[Gmecm] TBI Swap - Iron Duke Tech IV

[Andrew Gibson]

>I failed to qualify the HP reference being a non issue when SEFI becomes 
>batch, IOW above a certain RPM or at WOT.

  At higher RPM you have much more air going in. More air = higher air velocity. Also, 
  even with the valve closed there will be enough turbulence to mix the fuel well. And 
  considering the time you have to fire the injector. At 750 rpm you have a 0.16 second 
  time frame from start to finish in order to make sure the fuel gets there. At 4000 RPM 
  you have a 0.03 second time frame. Given the delay of lifting the pintle in the injector 
  you don't have much time. So at higher rpms it just makes sense to batch fire to 
  ensure you have the fuel available to burn. Besides full throttle runs an enrichment 
  program in open loop for more power. Fuel economy and emissions go out the window 
  at that point.
   
  >I'm confident you meant less in lieu of _MORE_ fuel, as this would
>defeat the intent and have a detrimental effect on emissions. 

  Actually I meant burning more of the available fuel. If the fuel is mixed evenly through 
  the air you will burn more of it. If it's only mixed with half the air, only half the fuel will 
  burn. Half would is an extreme example though.
   
  >As long as the statement is qualified to represent part throttle operation.

  Even at full throttle high rpm a TBI still fires at TDC.
   
  >My thoughts were in reference to when injector 
  >sprays fuel at the back of a closed valve.  This puts injector opening 
  >B4 ignition!  No disagreement during part throttle.

  Yes batch firing will spary fuel at a closed valve. But once again you have power enrichment and a high air velocity to make up for it.
   
  >Could the base timing value in the ECM be adjusted to compensate for
>either case?
>The whole problem of when the ECM is triggered relative to spark event
>(base timing) seems pretty easy to overcome.

It can be if you are willing to play around with it and have a PROM burner. 
  Interrestingly enough, so you have the info, the Iron Duke DIS relies on a 7 pulse 
  signal from a crank sensor. The Ignition module translates this into a 4 pulse signal for 
  the ecm. So in thoery it could run with a distributor if the timing tables are changed. I 
  will be finding out soon as I'm putting the 1bbl tbi on a 250 chev 6cyl. I'll be using a 
  4.3L module to run the coil and est if it works. Which once again in theory, it should.
   
  >The ICM (in the V6 case, anyway) is referenced at 60 degrees,
>and the distributor is referenced at 0 degrees. For an application
>using a distributor to trigger an ECM designed for DIS (i.e. 1227730
>running $A1 for MPFI), couldn't the distributor just be installed at 60
>degrees instead?

  You could, but unless the ecm uses a cam sensor it will not make a difference.

		
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