Considering Injector Change..

[Bruce Plecan]

> I'll give you a little personal experience...I am running 55 lb/hr
injectors
> in my GN, up from the original 28 lb/hr units.  I suffer absolutely no
> driveability or mileage problems with these and the stock ECM (I of course
> have matching chips for the bigger injectors).

With the SEFI, that is *expected*.

> I agree that their idle stability in theory should have some problems as
> pulse width decreases, but we don't seem to have hit it yet.  I don't
recall
> off-hand what my idle pulse-width is.

The 55ers happen to be very linear down to .9 msec as I recall.

> I have a friend with a batch fire DFI who recently went up to 72 lb/hr
> injectors, and his idle quality, cruise, etc. are good as well.

Well there are two *types* of Batch fires.  One that fires all the injectors
per crank revolution, and one that fires one cylinder bank per crank
revolution.  Firing the banks alternately per revolution, gives you the same
available *timing* as SEFI.

We had been
> told by some people that we'd need to go to a sequential ECM for better
idle
> stability to run the 72s, but they seem to do OK.  I know of several
street
> (well, sorta street) cars running 96s with sequential ECMs with no real
> driveability problems.

Depends alot on how linear, and how fast the injector can open / close.
That is what idle quality is about.  And then we get to the P+H styles.
Grumpy
>
> Good luck!
> Kendall Frederick
>
> > -----Original Message-----
> > From: owner-gmecm at diy-efi.org [mailto:owner-gmecm at diy-efi.org]On Behalf
> >
> >
> > Well, are you sure that you will eventually need bigger injectors???
> >
> > One of the cons of running big injectors is that the flow rates at very
> > low PW values are questionable.  There is a physical limit to the
minimal
> > open time where the injectors are no longer that accurate.  The value is
> > around 1.3ms (or so I've read and heard).  Thus, idle quality can
suffer.
> >  But - you can tune your car yourself!  That's a big plus.  You can tune
> > your idle A/F ratio and alleviate the con that I mentioned above.
> >
> > If you are never going to add heads and cam then I say stick with
> > 24lb SVOs
> > (which are really 26lb injectors when looking at GM standards).  If you
> > will definitely do heads and cam then I would consider 30lb injectors.
> > But, you need to be 100% sure :-)  Hey, now that I think about it
> > - that's
> > a great excuse!  ... ...
> > 'But honey, I have to buy a new set of heads and a cam because my
> > injectors
> > need them!'
> >
> > Hahahhaaa.
> >
> > Cya
> > tim
> >
> > At Sun, 23 Jul 2000 16:40:37 -0400, "Rodney Fulk"
<elixir at pathwaynet.com>
> > wrote:
> >
> > >
> > >I have a currently stock '94 LT1.
> > >I am considering changing out my injectors for larger ones. The ones
> > >I have
> > >have over 140,000 miles on them and are likely due to be changed. I
> > >am
> > >flowing a little more air then stock and I figured being able to throw
> > >more
> > >fuel at the engine would be good. Especially if I decide to go with
> > >a NOS
> > >system I want the injectors to be able to handle the pressure.
> > >
> > >I understand I have 24lb injectors now. If I go to 30# or 36# injectors
> > >I
> > >won't be hurting anything will I? I AM using LT1 edit and can change
> > >the
> > >program to reflect the added injection.
> > >
> > >I am guessing my duty cycle will be less that way.
> > >But can someone tell me the pros and cons to doing this change before
> > >the
> > >engine really needs it?
> > >
> > >I figure though that if I am going to buy injectors I only want to buy
> > >them
> > >once.
>
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