WRX Quest for MPG

Maintenance/Repairs
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21

The problem with E85 is that your entire fuel system has to be designed and built to handle the alcohol. We are talking about the plastics and rubber in the many seals and joints the deteriorate and eventually are destroyed when you use E85. It is not just about changing the computer set up or the injectors. Use E85 in a vehicle that wasn’t built for it from the factory means all kinds of problems. Not in one or two tankfuls, but in a year or two of consistant use of the E85.

Next you bought a performance car. At the time you signed on for it you could have purchased a non turbo Impreza. Sorry you are disappointed with the real world mileage. Don’t blame it on the turbo. When you step on the gas the turbo spools up and pushes more air into the cylinders and that needs more fuel to provide the proper air/fuel mix to maximize non polluting combustion.

I didn’t say you would kill the resale value of your car. Just don’t expect someone to pay the extra $2,000, $3,000, or $4,000 your modifications will costs. Most of the mods you are contemplating are performance oriented and will not improve your gas mileage anymore than getting a car with a turbocharger. High flow exhaust for instance is made to go with high flow induction systems such as the turbo. You may get more power, but you won’t get more mpg.

Stick with the stock WRX. If you find the K&N system is helping good, the other mods you are looking at cost a bunch and will have little impact on mpg. You can buy a lot of fuel for $4,000. If you really have to improve your mpg trade in your WRX before you rack up too many miles and buy another car. This time look for the performance you really value, MPG. Don’t worry about the other performance that many seek, low ETs for 0 to 60.

22

MCM, E85 conversion is more than retuning, it’s making sure that every component of the fuel system is compatible with E85. Many plastic and some metals are not. That’s why I would never trust a conversion. Only factory flex fuel vehicles are guaranteed to be compatible.

hmmm - UncleTurbo beat me to it. Gotta type faster…

23

I won’t know how to compare it to a supercharged Mustang, but WRX is a very HOT small car. They really fly, and with AWD they just dig so the acceleration is very, very impressive. Not a surprise to me they get relatively poor mpg. If I had one I think I’d enjoy the power and worry less about the mileage. Considering the performance the WRX gets pretty decent mpg.

24

(I keep typing up posts and they keep being lost)

I spoke to the owner of AZ DynoComp on the phone. He suggested against E85 for all but the most agressive tuners. They basicly use it instead of very expensive 109 octane.
He did say that the new programable ECU would provide better cruising MPG, and that a package with exhaust bits and ECU is even purchased for new WRXs by dealers, and those vehicals all are getting better hwy mpg.

Doing the math with out the “savings” of E85 makes this project look far worst.

Cost for modification $2036
(2008 WRX - Only)
Dyno-Comp: (STAGE-2): “Steath Fighter”

  • Drop-In High Flow Filter
  • SPT Exhaust System (5-Dr Hatchback)
  • COBB Down Pipe with High Flow Cat
  • “Dyno-Comp/COBB Pro-Tuned Tuned”
    *COBB Access Port (ECU Flash)
    Flywheel HP: 300
    Flywheel TQ: 324

Eco-Tune, 25-28MPG over-all using 91oct @ $2.65gal
Est. Fuel Cost = $4332 @ 25mpg (savings $377)
$3868 @ 28mpg (savings $841)

They also offer just the progamable ECU (Cobb Access Port $695) with many progams to pick from.

I am a software guy, and I keep thinking the factory ECU may be the issue. Getting 21mpg and then resetting the ECU and suddenly getting 27 on the same roads, suggests something funky with the stock progam. It also seems to be running better now, was almost hesitating as well when getting 21mpg.

The Cobb ECU may seem like the only half sane option at this point.

25

Something to note: The Suzuki SX4 AWD manual gets 30 mpg highway.

26

yahoo autos:
SX4 Manual AWD
2.0L I4, 16 valves, 143 hp @ 5800 rpm
5 speed manual transmission
21 mpg city / 28 mpg hwy

Impreza Base
2.5L H4, 16 valves, 170 hp @ 6000 rpm
5 speed manual transmission
20 mpg city / 27 mpg hwy

WRX
2.5L H4, 16 valves, 265 hp @ 6000 rpm
5 speed manual transmission
18 mpg city / 25 mpg hwy

Well that’s good that someone else makes a manual AWD, and that is still 3mpg better. Just about every other car (no super expensive) that offers AWD, only offers it with Automatic transmittion.

27

I believe the new 2010 Subaru Legacy with CVT get the best MPG of ANY AWD car. It is on par with Camry/Accord in highway MPG and size. What else do you want?

28

A K & N filter is going to do near nothing for fuel economy so I’d like to hear the details behind how you “reset the ECU” and gained 4-6 MPG.

29

I didn’t claim it was a magic fix.
Doesn’t change the facts. Car was getting 21mpg for months. Driving like crap.
Unplug the battery for an hour, and plug it back in. Car feels dramaticly better, no hesitation, and freely reving.

Car has been getting 27mpg for the last 3 tanks of gas, no change in behavior. I have a set area for work calls, so my driving habits are pretty set. Will this stay? I have no idea or hope. But if something stupid is going on with the ECU, I’m willing to reset it once a week.

30

Luckily I know exactly how it compares. As I sold more than few when I was selling cars for a living. I almost bought one for myself, but I didn’t like the tubro lag, and prefer RWD cars anyway. There’s alot to like about the WRX though. But if operating expenses were a concern a non-tubro Impreza or Forester would both be more economical to run.

31

The 2008 WRX really has little turbo lag. It generates full torque at 2100 rpm. The 2009 WRX is a very quick car for the money. I believe it bests the STI in 0-60 with 4.9 secs. Of course that requires a clutch drop.

On the other hand the 2002-2005 WRX with the 2.0L(mine) has a serious case of turbo lag. It is a pig stock until you sweep the tach to 3500 RPM and the power comes on with a fury.

32

MCMunroe:

The fact that your CEL is on is proof that your car isn’t “running fine.” Have the codes read: I’ll bet you have a “too lean” error. Running slightly lean elevates combustion temperatures (particularly in a turbo car), creating the potential for engine damage if done for a prolonged period.

Also, turbos generally are an inefficient means of producing extra power in “sporty” applications. A “properly” sized turbo can be more efficient than a larger engine of the same hp, but that requires using a large, laggy turbine wheel. Most sports cars will use a small turbine and accept bad MPGs.

Instead of spending $3K on stuff with unproven payback and potential reliability issues, perhaps you could investigate a turbo delete? You’d still have a cool-looking car, improve MPG, and now the engine would be “overbuilt” for the application, so it should be reliable.

And I know I’ll get flack for this, but it’d be okay…ish to mix E85 and normal gas, starting at 10% E85 and working slowly up, until you “pop a code,” then back off 2-3 gal. (Of course, now that the ECU’s been altered, I’d be less certian of this advice). Remember to add 1/3 to the cost of E85 to compensate for the lower energy content.

33

I haven’t had a go in the 2.5L WRX yet, but I was looking at getting a 2004 model when I was car shopping last time around. Overall I liked it, but I was turned off by the turbo lag and the fact that it’s inherently more mechanically complex due to it’s AWD, more stuff to potentially go wrong. And you mentioned to get the performance numbers out of it that you see in the magazines, you have be willing to really abuse the car. With my Mustang, all that’s needed for a quick launch is a clutch drop at more modest 1800 RPM. I can do that all day long. But with a WRX you’ll break something after a few high RPM drops. The worst offender of all is the Honda S2000, on paper it’s pretty quick, but in order to get that sub 5 second 0-60 time you need to drop the clutch at around 6000-7000 RPM. In a stop light grand prix situation most owners aren’t willing to subject their car to that, and the S2000 gets smoked by far lesser cars off the line. But then again the S2000’s natural territory is road course not the drag strip.

34

The CEL isn’t “doing something stupid,” it’s warning you that the engine is being forced to operate outside design parameters! The reason you’re getting better MPG is that the car is being run in over-lean conditions…the ECU is trying to enrich the mixture, but has run out of control authority.

Normally, cars are run “rich of peak” exhaust gas temperatures. Lean it further, and you’re running “at peak,” and will most likely damage the engine in short order.

Lean it even further, and you’ll be “lean of peak.” Cars have been made to run LOP, and it can be (esp. with EFI) a safe thing to do when properly engineered. It will destroy the cat, so if you have smog checks in MN, you’re hosed, otherwise, you might not care, other than the now-permanent CEL.

The BIG problem is, you have NO IDEA if you’re LOP, ROP, or whatever. Have you even hooked a EGT guage up to the car? The first “lean-burn” cars were only possible with lots of “really smart” engineering; here, you’re throwing aftermarket parts into the mix and hoping for the best.

Worst-case scenario: you’re LOP in normal ops. One day, you decide to do a little “spirited driving,” and at WOT the mixture is enriched 'till you’re at peak EGT at maximum power output. Engine meltdown ensues. Remember that you’re dealing with an engine that’s already being asked to do more than a normally-aspirated one.

As someone who’s owned a WRX in snow country, the soft rubber+wide tires result in a car that doesn’t do any better in the snow than most FWD cars, with the exception of pulling steeper grades. Also, low ground clearance limits usefulness on unplowed roadways.

Sell the speedster; buy a car that more accurately meets the “mission profile”: high MPG HWY ops in all-weather conditions.

35

You all may find this article on ethanol interesting.

http://www.wellworthproducts.com/articles/ethanolgasoline.asp

36

I can confirm, no noticible turbo lag in the 2008 WRX. As all '08 Owners am a bit miffed that '09 upped the HP.

37

The Check Engine Light, never came on.
Please check what I posted please.

38

MCMunroe wrote:

Yes, the car runs decently right now stock on E85,
but the damn engine light comes on dissabling cruise
and traction control.

I too read that thought you implied the engine light came on because of the E85.

This whole thread has confused me.

If I understand it correctly, the OP has a performance car and he’d like to invest in something that will save him fuel costs.

The various ECO-Tune options all appear to be sure money loosers.

Then the “disconnect the battery to reset the ECU and install K&N filter” produces a boost of 5 MPG. Something is very questionable with this claim.

The costs involved in getting the car to run on E85 for the long term will outweigh the benefits.

What happened to keep the car tuned & maintained, and drive as though there was an egg under your foot? If saving money is your primary goal, I truly believe this approach is your best option.

39

Reference to the E85, was one time. Long ago. Not recently. Just to suggest that it’s not that hard to get a car to use it.

No engine light this time. And my “claim” is factual in this instance. I’m not saying “do this to your car for +MPG”, I’m saying my car was getting really bad MPG, and uplugging the battery (reset ECU), made it better again. The engine light had not been on during the months of poor MPG.

I appologies for trying to share all information and getting all confused and focused on the wrong things.

I’m done, thanks for all your posts.

40

Hey–I’m a fellow 2008 WRX owner, and I think don’t think you need to go for E85 just for better mileage. Actually, from what I understand, E85 has less energy content than gasoline, so your mileage will go down. Even running E10 (which is what seems to be sold at every pump here in Colorado) you’ll lose a bit of mileage.

However, I’ve been averaging 25-27 MPG in my WRX, and I don’t use any specific hypermiling techniques (especially the ones that tend to anger fellow drivers). I will skip 2nd and 4th and shift at about 2500 RPM. Even with that, I accelerate ‘moderately’ (my definition), but that still tends to be quicker than most soccer mom land yacht SUVs–I’ll put the pedal down maybe an inch and lift when I shift. One thing: Safety first. I won’t try to merge into 65MPH traffic at 45. I can still get 25mpg with 2 or 3 full-speed-ahead runs to 75 to merge on the interstate.

I’ll also leave the car in 5th when I’m going down hill or slowing to a stop–the injectors shut off if you’re off the gas and above idle–I’ll clutch in at about 20MPH to keep the car from lugging, and to downshift quickly if I need to.

I have a long, steep hill I have to climb to work–this kills my mileage more than the descent on the way home helps my mileage. Without that hill, I think I could pull closer to 30MPG in mixed driving.

An interesting note is that my previous car was a 2000 Outback, and with the same commute I’d get 19-20MPG. So with the turbo and running premium gas, I get a 25-30% increase in mileage.

I have been playing with the MPG display (using trip B to measure segments of my drive–trip A is my tank-full MPG), and I’ve found that my WRX (all stock) tends to get 23MPG at 80MPH, 25 at 75MPH, 27 at 70, and 33 at 60. Most of the 45mph roads around here have stop signs less than a mile apart, but I think a steady-state 45MPH might get close to 40MPG. That hill I was talking about? 12 MPG if I catch all 3 red lights. Overall, I’m finding that keeping an eye on the AVG MPG meter is the most helpful thing for improving my mileage.

As an aside, when it snows, I care less about mileage than I do about giving myself as many safe plays as possible on the road: I’ll leave the car in the lower gears longer so I can slow down gently using the throttle, and I’ll leave a lot of space in front so I can avoid panic stops. This will bring my mileage down, but, again, mileage is less important than safety.

All that to say, don’t focus on tuning your car or trading it: there’s a good chance you can get better mileage just by changing the way you drive, and it doesn’t have to be boring.