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Guest Message by DevFuse

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Improving Gas Mileage? (also MAF discussion)

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27 replies to this topic

#1 Guest_oquipah_*

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Posted 18 April 2001 - 10:42 PM

After my first real "road trip" in the new 'ru, I'm a little disappointed with the gas mileage. Of course, I'm used to my 85' Honda (450 Miles per 12.5 gallon tank-no matter what kind of driving). I realize that AWD, and the added weight that comes along with it eat up gas.

With gas prices rising on what seems to be an hourly basis, what are some mods for improving gas mileage short term, while improving performance ie. HP, Torque... long term?

I have the K&N Filter which claims in improve gas consumption, but I really don't see it unless I'm doing 80+MPH on the highway.

It's hard to save $$ for performance mods when all of it goes towards gas!

98 Legacy GT
(BTW-it's a 5 speed)

*** 5/28/2001 *** Added MAF to thread title for easy find in archives - SmashPDX -

#2 Guest_LBSC_*

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Posted 19 April 2001 - 05:15 AM

If you're typically driving 80+mph, then probably the best thing you can
do to improve mileage is slow down a little. Wind resistance goes up as
the square of the velocity, I believe, so going fast cranks up the wind
resistance quite a bit. Drive non-aggressively, of course; a nice steady

You could try synthetic oil and gear lube (or ATF). That ought to get you
a couple percent improvement.

#3 Guest_joshmould_*

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Posted 19 April 2001 - 07:50 AM

well, an underdrive pulley will score you a couple o' miles per gallon. also get ridda the intake silensers <sp?>. other than that, there is not a whole lot you can do.

btw, im guessing you just got a drop in panel replacement k+n filter? if so i think you should get a cone filter, and just remove everything before the maf. also, to bypass the silencer that is just before the throttle body, you could get an older intake which does not have the extra silencer. i think you would have to look at pre-95 my cars.

#4 Guest_Brukst4e_*

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Posted 19 April 2001 - 09:37 AM

I'm getting ready to install an UNORTHODOX underdrive pulley on my 97 OB. Shortly after that I'll be taking a BIG road trip. I'll post my findings in a new topic when I get back. Which will probably be around May 22nd.

#5 Guest_oquipah_*

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Posted 19 April 2001 - 10:16 AM

Well, I don't "typically" drive 80+, but I like to burn the carbon out of the engine every now and then. and since the car is new to me, and the first one with some juice behind her, I like to test it out. I figured the first real long Road trip was a good trial run.

I've read a lot about the UOR Pulley and it will probably be on soon. As far as the intake goes, yes it is the drop in replacement, not a cone. I was originally thinking about getting a Weapon R intake system, but with too many negative press/testimonials regarding MAF failures/turbulance problems, I opted to play it safe. . . for now.

Brukst4e- definitely post your results! Interested in pre/post mileage averages.


#6 Guest_Brukst4e_*

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Posted 20 April 2001 - 09:00 AM

I spent about a 1/2 hr on the phone talking with Dale Teague. He had a 1996 Legacy (can't remember for sure),but he said he put and UNORTHODOX pulley,Dragon intake cone,and 2 1/2 inch Stromborg exhaust from the cat on back. With these three mods he got alot more power and would get 30 MPG all day with "normal" driving. But IF you kept your foot in it the MPG went down quit abit.

#7 Guest_kevinsUBARU_*

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Posted 20 April 2001 - 01:40 PM

Yeah, but his is a 2WD Legacy...1995 if I am not mistaken :)

#8 Guest_subyroo_*

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Posted 20 April 2001 - 09:57 PM

Hi there, if my add my 2 cents worth here, there is one thing to remember - YOU CANNOT HAVE PERFORMANCE AND FUEL ECONOMY TOGETHER - one cancels out the other, any Mechanic worth his salt will tell you that FOC (free of charge).

The choice is yours, your car is set up to achieve a blend of both - but some cars do improve a little of one or both from aftermarket mods, but read your warranty closely first BEFORE you do the them - NOT AFTER!!!

#9 Guest_meep424_*

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Posted 16 May 2001 - 09:15 AM

We own a 97 legacy and a 97 pathfinder. MPG is the p-car has been a pain, but I found a great read in a 4wd mag with a successful solution. I'm thinking of applying it to the legacy as well.

Synthetic oils in the p-car made a difference, after doing motor, tranny, xfer case and diffs. Manual disconnects on the front axle helped too. The most interesting was the intake...

Cone filters under the hood help the car breathe, but they also pull in hot air. In-town driving leaves hood temps quite high, and the air isn't as efficient.

So-- on the p-car I kept all the stock plumbing but totally insulated it with pipe tape from home depot... the stuff with sticky on foam rubber, backed with shiny aluminum film. $2-3 per roll. On the filter box I did better by covering it with trimmed 1/2" styrofoam and wrapping that in Al foil and glue. Noticed a 1+mpg increase in the truck-- figure it will work for the 4 feet of subaru intake plumbing as well.


#10 Guest_remarcable_*

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Posted 16 May 2001 - 10:48 AM

When I removed the factory intake silencer (snorkus) I noticed a decrease in gas mileage. pretty substantial, about 15mpg down from 20-25 which is what I usually get.

Putting on my amsoil panel filter did not really seem to help.

(and yes, I was resetting the ECU during each change).

Then after getting my stromung single-tip exhaust on and resetting the ECU again I was pleasantly surprised to find myself getting 25MPG again around town.

Of course I only get that when driving without a lead foot.

With my normal driving style I get around 20MPG which is pretty good considering the car is either accelerating or braking the entire time I am driving it.

Now all I need are some big yellow stickers to really help me go faster.

#11 Guest_coolb72_*

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Posted 16 May 2001 - 10:55 AM

You can do a number of things that will save you some money at the pump..
1.) unless your owners manual tells you to put prem.fuel then just use regular unleaded(this should save you $.20 a gallon or save about $3.00 per full tank. the idea of prem.fuel is great if your car really needs it but most of time its just a huge waste of money.
2.) keep your tires inflated to factory specs
3.) keeping the engine tuned up always helps
4.) dont carry around useless junk in the truck..weight makes your engine work harder
5.) use the a/c sparingly
6.) if you have a roof rack or ski rack take it off. racks are a huge aerodynamic drag.
7.) avoid drag racing and quick deceleration.
8.) keep the rpm under 5k..taking her to redline will only suck the gas at a higher rate.
9.) avoid extended idling and short trips.
most of these tips are free, but driving moderatly is the most likely way to save some money. this sounds like no fun but the reality of it is that gas prices are going to be rising all summer so its either drive like a bat out of hell and have no money or drive easier and have a little change in the pocket. peace

#12 Guest_mile hi sub_*

Guest_mile hi sub_*
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Posted 16 May 2001 - 02:53 PM

With my '95 Impezza Coupe with a '94 turbo motor the gas milage has been anything but impressive.
One thing I found was that on a warm day in traffic the underhood temp was 177f and under the
fender it was 100f my K&N now lives under the fender I noticed an improvement in milage and
performance. Also synthetic oil, light flywheel,3.9 rear ratio, helped and I also am going for an underdrive pulley.I have heard that you folks with monster stereos may have a problem with keeping the battery
charged with this pulley?? How about water injection?

#13 Guest_Seatbelt_*

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Posted 17 May 2001 - 10:36 AM

Weight is one of the biggest killers for gas mileage. I read somewhere (AAA publication? Shell gas publication?) that for each extra pound of vehicle weight you'll use an extra gallon of fuel over the life of the vehicle. Not a lot, unless you can remove a couple hundred pounds of needless stuff. I've lost 20 lbs in my Miata, but the wife hasn't yet given me the go ahead on her Subie. I'm guessing when gas prices hit $2/gal this summer, she'll relent...

Easy stuff to remove in a typical car: owners manual (read it, remember it), rear floor mats if the rear seat is rarely used, drain some washer fluid (use rain-x instead), take off bike rack/ski rack when not in use, check under dash and in engine bay for brackets, etc. not used in a car with your trim level... If you really feel compulsive about it, there's plenty of weight that can be shaved off with a dremmel rotary tool, but be absolutely sure that its completely unnecessary! Some folks will remove trunk carpet, replace the spare with a AAA card and can of fix-o-flat, yank radio & speakers if not used, etc. Also, some aftermarket parts can weigh significantly less than the OEM bits. Catback exhausts can often weigh half that of the OEM exhaust. Lighter wheel/tire combos can also be had aplenty.

An added benefit to this kind of gas savings through weight loss is improved acceleration and handling... oh, and yanking stuff doesn't cost a dime, just time. good luck!

#14 Guest_Legacy777_*

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Posted 17 May 2001 - 03:31 PM

I think that's gettting a little anal ;) for so little weight, but hey....to each is their own.

#15 Guest_JRAYQUEZ_*

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Posted 18 May 2001 - 08:04 AM

I waited awhile befoe I posted because I wanted to be 100% sure about this. I installed a jc sports air intake about a month ago and have monitored the miles per tank closely.

The first couple of tanks didn't see any improvement (240 miles per tank) only because I was experimenting with the new product (racing whom ever I could, taking it up to red-line). I was pretty impressed that I was still getting the same MPG considering how I was driving. So the next tank I let my wife drive the car exclusivly and she got 290 miles on the tank!

Since then I have been getting about 275 miles per tank. The intake is a little pricey but to me it was worth it, better gas mileage, and a much meaner sounding car!

I guess I should mention that it did create a little bit of a "bogging" problem with the fact that the car is sucking in way more air, but no increase in fuel pumping capacity. I only experience this problem from a complete stand-still, then "mashing" to full throttle (something you shouldn't do anyway) I plan to install an in-line fuel filter (about $50) and I am pretty sure it should take care of this problem. But I have had no MAF sensor problems that some subes have had after installing an aftermarket air intake.

#16 Guest_Legacy777_*

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Posted 18 May 2001 - 09:09 AM

Just curious....how would installing an in line fuel filter help the bogging from mashing the throttle? Did you mean to say fuel pump?

Also about the MAF sensor. You're lucky you don't have any problems with it now. I don't have any problems with mine either now, that it's been replaced. However, I don't think you're out of the woods. Over time the MAF will most likely die. The turbulant air really reaks havoc on the sensors. I'm trying to think of a way to fabricate some sort of air vein type thing to put in the filter, just before the MAF to help straighten the air. Haven't had much luck with it though.

#17 Guest_JRAYQUEZ_*

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Posted 18 May 2001 - 09:21 AM

Good catch! You're right...I meant fuel pump not fuel filter. How long did it take before you found out you had MAF failure on your car? Before I bought the intake I talked to jc sports about it, and they said they would warranty against MAF failure if it was caused by their intake. But hopefully it never gets down to that.

#18 Guest_meep424_*

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Posted 18 May 2001 - 10:31 AM

MAF Breakdown?

I've been running a JC sports intake for about 35,000 miles with no problems on our '97 legacy brighton. On the other hand, I haven't oiled the filter much either-- stays pretty clean up in the hood.

Are some of the MAFs more sensitive than others? On the JC sports intake, the cone filter bolts directly to the MAF via a horn-shaped adapter plate. The intake of the MAF has a fine metal screen immediately before the air reaches the resistors-- presumably to help "straighten" the air.

I do have the same problem with hesitation if I give it too much at low rpm. It doesn't like that. Realized increase in mid-range torque but no difference in top-end hp by the best I can tell. Hard to say about mpg-- You can certainly dip in harder and reduce mpg, but in normal driving I can't say I've seen much of an improvement.

After 35,000 miles, should I still be wary about MAF failure? I ask because I've been thinking about reinstalling the oem intake and insulating it completely, which gained 1-2mpg in our nissan truck.



#19 Guest_Seatbelt_*

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Posted 18 May 2001 - 11:44 AM

Weight is evil... :evil:

Especially in a sports car like the Miata. It makes me anal about weight savings in my Miata Support Vehicle as well... :)

#20 Guest_Legacy777_*

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Posted 18 May 2001 - 03:02 PM

Here's my experience, "drama" if you may.

***Story Time***

Back in the summer of 98 I got my cone filter. Back then, there was absolutely NOTHING for my car, or at least to my knowledge there wasn't. I put the filter on at 117,750 miles. I had intermittant problems where I would just loose power for some reason or the car would just die. I chased this ghost for more than a year. One day home from work, it died on me, and would not start back up....which was the screwy thing....it usually started back up. Well, I had my hunches it was the MAF sensor, but up until that point, no code. At $300 a pop....not something I wanted to change just for the hell of it. So at 138,287 miles I replaced the MAF sensor. That's almost 21k miles, which is not too long....however my MAF sensor had been around for a while before the cone filter, so I'm sure that probably helped in its demise.

I would say you are never "out of the woods" for a MAF sensor failure. It could happen soon, it could happen later, or could not happen at all. I guess it depends on how sensitive your particular sensor is, how you drive, air conditions, etc. The main killers of them, is turbulant air, and more quantity of air. The latter I think probably isn't as big a factor as the turbulant air. I would like to make something that goes in just before the MAF that has some sort of wind veins to help straigten the air. This would help the turbulance, as well as help get a more accurate reading for the computer.

As far as JC Sports warrantying their intakes....more power to them. I'm not quite sure how they can do that....but it's not me. They've been known to be a little shady at times. So I wouldn't hold my breath if I were you. As far as performance. You should have noticed most of the increase in performance in your high end, with a little more low, and so-so change in mid range. Well that's what mine was like. You should Definitely get more high end, quicker revving to redline, etc. That was one of the big things for mine. It revs SOOO much quicker with the cone filter on. Remind you, I do not have an aftermarket intake. I am using the stock subaru plastic one.... I did some modifications to the bracket and arm to make it stay.

Well that's my saga with the MAF sensor. I really don't know what to tell you. I think I was one of the firsts, at least on this board to have a MAF sensor failure. It's a pretty important sensor...if it's messed up....the whole engine will run like crap or not the way it's suppose to.

I think I covered your questions.....if not, or if you have more let me know.

EDIT: One more note, you really should oil these filters every 10k at the most. I know some say you can go longer or what not, they're not paper elements, if the oil dries out, you LOOSE you're filtering ability and will let contaminents in your engine. I actually do mine every 6000 miles, every other oil change. re-oiling it is cheap compared to the alternative of engine crappin out

#21 Guest_meep424_*

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Posted 21 May 2001 - 04:49 AM

Hey Thanks Josh,

I appreciate your feedback. I'll make a note of the oiling frequency for the filter. At least now I know what to look for if the engine starts to act weird. So far, so good, however, so I'm pretty happy. I have had a spark wire burn out, but that's been the only electronic failure on the engine since its purchase. Leaky oil at the main seal & pump, however, is another story.

I'd really like to see if the MAF would pipe immediately to the throttle body, then add a hood scoope & filter setup to immediately grab fresh air from the outside. Lower air temp would help power and mpg, shorter plumbing would further help power. Based on the sensitivity of the MAF, however, such a compact setup might introduce too much turbulance from the outside. More food for thought, I guess.

Hey Thanks!


#22 Guest_submannz_*

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Posted 21 May 2001 - 02:42 PM

To fix turbulence problems the best bet is a venturi from the air filter to the MAF sensor.

The majour cause of turbulence is the intake system not secured strong enough. When the intake system vibrates around it causes turbulence also.

As an exaggeration of a venturi like a funnel.


#23 Guest_MailmanX_*

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Posted 25 May 2001 - 07:25 AM

My son is currently on his way back to Southern CA from Seattle in the '93 Legacy L Sedan (AWD) that I purchased for him. He called me last night from the Redding, CA area to say he's getting 32 MPG. He has been driving about 70-75 MPH on I-5. The car is completely stock. No changes to intake or exhaust, etc. The only thing I did when I bought it was to put in all new filters, new oil (plus slick 50, which I know some people hate, but I've used it successfully for MANY years), and new plugs and wires.

I don't understand why so many people seem to be getting much worse MPG than this car is getting. Maybe we were just really lucky with this car. It sure runs great!

#24 Guest_JRAYQUEZ_*

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Posted 25 May 2001 - 08:21 AM

Does where you live, in terms of altitude, have any bearing on your cars MPG? If so what would have a better effect, higher or lower?

#25 Guest_MailmanX_*

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Posted 25 May 2001 - 08:45 AM

Seattle is at sea level. Where my son lives in Southern California is also very near sea level. He has gone through a few mountain areas on his trip, but nothing over 4500 feet. I doubt that in our case altitude has any bearing on the fuel mileage.

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