The Subaru SVX World Network   SVX Network Forums
Live Chat!
SVX or Subaru Links
Old Lockers
Photo Post
How-To Documents
Message Archive
SVX Shop Search
IRC users:

Go Back   The Subaru SVX World Network > SVX Main Forums > General SVX Babble

Reply
 
Thread Tools Display Modes
  #16  
Old 05-19-2008, 07:53 PM
lilbrudder lilbrudder is offline
i can make it on my oooowwwnn!
 
Join Date: Apr 2007
Location: las vegas
Posts: 237
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.
Reply With Quote
  #17  
Old 05-19-2008, 08:02 PM
oab_au oab_au is offline
Registered User
Subaru Gold Contributor
 
Join Date: Mar 2001
Location: Coffs Harb, Australia.
Posts: 5,032
Significant Technical Input Registered SVX
Don't agree with any of this.

Quote:
Originally Posted by crazyhorse View Post
The valves would burn due to the increased combustion temps and pressures that the higher octane brings. (Because of the slow burn) Add in the fact that the old US stuff didn't have hardened valve seats, and you have a recipe for destruction.

The other thing to remember is that back then "regular" was 110 octane.
AvGas could have been upwards of 200 octane!

Modern AvGas is 100-130 octane, depending on air/fuel mixture. It's not rated the same, so a direct compairison is difficult. The older chemistry was rated the same as today's pump gas.
A change of octane doesn't increase "combustion chamber pressure or temps."

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.
__________________
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.
Reply With Quote
  #18  
Old 05-19-2008, 08:31 PM
crazyhorse's Avatar
crazyhorse crazyhorse is offline
242,000 mi on oem trans
 
Join Date: Aug 2007
Location: Greeneville, TN
Posts: 1,111
Registered SVX
Quote:
Originally Posted by oab_au View Post
A change of octane doesn't increase "combustion chamber pressure or temps."

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.
Hmmm I'd have thought for sure, that the slower burning characteristics would have raised temps & pressures.

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.
__________________
[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.
Reply With Quote
  #19  
Old 05-19-2008, 08:33 PM
kwren's Avatar
kwren kwren is offline
Registered User
 
Join Date: Aug 2006
Location: washington state
Posts: 3,499
Sounds reasonable!

Quote:
Originally Posted by oab_au View Post
Yes Keith, there has been octane changes since we moved from using Kerosene.

Well don't know about the USAF. but the burn speed is fairly constant for most of the hydrocarbons, at the same temp/pressure, regardless of the octane rating.
If the burn speed was slower, we would have to change the spark advance, with different octanes. We only have to change it to suit the compression pressure/detonation point.

Harvey.
Kerosene is still used as Jet fuel?

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!
Reply With Quote
  #20  
Old 05-20-2008, 04:26 AM
dragoontwo dragoontwo is offline
Registered User
 
Join Date: Dec 2007
Location: Clarksville, TN
Posts: 325
Registered SVX
The army still uses jp-8 which is basically a higher grade kerosene in their helicopters, and most ground vehicles.
__________________
'92 SVX LS Pearl White - 6mt
Reply With Quote
  #21  
Old 05-20-2008, 08:49 AM
b3lha's Avatar
b3lha b3lha is offline
Phil & Belha
 
Join Date: Aug 2001
Location: Alcyone Limited, Buckinghamshire UK
Posts: 2,671
Quote:
Originally Posted by oab_au View Post
...we would have to change the spark advance, with different octanes.
Isn't that exactly what the ECU does?

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.
__________________
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
Reply With Quote
  #22  
Old 05-20-2008, 02:29 PM
lechnoid's Avatar
lechnoid lechnoid is offline
Tech & Almost Lawyer
 
Join Date: May 2008
Location: St. Cloud, Minnesota, US
Posts: 91
Quote:
Originally Posted by oab_au View Post
There is no different in the burn speed of 92 octane to 98 octane. The only difference is in the 'flash point' of the fuel. This is the temp/pressure that the fuel can stand before it will self-ignite. A higher octane can stand a higher combustion chamber temp/pressure, before it will self-ignite/detonate.
It won't make it run rich or hurt the cats.

Harvey.
I agree and at the same time disagree, nothing personal. You are correct on the octane rating and the flash point of the fuel. However, the slower burn prevents knock in a number of ways beyond raising the flash point. Knock can be caused by lots of different things as you're well aware. Hot carbon chunks, hot spark plug bases, bad plug wires, excessive engine heat, and many others can all lead to detonation. However, even on an engine running at normal temperatures with no carbon build up or any other flaw or defect, knock WILL still occur, albeit minor. This is a less serious example of the fuel in the combustion chamber igniting at both the piston and the plug at the same time. Picture a combustion chamber from the side, with the plug being top center. In lower octane fuel, due to the high rate of burn speed, it is possible for the center to not get burnt as fast as the sides. As the sides burn together, the now separate flames are able burn into each other, colliding and causing knock. This will produce enough of a signal for the knock sensor to respond, but not with enough voltage that the computer will care to do anything about it. A slower burn reduces the frequency of this occurring.

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.
Reply With Quote
  #23  
Old 05-20-2008, 04:25 PM
GreenMarine's Avatar
GreenMarine GreenMarine is offline
From POST-***** to LURKER
 
Join Date: Dec 2002
Location: Raleigh, NC
Posts: 5,873
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
__________________
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...
Reply With Quote
  #24  
Old 05-20-2008, 06:12 PM
oab_au oab_au is offline
Registered User
Subaru Gold Contributor
 
Join Date: Mar 2001
Location: Coffs Harb, Australia.
Posts: 5,032
Significant Technical Input Registered SVX
Quote:
Originally Posted by lechnoid View Post
I agree and at the same time disagree, nothing personal. You are correct on the octane rating and the flash point of the fuel. However, the slower burn prevents knock in a number of ways beyond raising the flash point. Knock can be caused by lots of different things as you're well aware. Hot carbon chunks, hot spark plug bases, bad plug wires, excessive engine heat, and many others can all lead to detonation. However, even on an engine running at normal temperatures with no carbon build up or any other flaw or defect, knock WILL still occur, albeit minor. This is a less serious example of the fuel in the combustion chamber igniting at both the piston and the plug at the same time. Picture a combustion chamber from the side, with the plug being top center. In lower octane fuel, due to the high rate of burn speed, it is possible for the center to not get burnt as fast as the sides. As the sides burn together, the now separate flames are able burn into each other, colliding and causing knock. This will produce enough of a signal for the knock sensor to respond, but not with enough voltage that the computer will care to do anything about it. A slower burn reduces the frequency of this occurring.

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.
OK, you are still relating the burn rate of the fuel to the Octane rating. The burn rate of the fuel is dependant on, the temp, the pressure, the turbulence, and the mixture strength. The octane rating has no effect on the burn rate.

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.
__________________
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.
Reply With Quote
  #25  
Old 05-20-2008, 07:19 PM
kwren's Avatar
kwren kwren is offline
Registered User
 
Join Date: Aug 2006
Location: washington state
Posts: 3,499
Lots of information here!

Quote:
Originally Posted by oab_au View Post


OK, you are still relating the burn rate of the fuel to the Octane rating. The burn rate of the fuel is dependant on, the temp, the pressure, the turbulence, and the mixture strength. The octane rating has no effect on the burn rate.

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.
How much is actually correct??

Anyone know for sure

Thanks,
Keith
Reply With Quote
  #26  
Old 05-20-2008, 07:25 PM
oab_au oab_au is offline
Registered User
Subaru Gold Contributor
 
Join Date: Mar 2001
Location: Coffs Harb, Australia.
Posts: 5,032
Significant Technical Input Registered SVX
Quote:
Originally Posted by kwren View Post
How much is actually correct??

Anyone know for sure

Thanks,
Keith
Well probably just the bits that I wrote.

But a good Googling should tell you what you want to know.

Harvey.
__________________
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.
Reply With Quote
  #27  
Old 05-20-2008, 07:43 PM
kwren's Avatar
kwren kwren is offline
Registered User
 
Join Date: Aug 2006
Location: washington state
Posts: 3,499
It just depends....

on who wrote the Google

Take care,
Keith
Reply With Quote
  #28  
Old 05-20-2008, 07:44 PM
YourConfused YourConfused is offline
Registered User
 
Join Date: Jan 2007
Location: Austin, TX
Posts: 1,276
Quote:
Originally Posted by kwren View Post
How much is actually correct??

Anyone know for sure

Thanks,
Keith


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.
__________________
"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."
Reply With Quote
  #29  
Old 05-22-2008, 11:28 PM
VICSVX's Avatar
VICSVX VICSVX is offline
Never Forget
 
Join Date: Nov 2006
Location: Tucson, AZ
Posts: 383
Registered SVX
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?
Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -6. The time now is 06:40 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
© 2001-2015 SVX World Network
(208)-906-1122