[Diy_efi] injector advance

[Bevan Weiss]

A 4stroke cycle is still only 360degrees of the cam.  If it was 720degrees
then you'd have the intake valve open on both intake and power... Which I'd
say would leave you with too much of the first, and not much of the second.

I think that you should time everything off the cam.  It makes much more
sense.  You have a cam sensor I assume...

I'd imagine the Marelli ECU will begin injecting at 300degrees of the cam.
This allows for 30degrees of injection on a (mostly) closed intake valve and
then 90degrees of injection on a (mostly) open intake valve.

It's best to reference everything to just before the intake valve opens.  Ie
cylinder 1 TDC before intake.

Droplets of fuel are indeed atomized when contacting the hot inlet valve,
which allows for slightly more fuel mixture to enter the cylinder.  It's
preferred to inject directly into the cylinder however as that guarantees
that all you inject will enter the cylinder.  It also makes the performance
more proportional to the atomization of the fuel by the injector (and fuel
pressure) than the speed of the intake charge.

It would appear that you're injecting 30degrees on the crank (15degrees on
the cam) after the Marelli ECU does.

I'm of the opinion that a fixed injection 'advance' isn't appropriate.
Especially if you're already running a fully sequential injection strategy.

You should inject fuel for however long is needed stopping just before the
intake valve closes.  Ie the advance will be highly dependant on both engine
load, and the RPM of the engine.
More RPM generally evolves from higher load, hence you need maximum fuel
injection in the least time.  In this case your figure of 450degrees before
combustion TDC may not be enough.  On the other hand if you're just idling,
then your 450degrees may be way to much and you'd be injecting on an
entirely closed valve with injection stopping before the intake valve is
even open.


Bevan 

> -----Original Message-----
> From: diy_efi-bounces at diy-efi.org 
> [mailto:diy_efi-bounces at diy-efi.org] On Behalf Of Gianmarco 
> Rizzo (BE/EAS)
> Sent: Thursday, August 05, 2004 9:38 PM
> To: 'A list for Do-It-Yourself EFI'
> Subject: RE: [Diy_efi] injector advance
> 
> Hi Bevan
> 
> well, a full 4 stroke cycle takes 720 degrees. i take as 
> reference compression stroke TDC, therefore 450 degrees is 90 
> degrees before exhaust phase TDC. considering the somewhat 
> large valve overlap in bike engines, this should be ok. the 
> inlet valve opens 20 degrees before exhaust TDC and closes 
> 240 after. the original Weber Marelli ECU injects 600 degrees 
> before compression TDC
> 
> i am using sequential. i didnt write the strategy code but i 
> am in close connection with the guy who did
> 
> ciao
> 
> gm
> 
> -----Original Message-----
> From: diy_efi-bounces at diy-efi.org 
> [mailto:diy_efi-bounces at diy-efi.org]On
> Behalf Of Bevan Weiss
> Sent: Mittwoch, 4. August 2004 23:53
> To: 'A list for Do-It-Yourself EFI'
> Subject: RE: [Diy_efi] injector advance
> 
> 
> 
> There's only 360degrees in a full revolution.
> If you're injecting 450degrees advanced, then you're 
> injecting 120degrees before the previous ignition event... 
> Which just doesn't make sense.
> 
> Injection should really be timed to the closing of the intake 
> valve as opposed to any ignition event.
> You want injection to be stopped once the valve is closed.  
> So the start time will depend on how much fuel you need 
> injected and how fast the engine is reving.
> 
> Which injection strategy are you using? Batch or sequential
> 
> 
> Bevan
> 
> 
> > -----Original Message-----
> > From: diy_efi-bounces at diy-efi.org
> > [mailto:diy_efi-bounces at diy-efi.org] On Behalf Of Gianmarco Rizzo 
> > (BE/EAS)
> > Sent: Thursday, August 05, 2004 2:06 AM
> > To: 'A list for Do-It-Yourself EFI'
> > Subject: [Diy_efi] injector advance
> > 
> > 
> > Hi all
> > 
> > anyone with information on what injection advance to use? i am 
> > currently injecting 450 degrees prior to combustion TDC.
> > 
> > is there any relation with fuel evaporating at the contact 
> of the hot 
> > inlet valve?
> > 
> > rgds
> > 
> > 
> > 
> > gmr
> > _______________________________________________
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> > diy_efi at diy-efi.org
> > http://lists.diy-efi.org/mailman/listinfo/diy_efi
> > 
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