Injector Timing? Reference Periods? refereencing what?

[Monty]

I have 383 LS6 stroker and changed normal table injector timing by adding 0.95 across the board at all temps - left makeup table wth stock setting of 5.55. This made starting quicker and smoother at all temperatures and make throttle response better at all engine speeds. This means that the "normal" injector timing table at normal operating ECT's is equal to the 6.50 boundary entry. I have a 232/234 duration at 0.050 lift cam just for reference. I am very pleased with the improvement.

Comp Cam Hydraulic Camshaft Specs:
Installed at 110 intake centerline
Gross Valve Lift 0.630 intake, 0.633 exhaust
Duration @ 0.006 tappet lift 281 intake, 283 exhaust
Duration at 0.050: 232 intake, 234 Exhaust
Lobe Separation: 112.0, Idles well at 900 RPM
Comp Cams Ultr Pro Magnum Rocker Arms (1.8 ratio)

Yeah that's what i did with mine, at 0.53 though i put the makeup at 6.08 to correspond with the 0.53 bump in the normal, but last few weeks found that cold starts are fouling out plugs, so i took the make up back to 5.55 and reversed the normal.. well see the affects of that with a cold start this morning ..

Was really wanting to understand what everyone was saying in this LONG thread so i could add things up more correctly with the overlap numbers, rather than just guessing around..

Also i noticed that with the bump in normal and the makeup at 0.53 my off idle to mid torque was much improved, now after changing the normal to negative 0.53 and putting the makeup back to stock i haven't as much torque ..

btw i still dont understand this cam overlap thing so anyone please feel free to help me .. thanks

[sarg]

oops!

[pontisteve]

Was really wanting to understand what everyone was saying in this LONG thread so i could add things up more correctly with the overlap numbers, rather than just guessing around..

To put it into context, the whole thing is about vaporization of fuel in a stock setup, and about not throwing out fuel on the cammed up side.

In a stock rig, the injector sprays onto the back side of an intake valve. Both valves are in contact with the heat from the combustion chamber, but only one valve ever looks like it's been hot, right? That's largely because the intake valve is being cooled off with fuel, and nothing cools the exhaust valve directly.

In stock form, it's about turning raw gasoline (liquid) into burnable vapors (gas). Raw liquid gas doesn't burn, only the vapors do. So we use an injector at 58 psi to turn big gulps of liquid fuel into small droplets of gas. EFI and it's high pressures do this wonderfully to begin with, compared to the raindrops of fuel coming out the bottom side of a carb, right?

Then we spray this fine mist in a cone pattern onto the back side of the intake valve, and we shape the cone to hit near the edge of the valve, by the seat. This way it cools off the hot sharp edge of the valve, and as the valve opens, the air flowing in tends to shear the droplets into even smaller droplets.

Since the cool fuel hits the hot valve, it tends to vaporize and become a gas. So picture it in your head. The intake valve is closed, the motor is idling, the injector PW is maybe 2 - 4 milliseconds at idle, and the injector delay table is programmed to spray onto the valve just before it opens. This way, other cylinders going up and down don't inadvertently steal the air and fuel vapors out of this intake runner.

The injector will have a start time and an end time. The delay table back-calculates the injection timing. So let's say the intake valve is going to open at X degrees of crank rotation in the engine cycle, and the engine is idling so it only needs 3 ms of pulsewidth. The injector would END its spray pattern just before X degrees rolls around. So it would have to START it's spray pattern at 3 ms before X in order to finish by X. If the pulsewidth jumps up to say 15 ms at WOT, then the injector would finish by X still, but start at 15 ms before X.

Here's where it gets interesting. You can calculate the engine speed, the 720 degrees of crankshaft rotation (the cam runs at 1/2 the speed of the crank), and you can figure out exactly how many milliseconds (ms) of time becomes how many degrees of crankshaft rotation. That's just math. So if you're only idling, that start and end of injection time (SOIT and EOIT) will be very close to the time when the intake valve is about to open.

So picture the closed intake valve, the injector opens for a few ms before the intake valve opens, and it closes just before the intake valve opens, making sure that fuel is now vaporized, broke up into little bity pieces, and basically a gas cloud at this point. Then the intake valve opens, that gas cloud immediately gets sucked into the cylinder, and it's ready to be exploded.

Now picture a cam change. We have a cam with a lot of overlap (because it sounds cool at the local drive-in). The intake valve and exhaust valve are now open at the same time, in a way the factory never intended. The intake manifold has vacuum in it (at this point, that vacuum is coming from the other cylinders!), so the intake runner is in a state of low pressure - vacuum. The exhaust system on the other hand, has high pressure in it, from those other cylinders firing and trying to get out thru a small pipe, causing some backpressure.

Now both valves are open at the same time, so the high pressure goes towards the low pressure. That means the exhaust goes in the exhaust port backwards, goes thru the combustion chamber, and exits out the intake port. It pushes some of this nice vaporized fuel cloud backwards, up into the intake manifold. (This is called reversion or standoff in carb speak). But that doesn't last long, and then it reverses direction and the intake charge now gets sucked out the exhaust valve instead.

But our computer calculated just the right amount of fuel, no extra. So we can't afford to lose any fuel out the exhaust valve, or the cylinder runs lean. So we end up richening up idle to compensate for the lost fuel. This is why cammed up cars like to be richened up at idle and low speeds.

We could move the injection timing back some, so that we don't inject fuel into a valve that has already opened. And that might be good, if we have a longer duration cam than stock, but we don't really have any more overlap. So maybe for a mild cam, that works well.

But if we move EOIT back like that, we make it more likely that the other cylinders steal fuel from our intake port. We also still have the problem that as soon as the intake valve opens, some of that fuel is going to go right out the exhaust anyway.

So if the cam is pretty big, we go the opposite way of common sense. We inject the fuel later, onto the back side of an intake valve that's already opened. Why? Well, with longer duration, we can't start the injection any earlier, or we'll end up injecting on the previous engine cycle, where the valve is still open from the last time. So we're going to lose some of that fuel vaporization by doing this, but we are going to be able to time the injection more properly to the longer duration cam.

We're also not building up that cloud of fuel, just so it can easily get pushed back up the intake, or straight out the exhaust, as soon as the valve opens. Better that we spray it in as we go, instead of 'building it up just to get stolen' all at once.

On here, guys are trying to time the injection so that the exhaust valve has already closed. So that means a few degrees after TDC, instead of a few degrees before TDC for EOIT to happen. But what I think is being overlooked is the fact that at WOT, the injector duty cycle is supposed to be roughly 80%, right? So the injector is open 80% of the entire 720 degrees of crankshaft rotation. Which means it must START long before the intake valve opens, and end long after the exhaust valve closes.

Because of this, I theorize that it's not really about the exhaust valve open/close points, as much as it is about starting the injection at the right time (to match the new cam opening/closing points), and about not having the cloud of fuel stolen or completely evacuated out the exhaust valve.

More common thinking is that it's only about the overlap period, and losing so much fuel out the exhaust, and not so much about having fuel stolen from the intake runner by other cylinders (or pushed back up the intake by exhaust pulses during overlap).

At higher speeds, all this stuff sort of works itself out. But at lower engine speeds, the overlap may be the exact same amount of crankshaft degrees, BUT the amount of actual time it takes to pass thru those degrees (a product of RPM) is much longer. So it's sort of like trying to play ping pong in slow motion. It just don't work.

My best guess about what to do here is to experiment with EOIT by slowly adding to it, making the injector start and end it's on-time later in the engine cycle. (Unless you have a mild cam, then maybe go the other direction). I would start by adding 10 degrees of delay at a time, and monitor the results. If you are improving the situation, you'll notice that the engine is getting richer on the wideband.

This is because the correct cylinder is actually GETTING the fuel you injected for it. So an increase in a/f ratio is an indicator that you're improving your situation. Obviously, you'll end up going back to your airflow model and leaning the car out to compensate eventually.

If it liked 10, add another 10 and see what happens. It's tough to say exactly how much a motor would like, since all cam overlap periods are going to be different. But somewhere between 20 and 40 extra degrees sounds about right.

The LS1 PCM doesn't go by actual crankshaft degrees in their delay table though. They go by reference periods. Each reference period is 90 degrees. So if you want to add in 10 degrees, you would add .11 reference periods. Also noteworthy, some clever fellow on here decided to take an engine on the stand, and test it to see where the 720 degree cycle actually starts at, and found that it started at -784 (if I remember correctly). That's just about where the cam sensor is relative to actual TDC on #1, and about actually sensing the crank magnet go by BEFORE the cycle starts, so the PCM has time to get it's act together by the time the cycle actually starts.

That's unimportant if you're just going to add 10 degrees at a time until the motor doesn't reward you any further. But it is important, if you have drawn up a 4 cycle chart on paper, and are trying to actually calculate when the injection timing is going to end, compared to when your cam valve open/close points happen.

And just when you think you've got it all mastered... "did you degree the cam in, and has the chain stretched any since?". heheh

It's not rocket science. Just add a little delay in at a time to the normal table, and probably leave everything else alone. I am a bit less informed of exactly how the makeup thing works, but I'm sure it's about the same way. I believe makeup is made up of things like acceleration enrichment and other last-minute changes to fueling, while normal is the typical fuel injection cycle.

[sarg]

Excellent post Steve! Now I just need to go back and re-read to understand makeup further.

[pontisteve]

Well, that's my take on it anyway. I would love to hear other people's theory about how it works as well!

My perception is based on what Greg told me about it, combined with doing hours and hours of analyzing the 720 degree engine cycle on a paper graph. FYI, I think it's fairly important to also understand that what the exhaust valve is doing is somewhat irrelevant, if the intake valve is still closed. That, and realizing that at idle, the injector is only open a few ms, but at WOT, the injector is probably open for around 576 degrees (if inj duty cycle is 80%).

[aldrichg9]

Wow!
Ive read through this thread several times over the past six months and this is probably the best summary of the whole thing anyone could read.
Enough to be informative but also not spilling the beans on the whole thread.

[sarg]

Interestingly enough I have been going through this and ran my valve events. I have very little overlap in my cam, only around 4* of overlap. Here is my calculations, using sound engineer's spreadsheet, which in turn matches Lunati's cam card exactly. I am kinda wondering where exactly I should target for my injector timing. With this cam it seems if I target just as the intake valve opened it would be pretty close to catching the tail end of the exhaust valve closing and getting some of that "velocity" from the overlap. Thoughts?

IVO BTDC 4.5 355.5
IVC ABDC 42.5 582.5
EVO BBDC 53.5 126.5
EVC ATDC -0.5 359.5

Intake Exhaust LSA Advance
227 233 113 4



Intake 227
Exhaust 233
LSA 113
Advance 4

IVO IVC EVO EVC
4.5 42.5 53.5 -0.5

355.5 582.5 126.5 359.5


Plugging that into Soundengineers other spread sheet I get this information:

EOIT vs Camshaft

Boundary 6.5 EOIT
Normal 5.55 300.5
EVC ATDC -6
IVO BTDC -18
New EVC ATDC -0.5
New IVO BTDC 4.5

Original EVC IVO Overlap
True Events 354 378 -24
After EOIT 53.5 77.5

New New EVC New IVO Overlap
True Events 359.5 355.5 4
+/- +/-
Difference 5.5 -22.5

EVC IVO
New EOIT 306 278
New Normal 5.61 5.3
True EOIT 359.5 355.5
True Normal 6.21 6.16

[sarg]

Can someone explain what is meant on Soundengineer's spreadsheet by NEW Normal and TRUE Normal and why they are different? After re-reading this thread, I am pretty sure I have a grasp on most of this, but that was one thing I am not sure I saw an answer to.

[JamesLinder]

okay, I have tried a lot of different EOIT settings for cold engine temps and normal operating temperature, and based on all my testing I could not realize any improvement from what GM originally put in this table. I agree with the recommendation to leave these as GM set them unless they have a different ECM than the one that came from the factory in my 2000 SS Camaro.

[robstah]

Hey, thought I would bump this up and see if anyone is still playing with this idea. I had this weird power dip right after idle to rolling and stumbled (like the car, ) into this thread. After racking my brain for a good hour reading this whole thread, I decided to try out Scott's spreadsheet on my car and that dip is basically gone. This was just from increasing the normal table by the offset provided through the spreadsheet. With a tsp224r 224/224 .581/.581 LSA114+4 cam, the spreadsheet came back with 6.14, which was a change of .59, so I offset the whole table by that much. The idle is rock solid now, the dip is nearly gone (will be gone when I clean up the MAF transfer some), and there is definitely more torque down low. I also had a switching problem below 2000RPM with my O2s and long tubes, and it looks like switching is much better down there, but at idle it's still a problem, so I am running a hybrid open loop for idle fueling for now. I couldn't really push the car much due to the drizzle, but I will report back on other factors like exhaust smell a bit later.

[HartRod]

Crazy knowledge on this board!

[LSxpwrdZ]

I did a dyno comparison with multiple settings a year or so ago. I'll try to dig up my post somewhere on this topic along with the spreadsheet.

Edit*** found the spreadsheet
and the link to post: http://www.hptuners.com/forum/showth...l=1#post292336

What I have found is that you can't generalize the EOIT only on the new camshaft. The size of injector you have plays a huge role as well. And with the Gen3 PCM you are always trading one or the other. To gain idle quality and drivability you generally will loose a little up top and vise versa. Size the injectors just right (by targeting 80-85% duty cycle) and these settings wont affect WOT power nearly at all and any small adjustments would be for idle quality and part throttle power. This spreadsheet just shows how small the actual tactive effort difference is at partial throttle with these settings played around with. However if you look the post under the post in the link above you'll see I did a dyno comparison at WOT on a H/C/I LS1 using siemens 60's. EOIT made a huge powerband and peak hp difference by playing with EOIT.

[robstah]

Just to mention it, I do have stock injectors and this is on a 5.3L LM4. I also noticed a faster cranking as well, where before would catch after a couple of cycles and with EOIT increased, it catches on the first cycle. When shutting the car off too, there is no goofy stumble anymore.

My question is something like .59 (53ish degrees) too much? So far with how everything is acting, I have no problems trading a bit of high hp for it.

[LSxpwrdZ]

On stock injectors you are probably not sacrificing any hp up top.

[robstah]

On stock injectors you are probably not sacrificing any hp up top.

Sounds good to me! I'll try and toss 'er on a dyno here soon. Thanks James!

[benno25]

I did a dyno comparison with multiple settings a year or so ago. I'll try to dig up my post somewhere on this topic along with the spreadsheet.

Edit*** found the spreadsheet
and the link to post: http://www.hptuners.com/forum/showth...l=1#post292336

What I have found is that you can't generalize the EOIT only on the new camshaft. The size of injector you have plays a huge role as well. And with the Gen3 PCM you are always trading one or the other. To gain idle quality and drivability you generally will loose a little up top and vise versa. Size the injectors just right (by targeting 80-85% duty cycle) and these settings wont affect WOT power nearly at all and any small adjustments would be for idle quality and part throttle power. This spreadsheet just shows how small the actual tactive effort difference is at partial throttle with these settings played around with. However if you look the post under the post in the link above you'll see I did a dyno comparison at WOT on a H/C/I LS1 using siemens 60's. EOIT made a huge powerband and peak hp difference by playing with EOIT.

Great info!

Previously I delayed my EOIT at idle in steps and found that the WB read richer and richer up to a point. I left it at the point where delaying things further stopped showing richer on the WB. Do you know if this method will be close to making the most power/torque at higher revs?

I have an LS3 with Texas Speed 235/239 cam and 260cc PRC heads and would like to make the most power possible from this thing. I'm also running 50Ib injectors and injector duty only seems to get up to around 70%.

Where should I look at, or how do I determine where my EOIT should be set? Or is a dyno the only way to determine this?

FYI, I have an ITB intake on this car which cures any drivability (bucking/surging) and don't care about idle quality at all. My car idles pretty much like a stock cam even with the 235/239.

Cheers
Benno

[pontisteve]

James point about injector duty cycle is right on. A correctly sized injector should be 80 - 85% duty cycle. Looking at it another way, the injector should be turned on 80% of the 720 degree engine cycle, or 576 degrees. Assuming that, you should be able to calculate ideal injector timing if you know the cam specs. But there are always variables. Is your cam degreed in exactly to spec? Has your chain stretched since then? What about the injector offset for battery voltage? Injector on-time doesn't mean spray time.

What if your injectors are over-sized? Then the entire fuel amount is injected in a shorter time period. If you go too far one way or the other, you might risk injecting onto an open intake valve from a different engine cycle. What about the amount of time injection is taking place during overlap?

There are two trains of thought I like here. First one is just try adding 10 degrees at a time and see how it runs. We don't need to get it perfect. Within 10 degrees is probably completely acceptable. And the second one is the method where you add injector timing until the air/fuel ratio quits richening up. I like this idea because it makes sense that if we increase combustion chamber efficiency in use of fuel, there will be some fuel left over.

Just as if I get wiser with my paycheck spending. The wiser I get, the less I spend unnecessarily, and the more I have left over when I'm done. And so it is with fuel. It also seems over-rated. In almost every case, it appears that adding between 20 and 60 degrees is about right.

[benno25]

James point about injector duty cycle is right on. A correctly sized injector should be 80 - 85% duty cycle. Looking at it another way, the injector should be turned on 80% of the 720 degree engine cycle, or 576 degrees. Assuming that, you should be able to calculate ideal injector timing if you know the cam specs. But there are always variables. Is your cam degreed in exactly to spec? Has your chain stretched since then? What about the injector offset for battery voltage? Injector on-time doesn't mean spray time.

What if your injectors are over-sized? Then the entire fuel amount is injected in a shorter time period. If you go too far one way or the other, you might risk injecting onto an open intake valve from a different engine cycle. What about the amount of time injection is taking place during overlap?

There are two trains of thought I like here. First one is just try adding 10 degrees at a time and see how it runs. We don't need to get it perfect. Within 10 degrees is probably completely acceptable. And the second one is the method where you add injector timing until the air/fuel ratio quits richening up. I like this idea because it makes sense that if we increase combustion chamber efficiency in use of fuel, there will be some fuel left over.

Just as if I get wiser with my paycheck spending. The wiser I get, the less I spend unnecessarily, and the more I have left over when I'm done. And so it is with fuel. It also seems over-rated. In almost every case, it appears that adding between 20 and 60 degrees is about right.

But does adding injection timing at idle until it stops getting richer also make the best power at higher revs??

Benno

[LSxpwrdZ]

All of these are good questions, the answer is that while optimizing the EOIT at idle partial throttle is definitely going to help in the low rev region, it is all ultimately going to be determined by the injector size and valve timing. And optimizing one end of the spectrum may cause havoc on the other in relation to RPM. This is why to obtain a truly optimal setup it is truly best to size the injector so that you are reaching at least a 70% duty cycle so that the WOT EOIT doesn't really matter. I did do some further testing with smaller injectors from my 60lb injector test and the smaller injectors weren't nearly as susceptible to EOIT causing power shifts. And truly a dyno with excellent repeatability is the only way to truly know if the EOIT settings you have are correct.

Gen4 stuff has it good because there are multiple tables that define EOIT vs RPM or vs ECT. This allows the EOIT to be calibrated for all RPM points instead of being stuck with one setting vs ECT.

[JamesLinder]

I really believe that anyone other than a professional tuner would be wasting ANY and ALL their time messing with EOIT.
Although even a blind squirrel will eventually find a nut in the dark, in this case it will probably be a poison one. Without
the dyno, the experience, and knowledge of a professional tuner your chances of getting positive results messing with
these settings are very poor. There are a ton of other settings you should focus on that are tunable by everyone with
great success. There are more GM settings you should just leave at the factory values than those that need to be tuned
to get most modified engines to perform optimal.