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Thread: LFX Fuel Injector Dwell Time

  1. #1

    LFX Fuel Injector Dwell Time

    Anyone have any specs/info on the factory LFX fuel injectors (2015 Camaro)? Found the GM/AC Delco part number (12634126) but can't find much info on them.

    Recently installed Mace cams and am in the process of tuning them. Wondering what the dwell/dead/lag time is for these injectors to help with setting the SOI (start of injection).

    At low RPMs the crankshaft is only spinning a few degrees but at the higher RPMs the delay in terms of crank degrees is much greater. With that said, anyone know when, in general, to set SOI? Most of what I've read says the earlier the better for direct injection so figured I'd set the SOI right as the exhaust valve closes then adjust from there to see what difference the timing makes.

  2. #2
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    Love the scientific approach here! Unfortunately you probably won't find that kind of data publicly available.

    Some points to consider:

    You're going to need some time on a dyno to sort this out.

    The only time SOI advance from stock is needed is if the EOI ends up running so late that it causes a loss of power. If EOI is later than 180* BTDC, you should try incrementally advancing SOI to see if there is a power gain.

    OE SOI settings generally aim to start the injection as late as possible to fit the OE performance profile. Stick to this strategy and only advance SOI if your EOI is an issue.

    You can advance EOI by raising the DI rail pressure. If you go this route, make sure you still within the limits of the pump (they have an internal mechanical pressure relief, stay as far away from this as possible).

    Know where your exhaust valve closes, and DON'T advance SOI too close to this. You've modified the cam profile, which I'm assuming includes increasing the duration, and hence retarding the exhaust valve closing event.

    It is unlikely you will need to do much / anything with the SOI if all you've done is installed the cams. The LFX has relatively large fuel injectors. Having tuned these for boost, they needed very few changes to the injection timing, and this had a much larger impact on fuel system requirements than the cams will.

    Good luck!

  3. #3
    Thanks for the detailed answer.

    My previous tuner slightly changed (mostly delayed) the SOI from stock and also raised the desired fuel pressure of the low pressure pump, from 43.5 PSI to 52.0. Not sure how this affects the rail pressure.

    So far the only changes I've made to the SOI table is delaying any cells that would've injected fuel before the exhaust valve closes. I got the exhaust cam card from Mace (they wouldn't send me the intake cam card though, stating that they don't have that info... not sure how that's possible ) and it shows that the exhaust valve lift is 0.004" @ 25.45 deg ATDC, so I just rounded this to 26 to assume fully closed and then further subtracted from these numbers any retard from the VVT table. Haven't touched the rest of the table yet, but after seeing knock at low RPM/high load I thought maybe I need to adjust the SOI in those cells, and away I went down a rabbit hole.

    Also read on this forum that a good target for SOI is "around" 270 BTDC, when the piston is moving the fastest and thus fuel atomizing would be most effective. So if the injection time in crank degrees is 48 (4000 RPM, 2 ms PW), then set SOI to 294 plus the dwell time. Makes sense to me, not that I know what I'm talking about. Was thinking I'd assume a 0.5 ms dwell time if I couldn't find the info, then from there could add or subtract and see if the lambda increases (exhaust valve still open) or decreases (better combustion).

    I'll take into account what you said and make sure the EOI doesn't go past 180 deg BTDC.

    Another question(s):

    There is an "SOI ECT Offset" table but the axes are airmass and RPM, there's no ECT anywhere. But there's also an "SOI ECT Offset Mult" table too which is numbers (0 to 1) based on ECT. Guessing the multiplier table and offset table are multiplied together to get some amount of retard (offset table is all negative numbers) applied to the SOI? If that's the case, the multiplier at 167 (deg f) ECT is 0.213 and at 194 ECT it's 0 - wonder if I could zero the 167 cell so it doesn't affect the SOI table at operating temps. Typically run around ~180. Can post a tune if it's easier to see; I'm on another computer at the moment.

    And do you know how the Boundary table works? Says "the latest possible crank angle that the injection pulse can finish for fuel to be delivered to the cylinder", but some of those numbers don't make sense to me. For example, at 6656 RPM the cell is 320, meaning (I think) injection has to finish at 320 BTDC, but if the exhaust valve closes at 334 BTDC (or later when including VVT table) that means the PW would have to be like 0.35 ms or less. Am I wrong it what the table means? Can/should these numbers be changed?

  4. #4
    Just updating this, for myself and anyone else who cares.

    Did a bunch more reading, albeit mostly Gen IV stuff as that is mostly what popped up with Google.

    Based on a stroke of 3.37" and rod length of 6.00", peak piston velocity is at about 75 deg ATDC (when moving from top to bottom; and I guess 75 deg BTDC when moving from bottom to top), not 90 deg like I thought/assumed. Used https://lmengines.com/pages/piston-velocity-calculator which also says what the piston velocity is at all RPM's, and from this found where the piston is moving the fastest throughout the injection cycle for given scenarios.

    Assuming I did this right, the below numbers are when SOI should occur to be injecting during the average greatest velocity, for pulse widths of 1/2/3/4/5 ms:

    RPM:
    1000 = 288/290/293/297/298
    2000 = 290/297/301/305/309
    3000 = 293/301/307/312/315
    4000 = 297/305/312/315/315
    5000 = 298/309/315/315/X
    6000 = 301/312/315/X/X
    7000 = 303/314/315/X/X

    For X, based on my math the result would have been some value that went past BDC (into compression stroke), and in most cases would also require the SOI to be before the exhaust valve closes, so for these I just used the value mentioned above (EVC based on cam card and VVT table). Again, these numbers don't include the dwell time which I still don't know (read in the GM manual that the injectors are initially energized with 64V and then held open with 12V, so I'm guessing this means the injectors open pretty damn quick?).

    With that said I Changed my SOI table back to stock for now (except where it's advanced past EVC) to see if that helps with the knock I'm getting at higher loads (seems there's knock at lower and higher RPM's, only when cylinder airmass is 0.6 g or higher). Haven't tested yet though. The stock numbers are closer to my numbers above.

    In reading from Gen IV stuff it looks like they have the same Injection Boundary table (13336) as I do, and as I mentioned earlier my numbers at higher RPMs make no sense whatsoever (stock numbers). Going to change the whole table to 500 or 512 and see what happens (500 is the biggest number in the table; 512 is listed as "Injector EOI Max Angle: This is the maximum angle (max EOI) the injector driver can deliver a pulse to. This determines the maximum pulse width at the current RPM. It is not recommended you change this value."). Not sure if you can go past 512; at high RPMs and long pulse widths you'd be going past 512.

    FYI the pressure relief for the high pressure fuel system is 2538 PSI (17.5 MPa) according to the manual. Normal operation (as per manual and also found the table in the Fuel System section) sets pressure to 2 - 15 MPa, based on RPM and airmass.

  5. #5
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    You should probably confirm whether it's real knock or not. You've changed the cams, which means you've changed the mechanical acoustics of the engine. You may need to adjust the knock sensor calibration to account for new / different mechanical noise from the valve train.

  6. #6
    I've been meaning to read more on knock but in the meantime I'm trying to work with what has already been "worked with" from my previous tuner, just in case his changes are what's causing any issues, instead of potentially chasing my tail changing other stuff and masking the primary cause.

    Just did a few quick scans and found that the knock is much less (almost none) where it was before, although I only did a few WOT pulls; will get more data in the coming days.

    Regarding the SOI ECT Offset tables I inquired about earlier, I believe they work as I thought: the multiplier table (based on ECT) is multiplied by the offset table (airmass vs. RPM) to get a value which is subtracted from the SOI base table to further advance SOI (table is all negative numbers, so the SOI cells are increased). I seem to be running very lean on cold starts, so I reduced the Offset Multiplier table by half and my lambda went from ~1.1 to ~1.05; figured the injection was happening too early and flowing right out the exhaust due to the new overlap I have; will reduce further to see how much it helps, but if I can't reach the commanded EQ ratio I think there's another table to adjust: Temperature Adder 33380 (Fuel > General) which you can use to increase the pulse width at cold temps.

    Haven't changed the Boundary table yet (one thing at a time), but noticed it's the same on all LFX tunes I can find, and on other Gen V V8 tunes and even other E39A tunes (non LFX) this table doesn't even exist; wondering if this table is not even used considering how nonsensical the numbers are (EOI set to exhaust stroke). Will adjust this in the near future to see what happens. The Gen IV guys have the same table and seem to be adjusting this to what makes more sense, like 500+ in all cells.

    Will start reading up on prediction coefficients soon too; still tuning my VVE in OL, and I get some seemingly funky numbers in certain cells. When I make very minor changes to the throttle (trying to slow down a few km/h) I'll suddenly be like 10% lean, but all other adjacent cells are +/- 3% or so, and under steady load everything seems close to 1.000; wonder if some of the predictions are messing me up. Pain trying to adjust the VVE when all numbers in a zone need to be fairly close or else the "calculate coefficients" throws everything outta whack.

    Still can't get the intake cam card from Mace (not sure how the only ones in the world that could/should/would have the info don't have it...), but possibly figured out a nonintrusive way to find the approx. IVO and IVC angles: will pop off the intake manifold to see the valves, crank over to TDC (or BDC) and keep turning until I see the valves just start moving. Will mark the socket at the very top when I first see IVO, again when I see approx. max lift, and again at IVC. Won't be terribly accurate but it'll at least give me an idea. meh.

  7. #7
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    We used a cam degree wheel when a cam maker wouldn't give us detailed specs about the cams. But, we had a spare engine for this, it was much easier to do out of vehicle.

  8. #8
    Spoke with Mace again and they still couldn't/wouldn't send the intake cam card but they did say that the cam lobe profile is the same as the exhaust. I popped off the intake manifold and attempted to find out when the valves first start to open and close but I guess it's easier said than done - not so easy to tell when the valve has moved only a few mils. I also compared the factory cam profiles on a bench, aligning them with the locking tool (EN-48383) and traced the lobe profile of an intake and exhaust lobe on a piece of paper (again, not terribly accurate), but in the end I got kinda sorta similar numbers. Looks like the intake valves first start to open somewhere around 39 deg BTDC and finish closing around 53 ABDC, and are fully open around 83 BBDC. meh. (Edit: see post #22).

    Also found it interesting that the Bank 1 (passenger side) factory exhaust cam has "LLT" printed on it (the other three camshafts have "LFX" printed on them); wonder if the same exhaust cams were used in the LFX, and guessing the fuel lobe for the Bank 2 camshaft was different than for the LLT.

    I changed the Injection Boundary table to 512 in all cells but didn't notice a difference. As mentioned below I'm wondering if this table is not even used.

    Cold starts are much closer to the commanded EQ ratio now that I played with the SOI ECT Offset/Multiplier tables; just made sure that the injection wasn't starting before EVC and then increased injector pulse width as needed. I originally lowered the whole Multiplier table by 75% just to make sure SOI was never before EVC at any cells but turns out that was way too much, so ended up keeping the Multiplier table default except near operating temps (made those cells 0 so I can just refer to the SOI Base table) and adjusted the appropriate individual cells in the Offset table instead - looks like SOI on a cold engine definitely needs to be sooner rather than later, to give more time vaporize the fuel I guess.

    Also realized that after all this time (~4 weeks) I've been tuning an "old school" way by having the MAF disabled, and I could've run the MAF and tuned both at the same time (also turned DFCO back on and just filtering it out). Read through Smokeshow's thread in the Gen IV forum (saw this awhile back but had no idea what they were talking about then), and now that I understand it a bit better I decided to enable the MAF, and the EQ Ratio error I'm logging seems more much consistent. For awhile it seemed like I was going in circles adjusting the VVE, changing some cells from rich to lean, to rich, etc., and having some cells consistently rich or lean no matter how many times I adjusted them. Hopefully this speeds things up.

    Once the fuel is dialed in a bit more I'll work on adjusting the spark and then the valve timing. Put the factory spark table back in and am getting less knock; still get a tiny bit at WOT in first gear but not too worried about it, but am still getting more than I'd like to see when under heavy loads and lower RPMs. Not sure if it's real or not, seems cylinder 3 is always the leader, accounting for most (or all) of the knock, so reduced the sensitivity for it by 10% (believe the knock sensor is installed closest to #3 as well). In some areas (4400 - 5200 RPM especially) I'll see 3 - 5 deg knock, but even after dropping timing by 8 deg there I still see knock - I assume this is not real knock? Again, only happens under higher loads at lower RPMs, so I could just downshift to avoid it, if I can't get rid of it.

    As for the valve timing, came up with a setup that will have both intake and exhaust cams fully retarded by redline and will also start off with minimal overlap at low RPMs and linearly increase toward redline. I'll start here and see if the cylinder airmass/VE increases at all. Not sure if there's much to adjust here without a dyno so just gonna wing it and see how things go.
    Last edited by KillboyPowerhead; 05-31-2023 at 07:06 AM.

  9. #9
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    Also found it interesting that the Bank 1 (passenger side) factory exhaust cam has "LLT" printed on it (the other three camshafts have "LFX" printed on them); wonder if the same exhaust cams were used in the LFX, and guessing the fuel lobe for the Bank 2 camshaft was different than for the LLT.
    Most (if not all) aftermarket companies use OE cam cores as a starting point, and there's little difference between the LFX and later model LLTs, the main difference being the LLTs had the traditional exhaust ports, and the LFX has a single exhaust port.

    As for the valve timing, came up with a setup that will have both intake and exhaust cams fully retarded by redline and will also start off with minimal overlap at low RPMs and linearly increase toward redline. I'll start here and see if the cylinder airmass/VE increases at all. Not sure if there's much to adjust here without a dyno so just gonna wing it and see how things go.
    You really do need a dyno to know whether you're making improvements. Unless these cams change the valve event timing beyond lift and duration, you probably won't need too many changes, except to reduce overlap in cases where the OE phasing profile commands it (scavenging, economy, etc).

  10. #10
    The factory intake cam table (WOT) looks more or less what I would except: advanced at lower RPMs and is retarded more and more toward higher RPMs. The exhaust cam table, however, seems almost backwards to what I'd expect, being the most retarded at lower RPMs and increasingly advanced toward higher RPMs. Figured I'd keep the intake cam table profile similar but reduce the values some since I already have more overlap with the Mace cams. For the exhaust though I was thinking of almost reversing the profile, to start off fully advanced and delay it more and more linearly toward redline. Granted, with all this said I'm basing almost everything off of this post: https://forum.hptuners.com/showthrea...VT-Tuning-info

    Factory intake cam WOT.jpg

    Factory exhaust cam WOT.jpg

    Anyway, thanks again for the input. Will keep updating this thread as I tune.

  11. #11
    Went for a long (300 km) road trip and got the fueled dialed in pretty well; set cruise control to 100 km/h and stayed in 6th gear for about a minute, then went to 5th, 4th, 3rd, then bumped up the speed to 105 km/h and repeated all the way to 130 km/h, plus did a few WOT pulls from 100 km/h to 140 in 3rd and 4th; this let me get the fueling within 1 or 2% for 1600 to 5200 RPM and 0.60 to 1.00 or so pressure ratio. Also did a bunch of low RPM driving (1000 - 1400) where it tended to be very lean, and my take-offs were real choppy and "studdery", but taking off from a stop is much better now - little bit more and I'll probably take out the wideband and continue fine tuning with the factory O2 sensors. The VVE map sure is ugly, nothing like what I've seen on Gen III cars, but all seems to be dialed in fairly close.

    Still playing with spark and only get knock under higher loads and lower RPMs. If I do a WOT pull in 1st I get little to no knock but in 2nd or higher I see some, and the lower the RPM when I go WOT the more knock I see. Will continue to lower spark in the high cylinder mass areas but am otherwise still adding 1 degree at a time to everywhere less than 700 mg, should be back to factory timing soon and then I'll start increasing toward what my previous tuner did.

    Started playing with the VVT as well. Only made one change so far but before the scanner was showing about 800 mg cylinder airmass max at WOT and after this one change I'm see 820 mg; MAF also increased about 100 lbs/hr. Basically just retarded both cams a few degrees from around 4000 RPM to 7200. Pressure ratio briefly went over 1.00 too.

    Seems we can't adjust the VVE tables (directly) for specific cam angles, and only the main table (both cams set to 0 degrees) can be modified. I guess the other tables would only need to be adjusted if the lambda/AFR changes because you changed the VVT tables? But even then I guess once the VVT tables are changed and set, you more or less leave them alone so you would just retune your lambda and thus wouldn't have to necessarily adjust any of the other VVE tables anyway? In any case I played around with the coefficients and figured out the formula, so you could indirectly adjust the other VVE tables by adjusting the individual VE Coefficient tables. Believe I saw the formula somewhere on this forum but can't find it now so I'll repost here:

    [Constant]+([MAP]*MAP)+([MAP^2]*MAP^2)+([MAP*RPM]*MAP*RPM)+([MAP_Intake]*Intake*MAP)+([MAP_Exhaust]*Exhaust*MAP)+([RPM]*RPM)+([RPM^2]*RPM^2)+([RPM_Intake]*Intake*RPM)+([RPM_Exhaust]*Exhaust*RPM)+([Intake]*Intake)+([Intake^2]*Intake^2)+([Exhaust]*Exhaust)+([Exhaust^2]*Exhaust^2)+([Intake_Exhaust]*Intake*Exhaust) = VVE cell value

    Where:
    Square brackets = value in that coefficient table (value is for entire zone)
    MAP = MAP value (row axis) in VVE table (value for an individual cell)
    RPM = RPM value (column axis) in VVE table (other value for an individual cell)
    Intake = intake cam angle selected in VVE table
    Exhaust = exhaust cam angle selected in VVE table

    So I guess if you wanted to change an individual cam table you'd adjust the respective cam coefficient tables, leaving alone the Constant/MAP/RPM tables so as to not affect the main table.

    Anyone know the limits of the VVT tables? With the Mace cams I've gone up to 24 degrees on the intake cam and 18 degrees on the exhaust (didn't even think about turning these down after the cam install - good thing there were no clearance issues... Mace says the valve lift is 0.4400" whereas the factory cams are listed at 0.4252"). The factory cam tables go to a max of 24/24. I assume the exhaust can go as far as the intake (to 24+) but not sure. Also not sure if 24 is the max allowable movement or if they can keep going. The GM manual describes how the cam actuation works but doesn't mention what the limits are (FYI, both cams are at their home position of 0 degrees at TDC; positive numbers in the intake table mean they advance by that many crank degrees; positive numbers in the exhaust table mean they retard by that many crank degrees). I imagine there would be no clearance issues even with the Mace cams because otherwise if an actuation solenoid (or maybe a cam position sensor) were to fail the cam could possibly go full advance/retard depending on how it fails, and thus your engine would be trashed due to a relatively cheap/non-critical part failing, but who knows.

    Edit: factory cam settings have exhaust going to 24 degress retard, not 18.
    Last edited by KillboyPowerhead; 02-22-2023 at 09:15 AM.

  12. #12
    Haven't been able to do many WOT pulls to test different VVT settings due to weather but I'm making a bit of progress. I was leaving the intake cam alone and focusing on the exhaust, retarding it more and more (from around 3000 RPM to 7200), but airflow and VE seemed to get worse. I advanced the exhaust cam and started getting better results (better airflow and VE as per the scanner). I wonder if there was exhaust reversion due to the integrated exhaust manifolds; when cylinder 1, for example, is on its way down from TDC, cylinder 3 is on the exhaust stroke, and being only a few inches away from each other I wonder if cylinder 1 would suck in some fumes (exhaust valve still open until about 26 deg ATDC); retarding the exhaust will only make things worse.

    Regarding volumetric efficiency, out of curiosity I used a few different equations and calculators to figure out what my VE might be, and at higher RPMs I'm seeing around 120%. Seems high, but I used multiple equations/calculators and multiple data points from a given scan file and they all give me the same result, within a % or so. The VE in the scanner (units of mg*K/kPa) is showing a high of just over 2400, whatever that number means. Seeing over 2200 lbs/hr from the MAF, 2300 in one instance, and around 9300 Hz or so (this is all at high RPMs at WOT).

    I created a math in the scanner for comparison using the following equation:

    (([50040.70]*2)/(([50030.90]/(286.9*[2126.240]))*3.564*[50070.56]/60*0.001))*100

    50040.70 = mass air flow in kg/s
    50030.90 = MAP in pascals
    286.9 = a constant
    2126.240 = manifold air temp in kelvin
    3.564 = LFX displacement in liters
    50070.56 = engine RPM

    Used another equation based on CFM (corrected for air pressure and temperature) and in every case was within a % of the above equation:

    VE = (CFM*3456)/(CID*RPM)

    CFM = cubic feet per minute of air (used an online calculator for this; affected by air pressure and temperature)
    3456 = a constant
    CID = engine displacement in cubic inches

    Still have more testing to do, but as tunerpro mentioned it's looking like the cam timing profiles will end up looking pretty similar to the factory profiles, and mostly just need to be changed (lowered) to adjust overlap (and get rid of emission-related stuff if so desired, which I believe my last tuner did anyway).

    And from my last post I was wondering what the max movement of the cams is; not 100% sure but based on what I've read about similar engines there is 25 degrees of movement.

  13. #13
    I stumbled upon this video: https://www.youtube.com/watch?v=tLpSbaJpdb8

    The guy is troubleshooting fuel injection issues (LLT but I imagine LFX is similar) and has a scope hooked up to the injectors; if I'm interpreting it correctly it looks like the dwell time is about 0.3 ms. Can see how he hooks up the scope at around 20:00 and shows the schematic and waveforms at 30:00. As per the service manual the injectors are energized with 65V to help open them quicker and then are held open with 12V, so the waveforms in the video look somewhat representative of that description.

    Weather has been more cooperative so I've been able to do a lot more WOT pulls. Seem to get better results (more airflow/airmass, more torque as per "Delivered Engine Torque" channel) with the intake valve at 0 degrees/fully retarded at 7200 RPM (have been keeping the 4000 or so RPM and lower untouched and adjusting 4000 or so and up); hitting over 2300 lbs/hr on the MAF consistently and over 800 mg airmass (highest was 840 so far); saw over 300 lb/ft delivered torque too, however that's calculated.

    Also seeing up to 4.0 ms pulse width at ~6300 RPM and 3.8 - 3.9 at 7000 RPM which would put my EOI just slightly past 180? BTDC, so if needed I may increase the HPFP pressure a bit. The max commanded pressure is 15 MPa but the scanner is showing nearly 16.0 MPa at times so I may try increasing it by 0.5 MPa at the most (pressure relief is 17.5 MPa so will try to stay 1 MPa away from that). With that said, currently I have SOI set to EVC at the high RPMs so maybe now I can advance SOI a bit based on a 0.3 ms dwell time.

    Got a few more intake/exhaust combinations to try and then will start working on the mid range. After that will try adjusting the SOI as described above (based on piston velocity) and then also the spark, just to see what happens; not sure if I'll be able to notice anything without a dyno; figure I'll just use the scanner to measure my acceleration to see if there's any difference. meh.

  14. #14
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    GM loves their peak and hold injectors. Smart design.

  15. #15
    Tried a few more VVT combinations; so far my best result was as already mentioned, with intake and exhaust both set to 0 at 7200 RPM, with intake at 0 and exhaust at 3 degrees a close second; seeing over 2300 lbs/hr and over 9400 hz on the MAF; up to 840 mg airmass and 2274 lbs/hr dynamic airflow; over 120% volumetric efficiency based on the formulas posted above. Makes sense that the intake would be fully retarded at high RPMs but thought the exhaust would be better off more retarded for more overlap (at 0/0 there's no extra overlap), but as mentioned I wonder if that causes exhaust reversion and so not as much clean air can go into the cylinder; wonder if the LLT with conventional headers would benefit more from retarding the exhaust valve.

    Going to do more WOT pulls with my best combos to get repeat data and then adjust the SOI as described earlier and see if I can notice any difference. I mentioned earlier that my previous tuner adjusted SOI and that the stock numbers seemed closer to my theoretical ideal numbers, but after comparing his numbers again I think his were actually closer to my theoretical ones once I accounted for the 0.3 ms dwell time, within a few degrees in the few random cells I checked. Maybe he was on to something... Been using the stock numbers this whole time.

    Also wrote up a simple math to find out the latest SOI can be to make sure EOI is at 180 BTDC: (([50112.254]/(1/([50070.56]/60/1000)))*360)+180. More so useful for high RPM's/long pulse widths. Basically just converts pulse width to crank degrees.

    So far my fastest acceleration has been about 19 km/h over one second in first gear (11 km/h in second gear but could probably be faster now with different VVT settings). Was hoping I'd be able to get to a 0 - 60 mph in 5.0 seconds but not sure if that's going to happen, at least not with the lame factory rear end (3.27 gears, open diff), but might get close. GM's official time for the auto is 6.2 I believe so maybe I can get down to 5.2. Was also wondering if I could get an under 13 second quarter mile, but again would probably need 3.91 gears to get anywhere close. Plenty of other factors at play too of course, and also still have to adjust VVT at low/mid RPMs, spark, transmission, etc.

    Used a couple of formulas to guesstimate my HP out of curiosity and think I'm nearing 400 HP, maybe 390+. If that's the case that's around 110 hp/liter at ~7200 RPM, not too shabby. Also based on dyno charts I've seen (haven't seen any with the Mace cams, just full intake/exhaust/tune, with and without e85) a bolt-on LFX has a BMEP of over 15.0. Don't think there are too many stock engines out there putting out this kind of power and torque vs. displacement (just too bad the car is so heavy...). Will hit the dyno eventually, when I think I've found the best settings for VVT, SOI, spark based on the scanner data.

  16. #16
    Haven't been playing with the cams much lately mainly due to weather. Have been looking at how the VVE works though; noticed sometimes when I make a change to the table my lambda doesn't necessarily change. Read through https://forum.hptuners.com/showthrea...ation-for-gen4 again a bunch more times and realized that at steady state the MAF is mainly in charge and so I guess the VVE isn't necessarily used, hense why changing the VVE wasn't affecting my AFR sometimes.

    I've tried using Smokeshow's formula to tune the VVE but could never get reasonable data; it always said I was 20 to 25% rich at steady state and idle even though my lambda was right near 1.000 - even when changing the VVE by 20% the formula still showed ~20% rich. A few suggested comparing "Volumetric Efficiency Airflow" ([2311]) to the MAF as a way to tune the VVE (starting at post #164 in that thread), and after spending a day playing with formulas and numbers I saw that a VE can be calculated from an airflow, so comparing it to the MAF, assuming the MAF is accurate, makes sense.

    Using Smokeshow's equation GMVE_af = (MAP*GMVE/IAT)*RPM/60*4, replace GMVE_af with VE Airflow ([2311.71]) and work the equation to get "GMVE" (see equation below); if your MAF airflow and VE airflow are equal you should get whatever value is in your VVE table at that RPM/pressure ratio (using 3 instead of 4 if it's a V6; also use MAT instead of IAT if you have it). I guess that also means each cell of the VVE table represents total mg of air in the engine (take cell value and divide by 6 and you'll get pretty close to "cylinder airmass").

    I'm using the following math to tune the VVE (with a wideband at this time):

    ([2311.71]/[11.92]/[50070.56]/3*[2126.240]*60)*(1+(([16.71]*(1+(([50127.238]-[68.238])/[68.238]))-[2311.71])/[2311.71]))

    Basically calculating the VE that's used to determine VE Airflow and then multiplying by the difference between the MAF airflow and VE airflow. This will produce values that can be directly copied/pasted to the VVE table. Of course, must be at steady state and MAF must be accurate.

    Not sure if any of this is common knowledge but after reading through this forum for who knows how many hundreds of hours I'm just finding this out.



    Edit: after driving around some more it looks like the following math, as suggested in that thread, works better to dial in the VVE:

    (([16.71]*(1+(([50127.238]-[68.238])/[68.238]))-[2311.71])/[2311.71]))*100

    The other math gets you in the right direction but does so slowly, whereas this math and multiplying by % seems to dial in the VVE much quicker. Might have missed a factor in the first math because it seems like the numbers generated are pretty much half of the difference that this new math provides, so it's like using this new math but multiplying by half % every time instead of full %.
    Last edited by KillboyPowerhead; 04-06-2023 at 08:56 AM.

  17. #17
    Just to add to my last post:

    Something that slipped my mind was the fact that you can't adjust individual VVE tables for different cam angles, and so you need to consider the intake and exhaust cam angles when adjusting VVE. If using my math above, you might see that a particular cell should be 1000, for example, but if that's during a time when the cams aren't both at 0 then you wouldn't want to change that cell in the base table to 1000, but rather work the cam coefficients (post #11) such that that particular cell for those particular cam angles is 1000.



    Can't find much info on how to tune the different VVE tables when you can't adjust them directly so not sure what is the best way to do it... Anyone have any input? I'm thinking I'll just set the cams to 0 across the board and dial in the MAF and base VVE table as close as I can (since all tables reference the base table/non-cam coefficients), and then to adjust the individual cam tables I'm thinking it'll be a set-and-forget type scenario where you figure out where you want the cams to be, adjust the coefficients to best suit each applicable table as needed and then just live with it - and with that said, I noticed that when changing a particular zone to suit one set of cam angles, another set of cam angles in that zone that was already off a bit became even farther off... So I guess a compromise is in order...



    Although I guess when it comes to steady state driving and WOT pulls the MAF is primarily used so maybe having the individual cam tables accurate isn't too big a deal.

  18. #18
    Just a quick update for anyone who cares:

    Using the new tuning method I got the MAF and VVE dialed in pretty well for where I regularly drive but still need to go on a road trip to fill in the rest of the VVE. My takeoff from idle is smoother now so this method seems to work.

    For the cams, going to do some steady state driving at 2k, 3k, 4k, 5k RPM (will consider 6k and 7k RPM based on WOT pulls) for a bunch of different cam settings and see where the airflow/airmass is highest (using both cams at 0 as a base), then from there I can fine-adjust the cams, and once the cams are set I can adjust the individual cam angle VVE tables as needed. Will test the cams every 5 degrees, from 0/0 to 20/20, 25 combos total, as the VVE tables only go up to 20 degrees for some reason (as mentioned I believe the cams can go up to 25 degrees, but I also haven't confirmed it's safe for either cam to go to 25 with these cams - probably is but not willing to find out via trial and error...). All the previous testing I did with WOT pulls is still good since the higher RPM fueling was dialed in fairly well, so more so adjusting the lower/mid range now.

    With the fueling and cams set I'll get the car dyno'd with a few different tunes, keeping the fueling and cams constant and trying different spark and SOI tables to see if there's any difference (or just have them dial in the spark if it's not too much time/money); will test my SOI compared to the factory's and my previous tuner's; and the factory spark vs. the tuner's.

    Regarding cylinder airmass, made a comment about this earlier in the thread, and after thinking about it it was pretty easy to figure out where it comes from:

    MAF/(RPM/60)/3 = cylinder airmass

    MAF in g/s will get you airmass in grams. Not sure if "cylinder airmass" comes from MAF airmass or dynamic airmass (or something else) but if the MAF is dialed in it'll work out. Started thinking about this while looking at the cam and spark tables, wondering what airmass exactly they're using (guessing based on dynamic airflow as that is the final airflow used in calculations, or so I've read).

  19. #19
    Another update.

    Think I got the intake cam settings figured out pretty well; just one more test to do then will start playing with the exhaust cam. Also thinking it makes sense to keep the intake cams where they are while I adjust the exhaust cams instead of resetting back to 0 like I originally planned - I'm guessing adjusting the exhaust cams doesn't have much of an effect on the intake cam profile. I'll adjust the exhaust cam in 5 degree increments like I did the intake, leaving alone the intake, and once I've figured out the profile for the exhaust cam I'll just make a few more slight adjustments (keeping the overall profile similar but changing the slope slightly) to both intake and exhaust just to see if there's any difference and then call it where ever I see the highest airflows.

    Also going to do similar testing at the cruising areas for fuel economy purposes (guess I could've been doing that the whole time... been focused on WOT). Will adjust the cams a couple degrees at a time and see if the airflow increases or not. Noticed with the intake set to 20 degrees while cruising (60 km/h in fourth gear, for example) my airflow was quite a bit lower than at 5 or 10 degrees (around 12 g/s compared to 17 or so, same pressure ratio). Got the cruising areas set to 0 again to readjust the MAF since I've been adjusting it a bit with the cams, then will go from there.

    Also noticed I was getting tons of knock (over 10 degrees at times) at lower RPMs and medium loads (like when getting on the highway gradually in third gear), and got worse as I advanced the intake. Not sure if it's partly because the exhaust is at 0 or if the engine really doesn't like the intake so advanced there. In any case as mentioned I set that area back to closer to 0, and there's no need to be so advanced there anyway (worse airflow).

    With the cams figured out and the fueling dialed in for both cams at 0/0 (MAF and VVE) I can then start playing with the VVE cam coefficients to finalize the fueling and then will schedule some dyno time to help with spark. Can definitely see the affect retarding the spark has on power; seem to get a lot of knock at 5200 during WOT and there is an obvious change in slope around there on the charts for RPM, speed, airflow, etc. where I retarded spark a fair bit.

  20. #20
    Think I may have the cams dialed in pretty well, although it's hard to tell because the data is somewhat inconsistent: the one cam settings that gave me the best airflow a couple of months back (was seeing up to 9400 hz on the MAF, up to 290+ g/s and 840 mg cylinder armass), I recently went back to but was only getting up to 9100 hz, 800 mg airmass (morning), and then the next day (afternoon) got about 9100 hz and 770 mg airmass. The rest of the tune was the same or very similar, so I'm wondering if the ambient air temp is to blame for the mixed results. Looked at logs of before I started adjusting the cams and was seeing 9200 hz but air temps were even colder than when I saw 9400.

    From what I understand, as air passes by the MAF sensor the sensor cools, reducing the resistance and increasing the current and thus frequency output, so I guess it makes sense that I'd be seeing higher airflow/frequency when air temps are lower. Temps have been consistent lately and I've tried quite a few cam settings, peaking a little over 9200 hz, 275 g/s, 800 mg airmass at 294 - 300 K intake temps and 308 - 314 manifold temps. MAF and VVE are dialed in pretty well I think, at least everywhere I actually drive. With the volumetric efficiency calculation I've been using I'm seeing 120% to 125% the whole time during WOT which is the highest I've seen.

    Seeing a change in slope in RPM for the worse at around 6300 RPM and that's where I have the exhaust cams change from 3 to 0 degrees, and in other logs where I maintained the cam position to redline the RPM rate of change stayed consistent, so going to play with this a bit more but otherwise I think the cams are in a pretty good spot - maybe not perfect but at this point and after dozens of trials I'm starting to not care as much either... too many variables when driving on the street, especially over a few month's time. Any settings where I saw a higher MAF frequency the temps were 10 to 20 K colder, so think I'm gonna call it here - maybe slight adjustments here and there but done with the main trials I think. The cam settings ended up being a similar profile to my already-tuned settings which I guess is somewhat expected since the Mace cams are very similar to the stock ones (same centre line, about the same lift, just longer duration).

    Going to play with the SOI again (been using stock for awhile), starting it as early as I can to finish by 180 BTDC and as late as EVC, and judge based on the rate of change of the RPM. Also playing with PE EQ ratio; was reading that this engine may prefer a leaner PE; been running at 0.85 lambda/12.5 AFR this whole time so will try going up to 0.88/13.0 and as low as 0.83/12.2.

    Got the spark table back to stock and not seeing much knock, only a bit when at WOT, especially in higher gears, but not too worried as I can just down shift. Been using 91 this whole time but thinking of switching to 93; will only cost a few hundred $ more over the course of a year so fudge it; will test the same way as with the SOI and PE: make a change and see if the engine revs up quicker.

    Will update again if/when I find anything noteworthy. Once I'm satisfied with everything and/or just can't stand doing this anymore I'll hit the dyno.

    Edit: changing the exhaust cam from 0 to 3 to redline definitely brought up the RPM rate of change. Will keep making minor adjustments to the cams to see if there is anything left to get out of them.

    Edit 2: recently did a WOT pull at ~281 K intake temps, ~294 K manifold temps (nearly 20 degrees C cooler than mentioned above) and hit over 286 g/s airflow on the MAF, almost 9400 hz and up to 843 mg airmass, the highest airmass I've seen. Temperature definitely makes a big difference in what the MAF sees (airflow and airmass up over 5% for a 20 deg C difference). Been able to go from 4000 to 7000 RPM in about 1.82, 1.83 seconds with the current tune (afternoon/warm temps); will see what SOI/PE/spark gets the best results and then will update. Doing several WOT pulls with each configuration at roughly the same temps, so may take a few weeks to try everything.
    Last edited by KillboyPowerhead; 05-17-2023 at 08:09 AM.