My duty % is at 105% n/a from about 5000-6400 RPM's!! I currently have 28lb injectors in with mods in my sig.. What size do you think would be good to go with? Would some 42lbs be an overkill? I plan on sticking some heads on it later...........

 

42 lb. svo's are my suggestion. Easy to tune and they will leave room to mod.
Hawk

 

As long as your AFR is holding steady at that RPM then you'll be fine. I've seen stock 28 lbers go 11.0 @127 with more room to spare. The DC was reporting close to 150% but the AFR was steady.

 

Once the injectors are driven above 90% duty cycles, they are no longer reliable for delivering the fuel flow commanded by the pcm. They may still deliver what the pcm is asking for or they may deliver less. Once the injectors go static you are really at the mercy of your fuel pump and its supplied voltage. The higher the duty cycle, the shorter the lifespan of the injector as well (voltage is supplied for a longer period of time per firing cycle). Also note that the reported duty cycle is averaged over all 8 injectors. Some could be higher and some lower, risking dangerous fuel conditions on an individual cylinder basis. 42lb injectors are recommended for h/c (either SVO or Delphi will work just fine).

 

No offense, but do you have an injector flow tester? or are you repeating what you've read somewhere else?
This is something that has been REALLY bugging me for a while now.

 

I have heard thru the grapevine that 90% to 110% is ideal duty cycle. This is all very confusing.

 

I take no offense, it's good to question internet posts. Keeps us all honest.

I do not own an injector flow tester (nor a shop which may need one). My previous post is based on the research that I have done on fuel injector operation. I have looked through the sticky on this forum, at info given by different manufacturers and aftermarket vendors, and at some of the SAE data. I found all of these sources to agree that injectors are at their best at delivering the amount of fuel needed by the pcm when they are operated below 85% duty cycles. Those sources also stated that an injector's ability to deliver consistent flow decreases above 85% duty cycle. I spent alot of time searching before I considered the 85% duty cycle to be a good rule of thumb. I have also experienced this firsthand while tuning my car with the stock injectors after ls6 intake and headers and then switching to Lucas 32# injectors using hptuners software.

To the original poster, its also possible for your tune to change your duty cycle requirements. If you have a lot of + fuel trims at cruise, then the pcm will add fuel when you enter PE mode (mostly wot). This will drive your duty cycle higher than it would be with a better tune.

 

I hadn't heard that before. Keep in mind that a duty cycle of 100% means the injectors are being tasked open 100% of the time. This would mean 110% duty cycle would hold the injector open longer than all the time. Duty cycles greater than 100% mean the pcm is attempting to open the injector for the next cycle while it is still open for the current cycle.

 

Before i loose track of this, the original question was request for upgrade recommendations.30# will work. but not leave anything over the top for
dry N20. And with the ease of tuning a 42# is a one time purchase. That
allows you to mod again.
MY.02
Hawk

 

Well it just so happens that I question this as well.
I have heard and read the exact same things and I have friends that seem to agree with what is out there, but I have yet to see any proof to back any of it up.
I have seen much evidence to the contrary.
I've seen factory PCM's reporting upwards to 150% DC and yet not having any fuel delivery problems. It happens with large dry shots through the MAF as discussed at length in the nitrous section of this site. It also happens during cold starts and when going WOT with a cold engine temp. The factory allows way over the 85% mark believed as the safe zone.
It would seem that 100% doesn't actually equal 100% the way we think.

One important fact that seems to be ignored is that the injectors are tested and matched at static. If static operation were inreliable then proper testing and flow matching wouldn't be possible running them static. It would require a driver circuit that could be cycle adjusted to the 85% point for testing. To my knowledge, this isn't the way it's done.
If running static were harmful for the injector then it also seems strange that we pay extra for matched injectors which have to have been run static.

While researching this myself on the net I did find a lot of information at sites like these: http://www.rceng.com/Default.htm
http://www.injector.com/faq.php#faq5

The fact that the vast majority of this information seems to be spread from companies in the business of selling injectors is very suspect.
One of the earliest mentions I have ever seen of the 80-85% deal was quoted from a man who owns one of these busines and claims to have first discovered this while testing injectors on his work bench. In the same paragraph he states that 'his' injectors that he produces and/or sells do not fall victom to this problem.
It all sounds much too convenient for me to believe without evidence of my own. It also doesn't explain why the factory that installs the PCM driving the injectors sends them out the door with no DC limitation whatsoever.

In one of the FAQ's in the second link, they don't really state that going static is a true problem, just that you lose control of PW obviously. At that point the injectors act more as a carburetor jet metering fuel based on pressure differental at the injector only. I personally don't see a problem with this as long as the AFR is where you wanted it.

I didn't mean to hijak this thread.

 

Well the a/f was off the wall lean on the 1st pull at 15.0 across the chart. After giving it some more fuel the duty % went up 105% and we got the a/f down too 14.1. I have a racetronix p&p. The car has gone 11.00 on these injectors but with a dry shot and mail in tunning. I was just trying to get it tunned right for the new wet kit which I really havent had a chance to spray due to me running lean and out of injectors n/a.

 

I have an H/C spray setup too and we maxed the fuel out and it was still running lean at 14.6 so we put in an upgraded fuel pump (walbor 255) and the a/f went down into the low 10's so we were able to back off the fuel. I am looking for 42 lbs injectors now to go with my 402.

 

I found this to be interesting. The guy doesn't sell fuel injectors, so I tend to believe him.

http://www.turbobuicks.com/forums/sh...threadid=20689