Just as the above reads.. Thanks in advance..

 

Atap gives you the injector pulse width (PW) in miliseconds (ms), and you can calculate the duty cycle from that. Here is an example for 5000 rpm:

Max PW = 60,000/RPM x 2
Max PW = 60,000/5000 x 2
Max PW = 24

Here is how you calculate the duty cycle:

Actual PW/Max PW = Duty Cycle

So if your PW at 5000 RPM is 20ms:

20/24 = 83.33%

<small>[ August 10, 2002, 02:10 AM: Message edited by: SSMAN66 ]</small>

 

My understanding of this calc. as follows:
% duty = (avg. pulse width X rpm)/1200

Your calc. assumes which size of injectors?

Any experts on this? I am upgrading mine now based on the above. Help please.

 

Your calculation is also correct. We just have two different formulas, but both give the same result. Here's an example:

Suppose you have a pulse width of 25ms at 5700 rpm.

By my formula:

60000/5700x2 = 21.05
25/21.05 = 118.8% duty cycle

By your formula:

25x5700/1200 = 118.8% duty cycle

<small>[ August 10, 2002, 02:08 AM: Message edited by: SSMAN66 ]</small>

 

Yep, as pointed out both formulas are the same (correct). The second just combines the 2 constants + percentage factor of 100.

They don't assume any size injector - it doesn't matter how big the injector is, the length it can spray at a certain rpm is fixed - a bigger injector can just get in more fuel in that window.

Chris

 

Here's a site that you may find interesting. HP vs. Injector Flow Rate

 

25x5700/1200 = 118.8% duty cycle

So assuming this equation, would a pulse width of 20ms be 100% Duty at 6k rpms?

100%*1200/6000 = 20ms

I have stock 01 injectors.. I believe they are 28.8lb

<small>[ August 12, 2002, 04:56 PM: Message edited by: LIL SS ]</small>

 

Yes, 20ms is 100% duty cycle at 6,000 RPM. Sounds like it's time for bigger injectors <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by SSMAN66:
<strong>Yes, 20ms is 100% duty cycle at 6,000 RPM. Sounds like it's time for bigger injectors <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" /> </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Haven't checked it yet.. Just wanting to make sure I am correct.. Thanks for the help..

 

Thanks for clearing up the confusion. Now help me with the concept of greater than 100% duty. How can an injector flow more than it is rated?
I have been running up to 119% on the gas but is running in a safe "rich" range. I would think that this condition would make it run lean. BTW, no KR and runs strong. I am in the process of upgrading to 30# SVO's because of this high duty condition.
TIA

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by BLUEBYU:
<strong>Thanks for clearing up the confusion. Now help me with the concept of greater than 100% duty. How can an injector flow more than it is rated?
I have been running up to 119% on the gas but is running in a safe "rich" range. I would think that this condition would make it run lean. BTW, no KR and runs strong. I am in the process of upgrading to 30# SVO's because of this high duty condition.
TIA</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">They cannot, it's just like the LTFTs are +20 which is commanding PCM to go (+) add 20% more fuel, it keeps increasing injector pulse width but like stomping on a gas pedal you want to go faster but there is no power left to give.

If your hitting 120% duty cycles and 80% is the max injector functions well that is 40% too high, so assume you have 26 lb injectors now and SVO #30 are 36 lbs that is about 30% larger still leaving you about 10% too lean
So why go with 36 rather then 42s ?

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Team ZR-1:
<strong> </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by BLUEBYU:
<strong>Thanks for clearing up the confusion. Now help me with the concept of greater than 100% duty. How can an injector flow more than it is rated?
I have been running up to 119% on the gas but is running in a safe "rich" range. I would think that this condition would make it run lean. BTW, no KR and runs strong. I am in the process of upgrading to 30# SVO's because of this high duty condition.
TIA</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">They cannot, it's just like the LTFTs are +20 which is commanding PCM to go (+) add 20% more fuel, it keeps increasing injector pulse width but like stomping on a gas pedal you want to go faster but there is no power left to give.

If your hitting 120% duty cycles and 80% is the max injector functions well that is 40% too high, so assume you have 26 lb injectors now and SVO #30 are 36 lbs that is about 30% larger still leaving you about 10% too lean
So why go with 36 rather then 42s ?</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">I noticed you said that if 80% is the max injector functions then you will be running lean if its over 80%.

do you know what the max is for stock injectors on a 98' LS1?

and if it is 80% and im getting 85% going by the math, then its time for bigger injectors , right?

 

Finnaly filled the bottle and did some test runs. A-Tap reports up to 24.14ms on the injectors. I have a 2001 with the 28lb injectors. A-tap also reports .90-.91 on the O2's when spraying.

If Max duty is 20ms, that means I am running at 120% duty.

Why would the O2's report a non lean condition and with 0 KR? Should I not trust the O2 readings?

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by WicketMike:
[/qb]</font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">I noticed you said that if 80% is the max injector functions then you will be running lean if its over 80%.

do you know what the max is for stock injectors on a 98' LS1?

and if it is 80% and im getting 85% going by the math, then its time for bigger injectors , right?[/QB][/QUOTE]

80% duty cycle is the accepted manufacturer level for "I need new injectors". When you put a set of injectors in a car, you size them to run at ~80% for the maximum duty that they are ever going to see.
If you exceed 80% duty cycle, will your injectors still provide fuel.....yes, to a point.

To determine if you are maxing out your injectors, you really need to trend out the data. On excel, or whatever, trend out the injector max available pulsewidth (ie 60000/rpm * 2) and your calculated injector duty (ie Injector Pulswidth / Max available pulsewidth). Multiply the Max available pulsewidth line by .9 to shift it down 10%
If you are maxing out your injectors, you will see the two lines merge into one for an extended RPM range. For the stock injectors, this usually happens from 5800+ rpm.

If you are getting 85% duty cycle, then I would not say that it is time for larger injectors just yet. The stock injectors will still perform at 85% duty cycle. If you are planning on going for more modifications in the future, then yes you should probably look into larger injectors.
In addition, the stock injectors do not fuel well above 6000 rpms, so if you are planning on modifications (or you already are) that make their peak power well in excess of 6000 rpms you should be looking for better injectors.

Good Luck,
<img border="0" alt="[cheers]" title="" src="graemlins/gr_cheers.gif" />

 

LIL SS, you can not use the stock o2 sensors for WOT. They can only be used for idle or cruise. The computer does not use them at WOT because they are totally inaccurate and do not give repeatable results. You have to tune with a wideband o2.

Gary