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6 cylinder- Do I need Premium gas?


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26 replies to this topic

#1 Audiophobe

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Posted 20 March 2006 - 06:50 AM

I just bought a high milage 2001 High milage LL Bean. At my first fill up I noticed the message that they recommend premium fuel.:mad: It seems to run fine on regular.
Do I need to use premium?

#2 otis

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Posted 20 March 2006 - 09:35 AM

they recommend premium fuel....

Do I need to use premium?


Who's "they?"

Here's my answer- put whatever gas you want in it. I think today's cars are sophisticated enough to run on lesser octane- you just wont see the performance. I have a car that uses 91 octane. when gas was >$3/gal, I thought I would use 87 octane to save money. the car worked fine, but when I "stomped" on the pedal- there was a noticable lack of power. The kicker came when I realized I was saving less than $5 a month. I figure the $5 is worth the small amount of pleasure I get.

#3 Audiophobe

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Posted 20 March 2006 - 11:32 AM

Who's "they?"

Here's my answer- put whatever gas you want in it. I think today's cars are sophisticated enough to run on lesser octane- you just wont see the performance. I have a car that uses 91 octane. when gas was >$3/gal, I thought I would use 87 octane to save money. the car worked fine, but when I "stomped" on the pedal- there was a noticable lack of power. The kicker came when I realized I was saving less than $5 a month. I figure the $5 is worth the small amount of pleasure I get.


"They" is Subaru. It says it by the fuel inlet and in the owner's manual.

#4 PAezb

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Posted 20 March 2006 - 12:23 PM

"They" is Subaru. It says it by the fuel inlet and in the owner's manual.


It's recommended, but not required (unlike Turbos which are *required* to use higher octane). Run the lowest octane, but not past 87, that your engine runs fine with without balking (pinging/knocking). If your prone to a lot of "spirited" driving, you might want to run higher octane once in awhile.

#5 Audiophobe

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Posted 20 March 2006 - 01:36 PM

That's what I thought.
I may put in premium every third tank.

#6 ballitch

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Posted 20 March 2006 - 07:35 PM

just meet "them" halfway, use medium grade or 89 octane.


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#7 Jack in Norfolk

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Posted 20 March 2006 - 08:42 PM

What if you use the 87 but then add a bottle of octane booster? I'm not sure about the ecconomics of this (cost of octane booster) but it seems like it could work.

My dad has to run 93 in his Lexus and hates to pay for it. My mechaninc was telling me that if he ran 87 in the Lex it would be a little rough for about the first 100 miles but then the computer would "learn" to function properly on 87. But as mentioned in this post, there would be a loss in performance. My mechanic said it would probably not even be noticable. I wonder if this applies to subes as well.....

#8 Audiophobe

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Posted 20 March 2006 - 10:29 PM

I think the octane boosters sold at the PEP Boys type stores don't add much octane.
I think I heard that the computer "well learn" theory once before. If I was sure it won't hurt the engine I'd be willing to lose some performance. I wish I could ask the previous owner what he (or she) used.

#9 1 Lucky Texan

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Posted 20 March 2006 - 11:49 PM

That's what I thought.
I may put in premium every third tank.


It takes a few drive cycles for the knock sensor to advance the timing from any retardation it does on the lower octane. Better to pick a grade and stick with it. If you DO want to swap grades regilaraly, reset the ECU after filling up with the different grade.

I run premium all the time.

Carl

#10 Subarian

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Posted 20 March 2006 - 11:53 PM

Engine computers tend to retard timing to avoid knocking. Lower octane gasoline is more likely to cause knocking, so the ECM retards the timing, reducing power, in order to protect the engine. In a car designed for regular gas, using premium won't get you any more performance, but in a car designed for premium, using regular will decrease performance.

#11 nipper

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Posted 21 March 2006 - 01:53 PM

Octane boost does ad octane (motortrend i think did a test .... too many Dr ofices last 3 months so i forget which mags i read.... i know they were shocked that they all worked) but its a pricey route to go sometimes.
Modern engines with knock sensors and puters can run on the next lower octane, but if you notice a substantial performance drop, you may have to switch back.
Turbos and supercharged motors need premium.

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#12 Chef

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Posted 21 March 2006 - 09:25 PM

Thos eoctane boosters cost a few bucks a bottle. If the difference per month is noly a few dollars, it's probably not worth it. Plus, the octance enhancers may provide a better octance level, but through using chemicals not good for long term use. Just speculating, don't really know for certain.

#13 Audiophobe

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Posted 21 March 2006 - 09:43 PM

Just a thought: Do you think that if the premium fuel provides better performance that, assuming that you don't gun the engine all the time, that would translate into better effeciency and slightly better gas milage enough to offset the extra cost?

#14 1 Lucky Texan

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Posted 22 March 2006 - 12:03 AM

Just a thought: Do you think that if the premium fuel provides better performance that, assuming that you don't gun the engine all the time, that would translate into better effeciency and slightly better gas milage enough to offset the extra cost?


This has been covered before and I'm not sure if a definitive answer has been found for all cars under all conditions.
I subscribe to the theory that the engineers have no incentive to recommend an expensive fuel for no good reason. It is counterproductive for marketing. Even if there were no difference in overall fuel COST (not mileage) there may be differences in engine and intake/exhaust component longevity.

Knock sensors are not there to permit regular use of lower than recommended octane fuel - they are to protect the engine from bad gas or emergency use of lower octane fuel, or environmetal conditions that could lead to knock (hot weather?)

Xylene and toluene can be used to boost octane if you have access to inexpensive, uncontaminated sources. Likely that is what the boosters on the shelf at the parts stores are anyway. Instructions for use can be found on the net. I think if you buy a 55 gallon drum it almost saves you some money. I dunno what you tell the insurance company after the fire though!

Carl

#15 Ranger83

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Posted 22 March 2006 - 12:57 AM

I've been using regular in my 06 3.0R for the last 2,000 miles.

Mileage is up a little, could be breakin. No obvious difference in performance.

We have a Nissan that gives the max power on high test and regular. 242 max hp with 91 Octane, and 237 max hp with regular.

#16 nipper

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Posted 22 March 2006 - 01:04 AM

Just a thought: Do you think that if the premium fuel provides better performance that, assuming that you don't gun the engine all the time, that would translate into better effeciency and slightly better gas milage enough to offset the extra cost?


yes your gas milage will suffer if you use a lowe octane then is recomended for the car. The car is designed to run at X octane for peak power and performance. The only excpetion is in higher altitudes where you can go down a octane level, but only if the the pump has not adjusted for it. for instance 85 octane is = 87 octane at sea level. The knoock sensor is not there for emergenices, it is part of the engine mgmt system. Cars ping with the AC on, and knock sensors try to deal with that. There are other normal conditions where engines ping and the knock sensor is there to attempt to deal with it.
Another thing to consider is if that engine has substantial miles on it, it may have carbon build up on the cylinder heads. This is a source of ping or knock, and the only way to handle it if you cant get rid of it through other methods, is to go up an octane. I would never go down more then one octane level on a car.

nipper

#17 Audiophobe

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Posted 22 March 2006 - 06:45 AM

So if the milage is affected there's not much advantage in going down in octane, considering the other issues.

#18 otis

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Posted 22 March 2006 - 12:27 PM

Just a thought: Do you think that if the premium fuel provides better performance that, assuming that you don't gun the engine all the time, that would translate into better effeciency and slightly better gas milage enough to offset the extra cost?

why do you want to run regular gas? is it only the cost? when i first read your posts, I thought you didn't care about performance. now it sounds like you do. here's what I suggest you do:

run premium for a while, then run regular for a while. see what you think about the performance difference. Then take a look at how much $ youre saving each month by using regular instead of premium. if the $$ amt is negligible or the performance penalty is too great, just use premium. I did that for my BMW and could not take the sluggish response and the $5 savings was not worth it to me to use regular gas. OTOH, if the savings was $20 and performance was negligible, I would have switched to regular gas in a heartbeat.

From MY experience (and a few others), I have seen NO change in MPG due to change of octane (either putting in prem in place of regular or vice versa). In fact, my average mpg went UP when I used regular (instead of the recomended premium) only because with the sluggish performance of my car, I felt like an old ninny and drove like one, and my BEHAVIOR increased my gas mileage.

Like I said before- just do what you want to do.

#19 Audiophobe

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Posted 29 March 2006 - 11:30 AM

Took everyone's advise.
-Regular: more sluggish, milage about 20mpg
-Premium: better performance (not exactly a track car though:)), milage about 20mpg.
-Bottom line: For 5%-6% more per gallon premium is worth it to me. Plus, what one of you said made sense. Subaru wouldn't recommend it if it wasn't better for the car because the need for premium isn't exactly a selling point.
Thanks for your input!

#20 Ranger83

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Posted 10 June 2006 - 06:43 AM

I've done a dyno run with my car and Regular. In another week or two I'm going back to do a run with Premium. I'm also going to do a run without any air cleaner.

The guy who runs the dyno predicts a 2-3 hp difference for Premium (we didn't get any codes showing retarded spark or detonation on the first run) and 1-2hp for the air cleaner, but I wanted objective data.

#21 Ranger83

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Posted 10 June 2006 - 06:46 AM

I've already done a dyno run with my car and Regular. In another week or two I'm going back to do a run with Premium - 93 Octane no less. I'm also going to do a run without any air cleaner.

The guy who runs the dyno predicts a 2-3 hp difference for Premium (we didn't get any codes showing retarded spark or detonation on the first run) and 1-2hp for the air cleaner, but I wanted objective data. To put it in perspective, that's about the difference from running your A/C (did runs with it on and off).

I've been switching fuel every 2,000 miles and I'm also going to do some acceleration tests with each fuel so that on-road performance is measured. I defy anyone to tell which fuel is in the car by driving it.

#22 1 Lucky Texan

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Posted 10 June 2006 - 10:07 AM

I've already done a dyno run with my car and Regular. In another week or two I'm going back to do a run with Premium - 93 Octane no less. I'm also going to do a run without any air cleaner.

The guy who runs the dyno predicts a 2-3 hp difference for Premium (we didn't get any codes showing retarded spark or detonation on the first run) and 1-2hp for the air cleaner, but I wanted objective data. To put it in perspective, that's about the difference from running your A/C (did runs with it on and off).

I've been switching fuel every 2,000 miles and I'm also going to do some acceleration tests with each fuel so that on-road performance is measured. I defy anyone to tell which fuel is in the car by driving it.


wow! I'll be anxious to see the results. Is there a way to cause the ECU to 'reset' and adjust for the higher octane gas? Or are you just gonna run for some time before and let the ECU adapt itself?

fun project - how much does a dyno-run cost?

Carl

#23 Ranger83

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Posted 10 June 2006 - 12:46 PM

The ECU running regular, didn't do anything - it ran normally as far as I could tell. I'll know more after the next run but I predict the difference, if any, will be within the error of different runs on the dyno - a couple whp.

I went to TDC Tuning in Concord, NH (http://www.tdctuning.com/). I went there because he does a lot with turbo Subarus (he has a Legacy GT) and because it's probably the closest AWD dyno to any of our offices.

A session can cost from $75 to $150 depending on how many runs and what data or tuning you are looking for. Mine was the first H6 he'd ever run but he has run many Subaru turbos and sells tuning parts for them.

There are some other AWD dynos in New England. However the numbers from one dyno to another don't usually compare: some facilities are very optimistic, others are not.

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#24 blitz

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Posted 10 June 2006 - 06:08 PM

Depending on the specific vehicle and the various sensor algorithyms (IAT etc.) ambient temperature and humidity can play a role in your octane selection. Often time you can get away with running a lesser octane on cooler/damper days, then as Nipper mentioned, altitude is a major factor.

If it were my vehicle, I'd run premium if it speced premium.

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#25 NorthWet

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Posted 10 June 2006 - 08:53 PM

One of the reasons a manufacturer would recommend premium fuel is that premium generally contains a better additive package, including fuel system cleaners. Better additives produce better running engines and happier customers. Fewer regular fuels contain these additives; so called "Top Tier" fuels, which conatin these additives even in regular, should make your car run happily.

"Octane" is not power, greater ignition advance is not power. The popular term "Octane" refers to a fuel's ability to resist chemical breakdown and spontaneous ignition (detonation). Higher octane fuels break down slower when exposed to high peak temperatures and time-related temperatures.

Higher octane fuels also burn slower, thus requiring greater ignition advance in order for the engine to develop peak pressure just past TDC. This slower burning and greater ignition advance actually means that more of the fuel's power is spent resisting the compression stroke. An "ideal" engine/fuel combo would require virtually no ignition advance.

For most of your everyday driving, your engine would probably be content burning 40-50 octane fuel, and if the engine was optimized for it would give better fuel economy than on 87+ octane fuel. 87/89/93 octane fuel is only needed when you start asking your engine to produce significant power, like accelerating or climbing hills. You can "gain" detonation resistance by running at a higher engine speed, which reduces the time-related aspect of the chemical breakdown.

My 2 cents: Running higher octane fuel than your driving style requires is a waste, but one we all do to some extent everyday. If you want the fuel additives, then buy a higher grade of gas or buy "Top Tier" fuels.




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