ULTM8Z

I posted about this a while ago and Dyno Don mentioned that there was some additional tuning to be done besides changing the injector constant. Basically, a friend of mine bought 24 lb injectors as replacements for the 19's in anticipation of dropping in a 350.

I guess what surprises me is the amount of tuning needed for this injector change.


My question is: What role does the injector constant play if I'm still having to touch the VE tables, AE tables, cold start tables, etc... Why wouldn't the injector constant be the global scaling factor that it should be?

RBob

iTrader: (1)

You didn't mention which code mask, let's assume it is $8D. The AE and crank tables are PW based (for the most part). So they need to be changed.

The VE table shouldn't need to be changed. But what happens is that the dynamic characteristics of the injectors are different. That is between the stock 19#'ers and the 24#'ers. For this you need to change the injector compensation tables.

There is a recent thread by GTA where I outlined some of the required changes.

RBob.

ULTM8Z

Oops, yeah it is an $8D mask.


I found the thread you're talking about. So I need to limit my BLM tuning to only messing with the injector constant rather than the VE itself. Though what I found odd was that GTA had to put in a value of 28# in order to get 24#'ers to run properly. Is that beyond what would be expected?

Then you mentioned injector compensation tables... hmm... I'll have to do a search on that one is about.

RBob

iTrader: (1)

Who knows why. To me it wouldn't matter that much. If the tune was correct for the previous injectors, then bringing it close again with the injector flow constant puts the tune back in the ball park. It could be caused by anything from an incorrect calculation in the XDF, to what fuel and pressure was used to rate the injectors, to what fuel is being used in the vehicle. Or, a mix of all.

One thing that is interesting is the Motron 60#'ers. I've seen those injectors advertised from 60 #/hr to 68 #/hr. When flow rating an injector it is the volume that is measured. This volume is then converted to a #/hr flow rate. So the density of the liquid used is also a factor. Back in the '70s gasoline weighed 5.7 pounds a gallon. In 2003 it ranged from 5.8 to 6.7 pounds per gallon (quite a wide variance). Not sure what it weighs today.

RBob.

ULTM8Z

The car was essentially bone stock with a factory tune. I never did scan the car prior to this, so I'm not sure what the data looked like prior. Probably should have checked it to verify that everything was in order before the swap.

Kevin91Z

iTrader: (1)

That's the strangest thing, because I took my 350 TPI intake with 24lbs injectors and dropped it straight onto a '90 305 TPI stock engine. My modified 350 chip worked with no additional changes needed. It even idles at 126-128 BLM's.

Perhaps because you started with a stock chip that is already rich from the factory, that you had to make so many more changes. My modified chip has been leaned out to make it work with the HOT cam.

ULTM8Z

That could very well be. Who know's there may be something malfunctioning that is driving his BLM's too. I'll have to dig deeper I guess...

JP86SS

iTrader: (1)

The electrical system may not be putting out enough at certain speeds, The voltage compensation may be getting you. See if the compensation is selected to use fuel pump or ignition volts. Could change it just to see if it helps. Low volts at idle will make tuning a PITA if voltage and FP varies.
Something to check.