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Thread: Injection Timing Assistance Requested

  1. #1
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    Injection Timing Assistance Requested

    Tried to dial in my setup before taking it in for a dyno tune. I'm not sure how much effort was put into "fine tuning" my combination. Horsepower and torque numbers were ok, but lower than I hoped. Arrived at the strip (post dyno tune) with 12 gallons of 93 octane and one can of Torco in the tank. I added 7 degrees of timing at all points below and to right of 3000 rpms and .64 grams spark airmass, lowered PE enable, and raised shift points by 200 rpm/2 mph during the session. After 9 passes, I was able to drop elapsed times by 8 tenths while picking up 7 mph.

    Combo:
    408 CID
    PRC 260cc heads
    Holley Hi Ram
    NW 102mm Throttle body
    57 lb FAST injectors
    9.5 to 1 compression (no turbo yet)
    4L85E Supermatic
    31x18x15s and 4.11 gears

    Cam is a TSP version of the BTR Racing Stage IV turbo
    Duration @ .050 = 234/239 ( I can't seem to find values at .006)
    Lift with 1.7 Rockers = .615/.629
    115 lobe separation
    110 Intake centerline

    Been reading up on injector timing, but I'm not there yet. Can someone give me direction? Seems like truck should be faster. Tune attached. Log from last pass attached. ERMs template attached too.

    Open to all other advice/suggestions too.
    Attached Files Attached Files
    Last edited by scottt28; 02-06-2017 at 08:31 PM.

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    Quote Originally Posted by scottt28 View Post
    Tried to dial in my setup before taking it in for a dyno tune. I'm not sure how much effort was put into "fine tuning" my combination. Horsepower and torque numbers were ok, but lower than I hoped. Arrived at the strip (post dyno tune) with 12 gallons of 93 octane and one can of Torco in the tank. I added 7 degrees of timing at all points below and to right of 3000 rpms and .64 grams spark airmass, lowered PE enable, and raised shift points by 200 rpm/2 mph during the session. After 9 passes, I was able to drop elapsed times by 8 tenths while picking up 7 mph.

    Combo:
    408 CID
    PRC 260cc heads
    Holley Hi Ram
    NW 102mm Throttle body
    57 lb FAST injectors
    9.5 to 1 compression (no turbo yet)
    4L85E Supermatic
    31x18x15s and 4.11 gears

    Cam is a TSP version of the BTR Racing Stage IV turbo
    Duration @ .050 = 234/239 ( I can't seem to find values at .006)
    Lift with 1.7 Rockers = .615/.629
    115 lobe separation
    110 Intake centerline

    Been reading up on injector timing, but I'm not there yet. Can someone give me direction? Seems like truck should be faster. Tune attached. Log from last pass attached. ERMs template attached too.

    Open to all other advice/suggestions too.
    Ok. Skies are parting. This is more of a a commentary than a question...

    Let's say that "IVO" is 18 degrees BTDC using Mowton's example. "IVO" in quotes means that intake valve STARTS to open at 18 BTDC. That's the point where the valve comes off the seat, but it is nowhere near full lift. I'll bet that full lift probably doesn't occur until 80-90 degrees or so later depending on the ramp profile. We never go from full closed to full open with nothing in between. Further, we know that ramp profiles on hydraulic cams versus solid cams, versus solid roller cams versus hydraulic roller cams, are different. We could also assume that opening ramp profiles are different than closing ramp profiles on the same lobe - and intake lobe ramps are different than exhaust lobe ramps. Ramp profiles are probably well guarded, but with the right equipment and enough time, we could map the intake/exhaust lobe opening and closing ramp profiles (assuming they are different). Using duration and the ramp profiles, we could come up with a total area under the "lobe curve". We could also map movement at the actual valve based on rocker arm ratio and design. I'll bet that the shape and size of the area under the "lobe curve" is different than the shape and area under the "valve curve".

    Log files will show us the injector pulse width (with a certain injector size/design moving fuel at a certain pressure) required to achieve the desired AFR at a specific engine RPM/load/ECT/moon phase etc. Right?

    If all that is more or less true, then the question becomes when to fire the injector knowing that injector takes X milliseconds and Y degrees of crankshaft rotation to fill the cylinder in such a way to achieve the desired AFR at a specific engine RPM/load/moon phase etc.,

    I wonder if you fire the injector too soon, will you upset the spray pattern? You might be washing down the lower part of the intake or the intake port in the head (depending on injector location and spray pattern). The whole deal might hit the valve stem and puddle on the backside of the closed valve. Maybe it puddles up between the closed valve and the seat. Maybe half the shot hits the valve margin and the rest hits the top of the piston. Maybe the whole mess bounces off the top of the piston and out the exhaust port past an open exhaust valve.

    Ed M. - I am working on your spreadsheet to make it a little more user friendly. I'm thinking that it'll be easier to document and test various settings rather than getting a PHd in mechanical engineering, fluid dynamics, physics etc...

  3. #3
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    I'm no good with explaining things - hopefully this might help you out...

    http://www.hptuners.com/forum/showth...for-help/page2
    2010 Vette Stock Bottom LS3 - LS2 APS Twin Turbo Kit, Trick Flow Heads and Custom Cam - 12psi - 714rwhp and 820rwtq / 100hp Nitrous Shot starting at 3000 rpms - 948rwhp and 1044rwtq still on 93
    2011 Vette Cam Only Internal Mod in stock LS3 -- YSI @ 18psi - 811rwhp on 93 / 926rwhp on E60 & 1008rwhp with a 50 shot of nitrous all through a 6L80

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    Quote Originally Posted by GHuggins View Post
    I'm no good with explaining things - hopefully this might help you out...

    http://www.hptuners.com/forum/showth...for-help/page2
    For whatever reason, I didn't find your thread when searching on injection timing. Thanks!

    Also - The new technology is incredibly sophisticated. Your explanations, and those of a few others, are generally very good. Some of us just need to read and read and read before it sinks in. Thanks again.

  5. #5
    Senior Tuner Higgs Boson's Avatar
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    just wait until you start tuning a gen v motor. ;-)

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    Quote Originally Posted by Higgs Boson View Post
    just wait until you start tuning a gen v motor. ;-)
    Yes, my hats off to those that have working spreadsheets for them - I still just "experiment" which still shows very nice things on the genV's
    2010 Vette Stock Bottom LS3 - LS2 APS Twin Turbo Kit, Trick Flow Heads and Custom Cam - 12psi - 714rwhp and 820rwtq / 100hp Nitrous Shot starting at 3000 rpms - 948rwhp and 1044rwtq still on 93
    2011 Vette Cam Only Internal Mod in stock LS3 -- YSI @ 18psi - 811rwhp on 93 / 926rwhp on E60 & 1008rwhp with a 50 shot of nitrous all through a 6L80

    ~Greg Huggins~
    Remote Tuning Available at gh[email protected]
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    Senior Tuner mowton's Avatar
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    Quote Originally Posted by scottt28 View Post
    Ok. Skies are parting. This is more of a a commentary than a question...

    Let's say that "IVO" is 18 degrees BTDC using Mowton's example. "IVO" in quotes means that intake valve STARTS to open at 18 BTDC. That's the point where the valve comes off the seat, but it is nowhere near full lift. I'll bet that full lift probably doesn't occur until 80-90 degrees or so later depending on the ramp profile. We never go from full closed to full open with nothing in between. Further, we know that ramp profiles on hydraulic cams versus solid cams, versus solid roller cams versus hydraulic roller cams, are different. We could also assume that opening ramp profiles are different than closing ramp profiles on the same lobe - and intake lobe ramps are different than exhaust lobe ramps. Ramp profiles are probably well guarded, but with the right equipment and enough time, we could map the intake/exhaust lobe opening and closing ramp profiles (assuming they are different). Using duration and the ramp profiles, we could come up with a total area under the "lobe curve". We could also map movement at the actual valve based on rocker arm ratio and design. I'll bet that the shape and size of the area under the "lobe curve" is different than the shape and area under the "valve curve".

    Log files will show us the injector pulse width (with a certain injector size/design moving fuel at a certain pressure) required to achieve the desired AFR at a specific engine RPM/load/ECT/moon phase etc. Right?

    If all that is more or less true, then the question becomes when to fire the injector knowing that injector takes X milliseconds and Y degrees of crankshaft rotation to fill the cylinder in such a way to achieve the desired AFR at a specific engine RPM/load/moon phase etc.,

    I wonder if you fire the injector too soon, will you upset the spray pattern? You might be washing down the lower part of the intake or the intake port in the head (depending on injector location and spray pattern). The whole deal might hit the valve stem and puddle on the backside of the closed valve. Maybe it puddles up between the closed valve and the seat. Maybe half the shot hits the valve margin and the rest hits the top of the piston. Maybe the whole mess bounces off the top of the piston and out the exhaust port past an open exhaust valve.

    Ed M. - I am working on your spreadsheet to make it a little more user friendly. I'm thinking that it'll be easier to document and test various settings rather than getting a PHd in mechanical engineering, fluid dynamics, physics etc...
    Scott,

    First off I have been going through some critical health issues and have not been participating on the Forum nearly as much and even have a draft response to your email from several weeks ago which I never got to finish...my apologies.

    I saw your post and wanted to chime in. I would appreciate any comments/upgrades to improve on my "manual" EOIT calculator spreadsheet. It was a crude attempt to support my learning process. The basis is to identify cam events (both .050 and more importantly the advertised), develop injection pulse times and crank degrees to help in the injector selection, map them to the "720 degrees" of injection time, formulate new Boundary and TEMP/RPM values to maximize injection coverage timing. Key goals are to identify idle and cam overlap scenarios to improve idle AFR results and for upper rpm area's take advantage of the higher piston velocity period as Greg has mentioned several times in his informative posts.

    If I have some time tonight, I'll go through your posts and offer some feedback.

    Ed M
    Last edited by mowton; 02-09-2017 at 07:02 AM.
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    Quote Originally Posted by mowton View Post
    Scott,

    First off I have been going through some critical health issues and have not been participating on the Forum nearly as much and even have a draft response to your email from several weeks ago which I never got to finish...my apologies.

    I saw your post and wanted to chime in. I would appreciate any comments/upgrades to improve on my "manual" EOIT calculator spreadsheet. It was a crude attempt to support my learning process. The basis is to identify cam events (both .050 and more importantly the advertised), develop injection pulse times and crank degrees to help in the injector selection, map them to the "720 degrees" of injection time, formulate new Boundary and TEMP/RPM values to maximize injection coverage timing. Key goals are to identify idle and cam overlap scenarios to improve idle AFR results and for upper rpm area's take advantage of the higher piston velocity period as Greg has mentioned several times in his informative posts.

    If I have some time tonight, I'll go through your posts and offer some feedback.

    Ed M
    Sorry to hear you're not feeling well. I wish you all the best.

    As far as injection timing... I spent a good chunk of yesterday been reading posts by GHuggins and schpenxel. In a nutshell, it seems that:

    Given that:
    - Peak piston velocity for a Chevrolet LS engine with a 4.030" Bore, 4.000" Stroke and a standard 6.125" connecting rod, achieves maximum piston velocity right around 73 degrees according to https://www.lmengines.com/piston-speed-calculator/. (The rod/stroke ratio and piston velocity changes around TDC allow you to calculate features such as theoretical max inlet demand - i.e the "greatest suck"), and your
    - Camshaft specifications (duration, lobe separation angle, and intake center line... preferably measured at .006 lift), and measured
    - Fuel delivery (actual pulsewidth observed in a log and measured in milliseconds and/or crankshaft degrees of rotation based on fuel injector size, fuel pressure and desired AFR given engine rpm/load etc)...

    We can:
    - Solve backwards for SOIT (Start of Injection Target), using the Fuel > General > Injection > Timing Boundary and Fuel > General > Injection > Normal ECT, such that
    - SOIT (Start of Injection Target), below approx. 2500 rpms, occurs just before the exhaust valve has completely closed if not put it back on a closed intake valve, and
    - SOIT (Start of Injection Target), above 2500 rpms or so, occurs right before peak piston velocity and BDC (Bottom Dead Center) of the pistons stroke and EOIT (End of Injection Target) at these rpm points before the intake valve gets within 20 or 30 degrees of being completely closed.

    Resulting in:

    - Greatest cylinder turbulence to atomize the fuel, which often leads to
    - Re-tuning VVE and MAF etc. to compensate for a better and more complete fuel burn, and
    - More hp and torque.

    If my logic is more or less correct, then the issue (again) becomes the software. I still think it's a little clunky. I wonder if the tool might some day include tools (injector timing calculator, piston velocity calculator AND a table to Start of Injection Target table) that'll allow us to tune without all of the extra calculations...

    I noticed in another thread, that the Normal EOI Target vs. RPM table had been zeroed out. I am trying to understand it.

    Again... hope you're doing ok Ed M

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    Here's a sheet I was playing with, dunno if it'll help but you guys can check it out if you want it. I started with one of the other inj calculator sheets and tried to make it a bit more visual.

    I haven't messed with it in months so if there's something wrong then feel free to fix it. It is not password protected or anything like that.

    EOIT gen IV - LS2.xls
    Post a log and tune if you want help

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    Yes... I found a copy yesterday. I like your graph. I've been playing with it between trades.

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    Quote Originally Posted by schpenxel View Post
    Here's a sheet I was playing with, dunno if it'll help but you guys can check it out if you want it. I started with one of the other inj calculator sheets and tried to make it a bit more visual.

    I haven't messed with it in months so if there's something wrong then feel free to fix it. It is not password protected or anything like that.

    EOIT gen IV - LS2.xls
    Quote Originally Posted by schpenxel View Post
    Here's a sheet I was playing with, dunno if it'll help but you guys can check it out if you want it. I started with one of the other inj calculator sheets and tried to make it a bit more visual.

    I haven't messed with it in months so if there's something wrong then feel free to fix it. It is not password protected or anything like that.

    EOIT gen IV - LS2.xls
    Given that:
    - Peak piston velocity for a Chevrolet LS engine with a 4.030" Bore, 4.000" Stroke and a standard 6.125" connecting rod, achieves maximum piston velocity right around 73 degrees according to https://www.lmengines.com/piston-speed-calculator/. (The rod/stroke ratio and piston velocity changes around TDC allow you to calculate features such as theoretical max inlet demand - i.e the "greatest suck"), and your
    - Camshaft specifications (duration, lobe separation angle, and intake center line... preferably measured at .006 lift), and measured
    - Fuel delivery (actual pulsewidth observed in a log and measured in milliseconds and/or crankshaft degrees of rotation based on fuel injector size, fuel pressure and desired AFR given engine rpm/load etc)...

    We can:
    - Solve backwards for SOIT (Start of Injection Target), using the Fuel > General > Injection > Timing Boundary and Fuel > General > Injection > Normal ECT, such that
    - SOIT (Start of Injection Target), below approx. 2500 rpms, occurs just before the exhaust valve has completely closed if not put it back on a closed intake valve, and
    - SOIT (Start of Injection Target), above 2500 rpms or so, occurs right before peak piston velocity and BDC (Bottom Dead Center) of the pistons stroke and EOIT (End of Injection Target) at these rpm points before the intake valve gets within 20 or 30 degrees of being completely closed.

    Resulting in:

    - Greatest cylinder turbulence to atomize the fuel, which often leads to
    - Re-tuning VVE and MAF etc. to compensate for a better and more complete fuel burn, and
    - More hp and torque.

    That said, I tried something a little different. First, use the calculator at Wallace Racing http://wallaceracing.com/cam-deg-calc.php to get additional values based on your specs. Enter the cam specs in the appropriate YELLOW cells. Next, enter values (injection boundary, normal ect and normal rpm) from your tune in the appropriate YELLOW cells. Don't enter anything in the gray cells. They should calculate automagically. Below approx. 2500 rpms, SOIT should occur just before the exhaust valve has completely closed if not put it back on a closed intake valve. Above 2500 rpms or so, SIOT should happen right before peak piston velocity and BDC (Bottom Dead Center) of the pistons stroke. EOIT (End of Injection Target) at these rpm points should take place before the intake valve gets within 20 or 30 degrees of being completely closed.

    I created graphs at each RPM interval to help show what is happening. The graphs update automatically based on values entered in the YELLOW cells. Basically, I am trying to show SIOT and EOIT at each RPM for an engine with specific camshaft specs, and measured fuel injector pulsewidth that corresponds to a specific AFR given engine rpm, load, etc - generally a WOT throttle pass down the dragstrip where engine and transmission are 1 to 1.

    I might try to add some lines for Peak Piston Velocity later. Right now, this info might have to be transferred to one of the "injection timing degree wheels" in these threads.

    The logic is all stuff that I ripped off from schpenxel and GHuggins and Mowton. Feel free to comment.
    Attached Files Attached Files
    Last edited by scottt28; 02-10-2017 at 09:28 PM. Reason: Adult ADHD

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    Not bad - not bad at all...
    Couple of things I noticed - ECT will always be one number (can you have it to where you enter one number in and it update the entire row?)
    Next - FI vs. NA - FI will nearly always need to be to where the majority of the time soi is after the exhaust valve closes or close to that point at lower pw's if for nothing else other than transient issues associated with it - Is there a way to incorporate this? Have a FI or NA switch if you will? Putting the cam soi illustration on the same page would help, but below the main tables? Is it possible to include the eoi and soi In the cam illustration with different colors illustrating each?

    Nice work...
    2010 Vette Stock Bottom LS3 - LS2 APS Twin Turbo Kit, Trick Flow Heads and Custom Cam - 12psi - 714rwhp and 820rwtq / 100hp Nitrous Shot starting at 3000 rpms - 948rwhp and 1044rwtq still on 93
    2011 Vette Cam Only Internal Mod in stock LS3 -- YSI @ 18psi - 811rwhp on 93 / 926rwhp on E60 & 1008rwhp with a 50 shot of nitrous all through a 6L80

    ~Greg Huggins~
    Remote Tuning Available at gh[email protected]
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    Quote Originally Posted by GHuggins View Post
    Not bad - not bad at all...
    Couple of things I noticed - ECT will always be one number (can you have it to where you enter one number in and it update the entire row?)
    Next - FI vs. NA - FI will nearly always need to be to where the majority of the time soi is after the exhaust valve closes or close to that point at lower pw's if for nothing else other than transient issues associated with it - Is there a way to incorporate this? Have a FI or NA switch if you will? Putting the cam soi illustration on the same page would help, but below the main tables? Is it possible to include the eoi and soi In the cam illustration with different colors illustrating each?

    Nice work...
    As far as ECT... I didn't understand what that value represents. In the description of the variable, it says it is added to the boundary. In our formulas, it is subtracted from the boundary... That was a follow up question from me to the guys in the forum. What is Normal ECT and how is it used?

    But yes, I could add it to the range of input variables and have it populate all the way across the row. Simple. Simple once I understand it...

    As far as Normal RPM... one of the guys at the end of thread referenced by GHuggins has the entire row of Normal RPM values zeroed out. Why would we zero out that row? What is Normal RPM and how is it used?

    Your other questions and suggestions are good too. Here's what I was thinking:

    - Have an input variable for PPV (Peak Piston Velocity) which would be calculated using the tool from https://www.lmengines.com/piston-speed-calculator/
    - Value entered into the field above could be carried over to the graphs which would basically add vertical lines at Peak Piston Velocity (in my case, about 73 degrees from TDC, BDC)
    - The "FI or NA Switch" could be added too. For my cam, the IVO is 7 degrees BDC. We could add an input variable to calculate when we want the injection to start based on that value. For instance, I want to SOIT to be 5 degrees after IVO... Similarly, we could have an input variable that captures SOIT delay/advance so SOIT is x degrees before or after "the exhaust valve closes or close to that point at lower pw's if for nothing else other than transient issues associated with it". We could also have it calculate the EOIT versus intake valve being completely closed. That way, you'd see the entire injection event within the window of intake valve movement...

    (Since we entered the PPV previously, the "entire injection event within the window of intake valve movement" would also be shown in comparison to PPV)

    - "Is it possible to include the eoi and soi In the cam illustration with different colors illustrating each?"... yep. I'll have to spend some time on it. What colors do you like?
    - You should be able to move the graphs anywhere on the sheet without screwing them up. The formulas behind the graphs are linked to the cells in the tables. Don't type over the gray areas in the table and you'll be ok. I need to put titles in each graph to show which RPM range it references though...

    Question for schpenxel... the values of .200 and .500. Can you tell me more about them? How did you come up with these numbers?

    Obviously, I still have more reading to do, but I needed to start somewhere. I like schpenxel's graphs better than the degree wheels... easier for me to grasp.
    Last edited by scottt28; 02-11-2017 at 08:13 AM. Reason: Punctuation

  14. #14
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    the normal rpm stops at round 4k so u can zero that out and use the boundary for rpm changes all the way to red line then u can tailor it to suit what your setup likes, the ECT is added to before the boundary so boundary is the final then both ECT and RPM are taken off, higher boundary number delays eoit or lower ect/rpm delay eoit

  15. #15
    Senior Tuner Higgs Boson's Avatar
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    I leave it all stock and raise the boundary by the amount the EVC moves so if stock EVC is 5 BTDC and the aftermarket cam EVC is 15 ATDC then I would raise boundary from 520 to 540 and that's it, leave ECT and RPM stock.

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    The degree wheel is easier for me to grasp, but that's just the way my brain works I guess Most everyone else likes Carson's and your way of illustrating it...

    Red and Blue are fine - Red EOI and Blue SOI?

    Normal RPM is zeroed out to take it out of the equation - you can use boundary for the same thing - rpm just breaks up the lower rpms a little finer

    ECT will only be one number at or around engine operating temperature which is why you only need one number for it

    I don't worry too much about peak piston velocity anymore - it's still important, but at the end of the day it only happens at a very small window of the injection event...

    Higg's - that works for some cams, but you might find your leaving a lot on the table - even OE cams benefit from reworking these tables
    2010 Vette Stock Bottom LS3 - LS2 APS Twin Turbo Kit, Trick Flow Heads and Custom Cam - 12psi - 714rwhp and 820rwtq / 100hp Nitrous Shot starting at 3000 rpms - 948rwhp and 1044rwtq still on 93
    2011 Vette Cam Only Internal Mod in stock LS3 -- YSI @ 18psi - 811rwhp on 93 / 926rwhp on E60 & 1008rwhp with a 50 shot of nitrous all through a 6L80

    ~Greg Huggins~
    Remote Tuning Available at gh[email protected]
    Mobile Tuning Available for North Georgia and WNC

  17. #17
    Senior Tuner Higgs Boson's Avatar
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    Yeah I just want to keep from losing fuel during overlap and I have not found much to be gained in the higher RPMs, but I haven't really messed with it too much in a while. I am tuning a LS2 in a 2nd gen camaro right now (assuming the builder corrects some wiring issues) and will have a chance to play with injection timing on it.

    Also, piston velocity doesn't really change with different bore and stroke sizing as far as I can tell by that calculator. You need a very very different engine to deviate from 68-74.

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    Quote Originally Posted by Higgs Boson View Post
    Yeah I just want to keep from losing fuel during overlap and I have not found much to be gained in the higher RPMs, but I haven't really messed with it too much in a while. I am tuning a LS2 in a 2nd gen camaro right now (assuming the builder corrects some wiring issues) and will have a chance to play with injection timing on it.

    Also, piston velocity doesn't really change with different bore and stroke sizing as far as I can tell by that calculator. You need a very very different engine to deviate from 68-74.
    Yes, usually a big block or something else to worry about it. Also injection timing may not show huge gains on the dyno, but you can tell it on the street or at the track.

  19. #19
    Senior Tuner Higgs Boson's Avatar
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    SOIT occuring at peak piston velocity......the intake valve is closed so why would piston velocity matter? No fuel comes into the cylinder until the intake valve opens.

    Setting SOIT to peak velocity with the intake valve open mean you spray well past spark.....except you can't inject with the intake valve closed anyways. The latest you could get fuel in is IVC @ .006 and the earliest is IVO at .006.....

    So you have to spray against a closed intake valve at higher RPMs, I can see delaying EOIT to closer to ICV, how close you can get it I don't know (maybe just a little past BDC) but that would mean the injector is spraying in fuel until a closer time to spark which means there might be more fuel closer to the plug since the piston is on the way back up by IVC but it would be less atomized I would think since it didnt spend any time against the closed valve but regardless, combustion would start that much sooner and stronger I would think thereby making it feel more powerful on the street but showing no gains on the dyno. How that affects emissions I also do not know.

    Any thoughts on that?

  20. #20
    Senior Tuner Higgs Boson's Avatar
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    Mar 2010
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    With the stock cam and injection you can see it always completes injection before IVO no matter what RPM (except around idle). At low RPM with a later EVC we can delay SOIT and still complete EOIT in time for IVC, injecting start to finish while intake is open.

    As the RPMs and airflow rise, we need more time to inject and cannot avoid overlap but hopefully the RPMs will pull that fuel back in rather than just spitting it out like at idle, the best we can hope to do is inject as late as possible I suppose, but where is the late injection limit? How many degrees before [email protected]? I think that's the real question here. Who cares when SOIT is at higher RPMs, the intake valve is closed anyways.