[Diy_efi] Timing Advance Curve?

[Mike]

At 08:35 AM 12/19/02 -0500, you wrote:
>Octane has everything to do with the speed of burn.  Higher octane actually
>controls ping by slowing down the burn.  This is why a very low HP/cubic
>inch engine doesn't necessarily gain power with higher octane.

Daniel,

You are wrong on all points, I take it you either havent been on this
list for long or havent read anything about octane, what it is or how
its measured...

Referring to your three sentences above, denoted as a to c:-

a.	Octane has negligible effect on speed of burn,
	ability to resist spontaneous ignition due to rising temperature
	or pressure has negligible relationship to the speed of burn,
	these are separate issues. It is possible to contrive a
	mixture of fuels to achieve higher octane whilst also reducing
	the burn rate but it is also possible to do the exact opposite.

	Think about the fuels used in F1, highest octane and faster
	burn then our engines, how else could they operate with reasonable
	power outputs at 15,000 rpm.

b.	Higher octane doesnt 'control' ping, it *only* means its less
	likely to ping ie more resitant to ping but has negligible
	relationship to speed of burn.

c.	Any HP/ci engine may not have any imporvement in power out if
	higher octane is used *because* higher octane fuels may not
	necessarily have more energy than lower octane fuels. However,
	if an engine is retuned for higher octane - such as advancing
	the timing or raising the boost then its possible to both
	improve economy and raise power output as required. So bear in
	mind there are four separate issues which 'might' overlap,
	and these are:

	-	Octane rating
	-	Speed of burn
	-	Energy content
	-	Volatility

Its possible with the large variety of fuel components available
(ie. Flammible petrochemicals) that a particular combination can
be reached for a particular aim - but it in no way means there
is an automatic causal relationship between octane and speed of burn,
none, zero - zilch !

I'm sure others on this list can articulate this better than can, I
dont know where you got your information from but its rather one
dimensional and makes woefully invalid generalisations which can
lead people astray - the issue is not at all as simple as you
suggest.

Eg. Here in Australia (amoung others) we have these fuels:-

1.	Unleaded, 92 octane (sometimes reaches 94)
2.	Premium, 96 octane, same energy as 1, same effective speed
	of burn - or actually a little faster as a porsch tuner has
	suggested to me.
3.	BP Ultimate, 98 octane *and* a little higher energy than
	1 or 2 plus a detergent/friction modifier of sorts but BP
	arent saying precisely. Recommended for high performance
	engines where higher speed of burn is more likely to occur.

There are others but I think you get the picture, have a search
for research octane number (RON) and motor octane number (MON).

rgds

mike



>Daniel R. Nicoson
>Equipment Exchange Company
>Phone:  (814) 774-0888
>Fax:      (814) 774-0880
>
>-----Original Message-----
From: diy_efi-admin at diy-efi.org [mailto:diy_efi-admin at diy-efi.org]On Behalf
>Of Mike
>Sent: Thursday, December 19, 2002 5:26 AM
>To: diy_efi at diy-efi.org
>Subject: RE: [Diy_efi] Timing Advance Curve?
>
>At 11:23 AM 18/12/2002 -0800, you wrote:
>>--- "Geddes, Brian J" <brian.j.geddes at intel.com>
>>wrote:
>>Well, if you are talking in that sense, simply up the
>>octane to cover the extra compression.  However, you
>>can run into a point of diminishing returns as far as
>>power output at higher rpms with the slower burn...
>
>Huh ?
>
>WHat has octane to do with the speed of the fuel burn ?
>
>Isnt octane a measure of the fuels ability to resist knocking ?
>
>Mike
>
>
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