[alfa] Re: alfa-digest V9 #1034

[George Graves <gmgraves@xxxxxxxxxxx>]

I'm no expert, but here's what I've read about octane requirements and 
to me it makes sense:

All things being equal, using a fuel that too low an octane for your 
engine will cause pre-detonation, or pinging whereby the air/fuel 
mixture ignites before the piston is past top-dead-center. Serious 
pre-detonation can damage connecting rods, hole pistons, etc. mild 
pre-detonation is hard on bearings. Increasing octane slows, or rather 
delays detonation, assuring, in high compression ratio engines that the 
air/fuel mixture ignites after TDC. This is GOOD except when it's 
delayed too much. If the piston is on it's way down when detonation 
occurs (post detonation) there is a possibility that valves could be 
opening while there is still burning going on in the combustion chamber 
and this can burn valves. This is less of a problem today with 
electronic fuel injection and variable valve/ignotion timing, but it 
could be a problem with our older Alfa Romeos. Use the grade of gas 
closest to the highest recommended by the manufacturer for that model 
car, but no higher.  I have a GTV-6 with a 3-liter six in it. The 
manual recommends 86 to 91 (US method) and I use 91. Hope this helps.

George Graves
'86 GTV-6

On Dec 22, 2003, at 12:28 PM, alfa-digest wrote:

>
> Date: Sat, 20 Dec 2003 12:40:40 -0600
> From: "Matthew Hanselman" <mjhanselman@domain.elided>
> Subject: [alfa] Quality of gas -- anybody use lower octane?
>
> Hi all -
>
> A big story over here at a local (bike) shop is the issue of high 
> octane gas
> actually being a lot worse for your vehicle than the lower grade stuff.
> Anybody have any experience with this?
>
> My spider's winterized for this season, so I can't verify.  But this 
> guy
> swears up and down that cheap gas works better in high compression bike
> engines, as well as motorboat engines.  He has a web page up saying his
> spiel, it's at http://www.motorcycleperf.com/techtips/gasoline.htm
>
> I'm curious and can't wait till spring to find out...
>
> - - Matt
>
> ______________________________________________________________
--
to be removed from alfa, see /bin/digest-subs.cgi
or email "unsubscribe alfa" to majordomo@domain.elided