Camshaft and Injector Timing

[Higgs Boson]

They are both part of the combustion process and matter to each other, but I don't find the need to move them around exactly together.

[rjw]

I'm wondering if all the setting to zero stuff that I did to the lower rpm cam timing in order to remove surging has messed up spark timing tables.....?

I'll look into it

[Higgs Boson]

You will want to zero the vvt spark in the areas you advanced the cam....so yes, more advance means more cylinder pressure which means you will want to adjust spark.

[rjw]

You will want to zero the vvt spark in the areas you advanced the cam....so yes, more advance means more cylinder pressure which means you will want to adjust spark.

still not clear on this.....if I advanced cam timing, which way do I go with spark timing?

as an example


cyl airmass, rpm, cam timing , high octane spark timing

oem .32 , 1200 , 13 , 31

my tune .32 , 1200 , 0 , ?

where should my spark timing be set to? 18 ?

thx

[Higgs Boson]

There is a table specifically for adding timing based around VVT action. I zero that out based on where I zero out the VVT table (under 3K RPM or so).

With more advance comes more cylinder pressure which mean less spark, but you don't have to take it out of the main spark tables, the VVT modifier adds a bunch of spark when the cam is retarding.

[rjw]

There is a table specifically for adding timing based around VVT action. I zero that out based on where I zero out the VVT table (under 3K RPM or so).

With more advance comes more cylinder pressure which mean less spark, but you don't have to take it out of the main spark tables, the VVT modifier adds a bunch of spark when the cam is retarding.

I found this one variable cam -> spark

[Higgs Boson]

Yes, zero that table where you zero vvt and then you can rework the main spark table in that area if you want.

[rjw]

Yes, zero that table where you zero vvt and then you can rework the main spark table in that area if you want.

getting back to the actual topic, soi, has Ben's theories been proven to be sound? curious as I try to learn more about all of this

thanks

[rjw]

In the equation that you posted above, where did you get the 60,000 figure from? Maybe I just need to pay more attention, its getting late...

rpm in minutes. 1 minute = 60 seconds= 60,000 milliseconds

[IARLLC]

I am still hoping that some day GHuggins will share his SIO secrets. He is getting good mileage improvements on GEN5 rigs by retarding SIO "a little" (in addition to the usual stuff), even getting good gains on 87 octane. I have read everything he has written on here about it....which leaves me wanting more. The SIO table seriously bugs me. It's not just that GHuggins gets some gains out of it.... Just look at one of these tables! They are a MESS! There is no way they can be right. Say, the transition that happens at 3000rpm below .4g cyl airmass. How can that be right? But what to do with it? Just blend? Most conversations are about top end SIO setting on boosted applications. I think I get that part by now. jarrah's formula helps on that end.

My only access to a GEN5 6.2 is a client with 16 2015 Denali XLs and 2 2015 Denalis. It is pretty rare that I get any real free time with them for experimentation, just diagnostics here and there. I have done what I wanted with the cam and ignition timing and airflow models but the REALLY UGLY SIO table drives me nuts! Have to leave it alone until I am more sure...

[Higgs Boson]

I am still hoping that some day GHuggins will share his SIO secrets. He is getting good mileage improvements on GEN5 rigs by retarding SIO "a little" (in addition to the usual stuff), even getting good gains on 87 octane. I have read everything he has written on here about it....which leaves me wanting more. The SIO table seriously bugs me. It's not just that GHuggins gets some gains out of it.... Just look at one of these tables! They are a MESS! There is no way they can be right. Say, the transition that happens at 3000rpm below .4g cyl airmass. How can that be right? But what to do with it? Just blend? Most conversations are about top end SIO setting on boosted applications. I think I get that part by now. jarrah's formula helps on that end.

My only access to a GEN5 6.2 is a client with 16 2015 Denali XLs and 2 2015 Denalis. It is pretty rare that I get any real free time with them for experimentation, just diagnostics here and there. I have done what I wanted with the cam and ignition timing and airflow models but the REALLY UGLY SIO table drives me nuts! Have to leave it alone until I am more sure...

Dont forget the car has variable valve timing and spark adders as well so it stands to reason the injection timing will also coincide. There are also lots of adders to the SOI table as well.

I have had the best results with a basically stock SOI table and raising only where I need more room to keep pulse width down.

If you install a big camshaft then you will want to adjust it slightly in certain areas but if not, leave it stock.

[wesam]

Dont forget the car has variable valve timing and spark adders as well so it stands to reason the injection timing will also coincide. There are also lots of adders to the SOI table as well.

I have had the best results with a basically stock SOI table and raising only where I need more room to keep pulse width down.

If you install a big camshaft then you will want to adjust it slightly in certain areas but if not, leave it stock.

Adjusted based on what ? for FI we need it to keep pulse width down ( lower than 6 ms) but for bigger cams how we could adjust it ?

[Higgs Boson]

Adjusted based on what ? for FI we need it to keep pulse width down ( lower than 6 ms) but for bigger cams how we could adjust it ?

same as any other car you adjust injection timing for. maybe this will help: https://www.hptuners.com/forum/showt...ance-Requested

[lt1z350]

Been reading up on this following a few threads and someone had said that the soi is based more on actually cam timing and size of cam. Change cam change settings otherwise stock is fairly close. I have been working on my own 2016 cts vsport tune the lf3 engine the atsv has the fl4 so been comparing tunes it has 45 more hp or so then the lf3 and shares a bunch of the same stuff but a little stronger bottom end and turbos have lighter compressor wheels but same size as lf3. So same cams same exact cam settings from factory but soi table on the lf4 (464hp atsv)is quite a bit lower all over then the lf3(420hp vsport) so from the factory some reason they chose to completely change the soi between the two engines. They run about the same boost stock 8-12 same compression but the lf4 has a lower over all ignition timing table too to go along with the lower soi. Just thinking something could be learned comparing two tunes on two engines that are nearly the same. I poked a bunch of the lf4 tune in the lf3 and made it lazy with out adjusting a lot more on it. I cannot ever get it to want to hold wot so don't know how much it is affected over all as I am missing something and my delivered torque exceeds the max boost torque table quickly so holds throttle at 56 percent or would have more data on wot and the change between two tables. Just know normal during it got lazy when driving it around easy. My wife babies the car as her daily dricerthe good thing here is she will notice a small change to normal driving that I won't as I am more about getting the most from it and drive agressive.
So two engines very much the same and two totally different soi tables.

[lt1z350]

atsv soi.PNG
vsport soi.PNG

So here is the two for anyone to explain why two of the near same engines have dramatic changes in soi. Keep in mind same cams same cam timing in program. Ignition timing is a little different a little lower on the atsv believe it or not as I thought it would have the more aggressive timing table. Maybe this can shed light on how they come up with adjusting it and why.

[GHuggins]

You say the cams are the same, but are the part numbers the same? Are the part numbers for the HPFP and lobe roller the same? I know GM will sale new DI motors with completely different HPFP lift lobes on the cams requiring the corrected part number HPFP to go along with it... If they're running a higher lift lobe profile then they can retard the injection timing further which is where when possible you get better fuel economy and hp with DI motors... Power gains through injection timing on DI motors is usually only achieved with after market cams using a 30% increase in lobe lift...

[lt1z350]

I did have my friend that works at chevy verify the part numbers and yes they are the same for alll 4 cams on the lf3 and lf4 and why this is weird. The changes made my car lazy in normal driving where it was lowered and as for up top they raise it but rarely see that high of airmass as closes throttle blade right when hitting that area where would see it run better or not so still fighting that end of my tune with no luck what so ever. It seems to think 58 percent open is 100 percent as every time I nail it it goes 100 briefly then right back to about 58 and stays there except where drops more for shifts but recovers to 58. I posted a thread if interested in helping as you did greatly on my tahoe.

[parish8]

great thread!

help me out here. lets say you spin the motor to 6400rpm.

one revolution at that rpm is 9.375ms.
start spraying at 355deg btdc, ignition is at 20deg btdc. total time to spray is 355-20 = 335deg.
(335/360)*9.375= 8.72ms of spray time

lets play it safe and call it 8ms of spray time. why is 6ms considered the limit?

[Higgs Boson]

great thread!

help me out here. lets say you spin the motor to 6400rpm.

one revolution at that rpm is 9.375ms.
start spraying at 355deg btdc, ignition is at 20deg btdc. total time to spray is 355-20 = 335deg.
(335/360)*9.375= 8.72ms of spray time

lets play it safe and call it 8ms of spray time. why is 6ms considered the limit?

if only it could be measured like port injection.

in reality, the ecm backs the spark way off (like to negatives) the closer spray gets to spark even though the tune says the limit is 5 or 10 degrees before spark, I have found it to need way more than that.

the 4 banger guys have said there are concerns with fuel puddling on the piston as well. you have to remember that there is way more fuel per ms with DI than port. you have to inject the same amount of fuel in a third or half the time and none of it sits on the intake valve, whereas with port most of it waits on the intake valve.

[tunerpro]

I did have my friend that works at chevy verify the part numbers and yes they are the same for alll 4 cams on the lf3 and lf4 and why this is weird. The changes made my car lazy in normal driving where it was lowered and as for up top they raise it but rarely see that high of airmass as closes throttle blade right when hitting that area where would see it run better or not so still fighting that end of my tune with no luck what so ever. It seems to think 58 percent open is 100 percent as every time I nail it it goes 100 briefly then right back to about 58 and stays there except where drops more for shifts but recovers to 58. I posted a thread if interested in helping as you did greatly on my tahoe.

The throttle blade closing is the Aisin TCM imposing torque limits on you.