yeah, put it in recirculate mode and you should see the mpg's go up.

But overall, the best suggestion I have is this. Move to Texas you stupid Canadian! I just got 32mpg in my car, 20mpg better than what you got, and I don't have to wear a jacket tomorrow either. Plus people don't talk funny here.

Haha, my bad attempt at humor. I know Canadians aren't stupid.
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Old 03-12-2008, 11:24 AM   #23
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Quote:
Step 3: Shutoff the car at stop lights after it's warmed up. Yep, 0.3 gallons of fuel per hour when the engine is idling. Doesn't sound like much, but what if you spend 3 minutes stopped at a stop light, and you get stuck at 5 lights on the way to work and 5 lights on the way back? Thats 30 minutes a day just sitting there doing nothing. For a 5 day work week, thats 2.5 hours, or 0.75 gallons of gas wasted. Go 300 miles a week and use 10 gallons of gas, thats 30.0mpg. Use 10.75 gallons of gas and its just 27.9mpg.
Silly... just silly... I'll personally burn an extra dollor or two worth of gas so I'm not being the center of attention by starting my car at each light, baking my turbo, and wearing out my starter....

And I'm telling you, the vented BOV on an Auto car with easy driving is not whats killing your mileage!!

Otherwise that was good advice, and should make a difference.... especially the tire pressure, this is quite important especially with AWD
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Old 03-12-2008, 02:07 PM   #24
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I run a VF30 with all mods needed, 283 to the wheels. When I was on the Cobb base map, 15 MPG, after some tuning I now get 22MPG and a lot more fun. A good tune will go a long way in helping to get the most out of your next fill up.
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Old 03-12-2008, 03:39 PM   #25
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Chapter/Region: TXIC
Location: San Antonio, Texas
Vehicle:
2003 Impreza WRX
BLUE

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Quote:
Originally Posted by GeneralTJI View Post
Silly... just silly... I'll personally burn an extra dollor or two worth of gas so I'm not being the center of attention by starting my car at each light, baking my turbo, and wearing out my starter....

And I'm telling you, the vented BOV on an Auto car with easy driving is not whats killing your mileage!!

Otherwise that was good advice, and should make a difference.... especially the tire pressure, this is quite important especially with AWD
Well if you come out nearly saving a gallon of gas every week. Thats' $3.00 saved per week going by 2 weeks ago gas prices. Looks like it's going to be sitting at $3.20 to $3.40 from now on though. There's 52 weeks in a year, comes out to saving $156 at $3/gal to $176.80 at $3.40/gal. I wouldn't think it would bake the turbo, but I wouldn't be too surprised if it did kill the starter within 3 years.

I swear I read somewhere that BOV's make the car run rich. Running rich means more fuel is being used. I'm really not too sure on this one though and don't have the time to look it up.

Rayme I think the block heaters are only like $25 or something? Really not too expensive at all, and seems like it would extend the life of the engine since cold starts are what kills engines.
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