Injector Duty cycle calculations

[Roger Heflin]

On Sun, 23 Jul 2000 timsiford at hushmail.com wrote:
> 
> >And if you are using tunercat, at least on the 93 LT1 his injector
> >constant is off.  
> 
> I am using TunerCat for the 730 ECM.  I have verified that the injector 
> constant is on the money (at least with the 'H' version of the .tdf file 
> and greater).
> 
> > The best on this motor was a
> >12.52 at 110.4.
> 
> Money.  That is really close to what I want to be running in the mph category 
> with the MiniRam ... just a tad bit more ET though.
> 
> > will be a 409LT1 SBC, with a 230/244-112 cam.
> 
> Holy shit man.  A man after my own heart.  I am trying to come up with excuses 
> for building a stroked 400 small block (420ci).  That engine is going to 
> rock.
> 
> >Running to higher rpms make more of a requirement of injectors, since
> >higher rpms mean less time to be open.  If his peak is alot lower than
> >yours is then that would do it.
> 
> I would actually think that his peak HP is higher than mine.  He is running 
> the 224/236 -112 cam and I am running a 218/224 -112 cam.  He also has a 
> phat exhaust (long tubes, 4" mufflex).  I have crappy 1-5/8" shorty headers 
> and flowmaster 3" catback.
> 

That would explain the .5 or so faster than mine.  I had 1.75 unequal
length headers, and a borla 3" single exhaust.  The new motor gets 
hooker long tubes and a dual 2.5" or a single 3.5 or 4".  The new
motor with everything on it should run in the 11.5 range.

I have looked at several tunings of LT1 and cannot figure out how they
are getting away with the size of injector that they are.   Alot of
them are runnning higher fuel presures, and it could be also that the
fuel pumps or the fuel rails cannot keep up on some of the other cars
but can on the 94+ cars.

 >
>What kind of times are both cars running? 
> 
> His car is a beast.  12.01 at 117+.  All naturally aspirated on the stock bottom 
> end
> Mine ran 12.58 at 108 all natural on the stock bottom end.  
> 
> His injector pulse widths are 10-11ms at 6000+ RPMs as reported by Diacom 
> and he has an SEFI engine.  Mine are 8.5ms at 6000+ RPMs as reported by 
> Diacom and I have a batch fire engine.  

I believe (if I remember right) having a run from a 94+ LT1 where it
changed from SEFI operation to batch fire at a certain RPM and TPS.
It was all in the same run, and appeared to change, and knowing diacom
it may be rigged to report it always as batch fire, and his injectors
may just be permanently open at those kind of rpms, I don't think he
could be getting by with only 10-11 ms out of 20.   The motor as
described would have somewhere around 410hp at the rear wheels, and
probably about 450hp at the motor.

450 / 8 = 56.25 lb of fuel per injector.

24 / 56.25 = 0.42 BSFC (which is dooable).

(24 * .9) / 56.25 = .384 (which is probably also dooable).

Given that after I leaned mine out, my motor got a bit hot when
running WOT for long periods of time (RR, 20 minute sessions), I
almost believe GM is running things excessively rich to offset not
having enough cooling system.   Mine was not lean enough to be
knocking, but it was a huge amount leaner than stock.   

			Roger

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