octane baby! (longish but possibly good reading)

[txrocco at sbcglobal.net (ATS - Patrick Bureau)]

one thing I dont understand then  if your theory would be correct
why do you need octane 105 to run a faster 1/4 mile. :)

I think you got it backwards...

ATS - Patrick Bureau - txrocco@sbcglobal.net
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=>-----Original Message-----
=>From: scirocco-l-bounces@scirocco.org
=>[mailto:scirocco-l-bounces@scirocco.org]On Behalf Of Erik
=>Sent: Monday, September 15, 2003 7:41 AM
=>To: Scirocco List; Dan Smith
=>Subject: Re: octane baby! (longish but possibly good reading)
=>
=>
=>There is theory that I have been working with for a while (working third
=>shift I have ALOT of time), and it goes a little like this:
=>
=>If the given Octane level is to resist Detonation (i.e. Hot spots in a
=>cyliner) essentially what you are doing is slowing down your
=>Flame front to
=>a controlable level (Cooling Effect). That being said you are
=>really getting
=>a slower and possibly a less efficient combustion process with the higher
=>Octane Rating fuel.
=>
=>  So with a lower octane rating in reality the Flame Front is
=>moving faster
=>and burning more quickly, so at that point in essence the motor is burning
=>more of the given fuel ingested into the motor during it particular
=>combustion process due to the faster flame front traveling across the
=>combstion area.
=>
=>Example:  87 Octane fuel has less resistance to detonation than say 94
=>Octane, hence there will be a hotter flame traveling arond the
=>cylinder and
=>conceivably (?) burning more of the air/fuel in the cylinder.
=>
=>One thing to remember with this is that it's not the Octane in
=>the fuel that
=>is making the power it is the cylinder pressure and camshaft
=>profile. While
=>a large cam will bleed off some presure in the cylinder it is
=>also allowing
=>a greater amout of Air/Fuel into the cylinder than a stock of
=>very mild cam
=>profile.
=>
=>This is why when a too low of Octane fuel is run a motor tends to
=>run hot in
=>most cases and will detonate under load.  Add the high Octane fuel and
=>Viola! cooler cylinders, no detonation.  Detonation being hot spots in the
=>cylinder that pre-ignite the Air/Fuel mixture before the ignition does.
=>
=>I get asked this question at least 10 times a day, "What Octane
=>fuel should
=>I run?"  I answer  "I can't give you an honest answer.  There are far too
=>many variables to this, compression, cam profile, altitude, timing curve,
=>car weight, gearing, etc."  What I try to convey is "Run the lowest Octane
=>possible."  See definition above.  "If the higer octane slows down flame
=>front you'll get a less efficient burn which equals less power."  I have
=>been witness several dyno tests run where a motor has 87 run
=>through it and
=>then 92 and the motors make less power BFC goes up and V/E goes
=>down.  Why?
=>Because the motor didn't need or want the higher Octane fuel.
=>
=>Before somebody say "HEY ASS what about Alch. and Nitro?"  Well those are
=>not conventional fuels.  Nitro is just totally nuts.  If you pour some on
=>the ground and throw a match on it, it won't burn.  Hit that same
=>spot with
=>a hammer and BAM!  no more fingers, toes or hammer.  Alch.  has a lower
=>Specif. Gravity that Gasoline so you have to run a greater volume in order
=>to make power.  Also note Alch. gets used in VERY high Compression
=>applications, say 13-1 and higher.  And if you notice it has a supreme
=>cooling effect.  This is part of the reason Top Fuel and Funny Cars don't
=>need cooling systems, and can run for as long and as hard as they
=>do.   Now
=>adays these two classes are running usually 75-80% Nitro and the diff in
=>Alch. This way they can keep the Nitro under control and still keep the
=>motor cool.
=>
=>
=>What was the original question again?  Oh yeah.  Higher Octane
=>fuel does not
=>equal better mileage.  Tell you Housemates to do less burn outs,
=>change the
=>oil, and replace the air filter, and run the lowest octane
=>possible that the
=>motor will live on.  An efficient package is the key.  If you've ever
=>noticed according to Bently most VW's total ignition timing is
=>21-23 degrees
=>before TDC.  Even the best Small Block Chevy is typically more than 30
=>degrees.  VW has very efficient cylinder heads.  They don't need alot of
=>ignition lead to make power.  A 93-97 275 H.P. LT1 makes .785 Hp per C.I.
=>and basic 1.8L 100 H.P. VW makes .925 H.P. per C.I.  sounds pretty
=>convincing to me
=>
=>This was just my .02, but what do I know?  Nothing about Weber
=>carbs that's
=>for sure!  :)
=>
=>Cheers,
=>
=>Erik
=>
=>----- Original Message -----
=>From: "Dan Smith" <sad_rocc@yahoo.com>
=>To: <scirocco-l@scirocco.org>
=>Sent: Sunday, September 14, 2003 6:27 PM
=>Subject: octane baby!
=>
=>
=>> Yeah, a corny play on a song title, but I couldn't resist.
=>Anyways, CO has
=>octane ratings at the pump ranging from 85 to 94. With gas prices ranging
=>from $1.77 to 1.99 respectively, I want to see if I can settle this hot
=>debate among my housemates. Does higher octane gas equal better
=>gas mileage?
=>And enough of a better mileage to make it cost effective? This
=>would be for
=>my relatively stock 84 8v, which doesn't deserve high octane gas if it
=>doesn't make a difference mileage-wise. When responding, please
=>try to keep
=>the formula equations to a minimum as high school chem was a long time ago
=>and I just squeeked by.
=>>
=>> TIA,
=>> Dan
=>>
=>>
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