[Diy_efi] Timing

[dh at busb.com]

I'm assuming that by more pedal you mean to press on the gas pedal and depress it toward the floor.  The energy to ignite the charge can come from many sources but a significant source is compression heat.  As the compression heat is increased the charge burns more quickly, therefore less advance is required.  But, compression heat is a function of the charge initial volume and that is proportional to the flow into the chamber which is inversely proportional to throttle position.  Vacuum is increased as the throttle is closed for a given engine speed.

I'm guessing you meant that Manifold vacuum decreases and carb flow increases.  Remember that as the manifold pressure gets lower (absolute) the vacuum increases.

To simplify, WOT requires less timing than part throttle operation.

If the vacuum advance on a Chevy is defective the headers will glow from the heat generated by inadequate advance.  Also note that there is no vacuum advance at start when mimimal advance is required.

dh
  ----- Original Message ----- 
  From: Bret Levandowski 
  To: diy_efi at diy-efi.org 
  Sent: Wednesday, September 28, 2005 6:33 PM
  Subject: Re: [Diy_efi] Timing


  From what I've seen on the vacuum advance on Chevy's, more pedal is more vacuum to the advance pod. Manifold vacuum decreases but carb vacuum increases.  Ski

  Rick McLeod <dunvegan at sbcglobal.net> wrote: 
    > If I make a quick stab at the
    > pedal, the only real change before downshift is
    > vacuum increase causing the vacuum component to
    > increase but I'm still reducing just the base? 

    shouldn't this cause a reduction in vacuum? Therefore
    causing a reduction in advance toward base?
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