06 STI and WRX Impreza - Premium fuel recommended or REQUIRED?

tough call, I think regular is 'allowed' in emergencies only. Also, in addition to a 'performance hit' it's POSSIBLE gas mileage could be REDUCED making the switch closer to an even tradeoff.

maybe you could give up bottled water or starbucks or Coca-Cola ($450 per barrel) to help pay the difference in price?

if you must run regular, shop for a different vehicle.

Carl

I wish that were possible.

I already do not drink Starbucks (expensive), Coke (try to avoid High Fructose Corn Syrup), or bottled water (costs more per gallon than gasoline and is a waste). I drink Brita filtered water.

I test drove the Legacy and the salesman seemed to believe that Premium was >> Do both of these cars REQUIRE premium fuel? Can I use regular fuel with >> a

It is required for all Subaru turbo models. Regular may be used in a pinch but you then need to drive accordingly, no heavy throttle/high boost or damaging detonation may result. Ask to see the owners manual, the info is in there. If you are harboring any ideas of buying one and not running it on premium all the time, don't bother. You want a different car.

You might see if there's a manual in which you could read the fuel requirments online at

or

I run premium in my '06 WRX (and will likely never run regular) and my wife's '03 H6 OBW. The OBW does run on regular, but I didn't like the performance effect. Since requiring premium is a negative selling point, I doubt FHI engineers would recommend it if they didn't feel it was 'necessary'.

Carl

Thanks for the responses.

Is there anything I can do in terms of aftermarket modification (in addition to driving conservatively) that will increase the cars MPG?

Thanks.

What Carl said about the WRX. If you're not willing to feed it a steady diet of premium, look for a different car.

My '99 Outback is happy as a clam on Chevron

89 Plus gas and decidedly unhappy on regular.

If you are talking STI, 93 Octane is the recommended fuel. 91 can be used (since 93 isn't available everywhere) but you may need a reflash of the ECU to avoid knocking. Anything below that can damage the engine. This is especially true if you are in a warm climate. If I remember correctly, 91 is recommeded and 89 can be used in a pinch for the WRX, but again, prolonged use of anything besides 91 minimum can damage the engine.

I had to put 89 in the STi once (premium wasn't available), and it went into limp mode (timing advance was reduced to 15 degrees from its usual 45) and gas mileage sucked. It went through the entire tank in 200 KM (about 120 miles) with no power at all, and it knocked at about half throttle. I'll never do it again.

I think you need to face the fact that these cars are not econoboxes and can't be made into same. If fuel mileage is your priority then you should not be looking at a turbo Subaru. The combination of a low compression engine, turbo, and all wheel drive does not add up to an efficient vehicle. And, there is no point to paying the extra cost to get the nice turbo drivetrain only to "drive it conservatively". Besides, once you get used to the boost you won't be able to do that anyway. Sorry to be a bit harsh but you really need to consider what is most important to you before you make your purchase.

They sell them in locations that don't have premium 94 AKI for hundreds or thousands of miles. In locations like that, they (yes, I've spoken with them) claim that the STi will simply retard the timing and run just fine on

92 AKI.

DO NOT GO BELOW 91, EVEN WITH OCTANE BOOSTER.

Also, many gas stations that claim they sell "92" in reality just sell 91.

Nothing that won't make the engine burn hotter (and not last as long.) However, if you don't really care about a 15+ or 20+ year lifespan of the car, look into Cobb tuning & engine management systems. They can override the default maps and run the engine leaner (less gas, more air.) This helps MPG somewhat.

On the other hand, on my bone-stock '04 STi, I was able to get what I estimated to be about 560KM out of my 60 liter tank. Using US gallons, that's about 35-37MPG. Of course, I basically coasted down hills, didn't take the car above 110kph (~70mph), tucked the side mirrors in, turned off

*all* electronics and even the inside air fan, kept the outside lights turned off and the inside gauges turned down low. I accelerated like a slug, didn't accelerate when climbing hills, and I washed it like a perfectionist before I started out. I kept RPMs when shifting below 2K, and kept it basically in 6th the whole time.

The drawbacks: there were two adults and about 300+ lbs of gear in the trunk and backseat, so I'm sure I could've done better. Plus that was with a mix of 91 and 0.25 of a tank of 94 and some octane booster. Full, clean 94 AKI would've probably gotten me another 20-30KM.

It was too hot outside to be playing those kinds of games.. the person I was with at the time didn't particular like me doing that, sweating inside that little hotbox of a car on a nasty, muggy summer day.

Number one thing, reduce weight. reduce rotating , unsprung mass(lighter rims), rotating sprung mass(lighter flywheel and crank/access. pulleys), and mass in general. If you don't need all the seats - take 'em out. If you feel like you'd call a tow truck instead of changing a flat anyway, leave the spare and all the tools out of the car.

Keep the windows up, especially at highway speeds. Drag loss with windows down is greater than HP used to run the A/C. Keep your foot outta the boost, never rev over 3500 before shifting. No fun, but saves gas.

none of these ideas are soob specific. many are impractical for most people.

The STI and WRX are the Corvette and Camaro of FHI. No one buys a Corvette for economy on regular gas.

Carl

I thought limp mode was when the engine management system shut down one of the cylinders? That happened to me when my '02 WRX blew a head gasket: felt horrible, jerky, nasty. Like the car was shaking itself to pieces.

Ah.. looks like it might be both. :)

Thanks for all the responses and for helping me get a better perspective on things. I guess one might say I'm trying to "have it all" - well sort of....I was just hoping to squeak a few more miles out of it by tweaking it somehow, this would lessen the impact on my wallet as I transition from my Accord Coupe V6.

I never considered the impact of having the windows open being more than the A/C? You say that keeping a window open will cause the car to lose more horsepower, are you saying that that in turn will waste more gas as more is needed to compensate? Or just that the car will run slower with the windows open?

The actual power available is, of course, the same, but more fuel will be needed to push the car down the road at 70mph because the drag coefficient may change from, say .33 to .36 /whatever.

Carl

DO NOT use less than 91AKI especially in a Subaru WRX STi, nor less than

89AKI > Using regular fuel will cause no damage. If you went on a dyno you

In the case of the STi, there was the timing retard (0-15 degrees of advance) and the MAP never got above 100KPa. It usually runs at 20 degrees at idle, 45-48 degrees cruising, and at full boost, the MAP shows 200 KPa.

Mechanic told me that was 'limp mode' because of the fuel

Knock causes damage, car knocks on regular fuel, ergo, regular fuel will cause damage.

Fellas, engines have knock sensors for a reason.

I had an 89 GL Turbo Wagon (EA82 / 4EAT) that I ran very hard on a long paper route for two years (20 miles of paved, hilltop roads interspersed with 20 miles of unpaved, washboard gravel roads, plus a 12 mile commute). For the first year I burned Chevron regular almost exclusively, for the second I burned Chevron supreme exclusively. There was never any damage to the motor from the regular gas. However, the reason I switched from regular to supreme was for mileage purposes. After averaging out my mileage (easy to do when you run the same route 365 days a year) on both grades of gasoline, I was spending ~$29 to fill my car with regular after three trips around the mountain versus ~$24 to fill my car when I burned supreme to do the same three trips around the mountain. Although no damage was done to the car, the timing retardation due to the regular gas killed both performance and gas mileage and in the end just cost me more money. So, for less money, I got the performance I was supposed to out of the motor, plus I've never had injector problems. I find this to be the opposite of the opinion that we merely benefit the oil companies when we burn supreme, but again, your mileage may vary on the stuff.

Having worked at the same station I fill up at, I can't tell you how silly I find it when I see women filling their sports and luxury cars requiring supreme with regular in an attempt to save money. I have seen benefit to burning supreme in enough cars, I don't bother to do the math anymore for myself. Besides, the price difference between regular and supreme never changes, so as the cost of both rises, the potential savings with regular diminish, while the possible benefits super has over regular stay the same.

Unfortunately, as others have pointed out, some cars just don't benefit significantly from the switch. So do yourself a favor and do a fair comparison for yourself using your own math, in your own car, and then make your assertions.

As for regular gas damaging a subaru turbo motor, I have 20,000+ miles of hard driving on a 160,000+ mile turbo motor to say that it won't hurt an EA82. I frequently had her to 5k RPMs and 100+MPH, however, the performance loss is not worth the pittance I saved at the pump.

~Brian