EFICalibrator - Thanks for the explanation. That's great information to know.
Like Mr Prick asked; is there a basic formula to use?
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EFICalibrator - Thanks for the explanation. That's great information to know.
Like Mr Prick asked; is there a basic formula to use?
It's hard to give you a single formula that will work most of the time since you guys all like to pick snowflakes for cam and head combinations. (No two are alike) To make things worse, different ECUs describe the timing with different units. Some use degrees of crankshaft rotation relative to TDC, others degrees relative to BDC, and many GM ECUs use "cam reference pulses." The cam reference pulse is still a unit of angle (which is time at a fixed RPM), so you're really tuning how much time "lead" you're giving the fuel delivery much like ignition timing. Just like ignition, there's a sweet spot that gives better results and it's possible to go too far. This is one of those grey areas that more experienced calibrators end up building a "feel" for as they do more of them.
That is a great explanation Greg, thanks.:cheers:
Greg- What did you find in your experiment with the 230+ cam. As I see it, if you go strictly by intake valve opening point, the values in B3702 should theoretically be reduced with a long duration cam because valve opening occurs "sooner" (more degrees before TDC). The situation is similar to that of a cold engine- the injector has to fire "sooner" to provide adequate atomization time. If the intake valve opens earlier, then it would stand to reason that you also have to fire the injector sooner to promote atomization. If you delay opening (with a larger number in B3702) then the injector is likely to be firing against an open, rather than a closed valve. However, you state that you "add delay" if necessary when tuning engines with aggressive cams, but stock offset values are smaller at low temperatures than they are at high temps. I'm trying to reach a logical conclusion and things just aren't adding up, which to me indicates that overlap is a more important consideration than intake valve opening point.Quote:
Originally Posted by eficalibrator
Often times the timing is to the degree where the intake valve closes LATER in the compression stroke, not that much sooner. If the piston is still going up in the exhaust stroke and you open the valve you will get too much reversion... As RPMs go up overlap helps fill the cylinders better, so i get why you would want to delay the injector firing because you will want to fire it where there is more air speed.Quote:
Originally Posted by dfe1
This is very interesting. I did a lot of experimentation with this:
http://forum.efilive.com/showthread.php?t=9288
I have a custom cam, but similar to the MS3. Here is what I came up with.... I think your results lend some merit to mine. Thanks and keep us posted.
--cut--
-1 RPM = 360deg crank rotation
-1000rpm = 360000 deg <---- typical big cam idle and to keep the math easy
-16.67 revolitions per second
-6000 degrees of rotation per sec
-0.0167 revs per ms
-6 degrees of rotation per ms
-Therefore when advancing the intake opening event by 2 deg, this means firing the injector .334 ms sooner.
--cut--
I wonder what this means for someone like me who is running a 60# injector in a stock engine? It seems I'm always fighting a rich condition at idle. I had assumed that was because I couldn't get the pulse width short enough. So, my "solution" was to zero out the small pulse adjust (B4005) and start pulling time out of the voltage table (B3701). Now, I'm wondering if my problem is because the bigger injector is slower to open....and therefore I need to reduce the offset in the timing table. http://www.motownmuscle.com/forums/i...milies/mmm.gif
Jeff, I would think that you would cause more problems & not actually solve the issue you are having. Your problem is the injectors cannot supply a small enough amount of fuel to give a stoich idle. Offsetting the injectors may change your wideband reading but you will still have too much fuel for the operating conditions.Quote:
Originally Posted by SSpdDmon
No, the fundamental problem is more likely that you have incorrect data for both short pulse adjust and offset tables. Both of these have a very large impact upon pulsewidth calculation at idle and cruise. If you're not properly converting from desired fuel mass to actual injection time, you have little hope of getting much else right.Quote:
Originally Posted by SSpdDmon
Well Greg, it's been my experience that you can only shorten up the IPW so far by adjusting down your IFR, MAF, or VE before you hit a wall with bigger injectors. At that point, you need to pull time out of the voltage adjustment and short pulse width tables. I've searched around and found what appears to be the right voltage adjustment numbers. But even with the short pulse table zero'd out, I'm still seeing 11:x AFRs at idle, which is why I was pulling more time out of the voltage table.Quote:
Originally Posted by eficalibrator
If you have some insight on how to correct this, I'm interested in listening to what you have to say (as are others I'm sure). However, just coming in the thread to essentially say "you're doing it wrong" and not offering suggestions isn't really helpful. It's frustrating. I understand you need to sell books and DVD's. But, I'd honestly rather you not post at all if that's all you have to offer.
I'm inclined to agree with you here. I just didn't go that far down the path in my first post since I thought it was self-evident. What you're most likely finding is that the ACTUAL offset really is shorter and needs to be recalibrated. The offset and short pulse adjust make up a very large percentage of the total idle pulswidth, so an oversized offset can have a very real impact upon your ability to get back to stoich. You're heading down the right path, it's just easier if you start with the proper data rather than trying to stumble upon it.Quote:
Originally Posted by SSpdDmon
This thread still seems to be going sideways. If an injector in a sequential system fires against a closed valve, then as cam duration increases, the question is should injector offset be increased or decreased? Lee's testing showed improved performance be increasing offset, but to me that doesn't match the logic of the concept-- unless there's a benefit to firing the injector closer to valve open, or after the valve has opened. The reference pulse has to occur before the injector fires and that being the case, increasing offset will delay injector firing. If the idea is to give fuel more time to vaporize, then offset should be reduced to compensate for an earlier opening intake valve (than with a stock cam).
It's interesting to note that the injection timing tables (B3702) for truck, LS1 and LS6 are identical, (even though cam duration varies quite a bit) although the values for the G van are slightly larger. What's also interesting is that the E40 and E38 ECMs have injector timing versus RPM tables and the values (expressed in degrees) generally increase with rpm. On the other hand, values in the timing versus ECT table (also expressed in degrees) are higher at low coolant temps than they are at higher temps. (Opposite of value change in an LS1 PCM). I'm trying to make sense of all this and not being very successful. Every time I think of a reasonable explanation, I find something that contradicts it. Any ideas?
1. is b3702 a delay in opening the injector?
2. is b3701 a compensator to a slow opening injector? note :that aust and usa tables are different but tables in b3702 are the same
The offset when increased will have the injector fire earlier not later.Quote:
Originally Posted by dfe1
I was reading an article the other day about direct port injection and one of the things it mentioned was firing the fuel near the top of the piston stroke on a cold motor for better emissions etc. This would explain why the injection times are lower when cold, they are firing the injector with the valve open. I guess they don't need the raw fuel puddling when it's cold.
That appears to be the case, I'm just trying to understand the algorithm. If a larger number means the injector is firing earlier, then the value would have to be subtracted from a base delay, I'd guess. If that's the case, then the injectors fire at reference pulse+delay-offset.Quote:
Originally Posted by 5.7ute
Quote:
Originally Posted by joecar
Hi Joe
I believe the injector timing is in crank regress and relative to TDC on the compression stroke?
Foe example on the LS2 the advance is 490 degrees when cold and 220 degrees at normal running temps, so the timing events for the LS2 are as follows:
Engine cold
Inj fires. 130 BTDC. CLOSED INLET VALVE
IVO. 16 ATDC
ICL. 118 ATDC
IVC. 40 ABDC
Engine hot
IVO. 16 ATDC
ICL. 118 ATDC
Inj fires. 140 ATDC. INLET VALVE BEGGINING TO CLOSE
IVC. 40 ABDC
From what I've been reading, the cold injection event is more beneficial to happen when the valve is open and closer to TDC, they dont want raw fuel puddling up on cold walls. Also, the articles state that it helps light off the catalytic converter.
Lee
Hi Gelf,Quote:
Originally Posted by Gelf VXR
That does make sense (relative to TDC compression stroke)...
The LS2 injector timing is directly in degrees... makes visualization easier...:cheers:
The LS1 injector timing is in milliseconds, so I have to convert that to degrees based on rpm:
offset[°BTDC] = 720 * Toffset * RPM/120000
where Toffset is in ms,
range of Toffset B3702 is 0° to 8°, so offset[°BTDC] range is 0° to 288° (at 6000 rpm)... does this make sense...?
BTW: oh, your IVO would be 16° BTDC (to give you ICL 118°).
Quote:
Originally Posted by joecar
Are you sure? 118 centre line, intake duration 204 degrees @ 0.05
118 ATDC - 102 = 16 ATDC
Oh, your duration is 204...?
Then you're right, your IVO is 16 ATDC (usually it's BTDC)... :)
(I thought it was 236, but maybe I'm thinking of someone else's cam).
What are your cam specs again...?
This is great info.
So... what about when you have a cam that has a lot of overlap? The LS1 and LS2 cams have none (negative overlap); so moving the injector firing event back and forth can be done within a pretty wide window. My cam is a custom grind for the track, and has a lot of duration, a 110 deg ICL and 21 degrees of overlap... so now the EVO event comes into play a whole lot more. Would you want the injector firing even earlier to take advantage of the pull-through effect of the exhaust? Or later, to minimize unburnt fuel passing through the cylinder?
The injector firing event of #1 cylinder is based off the crank trigger at TDC on #1. Also known as tooth #0 (on a 48 tooth crank trigger; 7.5 deg per tooth).Quote:
Originally Posted by Gelf VXR
I have been playing with "a brand-x stand-alone EMS" on my LS1 and you can set the ignition and injector firing events of each cylinder by degree or tooth. More importantly you can see exactly when the injector is firing in both ways as well.
The reason I bring this up is I was amazed to see how a slight movement of the injector firing event affects idle, AFR, idle load, and throttle response. You also immediately notice things like, your AFR getting leaner on the gauge, but the exhaust smelling like unburnt fuel. So far, adjusting the event so as to yield the richest idle mixture (the most burnt fuel at a fixed pulse width) seems to get me closest to optimal with everything else.
Yes, i was reffering to the stock calibration and cam - 204/211 118ICL and 216LSAQuote:
Originally Posted by joecar
My cam is 216/229 113ICL and 113LSA
Intake opens ~ 11-13 degrees earlier, ICL is 5 degrees earlier, inlet closes around the same time.
I propose to advance the B3702 5 degrees @ normal running temps in relation to the ICL.
I'm thinkin the optimum injector timing event is after the ICL event where intake velocity is highest and optimum for evapourating all the fuel.
Quote:
Originally Posted by Goldfinger911
I was considering the the exhaust valve timing when cold, if the valve is open later, then perhaps the timing should be retarded in line with the difference from the stock cam. For example the stock cam closes 6 BTDC, my cam closes 1.5 ATDC, so I might need to retard 7 or 8 degreeswhen cold??
Hmm. Thats what I was thinking. Regarding cold running... when my car starts up... the tune does retard timing and it sounds very mean out the tail pipe. The AFR is rich, but very stable. I have always wondered about this when cold.Quote:
Originally Posted by Gelf VXR
Wait... what stock cam has the EVC at 6 deg BTDC? I thought the stock LS1 EVC was 10.5 deg and the stock LS2 was 8.5 deg BTDC?
Mine is a bit more challenging to tune for; 242/248 .612"/.617" 112+2 LSA 110 ICL.
Stock cam specs attached
I dont want to sidetrack the thread.. but an LS2 cam has an LSA of 116 right? It would have to to give you an ECL of 114. Even though... the math doesnt work out right on the open and close events.
For example, isnt IVO = ID/2-ICL ? I think those numbers are incorrect.
Your assuming the cam is assymetric?Quote:
Originally Posted by Goldfinger911
In the context of tuning large overlap cams, with an emphasis on throttle response and idle control, this should work fine. (It may negatively effect emissions) Keep in mind that any previous VE or MAF mapping done in the reversion sensitive region will probably need to be revisited now that you have a cleaner wideband signal.Quote:
Originally Posted by Goldfinger911
I heard back from the garage carrying out my cam and head install today, they said the idle is smooth. This is stock LS2 and tune with LS7 injector calibrations with L92 heads, comp 216/229 cam.
One interesting difference I noticed with the injector calibrations for the injector timing when you add the ECT + RPM advance tabes, from 0 to 1020 rpm. Apart from that identicle.
The LS7 calibration has 20 to 65 degrees more advance than the LS2.
Bumping this old thread, it seems I made an error thinking injector advance was referenced to TDC on the power stroke
Stock LS2
Engine hot
IVO. 16 ATDC
ICL. 118 ATDC
Inj fires. 140 ATDC. INLET VALVE BEGGINING TO CLOSE
IVC. 40 ABDC
The injector couldn't possibly open as the inlet valve closes, could it?, the advance must be referenced to TDC on the induction stroke inlet valve opens. The injector opens 220 BTDC inlet opens / 140 ATDC ignition stroke, just after/during the combustion event, spraying onto the closed and very hot inlet valve, cooling it in the process and vaporising the fuel. Ref: RC engineering in this thread http://www.chevytalk.org/fusionbb/sh...hp?tid/199007/
The injector open & close time in relation to crank angle is variable depending on rpm (opens) and injector duty cycle (closes), there doesn't seem to be any fixed correlation to the inlet or exhaust valve timing events other than the injector closes variable time before the inlet valve opens, it is only when high rpm and 85% duty cycle is reached that the injector close time will be after the inlet valve has opened. See attached
For example at say injector duty cycle 85% is equal to 15ms @6400rpm, 1ms = 38 crank degrees, 15 x 38 = 570 degrees
720 - 570 = 150 degrees, the duration of stock cam is 204 degrees, its impossible for the injector to open and closed during the inlet valve closed duration.
Intuitively I would think that if there is any tuning to be done to injector timing its with regard to opening the injector at the optimum crank angle for the combustion event when the inlet valve is hottest to make the most of vaporisation and time before the inlet valve opens?? If your injectors are open when the inlet valve is open, time for larger injectors???
Hi Gelf,
Injectors are not necessarily fired at open intake valves... actually most of the time they are fired at closed valves.
Hi Joe
Yes, tuning injector advance so that it opening during the power stroke when the inlet valve is closed and at its hottest or earlier to ensure enough time for vaporisation well before the inlet valve opens, maybe even more so with overlap and open exhaust valve?
If your injectors are maxed out, you'll still be injecting with the inlet valve open
The way I understand it is the reference point is the end of injection, not start. So the end of injection is constant & the start varies.
I'm trying to understand, I checked the B3702 description as I was referring to LS2 data, but it is the same for LS1
B3702 LS1
"This table will offset the actual opening of the injector referenced to the reference pulses and engine coolant temperature"
B1205 LS2
"This table will offset the actual opening of the injector referenced to engine coolant temperature"
There was a thread on the "other" site, where a simulator was hooked up & the reference point was found to be the end of injection, which in a way makes some sort of sense. This would have the fuel charge always firing onto a closed hot inlet valve, giving time to fully vaporise the fuel charge before the intake valve opened. A large duration cam would have the fuel firing into an open intake valve, causing cylinder wall wash, as well as unvaporised fuel entering the combustion chamber.
Can you point me in the direction of the thread?Quote:
Originally Posted by 5.7ute
Think I found it. GenIII EOI fuel timing
Please pm me the link to that thread.