[Diy_efi] The Hunt effect

[Jim Butterfield]

Yes Yes, thats why in our Supercharged grand prixs we run 103 at the track and also drop a pulley size... dropping pulley size increases the pres into the cylinder but also adds heat. so higher octane will help keep the fuel from preigniting (detonation and Knock retard for us ODBII guys) allow more boost... without the higher octane we detonate like crazy and our pcms pull timing
 
jim

John Gross <jogross3 at hotmail.com> wrote:

Depends on what you mean by ?lights off?.  If you mean starting the burn in the cylinder, then no.  If you mean what it takes to make it explode, instead of burn, then yes.  However, the octane rating is an indicator of the fuel?s resistance to explosion.  The higher the octane rating, the higher the temperature and pressure needed to make the fuel explode *without* a specific ignition point.  

 

-----Original Message-----
From: diy_efi-bounces at diy-efi.org [mailto:diy_efi-bounces at diy-efi.org] On Behalf Of Van Setten, Tim @ ACSSD
Sent: Tuesday, October 04, 2005 10:48 AM
To: 'diy_efi at diy-efi.org'
Subject: RE: [Diy_efi] The Hunt effect

 

So is the real difference not the octane rating, but how the fuel lights off?  I have suspected that the fuels flame-ability index goes all over the place and nobody tracks it.  Just the octane rating......Tim.


-----Original Message-----
From: Bret Levandowski [mailto:skishop69 at yahoo.com]
Sent: Tuesday, October 04, 2005 7:40 AM
To: diy_efi at diy-efi.org
Subject: Re: [Diy_efi] The Hunt effect

Octane rating is the fuel's resistance to detonation under heat and pressure with no 'true' ignition source. I believe it equates to a higher flash point. So, running high octane in a lower compression motor that requires low octane could actually lower MPG as the lower comp. would prevent the mixture form lighting off completely. In the case of the caddy, using lower octane would cause detonation which would be picked up by the knock sensor retarding the ignition (which I believe he stated). This would then require more fuel to reach the same 'power' point reducing MPG.  Ski


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