I have a LT1 383 a cam similar to the hot cam, no cats and 10.8:1 compression.. everything else is bone stock.. I;ve got the programming dead on now and the car drives GREAT! However, while reviewing som some high speed WOT runs I logged with datamaster I noticed my injector Duty Cycle is going way past 80%.. it went up as far as 100.1%!! for 1/10 of a second.. however, it appeared to be in the high 80's to low 90's when it did break the 80% threashold.. now accels manual on tuning fuel injection says "near static DC is ok for short high RPM bursts" and then continues on to say cars that will see this DC for any length of time (road racing etc..etc..) should not exceed the 80% mark..


Will someone please review these figures? if my stock LT1 injectors are 24lb/hr which are rated at 23.8 #/hr in the stock programming (PCM) - and I'm seeing DC of 100% that means its flowing 23.8 lbs/hr at that moment.. correct? now if I want to get that to under 80% duty cycle I can just add 20% to that number to figure out what flow rate I need to stay under 80%?

i.e. 20% of 23.8 = 4.76 which would make the desired flow rate 28.56 to keep DC under 80%?? do I have this correct?

if it is correct than I have another problem.. that puts me right at the cusp of to go with a larger injector or just increase FP... I can achive the 28.56 #/hr with the 24#/hr injectors by bumping the fuel pressure up to 60psi.. however, that seems like ALOT! conversly I can go to the 30 #/hr injectors and get 28.7 #/hr at 40 psi... which way to go? I'm thinking 30/lb injectors since this will allow for any future mods I might do...

Oh, also if a new injector is needed what is a good affordable and reliable brand?


Many Thanks and Merry Christmas!

 

Well a 100% duty cycle means that the injectors are just held open, not turned off. This is very strange.

You don't mention your current fuel pressure but, assuming it's about 45psi, bumping it to say 55psi would increase WOT fuel flow by 10%, which should bring the DC down.

In any case try bumping FP to 55psi to see what happens to the DC.

 

just increase the pressure some 5-7psi, readjust the part throttle tune...should be minimal to get it back on. Then make WOT pass again. Measure results. Repeat if necessary.:cheers:

 

Ski - According to Accels Injector Flow vs. Fuel Pressure matrix cranking the Fuel Pressure up 5-7 psi will only yeild between 24.41 - 25.73 lbs/hr.. this seems short of my calculated requirment of 28.53 #/hr for sustained high RPM speed.. (I'm tring to avoid going over 80% DC so to keep the coil in the injectors cool to prevent breakdown during endurance events.. :blueangel:


BTW: I also noticed an Adjustable Fuel pressure reg is 116 bucks!! :eek:
a whole set of injectors is only 245!!

I probably don't understand this whole thing to well since I'm a newbie at programming.. can the direct correlation to DC and Flow rates be made?is it correct to assume since I was seeing a 100% DC that the injector was flowing 100% of its capacity (or close to it). thereby adding a injector that flows 20% more fuel will achive 80% DC in the same area that the old one flowed 100%? or is there some crazy formula ro figure out DC that has some kind of multiplyer involved.

thanks for everyones help!


[Modified by BluByU, 8:36 AM 12/25/2003]

 

ttt

 

Blubyu,
Do a search on injectors/pressure. Ski has explained the injector hypothesis many times.
He and Corkvette1 both run 24# injectors in 406's running high 10's and very low 11's.

 

I have 30lb FMS injectors and stock FPR. Works great.

 

blubyu,

I am not saying 5-7 will yeild perfect results, first time out. That is why I said to test it, measure the results, and repeat process.

Running at over 80%-90% is NOT going to hurt anything unless your in an endurance race and sustaining high RPMs for extended times.

Post your 02 counts for me in 3rd gear WOT vs RPM. With it as is and I will show you why your going past 80-90%. Also include your inj pulse width (ms) vs RPM for that same run :cheers: :seeya


[Modified by ski_dwn_it, 12:28 PM 12/25/2003]

 

I emailed you the datamaster file.. I dont know how to retrieve just the data your looking for out of it... :confused:

 

blubyu,

Got the email. but can't look at the information. Extract it and save it as Text file, then I can view it.

Thanks :cheers:

 

ok.. i gave it a shot.. I think i did it right.. I emailed it to you in .txt and .csv (excel) format.. :cheers:

 

Yes i looked at the data and as I thought might be the case, this is what I see.

Your duty cycles towards the upper RPMs are in the 95% range, but at the same time your running EXTREMELY rich off your 02s which means your using more inj than your need, driving the DCs up to these higher %s.

I would suggest a slight raise in pressure, like 5 psi, then a trimming of the the fuel at WOT back to where the 02s read a max of mid 800s. This will give you ~8X% for a duty cycle and you will also get a better spray patters wit the little higher fuel pressure.

Hope this helps. :cheers:

 

ordering AFPR now.. In the mean time I just VEmastered the WOT fuel tables and as you suggested it did pull out some fuel! Time for road test! :yesnod:

*edit*

Thanks!! :thumbs:


[Modified by BluByU, 8:12 AM 12/26/2003]