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Thread: How far are you guys letting EOI drop?

  1. #1
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    How far are you guys letting EOI drop?

    Lately I have been tuning quite a few Gen 6 ZL1's with full bolt ons, varying pulley setups, with meth and full E85(E80 from the track). At the same time I have been testing the JMS FuelMax on my personal Z06 to see what I can squeeze out of the stock system. With that said, typically I tune SOI on the ZL1s in the base table and alcohol offset as to not exceed 360 and I try to keep the EOI above 180 and the pulsewidth around 5.5ms max on the hit and then down to 5ms by redline as the meth ramps in and takes over for the extra fuel needed. Not to start a discussion about relying on meth as fuel or anything please, I keep advising the shop I am working with to come up with a better solution, but they and their clients are okay with leaning on Meth for this. I have advised to add the JMS to assist with fueling on the hit while the meth ramps in. The JMS really does help with fueling on these cars. Not a ton, but for a bolt on car I would say it is a no brainer.

    Anyhow, on my personal car I have tuned SOI to not exceed 360 SOI, but when I really push the fuel system it will creep up to 365 which is still after EVC so I'm not too concerned. But as I ramp up the ethanol content past E70 the EOI starts dropping as low as 140 which means I'm spraying into the compression stroke by 40 degrees. Low side maintains 80psi due to the JMS, the high side stays at 2600psi or higher(usually only drops to 2600 psi around 5200 rpms and then climbs back up to 2900-3000 until redline), and the injectors range from 6.3ms on the hit and drop down to 5.8ms by redline. Commanded Lambda stays on target the whole run and the car runs strong.

    First, before you say "you're out of fuel", I already know that I'm at the limit but that isn't my question. My question is, do any of you guys ever spray into the compression stroke(past 180 EOI)? I know Doug at ECS does this on his personal 2019 Z06 with full bolt on and pulley and STOCK fuel system. He does have a ZR1 low side since it is a 2019 Z06. I'm pretty sure my JMS flows more low side than he does and I'm on a stock pulley and he is on a 2.3. For street driving I will be running E60-E65 as this keeps SOI/EOI between 360/180. But I want to run E75 during race events. I've read through a ton of old material on here to see if anyone had concerns or experience with EOI dropping below 180 degrees but most of the talks focus on SOI. Technically according to the stock Z06 cam profile I should be able to inject up to 368 degrees with the cam at zero retard so at redline my SOI could go all the way to about 375-376. But it is well documented that it is not optimal to spray at the end of the exhaust stroke even if the exhaust valve is closed.

    Anyhow, new thread, new question focused on EOI. I'd like to hear some of your thoughts on this subject if you have any experience to share.
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  2. #2
    Senior Tuner Higgs Boson's Avatar
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    What is the IVC value on your setup? If you had a carb you'd be fueling the cylinder until then.

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    It's a stock C7 Z06 cam so I think its about 35ish degrees past BDC. That would put the maximum desired EOI timing at 145 degrees. If you account for the variable cam I suppose by redline that would be about 137 EOI. So I probably don't want to see the EOI drop below 150 based on this.
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  4. #4
    Quote Originally Posted by TriPinTaZ View Post
    It's a stock C7 Z06 cam so I think its about 35ish degrees past BDC. That would put the maximum desired EOI timing at 145 degrees. If you account for the variable cam I suppose by redline that would be about 137 EOI. So I probably don't want to see the EOI drop below 150 based on this.
    IVC is going to be the end target as intake airflow into the cylinder is largely responsible for fuel mixing. Most of the fuel mixing happens when intake air velocity is highest, around mid stroke 270-290 degrees. If you go past the intake stroke 5-10 degrees, not sure it will make much difference but I would bet if you had it on a load controlled dyno you could tell real quick if and how far into the compression stroke you can spray fuel. I would bet that combustion quality would suffer, power is going to drop and eventually you will get misfires from some of the fuel not atomizing enough to burn. A 5 gas analyzer would tell you even more.

    There is a EOI Max Angle parameter in most of the DI engine ECUs as well as the EOI Spark Offset to look at. GM did their homework here obviously so it would be good to see what those values are when you are spraying into the compression stroke.

    If you have a math channel set up for torque calculation you could experiment a little that way on the street and see when it drops off in power if no dyno is available?

    With the E70, are you seeing loss of power or any kind of indicator that you are not mixing all the fuel you are spraying? I bet you start to see black soot when it really is too far into the combustion stroke.

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    Quote Originally Posted by cadillactech View Post
    IVC is going to be the end target as intake airflow into the cylinder is largely responsible for fuel mixing. Most of the fuel mixing happens when intake air velocity is highest, around mid stroke 270-290 degrees. If you go past the intake stroke 5-10 degrees, not sure it will make much difference but I would bet if you had it on a load controlled dyno you could tell real quick if and how far into the compression stroke you can spray fuel. I would bet that combustion quality would suffer, power is going to drop and eventually you will get misfires from some of the fuel not atomizing enough to burn. A 5 gas analyzer would tell you even more.

    There is a EOI Max Angle parameter in most of the DI engine ECUs as well as the EOI Spark Offset to look at. GM did their homework here obviously so it would be good to see what those values are when you are spraying into the compression stroke.

    If you have a math channel set up for torque calculation you could experiment a little that way on the street and see when it drops off in power if no dyno is available?

    With the E70, are you seeing loss of power or any kind of indicator that you are not mixing all the fuel you are spraying? I bet you start to see black soot when it really is too far into the combustion stroke.
    The EOI max angle parameter value makes no sense in the tune as it is set to 350 meaning it would spray right through spark. So I don't think that is even an valid value. I see no change in reported torque value form the ECU whether EOI is 180 or 140. I also see no black soot or black smoke under WOT. Power feels the same but I don't think my butt can feel a minor power drop when you have over 700HP. I'm going to run some tests using draggy on the street and see if there is any power drop off(measured by 60-130 times) between E55 and E75.

    I would think that an EOI of 160 or before (meaning less than 20 degrees past BDC) would be perfectly fine without a power drop. The piston speed is still slow at that point and the intake valve is still open. I made this thread because the car runs great on E55 with EOI around 180 and it also runs great on E75 with EOI hitting 140. Max SOI is 365 in either case but usually is under or at 360.
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  6. #6
    I guess we don't know if GM is referencing the same event for the EOI Max angle, as I looked at my shop ATS V and found the value as 512. But I guess it doesn't really matter at this point unless it starts limiting when you are spraying.

    The values you are seeing for EOI don't seem like they would cause a problem but testing will show you.

    Let us know what you find!

  7. #7
    I’d love something concrete on this as well. I’ve been tuning a gen3 coyote on an upgraded gdi pump, which I actually believe to be the stock LT5 pump adapted to a coyote. As such, I started pushing eoi further and further back to allow more injector flow to go along with the added pump capacity. I got all the way to the upper 50 deg btdc range because And felt ok with it because numerous sae article indicated they ran it even past spark and the ill effect was only soot production. Other sources like this one [ https://www.hpacademy.com/forum/gene...ship-for-power ] seemed to think up to 20 deg before spark is ok. Well I had an unexplained loss in top end power. I started digging deep and plotting lots of data and it seems as though when I get below about 100 or 110 deg btdc it start adversely affecting power. However, this isn’t a hard limit as it may increase as rpm rises. I don’t know if the extra “late” fuel is hurting charge motion, just wetting the piston, or simply doesn’t have enough time for atomization. If interested I can try to post a plot showing eoi vs acceleration times.

  8. #8
    Senior Tuner Higgs Boson's Avatar
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    Quote Originally Posted by cadillactech View Post
    I guess we don't know if GM is referencing the same event for the EOI Max angle, as I looked at my shop ATS V and found the value as 512. But I guess it doesn't really matter at this point unless it starts limiting when you are spraying.

    The values you are seeing for EOI don't seem like they would cause a problem but testing will show you.

    Let us know what you find!
    512 - 360 = 152

  9. #9
    Quote Originally Posted by Higgs Boson View Post
    512 - 360 = 152
    Ya I did that math so I would assume that is 150 degrees ABDC of the intake, which leaves 28 degrees for spark, which makes sense.

    The value for the V8 at 350 doesn't really make much senses though right?

  10. #10
    Quote Originally Posted by engineermike View Post
    I’d love something concrete on this as well. I’ve been tuning a gen3 coyote on an upgraded gdi pump, which I actually believe to be the stock LT5 pump adapted to a coyote. As such, I started pushing eoi further and further back to allow more injector flow to go along with the added pump capacity. I got all the way to the upper 50 deg btdc range because And felt ok with it because numerous sae article indicated they ran it even past spark and the ill effect was only soot production. Other sources like this one [ https://www.hpacademy.com/forum/gene...ship-for-power ] seemed to think up to 20 deg before spark is ok. Well I had an unexplained loss in top end power. I started digging deep and plotting lots of data and it seems as though when I get below about 100 or 110 deg btdc it start adversely affecting power. However, this isn’t a hard limit as it may increase as rpm rises. I don’t know if the extra “late” fuel is hurting charge motion, just wetting the piston, or simply doesn’t have enough time for atomization. If interested I can try to post a plot showing eoi vs acceleration times.
    Would love to see what you have observed!

  11. #11
    The acceleration time is corrected, as best I could, for different IAT and pulley size. However, I increased the EOI clip and got it back to the 115 range and the acceleration didn't do what I expected so I'm starting to doubt my hypothesis, so take it for what it's worth.

    EOI accel.JPG

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    [QUOTE=engineermike;654226]The acceleration time is corrected, as best I could, for different IAT and pulley size. However, I increased the EOI clip and got it back to the 115 range and the acceleration didn't do what I expected so I'm starting to doubt my hypothesis, so take it for what it's worth.



    Are you referencing Ford stuff? EOI of 115 would be well past IVC closing on a GM LT motor.
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  13. #13
    EOI in Ford-land is in deg BTDC-firing. So 90 deg would be halfway up the compression stroke and lower is later. SOI at wot is usually around 330, or 30 deg aTDC on the intake stroke.

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    OK in GM it would be the same then but a 115 EOI would be spraying past IVC on the LT1/LT4's. That would likely hurt power to spray that far on a LT motor. Where is IVC for the Coyote's on the compression stroke?
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  15. #15
    Ivc is about 125 but variable.

    Why do you say it’s bad to inject after IVC?

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    You no longer have any air swirl from the intake valve and the piston speed is increasing that far up the compression stroke. And I wonder how much pressure is in the cylinder at that point vs the pressure coming out of the injector. I would think this would negatively affect the fuel mixture and you can have uneven fuel distribution causing an uneven flame with lean and rich pockets. But perhaps I'm overthinking it.
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  17. #17
    I think it has a lot to do with the gdi geometric features in the piston crown. In the link I posted above he mentions some engines working well injecting within 20 deg of spark and others not. I’ve also heard of diesel performance being highly dependent on piston crown shape. The coyote piston is no different from the port-injected piston.

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    Quote Originally Posted by engineermike View Post
    I think it has a lot to do with the gdi geometric features in the piston crown. In the link I posted above he mentions some engines working well injecting within 20 deg of spark and others not. I’ve also heard of diesel performance being highly dependent on piston crown shape. The coyote piston is no different from the port-injected piston.
    The GM LT pistons differ from the LS pistons due to direct injection. I don't suspect anyone that has tested this on the dyno will be sharing their info. Many of the smart guys on here do this for a living so I don't blame them for keeping some things to themselves.
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  19. #19
    Couple new things to post. Courtesy of an F150 forum member, I learned how to build remarkably precise power and torque curves using VCMScanner. I modified the given equations with a Dynojet "correction factor" and also add in an SAE air temp correction.

    That allowed me to do some EOI testing, which showed excellent repeatability. Unfortunately, VCMscanner doesn't save Math PIDs when you Export, so the following power and torque curves were manually copied to Excel. This is the difference that EOI made on my Coyote. EOI is 20-30 deg difference between these two logs. I'm not sure if the power is sensitive to the absolute value of the EOI, as it was decreasing/later at high rpm, or if higher rpm exacerbates the difference, or if it's both. At rpm below about 6250 OR at EOI earlier than 110 BTDCf it didn't matter much. At rpm above 6750 OR EOI after about 90 deg BTDCf it starts mattering a whole lot.

    Dyno compare.JPG

  20. #20
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    Could have to do with piston speed at that RPM. How many times was this test run? From what I think you're showing is one pair of lines is EOI of 110 or sooner and the other in EOI of 90 or sooner? It looks like it definitely matters right around or after peak torque. It's been raining around here but I'd like to go out and do some draggy tests to see if my E55 vs E70 shows any difference. Then try E75 where my EOI starts dropping later than 140. I wonder where the power fall off is on the GM platform. I've heard 160 but no one has ever demonstrated or shared any definitive examples.
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