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Old 02-03-2009, 07:17 PM   #1
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Default Holy duty cycles batman!

Check out my duty cycle from the datalog I just recorded. This is the product of running more than the normal Greddy boost on the stock fuel system and asking the car for 11.0:1 A/F at redline. Before anyone gets on my case about it being too rich, I know - I just finished deleting the AFM and I swapped all my tables and settings over to the new MSQ for non-AFM and it seems that while smooth, the car runs about 1.5:1 richer everywhere, which was the reason for this datalog as I'm adjusting it back to where I want it right now. This log is at 6 psi peak but as you can see it tapers down to redline at 4ish - I'm not putting the 460's I have on my desk in the car until BEGI's downpipe gets here (they are welding it up currently).
Anyways, enjoy the snapshot... on a side note, is it even possible that this is accurate? Shouldn't the injectors have seized?



-Ryan
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Old 02-03-2009, 07:29 PM   #2
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I've seen 102% DC when i had 305cc injectors and 7psi of boost.


here's my issue with 460s:

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that was 232rwhp with spark 5* retarded from what's displayed
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Old 02-03-2009, 07:51 PM   #3
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Looks like you are quite near to the limits of the 460's (so long as you keep to original fuel pressure) but that bodes well for me as my plan is for a 11.5-12ish psi onset with approximately a good 10 psi at redline. I figure if I ever build the motor and need more boost than 14 or so, I can re-install the vortech fpr and slip in a small small disc as I've become familiar with tuning MS alongside the fpr...
-Ryan
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Old 02-03-2009, 08:28 PM   #4
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Now that I think more about it... 102% duty cycle? That makes zero sense to me... how exactly is that possible or is the MS just approximating and doesn't actually know exactly what the injectors are at..?
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Old 02-03-2009, 10:40 PM   #5
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im sure there's a percentage of error, im sure there's documentation on how it's calculated.
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Old 02-03-2009, 10:52 PM   #6
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I keep telling you guys that it can read all the way up to 120% in another thread but no one wanted to listen. Ecu reads higher, some way higher some not so much, but all read a bit higher. plenty of people have run up to 120% duty cycles on other cars before actually running out of fuel. Does that mean its actually past 100%? no. But it does read higher IMO
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Old 02-03-2009, 11:02 PM   #7
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My uneducated opinion:

The displayed duty cycle is derived from the calculated PW vs. cycle time. In calculating required pulsewidth, actual cycle time is not a factor- it simply multiplies VE x enrichments x Req_Fuel.

If the calculated pulsewidth exceeds cycle time, then duty cycle will display > 100%, even though actual duty cycle cannot exceed 100%. In other words, once actual pulsewidth equals cycles time, further increases in required pulsewidth (or decreases in cycle time) will not result in any additional fuel actually flowing through the injector, since the injector is already fully on.
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Old 02-04-2009, 03:35 AM   #8
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Thanks for the info Joe, that sounds like that's exactly what it does.. so duty cycle in MS is.. not a helpful or accurate data point at all pretty much. Kinda like the MAT data that you get from MS when running the stock AFM being totally bogus.. Comforting.
-Ryan
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Old 02-04-2009, 04:14 AM   #9
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by the way, at less than 5psi, you really dont need to run 11:1 man ... lean that up to at least 12.5 and I would probably go as high as 12.8:1 at that boost. I bet you will feel the difference seat of the pants. Obviously pay attention to knock, but 11:1 is way overkill
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Old 02-04-2009, 04:23 AM   #10
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As I said in the first post, I know. I had another thread from just a week or two back floating around here which shows a datalog from just a short time ago and I had it dialed into a perfect 12 and a half throughout the pull while in boost. I just changed over to no AFM and with this log was from the no AFM setup with an unchanged tune. Switching to no AFM richened things up a LOT (which doesn't make a lot of sense to me but whatever) so now I am re-tuning.

And pleeeease don't point out to me that it peters out to a measly 4 psi at redline... I know it's pathetic. But it's what I'm stuck with until I put the injectors in and I'm not putting the injectors in until BEGI sends me my downpipe because the normal Greddy half downpipe is so pathetic that even with the new injectors to allow tons more boost the exhaust would be so restrictive there would be no point. Any day now though they should be shipping it...

-Ryan
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Old 02-04-2009, 04:31 AM   #11
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Quote:
Originally Posted by ThePass View Post

And pleeeease don't point out to me that it peters out to a measly 4 psi at redline... I know it's pathetic.
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Old 02-04-2009, 05:18 AM   #12
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sorry bud, didn't read that first post close enough. 4psi at redline is better than 0psi at redline ... which is what I am running right now.
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Old 02-04-2009, 09:59 AM   #13
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Quote:
Originally Posted by ThePass View Post
so duty cycle in MS is.. not a helpful or accurate data point at all pretty much.
No, it's actually very accurate and quite useful. So long as it is < 100%, it is displaying true duty cycle.

If, under max boost at redline, you are only encountering duty cycles of 50% or 60%, then you know your injectors are too big and you should have gone with something smaller for better idle.

If, under conditions of not max boost or not redline, you are seeing duty cycles of 80-90%, then you know your injectors are too small and you're about to run out of fuel. Danger, Will Robinson!
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Old 02-04-2009, 10:44 AM   #14
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Quote:
Originally Posted by ThePass View Post
This log is at 6 psi peak but as you can see it tapers down to redline at 4ish
baby boost- eventually we all grow up.
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Old 02-04-2009, 10:45 AM   #15
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Damn.
I saw 152% when I had my stock injectors and she decided to spike to/past 12psi.

I let of the throttle and decided not to drive the car again until I put in the 550s.
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Old 02-04-2009, 11:16 AM   #16
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Quote:
Originally Posted by Joe Perez View Post
My uneducated opinion:

The displayed duty cycle is derived from the calculated PW vs. cycle time. In calculating required pulsewidth, actual cycle time is not a factor- it simply multiplies VE x enrichments x Req_Fuel.

If the calculated pulsewidth exceeds cycle time, then duty cycle will display > 100%, even though actual duty cycle cannot exceed 100%. In other words, once actual pulsewidth equals cycles time, further increases in required pulsewidth (or decreases in cycle time) will not result in any additional fuel actually flowing through the injector, since the injector is already fully on.
Joe is correct as usual. MegaTune calculates the pulse width needed to deliver the fuel it is supposed to be delivering, and the duty cycle it displays uses the calculated pulse width whether there is enough time to actually use this pulse width or not. Translate values of 100% or more (well, actually, more like 95% or more) as "I need more injector size to do this."
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Old 02-11-2009, 04:06 AM   #17
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Throwing out an update: installed the BEGI Downpipe and messed with the tune some more. Haven't thrown the 460's in yet, but I need to! I didn't change the MBC but I preloaded the wastegate arm just a hair to help spool and now it's about 1-1.5 psi higher across the rpm range. "105%" duty cycle now:


-Ryan
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