Please Help Define Injector Timing

[pontisteve]

The injector is only in the intake port, not in the combustion chamber, so exhaust valve position is not exactly a factor until the point where that intake valve starts to open. At that [overlap] point, the puddle mass (or gas cloud) on the back side of the valve is allowed to enter the chamber, and possibly make a fast exit right out the [almost closed] exhaust valve, right?

With a larger cam, the intake valve is opening sooner, and the exhaust valve is closing later. The overlap is likely increasing. Firing the injector earlier would keep it firing on a closed intake valve, but when the intake valve does open, some of the fuel gets lost out the exhaust valve. Also, firing too early risks having a different cylinder "steal" fuel from that intake port, which would enrich a different cylinder and enlean this one.

Firing later puzzles me. Unless you wait until after the exhaust valve closes to BEGIN injector spray, don't you still have the same problem with fuel mass getting sucked out by overlap? Or is the puddle mass built up on the back side of the valve so great [stock delay] that a much larger portion gets swept out the exhaust? If we're trying to jump over the overlap phase, we would have to have the new injector BEGIN be later than the old injector END, right?

How many crank degrees are we typically talking about here? And what about bore wash with this additional delay? Do I have my head on straight here?? This is more complicated by considering different sized injectors would have different start times, since it's back calculated from EOI.

I guess if we can't figure it all out, at least we would like to hear how one goes about calibrating the tables.

[S2H]

we've actually got quite a large thread on just this topic going on already...
I was able to prove on a dyno with a cammed car that moving the EOIT to a later point provided more torque across the board. More evident in the lower rpms and not as much in the upper rpms where the injectors are open for longer periods of time.

we have even come up with a worksheet to get us in the ballpark.
I've actually found so far that it seems you get larger gains up to the point of where the valve closes (0.006)... there were some gains past that point, but it was drastically less... 15~20 torque and then suddenly only 1~2 more beyond that point...

it seems like as long as you can find the point where your engine stops "short circuiting" by ending injection point later in the cycle, you can gain some power down in the lower rpms

I'm hoping to hit a local dyno this weekend(weather permitting) and show a stock EOIT setting vs later EOIT setting with a sizeable cam.


heres where I ended up with my worksheet
EVC based on .006 in the example in the spreadsheet right now


*Edit 08/10/2012*
Before you download, read further.
In further testing, I have found that Best power and torque typically occurs around Bottom Dead Center of the Intake Stroke where Intake air velocity is at its greatest... which means this worksheet doesnt really matter...
*End Edit*

[Baezi z06]

we've actually got quite a large thread on just this topic going on already...
I was able to prove on a dyno with a cammed car that moving the EOIT to a later point provided more torque across the board. More evident in the lower rpms and not as much in the upper rpms where the injectors are open for longer periods of time.

we have even come up with a worksheet to get us in the ballpark.
I've actually found so far that it seems you get larger gains up to the point of where the valve closes (0.006)... there were some gains past that point, but it was drastically less... 15~20 torque and then suddenly only 1~2 more beyond that point...

it seems like as long as you can find the point where your engine stops "short circuiting" by ending injection point later in the cycle, you can gain some power down in the lower rpms

I'm hoping to hit a local dyno this weekend(weather permitting) and show a stock EOIT setting vs later EOIT setting with a sizeable cam.


heres where I ended up with my worksheet
EVC based on .006 in the example in the spreadsheet right now

hi + thanks for these infos

i´m working on this in my car now

so then you put 5.97 value in your normal table right on what ECT
and do you also put 5.97 in all your make up tablet ?
What about the boundry do you leave it alone ?

my cam is
.006 Int: 297 Exh:307
@.050 Int opens 14 BTDC and closes 9 ATDC
LSA 114 +4 (110 ICL)
That´s EVC 35,5

i get 5,94 shiftet normal
and 6,61 actual normal

so do i use 5.94 in all columns, or diffirent in the lower ECT

thanks

baezi

how should i do it ?

[Baezi z06]

hi + thanks for these infos

i´m working on this in my car now

so then you put 5.97 value in your normal table right on what ECT
and do you also put 5.97 in all your make up tablet ?
What about the boundry do you leave it alone ?

my cam is
.006 Int: 297 Exh:307
@.050 Int opens 14 BTDC and closes 9 ATDC
LSA 114 +4 (110 ICL)
That´s EVC 35,5

i get 5,94 shiftet normal
and 6,61 actual normal

so do i use 5.94 in all columns, or diffirent in the lower ECT

thanks

baezi

how should i do it ?

but then again if i use this EOIT worksheet here below i come up whith another values EVC 5,72 ????


which one is it ?

baezi

[jimbos'ss]

I've been working with this a bit today. I started by adding 5% then 10% then went as high as 18% to the EOIT numbers. so far the idle has smoothed a bit, but i'm still getting a bit of an idle misfire. curious to see if anyone has any recent results working with the injection timing that relates. my cam is a 226/226 .598/.605 110+4 based on the calculator i should have used 5.83 in the table which is roughly 5%. That showed no measurable difference in afr or idle quality, so I continued to add until it did.

[S2H]

bascially, you'll find that if you go to a dyno, you can push the value until it stops picking up power...
if your injectors are smaller, and you are getting upwards of 70% IDC or more, you wont even see the effects of pushing it around in upper rpm's

if you have a bigger injector and are at a much smaller IDC, you will see the changes at all rpm's.

I've found that typically you see the most power and torque from pushing it till your EOIT is somewhere near the end of your intake Lobe on your cam...bascially getting all the fuel into the cylinder at the latest point possible for the most ideal amounts of fuel still atomized for combustion

with my current cam 248/252 112+4, I ended up making best power pretty much at BDC...


the unfortunate part about the stock PCM is that there just isnt a way to push it around in real time.
on my current setup I use a Holley Dominator, and I can push that value in real time..
to the point where I can do a dyno pull, let the PCM correct the fuel within .1 AFR in real time, and I can just repeat until I see the most power....
on a loaded dyno with an eddy brake, I can hold it at any given rpm, and just push the EOIT till it shows the most power...


on a stock pcm, you cant really get an accurate measurement at idle from changing from one write to another because there are too many variables that change in that short time between writes.

typically, when you see it get the richest without any changing anything else in the tune, that is your best spot...that is when the most fuel can get into the combustion chamber, which means its going to be the most ideal spot for the EOIT to make power.
then you just lean it back out to where your A/F should be and life is good.


you typically wont smell raw fuel at ilde unless you are spraying before the exhaust valve is closed, or if you are extremely rich and have a lot of unburnt fuel in the cylinder, or in some cases, if you are pushing your air/fuel mixture back out the intake from reversion..

[jimbos'ss]

ok based on everything i've read in this thread
cam comparison is:
stock new
evo 105.5 107
evc 383.5 385
ivo 333 328.5
ivc 617 603.5

so based on (-784+(normal(5.55)+Boundary(6.50)*90=300.5
that's roughly 33* before the ivo on my stock cam and 28.5 degrees before the new cam's ivo.
now given the overlap on my cam i'd want to shift my SOIT to after my exhaust valve closes so I would need to know the relation between inj pw and crank degrees. without that it's just a best guess. at idle my car has a 3ms inj pw.

If I can figure that out I would be able to easily figure out what I wanted for my EOIT. anyone got a formula for ms to crank degrees so i'm not guessing on the numbers I enter into the normal table?

ok so after so basic math each injector fires for aproximately 1/5000th of a crank shaft revolution based on 3ms pw and 950 rpm so that means if i did the math correctly the SOIT to EOIT is on a fraction of a crank degree. sooooooo if i wanted to delay the SOIT till after the EVC i would input (-784+(boundary(6.50)+X)*90=386 and find for X. X would equal 6.50. Am I on the right path????

[S2H]

ok based on everything i've read in this thread
cam comparison is:
stock new
evo 105.5 107
evc 383.5 385
ivo 333 328.5
ivc 617 603.5

so based on (-784+(normal(5.55)+Boundary(6.50)*90=300.5
that's roughly 33* before the ivo on my stock cam and 28.5 degrees before the new cam's ivo.
now given the overlap on my cam i'd want to shift my SOIT to after my exhaust valve closes so I would need to know the relation between inj pw and crank degrees. without that it's just a best guess. at idle my car has a 3ms inj pw.

If I can figure that out I would be able to easily figure out what I wanted for my EOIT. anyone got a formula for ms to crank degrees so i'm not guessing on the numbers I enter into the normal table?

ok so after so basic math each injector fires for aproximately 1/5000th of a crank shaft revolution based on 3ms pw and 950 rpm so that means if i did the math correctly the SOIT to EOIT is on a fraction of a crank degree. sooooooo if i wanted to delay the SOIT till after the EVC i would input (-784+(boundary(6.50)+X)*90=386 and find for X. X would equal 6.50. Am I on the right path????

you are overthinking this....
you dont need start of injector timing.. .its back calculated by the pcm
you only need end of injector timing....
and as I stated... its going to be closer to Bottom Dead center for optimum power and torque..

GM made the point so that it would be more friendly to emissions and you could benefit from fuel evaporating on the back side of the closed valve... great for emissions at idle, does no good at WOT where the stock injectors are pretty much statically open...
as a matter of fact.. at WOT, once you hit 80% Duty cycle... it doesnt matter where you put the EOIT, you wont see any changes in power
where you benefit from EOIT is in the Lower rpm's

finishing somewhere around Bottom dead center gives you the most power because you have the most velocity pulling the intake charge into the combustion chamber...your injectors are still spraying on the back of the valve...thats how the injectors are aimed...the valve is just just open instead of closed.


I stopped worrying about the math quite some time ago...
I just take it to the dyno and push it till it stops making increases in power...
which as I have just said.. is usually somewhere close to Bottom dead center on the intake stroke...

[jimbos'ss]

I was actually thinking about this I don't have access to a dyno so just street tuning for me. I was thinking of placing the EOIT somewhere between peak intake valve lift and BDC on the intake stroke so the intake velocity would be pretty high. Tomorrow when I get around to testing it out on my car i'm gonna go with 465* which would put me well after EVC and at peak intake valve lift. It will be pretty close to BDC on the intake stroke. I'm just hoping to improve the idle and part throttle response and power deliver while saving some of the fuel i'm blowing out the exhaust.

[S2H]

I was actually thinking about this I don't have access to a dyno so just street tuning for me. I was thinking of placing the EOIT somewhere between peak intake valve lift and BDC on the intake stroke so the intake velocity would be pretty high. Tomorrow when I get around to testing it out on my car i'm gonna go with 465* which would put me well after EVC and at peak intake valve lift. It will be pretty close to BDC on the intake stroke. I'm just hoping to improve the idle and part throttle response and power deliver while saving some of the fuel i'm blowing out the exhaust.

spraying the fuel as late as possible = no losses out the still open exhaust port

just because the valve is starting to close, does not mean you dont have velocity

you could really go crazy and try to figure out where the most velocity happens....or you can use an engine analyzer program to show you best velocity at various rpm's...
the unfortunate part, is most of our LS1 pcm's do it by temperature only and dont account for rpm...
this is where the LS3/ls7 pcm's shine.. because you can adjust eoit by rpm which means you can optimize it for any given rpm making it match for best velocity based on relative injector pulsewidth(you would need a 2 axis table with IPW and rpm to make it perfect)

[jimbos'ss]

I'll give it a try close to BDC. The only thing that concerns me right now is the boundary table. I was planning on leaving that at the stock setting of 6.50, but other than being combined with the normal table I don't know what effects it has in the OS. does it need to be higher than the Normal table numbers? for example if I needed a value of 14.0 to achieve a desired EOIT, would I want the boundary set at 7.5 and the normal table set at 6.5?

[S2H]

its a combined value....
no idea why they didnt just make it one table...
but it doesnt matter what vales are in each table... it just matters what they both add up to.

[jimbos'ss]

its a combined value....
no idea why they didnt just make it one table...
but it doesnt matter what vales are in each table... it just matters what they both add up to.

Ok thanks, that's what I was hoping for.

[jimbos'ss]

This little experiment actually turned out quite nicely. No more lean misfires at idle, no more raw fuel smell in the exhaust, and my WB is no longer reading lean. The car drives a bit smoother as well. I love when things workout! The only negative side I have seen is the NB o2's seem to be taking longer to start oscillating at idle.

[yellz06]

What was your final value for both numbers?

[Vettzilla2000]

I have decreased injection timing and smell still there how far can i go??

[anniversaryss]

Any more input on this subject. I'm still a little confused.i have a 234/244 cam and would like to figure out a starting point to working on EOIT.
Do I add the same to my makeup as I would to my normal

[1364838952]

Annivers-there are PLENTY of posts about EOIT.. Just do a quick search and you will find TONS of information on how to perform all of the math. I think JImbos posts above make the most sense though. Go back and read what he typed about BDC and tying injector timing to that event. From what I have read, some people say to "just experiment with different settings" until you find what your car likes. Others want to drill down specifically on valve events. I think it comes down to what type of cam you have-LOTS of over-lap, or just a little over-lap, or no over-lap. Cam type is going to determine exactly how much you have to alter your EOIT. Some believe that on cams with overlap (lots, or little) that you want to start the injector spraying AFTER the exhaust valve has closed so that you are not losing raw fuel into the exhaust system. This means your EOIT will occur while the intake valve is open-which is DIFFERENT than how GM intended it to work. GM wants the injector to be done spraying BEFORE the intake valve opens. In fact, if you check a factory LM7 cam timing events you will see that the injector sprays on a closed intake valve, and actually STOPS spraying on that valve a full 75 degrees (crank degrees) before the intake valve opens. That gives that fuel time to sit on the back of the valve and cool the valve, and it allows the fuel time to atomize and turn from a liquid into a gas for better combustion. Firing on a closed intake valve also means you can't wash your cylinder walls down with raw fuel by spraying liquid fuel past an open intake valve directly onto a cylinder wall. Once you get into a bigger cam with over-lap, you have to take into account when your injector is spraying fuel. If there is fuel sitting on the back of the intake valve, and it opens, and the exhaust valve is still open, you are going to lose a part, or portion, of that fuel out the exhaust, or reversion from the exhaust system could blow that gas cloud back into the intake manifold allowing it to be ingested by another cylinder. Either way, over-lap is going to drive when you have the injector spraying the fuel. Further, the amount of over-lap is going to be the biggest determining factor on injector timing.

I take no credit for any of the thoughts I typed above. Like I said, I have spent the last 2 days reading nothing but EOIT threads and these are the things that have stuck with me. If you decide to mess with this, please post back and let us know your results. There seems to be a lot of discussion, but very little real world data findings posted back for the rest of us to see.

[anniversaryss]

Thank you. Yes I've been reading myself trying to get to what's what.
I understand what GM intended to do but it seems like that works best for stock or mostly stock applications.
In my case with a cam with lots of overlap , From what I e read you want to delay the timing. At least enough to even if the intake valve Is open it will still be enough to get the fuel into the cylinder even if the exhaust valve isnt fully closed you wont lose as much out of the exhaust.
I'm gonna play around with it when I can and report back when I can.