Injector Timing? Reference Periods? refereencing what?

[pontisteve]

I think the only true way to 100% test this ourselves might be on an engine with an in-cylinder pressure transducer (the spark plug type) and a scope. I have a pressure transducer for my Picoscope, but it's not a spark plug. Although I guess it would work too, actually. The nice part about the Picoscope software is that I can measure the peak pressure points (TDC compression), and mark the highest point on there, then mark the highest point on the next TDC compression pressure spike.

Once you basically mark off the 0 - 720 engine cycle, the scope software will let me divide that area up into 720 degrees and also lets me divide that into 4 sections to see the 4 strokes. This gives me piston position. From there, all I need is to measure the cam signal and injector control signal. It might not be dead accurate down to 1 degree, but it would probably be within a couple degrees.

While not taken for this purpose, here is a screenshot of my Pico measuring the compression waveform of some stock 80's V6 car (note the seriously low compression!). The peak cylinder pressure points were marked as best as I could identify them while zooming in, and then the software splits that into the 720 degree engine cycle, and the four strokes. If I had a cam sensor waveform on a 2nd channel of the scope, and an injector control waveform, I could identify the number of degrees between the crank sensor signal and the injector EOIT. The problem is, and I don't know how Bluecat did this, how do we know which of the 24 crank sensor signals represents TDC compression on the cylinder we are later injecting fuel into?

[JasonS5555]

Hey Steve,

I was thinking of using an inductive pickup for like a timing light on the #1 cyl to figure out when tdc was, again not accurate to a degree but close. But then how do you capture where / when the inj is being commanded to fire?

Jason

[LSxpwrdZ]

All this goes out the window with properly sized injectors for your application. The EOIT doesn't change anything if you are 70%+ on duty cycle on the injectors, but it can help the idle and drivability. If you look back in the thread you'll see I did some comparison data on the dyno to see what was affected and the power output at light throttle of each setting. I found that light throttle was the most impacted by the adjustments when the injectors were sized properly for the engine. I also tested it with significantly oversized injectors (60lb Siemens) in a NA heads/cam/intake LS1. Duty cycle was 40-42% if memory serves. EOIT played a huge role in overall powerband and peak numbers, I found that once you optimised power the vehicle drove like crap. So moral of the story on the Gen3 stuff use smaller rather than larger injectors so that your WOT power is still there but you can have the freedom to move around EOIT for idle/part throttle without sacrificing WOT power.

[pontisteve]

Just to walk you thru this compression waveform, let me lay it out. The two vertical dark black dotted lines are what I determined to be TDC compression events, after zooming in on the waveform and centering the tracers on the middle of the compression peak. (This is less than perfect though really, because there is no exact peak due to piston dwell. It's a bit of a guesstimate, based on the middle point of the pressure trace slightly further down the graph). It's really close though.

The bottom horizontal dotted line is the 0 PSI point. This would be atmospheric pressure. The top dotted line is a measurement of peak pressure. In this case, it's coming in at a whopping 54.71 PSI. How does this worn out V6 even run? LOL

The left vertical line would be the first of four strokes. The light gray vertical dotted lines are the other 3 strokes, ending up at the 5th stroke, which is really the first stroke starting over again on the next engine cycle, at the next TDC compression point.

Starting at the 0 degree point (left vertical dark black dotted line), we see the four engine strokes: Decompression, exhaust, intake, compression. I say decompression because this cylinder is just pumping, not combusting, since there is no spark plug. The in-cylinder pressure transducer screws into the spark plug hole.

On the next stroke, we have exhaust. Note that exhaust starts losing vacuum around the 207.1 mark, just before BDC. The exhaust valve is open from about 207.1 to just past the 259.4 mark, and atmospheric pressure is attained. In short, there isn't enough exhaust restriction at idle to cause there to be any pressure in the cylinder on the exhaust stroke. Even for the crappy exhaust that this 6 cylinder Monte Carlo probably had on it.

The next stroke begins near 259.4, and is the intake stroke. Here, you see the cylinder drop below atmospheric pressure, achieving somewhere around -10 PSI. Remember 1 psi = 2.036 InHg (inches of mercury), so -10 PSI is roughly 20 inches of vacuum.

Finally, you see the compression stroke bringing cylinder pressure back up to 54.7 PSI again. In the bottom right corner, you see 369.18 RPM listed. That's the amount of RPM it took for the engine to produce one cycle. Which means actual crank RPM is 2x that, or 738 RPM.

If this waveform had a crank sensor shown on another channel, and an injector ground signal shown on the 3rd channel, we could see how the crank sensor relates to injector timing. Then, we would just have to flash the car a lot, and show the changes to see how injector timing moves relevant to the changes. Perhaps you could set both Boundary and Normal to 0 to see where the actual signal ends up aligning with the crank sensor, so we know what tooth represents TDC on that cylinder.

[pontisteve]

Just for reference, here is an idle waveform I captured of a radical small block Chevy at idle. It had a pretty huge cam, as I recall. I think the motor was worth about 600HP. Notice the very different exhaust shape. The truck had huge race exhaust on it.

Despite the race exhaust, notice that the exhaust stroke did net some cylinder pressure. The high compression and high cylinder pressure must have contributed to the positive pressure. Exhaust pressure probably peaks right where piston speed was the fastest on the exhaust stroke. Peak cylinder pressure on the compression stroke on this badboy was around 175 PSI.

[pontisteve]

All this goes out the window with properly sized injectors for your application. The EOIT doesn't change anything if you are 70%+ on duty cycle on the injectors, but it can help the idle and drivability. If you look back in the thread you'll see I did some comparison data on the dyno to see what was affected and the power output at light throttle of each setting. I found that light throttle was the most impacted by the adjustments when the injectors were sized properly for the engine. I also tested it with significantly oversized injectors (60lb Siemens) in a NA heads/cam/intake LS1. Duty cycle was 40-42% if memory serves. EOIT played a huge role in overall powerband and peak numbers, I found that once you optimised power the vehicle drove like crap. So moral of the story on the Gen3 stuff use smaller rather than larger injectors so that your WOT power is still there but you can have the freedom to move around EOIT for idle/part throttle without sacrificing WOT power.

I can say that looking at this subject closely, you would certainly want to have the right size injector. All my work and thoughts on this subject assume around an 80 to 85% duty cycle, because of a properly sized injector. If you have a very wrong-size injector, you're probably going to find the engine is much more sensitive to having the injector delay wrong.

Remind me James, what EOIT did you find for peak power? I'm guessing it would probably be in the 540 to 630 range with a medium sized cam. And what EOIT did you find best for low RPM power and driveability (using the right injectors)? Here, I'm guessing 420 to 540, probably closer to 460.

[LSxpwrdZ]

I can say that looking at this subject closely, you would certainly want to have the right size injector. All my work and thoughts on this subject assume around an 80 to 85% duty cycle, because of a properly sized injector. If you have a very wrong-size injector, you're probably going to find the engine is much more sensitive to having the injector delay wrong.

Remind me James, what EOIT did you find for peak power? I'm guessing it would probably be in the 540 to 630 range with a medium sized cam. And what EOIT did you find best for low RPM power and driveability (using the right injectors)? Here, I'm guessing 420 to 540, probably closer to 460.

Look at posts 389, 390 and 393 in this thread

[JasonS5555]

So idle with your setup was best with SOIT around 350 and EOIT at 363.

My combo idles and drives better with it quite a bit later. At least with my cam, SOIT at 350 is still well into overlap...

Jason

[yellz06]

I think this was explained on the other tuning site.

[JasonS5555]

My thinking it that with only control of EOIT, wouldn't you want something more like 70% duty cycle? The reason I'm saying this is that for part throttle I think you'd want EOIT to be lets say 500 (which seems to work well on my car), but at WOT, if EOIT is at 500, you wouldn't want SOIT to be until the intake had closed from the last cycle. In my case that's about -114 degrees. Looking at the attached graph, everything is good with my setup until about 6000 RPM when duty cycle is 85%.

WOT inj.jpg

But in the inj pw was shorter as it is in the graph below, its easier to get all the fuel in since SOIT doesn't get close to the previous cycle intake valve close. You could even more the EOIT toward say 460 and get better mixing before ignition.

WOT short PW.jpg

What am I missing?

Thanks,
Jason

[JasonS5555]

I think this was explained on the other tuning site.

What was explained?

[LSxpwrdZ]

You have to take into account ALL variables. Not everyone is using the same injectors, different engine combo's will require different amounts of fuel at idle/part throttle. A blanket statement that you target EOIT based on XXX cam specs isn't going to fly. My same engine combo requires completely different EOIT parameters depending on which injectors I am using at a specific time. The best method is to test this on a loaded dyno at various engine speeds and loads to verify power/torque output.

[pontisteve]

You have to take into account ALL variables. Not everyone is using the same injectors, different engine combo's will require different amounts of fuel at idle/part throttle. A blanket statement that you target EOIT based on XXX cam specs isn't going to fly. My same engine combo requires completely different EOIT parameters depending on which injectors I am using at a specific time. The best method is to test this on a loaded dyno at various engine speeds and loads to verify power/torque output.

I tend to agree that dyno testing would be king, if you had lots of spare time to test with. But I would think that idle on any cam with considerable overlap would be pretty predictable. We should want the earliest injection time possible, that starts after the exhaust valve closes. That would put as much heat and vacuum on the situation as possible. Whether the injector is huge or small, getting as much time as possible that the fuel can be in the cylinder should help mixing.

For WOT, I have an idea or window of when it would have to be (I think), but couldn't say for sure. Here, I think dyno testing would really be key more so than just calculation based on valve events. Although we know that valve timing would set the boundaries for what we could try.

[JasonS5555]

So the same would apply to the blanket statement I was questioning that 80% duty cycle is desirable...

Thanks,
Jason

[Super73]

Keep in mind that having an injector that has 80-85% IDC at WOT provides low end resolution at idle. My truck for example idles at 3% IDC while being a touch fat .95-.96 Lambda (I will be cleaning this up a little). Now, think if these same injectors and fuel pressure were used for gasoline (I run E85) and it idled at stoich. My guess is IDC would be 2% or less while WOT would drop to the high 60% - Low 70%. At some point the injector is going to have trouble firing at idle as the PW gets smaller.

There are several reasons to have a proper injector.

[LSxpwrdZ]

I tend to agree that dyno testing would be king, if you had lots of spare time to test with. But I would think that idle on any cam with considerable overlap would be pretty predictable. We should want the earliest injection time possible, that starts after the exhaust valve closes. That would put as much heat and vacuum on the situation as possible. Whether the injector is huge or small, getting as much time as possible that the fuel can be in the cylinder should help mixing.

For WOT, I have an idea or window of when it would have to be (I think), but couldn't say for sure. Here, I think dyno testing would really be key more so than just calculation based on valve events. Although we know that valve timing would set the boundaries for what we could try.

I agree that a good starting point can be achieved based on valve events and back calculating the SOI based on pulsewidth and rpm. At that point you could calculate an injection centerline that may be easier to interpret based on various injectors, fuel demands and camshafts.

So the same would apply to the blanket statement I was questioning that 80% duty cycle is desirable...

Thanks,
Jason

The target of 80% or around that point isn't a blanket statement though, it's a result/fact/observation. With oversized injectors on a Gen3 PCM where there is no RPM EOI adjustment you are fighting a balance between peak HP/powerband vs. good idle/drivability at low load/rpm. With an injector that is spraying a larger portion of time (500* or more per cycle) the peak power is not affected by EOIT. If/when it is affected it is within margin of dyno error pull to pull which leaves free reign to do what you please at low throttle and engine speeds. This is just an observation I've seen with the testing I've done with stock size injectors or slightly larger.

[Randy WS6]

I have a very large cam to check cam card shown , It was custom made for my 442cid. by Tick Performance, nitrous car, speed density tune. and a 2000 Ls1 F-body mini mini mods . Very bad fuel smell at idle , The injectors are Siemens 80lbs
Static Flow Rate @ 43.5PSI ( 300kPa ) w/Gas: 80 lb/hr = 875 cc/min
Offset: 0.065ms
Turn on time @ 14VDC: 1.3ms
Turn off time: 0.7ms @ 600KPa
and have 60lbs fuel pressure. Can some one help me on setting the injector timing , I tried the speed sheet, but it confusing me with this cam.
12-13-2015 1;13;07 AM.jpg

[odom1957]

I had a bad fuel smell at idle also, but was also getting misfires and bucking at idle and very low rpm. After reading a couple of threads, I decided to change my timing.

Factory: Boundary - 6.15, Normal/Makeup - 5.5ish
Current: Boundary - 6.5, Normal/Makeup - 7

Absolutely no idle issues or misfires at very low pulse widths anymore and picked up noticeable torque. Fuel smell is completely gone and runs smoother.

I'm running 42lb EV6 injectors, Super Victor Intake, NA 350 vortec, and 50psi fuel pressure.

[GrannySShifting]

James Ive played with this some, but not with anything running at @55% duty cycle like your car was (and my old cam only setup was running 60# injectors - I wonder what that extra 20 hp you found up top would have done me back then LOL) In summary, you found that on that particular setup, changing your Normal table from 5.55 to 6.25 helped low rpm torque/driveability correct?

Am I right in assuming that at WOT you had to go the opposite way to see the gains you said you saw? Did you lower your Normal value below stock 5.55 even? If its referencing End Of Injection Timing, if theres an ideal place to start it, it would makes sense you would have to move it forward. What normal number did you end up with?

Applying this to E series ECUs, should be delaying (making the numbers in degrees bigger) EOIT at low rpm, adv them at upper rpms (lower numbers than stock) and interpolating between right? ***for setups that have larger than necessary injectors*** I dont have access to my dyno anymore which sucks for being able to A-B-A test things. Fuck you fire.

Gonna bump this back up cause I stumbled onto this on my personal car....

Basically I picked up powerband and tq/hp all across the rpm range especially up top just changing EOIT. Here is a dyno graph of my LS1 Formula. Here's a mods list

105k mile LS1
235/243 112 Cam
60lb Siemens Injectors
FAST102 / 92mm TB
ARH 1-7/8 Headers and Ypipe with Cutout
SD with 4" pipe and 106mm Lid

On the graph the ONLY change to the tune was the EOIT. I'm not going to give specifics mainly due to every setup being different. I just thought I'd share that EOIT is a tad more important than most let on!

[JamesLinder]

We chose the magic stick 3 camshaft for my new 408 Tx Speed stroker. After reading about all the EOIT information on the internet and studying the books I have on tuning, it appears to me that the "Boundary" should be set approx. 22 degrees earlier than stock because of how much earlier the inlet valve opens than stock, and that the "Target" needs to be set approx. 22 degrees later than stock because of how much later the exhaust valve closes than stock. To accomplish the latter, I must increase Target by a total of 44 degrees to make up for the amount the Boundary was reduced plus the additional 22 degrees of delay from stock setting. These changes are obtained in HP tuners by subtracting 0.25 reference periods from the stock Boundary setting and adding 0.500 reference periods to the stock Target settings. Narrowing the injection "window" on both ends, which is what this will do, makes a lot more sense for a performance camshaft with valves opening sooner and closing later than stock than what I've seen in most other posts. I will have my car running around the middle of next week and will let you know how this works.