Injuneer had posted in other threads that he belived the inj dc in data master to be incorrect, I did a little in vestigation and am now more confused than ever can some one help me understand. I thought Inj dc was a percentage of time that the injector was open. After looking at kevins datamaster I was kinda puzzled as to the readings of over 100%. I thought at 100% the injector was being held open and not being pulsed at all? Anyway I found a chart that agrees with datamaster and a formula that I just kinda came up with to find inj dc that disagrees with datamaster. Any input is appreicated. And I am not trying to "sharp shoot" fred I am just trying to understand.

Rpm % #of cyl = inj firings/min % 60 = inj firings per/sec * Bpw in m/sec = total time inj is open % 1000 = injector duty cycle

I applied this formula to Rec 104 in kevins log and came up with 15% where datamaster is saying 60%, confirming freds theory.

But then I found this table that agrees with datamaster?
http://www.ecanfix.com/~mdhamilton/dutycycle1.html

 

I am not questioning the definition of duty cycle and how you calculate it. And if you look at the BPW's in DataMaster, and use the standard definition of DC, you get the DC values shown in DataMaster. But, the BPW's would appear to be the incorrect part of the equation.

The simplified form is (RPM x BPW) / 1200 = Duty Cycle %

e.g. (6000 x 17.00) / 1200 = 102,000 / 1200 = 85%

 

Fred, why do you think the pulse widths are incorrect?

The engine is moving up to 337 grams of air per second according to the MAF. That's 1213 Kg per hour. 2675 lbs per hour. 334.4 lbs/hr through each cylinder. At a nice 12.5:1 Air:Fuel ratio, he would need 26.75 lbs/hr of fuel from each of his 24.92 lb/hr injectors--well over 100% and I didn't use the pulse widths to get it.

Are the MAF values incorrect as well? But incorrect by about the same amount?

Sounds to me like he just needs bigger injectors.

 

He is throwing a maf code though, and those numbers from the maf can easily be corrupted with the maf calibration tables and by porting the maf or running an after market. But I still don't under stand how you gte a number that is greater than 100% on duty cycle unles it is figuring the duty cycle off of what the pcm is calculating it needs to send instead of what is happening at the injector.

 

Yea i don't know what's up w/ the MAF code...it only throws the SES light everynow and then! I'm gonna throw them syclone injectors in there and see what happens! I'm guessing by your SN this is Craig? Just wondering how you knew my name?

 

I'm not Craig if I'm whom you are talking to, I'm Troy, Your name is the name of you datamaster .uni

 

ahh..i thought about that after said it...i didn't know b/c my friend craig is on here but i didn't know his screen name...and he drive's a RC RX-7 that's where i got that from..the whole two rotors thing!

 

Ok I'm a chinook pilot thats where the Two rotors really comes from, I was expecting some one would think I was a rx-7 guy though

 

I outlined my concerns with the DC in the other thread.... simply allowing a very fat 0.50 #/Hr/HP, he would have to be making 450flywheelHP to see a calculated PW that produces a 113% DC on a 24.92# injector. Look at his mods list, which as I recall had a cam, but no head work, and tell me how he is making that much HP?

I have seen repeated cases of basically stock, mild bolt-on LT1's that TTS DM shows as close to 100% DC. We know that isn't accurate. There is a flaw in the TTS calculation, or the way it interprets the PW data from the PCM. The HPP scanner cartridge had a similar quirk, and routinely came up with pulse widths that appeared to be almost double what they should have been.

Do your calculation for the 325gps that he is seeing at the point where he shows a 113% DC. You get a 103% DC, not a 113% DC.

Or, another check.... a typical 275HP stock setup will show peak air flow up to 240gps. He has an air flow 40% higher than that, which would prorate up to 385HP. I think that may be an accurate guess at where he really is, unless there are a bunch of mods he hasn't told us about.

 

Nope...just intake, headers, cutout, cc306, springs, 1.6rr, those are the MAJOR mods...i mean this car always has been a freak though..it ran 13.3 @107 with headers/cutout/intake w/ 2.2 60 ft.

 

I agree that some of them can be sound way out there, Fred. I think much of that can be blamed on tuning (or lack of it). When most bolt-on cars without tuning will be running 11:1 or even richer, as mine was, that skews what one might expect using BSFC formulae with assumed numbers, etc.

But in this case, he must be making quite a bit of power with as much air as he's moving (especially since it isn't running well)--probably in the 340-350 RWHP range, and 103 % isn't that far off.... Say the computer was calling for what would have ended up a 11.5:1 ratio instead of 12.5 (which could easily happen when messing with the injector constants, etc). That's enough to make the difference. But if he does have a ported MAF then naturally these numbers don't mean much as we (nor the computer) don't really know how much air he is moving.

In any case, when I calculate the numbers for my own car from Datamaster runs that were on the dyno so I have an accurate AFR to use (and untouched MAF), they always come out within a couple percent. Close enough I don't see any evidence with which to question them. I'm at around the same power level and I use 30# SVO's.

 

Nope stock MAF and MAF ends....

here is the tune i'm using!
http://www.bfranker.badz28.com/LT1Ed...ds&cam_306.lt1

I know i don't have h/c but his is they only one i can find that makes my car run halfway decent!

 

DC% is the amount of time in msec that the inj is open (this is PW) divided by the time for the crank to make two revolutions (being sequential firing skeme). The equation:

(RPM x PW)/1200 = DC% is correct for LS1 cars.

It is very possible that the DC is over 100%. This means that the injector has gone static and you are most likely running very lean at WOT.

At 6000 RPM it takes the crank 20 msec to make two revolutions, so if the injector's PW is 17msec at that moment in time, the DC is 85%.

17msec/20msec = 0.85