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#16
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all I know is my car runs poopy on cheap gas and very good on premium (with boosters). this could be a good experiment, you run bad gas I'll run good gas and we'll see goes longer.
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#17
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Don't agree with any of this.
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They did not need harden valve seats, they used Tetra ethel lead to lube them and raise the octane. Back then the octane was about 85, 200,,,,,,,,,still havent got there yet.. The chemistry remains the same, we just have two system to rate it Mon and Ron. Harvey.
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One Arm Bloke. Tell it like it is! 95 Lsi. Bordeaux Pearl, Aust. RHD.149,000Kls Subaru BBS wheels. 97 Liberty GX Auto sedan. 320,000Kls. 04 Liberty 30R Auto Premium. 92.000kls. |
#18
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I misspoke about chemistry. I meant that the older fuels were rated the same way (RON) whilst current AvGas is rated with MON, on a rich, or lean scale. These scales are based on boosted, or non boosted applications. The higher ratings are for richer, boosted applications.
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[SIGPIC]http://www.subaru-svx.net/forum/image.php?type=sigpic&userid=5569&dateline=1207440 507[/SIGPIC] Naught but by the grace of God "42" Current Stable By Age:'89 Subaru XT6 Silver "Audrey" as in Hepburn '96 SVX LSi #767Brilliant Red "Lil Red" Now on the front burner. Looking for a totalled, but running parts car. |
#19
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Sounds reasonable!
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Maybe changing the time of the spark is how it is done with the switch to use the lower octane for SVX with the ECUtune Subaru SVX Stage 1v5 Performance Module Is interesting subject for sure. Keith Last edited by kwren; 05-19-2008 at 11:14 PM. Reason: found it! |
#20
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The army still uses jp-8 which is basically a higher grade kerosene in their helicopters, and most ground vehicles.
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'92 SVX LS Pearl White - 6mt |
#21
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It was my understanding, from reading the Subaru ECU patent that the ECU has a base timing map for the lowest octane fuel it can burn, and a maximum allowed advance map. The learning system starts off with the base timing and then gradually advances it until it detects knock and then backs it off a bit. Since discovering that the JDM cars have different fuel and timing maps to the UK and USA cars, I've been running mine on 99 octane. I think it runs smoother on 99. If I can't get 99 and have to use 95 or 97 instead, it runs rough for a while.
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Subaru ECU and TCU Website 1992 Alcyone SVX Version L 1992 Alcyone SVX Version L 1994 Alcyone SVX S40-II 2004 Subaru Legacy 2.5 SE Sports Tourer 1996 Subaru Legacy 2.2 GX Wagon 1988 Subaru Justy J12 SL-II |
#22
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As for the effect on the cats, the slower burn means that by the end of the exhaust cycle, some of the fuel is still burning or is not burnt as it leaves the engine. Without tuning adjustments for the octane change, this will cause a rich condition. Running consistently rich is one of the most frequent causes of catalyst failure. Think of a muscle car running a short, wide open exhaust running on race fuel. I know I've seen flames come out the rear. There would be no flames if the fuel was fast-burning. |
#23
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There's quite alot of different angles on Octane and Hydrocarbons going on in this thread...
Just "Octane rating" or Wikipedia it... There's plenty of reading out there to be trusted. If I wasn't doing Chemistry homework I'd type up my 2 cents on it. Did it on NASIOC already so if you are a member on there feel free to search it... So far though the most "right" answer I have seen goes to Harvey... I'll post again tonight if I finish this stuff and get dinner before it gets too late... ~ Chris
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2020 Subaru Outback Touring - Wife's first Subaru 2005 Volvo V70R - 5-cylinder love! :Heart: ** SOLD **1998 Subaru Legacy 2.5GT Wagon - MOST RELIABLE car I've ever owned ** SOLD **2006Subaru WRXSTi (Former "Boxer4Racing.com / Continential Tire" STi) - Built EJ22t block / EJ207 JDM STi "big port heads" - 9,000rpm MONEY PIT!!! ** SOLD ** 1995 "Tree-Hugger Green" SVX L AWD(5 MT) --- "Gumby" 130K miles #399 in MY95, my original love... |
#24
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Lean mixtures take longer to burn, thats why we can have backfiring out the intake with lean mixtures, flame out the exhaust, and burnt exhaust valves, if the spark is not advanced enough to accomodate the slower burn. You are confusing two different things, pre-ignition, and detonation. Pre-ignition is when a glowing carbon piece ignites the mixture before the plug fires. This won't cause knock, it just starts the burn from two points, the same as an engine with two plugs per cylinder does. If this state continues it can lead to burning a hole in the piston due to the earlier ignition and the extended heat period that the cylinder has. The octane rating has no effect on pre-ignition. Detonation is when the plug starts the burn, and the flame front moves out across the combustion chamber, raising the radiated temperature and the pressure that the mixture, that is furthest from the plug has to endure. If the octane rating is not high enough this end gas will spontainously combust (explode), this instainous pressure rise, causes the sound we call Knock/detonation. It is the octane rating of the fuel that allows it to resist this condition, and reduce knock. The higher the octane the less tendenacy to knock. b3lha Quote: Originally Posted by oab_au ...we would have to change the spark advance, with different octanes. Isn't that exactly what the ECU does? Quote: Yes Phil, but not because of the burn rate. We retard the ignition to reduce the amount of time that the end gas has to endure the temp/pressure, to reduce the knock. This also reduces the torque. Using the highest octane that the engine needs, achives the highest pressure acting on the piston, and the highest torque.
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One Arm Bloke. Tell it like it is! 95 Lsi. Bordeaux Pearl, Aust. RHD.149,000Kls Subaru BBS wheels. 97 Liberty GX Auto sedan. 320,000Kls. 04 Liberty 30R Auto Premium. 92.000kls. |
#25
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Lots of information here!
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Anyone know for sure Thanks, Keith |
#26
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Well probably just the bits that I wrote.
But a good Googling should tell you what you want to know. Harvey.
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One Arm Bloke. Tell it like it is! 95 Lsi. Bordeaux Pearl, Aust. RHD.149,000Kls Subaru BBS wheels. 97 Liberty GX Auto sedan. 320,000Kls. 04 Liberty 30R Auto Premium. 92.000kls. |
#27
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It just depends....
on who wrote the Google
Take care, Keith |
#28
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They are all correct, just ask them. Harvey has been getting it the closest as far as I know and have read over the years.
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"They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety." Benjamin Franklin blk 92' LSL w/ average mods pics here http://s306.photobucket.com/albums/nn277/yourconfused/ Cash68: "Hmm, I wouldn't brag about beating Escorts. That's like saying you tricked a retarded person." |
#29
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hmm, ive been running 99 for the last 2yrs and i get round 21-22mpg with a smooth engine...however now that gas is an arm and a leg i filled up using 95 (half 99 half 95) and knockin is way noticable and mpg so far is crap!
i was told that in 1994 (the year of my car) that there was only leaded and unleaded....the unleaded was premium and thats the gas subaru said to use well now, with all gas unleaded....is premium needed stilll? or can i use regular? will the ECU learn after awhile and the knockin stop and mpg go back up? or shud i stay with premium? |
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