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Low Octane Fuel Economy Tune?


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Has anyone thought about developing a low boost low octane tune for the Accessport? With the rising cost of gasoline I know I'd appreciate having the option to run lower octane without fear of detonation. Wouldn't be too hard to use Cobb's economy map as a baseline and retard timing to keep detonation at bay. :)
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ummmmmm

 

 

well

 

 

you could just run wastegate boost with a slower throttle plate opening (much like si-drive). It would suck if you put in 87 octane with an economy map then if you want power, you can switch the map but then what? You have a tank of 87 in there lol...

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Sounds like you bought the wrong car.
[URL="http://legacygt.com/forums/showthread.php/proper-flip-key-interesti-159894.html"]Flip Key Development Thread[/URL] "Genius may have its limitations, but stupidity is not thus handicapped." - E. Hubbard
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Has anyone thought about developing a low boost low octane tune for the Accessport? With the rising cost of gasoline I know I'd appreciate having the option to run lower octane without fear of detonation. Wouldn't be too hard to use Cobb's economy map as a baseline and retard timing to keep detonation at bay. :)

 

Heh, the rising gas prices around here have actually made me care less. Does it really matter when 87 is $4.27 and 91 $4.47?

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guess it pays to live in the middle of nowhere sometimes... 93 octane is $3.85 by me

 

to the OP: you probably don't want to do that because likebmx045 said, you'd have to know you wanted power when you fill up your tank otherwise you'd have sub-par gas in there

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I think I paid $4.299 last time I filled up.
[URL="http://legacygt.com/forums/showthread.php/proper-flip-key-interesti-159894.html"]Flip Key Development Thread[/URL] "Genius may have its limitations, but stupidity is not thus handicapped." - E. Hubbard
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Ah come on guys. I expected more out of a Subie forum. Lets assume I'm not a newbie and have been tuning fuel injected cars for years and know the difference between 85 and 91-93 octane. My 'new to me' 05 Leggy is my new Daily Driver and I would really like to not have to fill up with premium every day. I understand I won't get max performance out of my engine by using lower octane but the cost savings would be nice considering my daily commute.

A nice safe tune could provide decent economy gains as well as allow a lower octane fuel especially given the super low compression ratio of the EJ255 motor. I find it hard to believe nobody else on this forum would be interested.

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Why'd you buy a car requiring premium fuel for a daily driver if you didn't want to put premium fuel in it?
[URL="http://legacygt.com/forums/showthread.php/proper-flip-key-interesti-159894.html"]Flip Key Development Thread[/URL] "Genius may have its limitations, but stupidity is not thus handicapped." - E. Hubbard
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I bought the car because I like it, and it has decent power. I'm coming from a completely race built 400+whp Hyundai Tiburon running E85 and tuned by me, so I know what I'm doing and mostly what I'm talking about. lol

Mfrs base their octane rating on what gives the most safe and reliable peak performance. Most turbocharged engines can actually make power using lower octane fuel if built and tuned correctly. Actually most newer management systems can adapt and provide peak performance regardless of octane level. Look at the new Sonata Turbo for example. Its rated for regular (85-87) unleaded. Granted that it has direct injection but the concept is still the same. It can actually make more power on Premium due to increased knock threshold but its designed to run on regular.

If you guys aren't interested in a lower octane tune because all you care about is MAX POWA then that's your prerogative. I myself would like to have more options than just 91-93 octane fuel and with full ECU programmability that is a viable option.

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I guess I'm confused.

 

You bought a turbo car, with the intention of tuning it for fuel that will make it have almost as much power as a naturally aspirated version of the same car? Seems like you bought the wrong car to me. If you wanted the economy and power of a 2.5i, then why didn't you just get a 2.5i?

 

No one is questioning your tuning abilities, or whatever your talking about with the Hyundai. But go ahead and tune your LGT to run 87 octane. Let us know how it works out.

 

Keep in mind, you bought a car that has "decent power" and all you want to do with it, is make less power and get worse fuel economy.

[URL="http://legacygt.com/forums/showthread.php/proper-flip-key-interesti-159894.html"]Flip Key Development Thread[/URL] "Genius may have its limitations, but stupidity is not thus handicapped." - E. Hubbard
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ask a fellow subaru tuner. Tuning for E85 wouldn't be a problem, that's pretty common amongst subaru performance lovers. You could tune it extremely conservative in terms of timing advance BUT with the nature of E85 itself, you're gunna go through more fuel than if you were to tune it for 87 or 91 specifically.

 

Typically E85 cars get worse mileage, though the fuel is cheaper. So I don't know why you'd go through the trouble of doing so.

 

 

aaaaand

 

what BAC said...

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you/someone can probably tune the car to run on 87 octane. Probably reliably as well. I wouldn't do it though because I don't think the car has enough power stock on 91 octane. That and regardless of fuel prices, you'll only be spending ~$3 more per tank anyways. is $3 worth the power downgrade?
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you/someone can probably tune the car to run on 87 octane. Probably reliably as well. I wouldn't do it though because i don't think the car has enough power stock on 91 octane. That and regardless of fuel prices, you'll only be spending ~$3 more per tank anyways. Is $3 worth the power downgrade?

 

+1

 

Sort of like the people who drive 30 miles round trip to save 4 cents a gallon

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In my past turbo cars I used an adjustable boost controller to limit the need for high octane. What I don't know about these newer Subaru's is how well the ecu pulls out timing if it sees knock. So, if the knock sensor is doing it's job, then if/when it reads detonation, the ecu should limit boost and retard timing.

Last time gas got expensive, I know people with stock turbo cars were putting in 87 or 89 octane to save a few bucks. Those are the same people that never used the turbo anyway, so they didn't even notice a difference.

 

In reality, it's your right foot that will determine the need for higher octane and more fuel. Being that it's .20 more per gallon for 91 octane here over 87, even on an average fill up it's about $3 more. I'd call that cheap insurance for not melting a piston.

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You can't just turn down the boost and expect to be able to go WOT on 87 octane. You HAVE to tune for fuel octane.

 

At the end of the day, you are really only saving at most $5/fill. Is it REALLY worth making considerably less power, and having a much less safe setup, just to save a big-mac every week?

[URL="http://legacygt.com/forums/showthread.php/proper-flip-key-interesti-159894.html"]Flip Key Development Thread[/URL] "Genius may have its limitations, but stupidity is not thus handicapped." - E. Hubbard
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over here in new england 93 is $4.25 :lol:

 

$3.99/gal or less a the Wellington S&S as of yesterday. There's a S&S gas on 28 in Wakefield too. If you shop there, I seriously suggest you check them out. 2 weeks ago I got it for $3.72/gal with my points.

 

Additionally, IMHO, a tune which optimized fuel economy while in low-load conditions would be best. I think most aftermarket tuners do this, and that's why many at Stage 2 see better mileage when their driving habits don't change. Safe AFR at WOT, but gas-sipping mode when cruising.

 

I swear I'm going to dickslap the next person bitching about the cost of premium relative to regular. It's a difference of $5 a tank AT MOST.

 

Anyone who bought a LGT for fuel economy is realizing now they made a poor choice. Corolla, Civic, Fruity Prius = good fuel economy. LGT = fun daily that kills it in winter.

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I agree to a point. Since I don't know Subaru ecu's use of knock sensors, you may be completely correct.

 

However theoretically , less boost results in lower cylinder pressure, which means less chance of detonation. If the ecu also retards ignition timing when detonation is detected, then the combination of lower boost and retarded timing should lessen the need for higher octane.

 

But, you are 100% right, saving a few dollars is a lousy reason to compromise a fun car.

 

When I want economy and some fun, I ride 2 wheels. It runs on 87.

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Me thinks a NON-all wheel drive 4 cylinder car would have been a better choice. Without a turbo completely.

 

 

How about a Civic? Echo? I hear they get pretty decent fuel economy ratings on 87 octane.

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But timing is optimized for the det resistance of higher octane. It's been seen time and time again that the Subaru ECU isn't the fastest when it comes to responding to knock.

 

And the thing about knock, is that the ECU can only adjust for it AFTER it happens. By then, damage has been done.

[URL="http://legacygt.com/forums/showthread.php/proper-flip-key-interesti-159894.html"]Flip Key Development Thread[/URL] "Genius may have its limitations, but stupidity is not thus handicapped." - E. Hubbard
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