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Thread: LFX Fuel Injector Dwell Time

  1. #21
    Did multiple WOT pulls with two different SOI settings, as described above: one early where SOI was set so injection would finish near 180 BTDC from 4000 - 7000 RPM, and one late where SOI was set to EVC (plus 0.3 ms dwell time). With the early SOI I was seeing the RPM go from 4 to 7k in about 1.82, 1.83 seconds and with the late SOI I was seeing 1.71, 1.72 seconds. Seemed somewhat repeatable taking into account air/manifold temps, same road every time. Also found a few papers suggesting earlier SOI is better for torque/power as it results in greater cylinder pressure, although in both cases they only advanced to 300 BTDC and no further.

    Going to test a few different PE settings and then update again.

  2. #22
    FYI did some more looking around for factory cam specs; still can't find anything specific about the LFX but did find specs for the LY7/LLT.

    At 0.006" lift:

    EVO = 49 BBDC
    EVC = 9 ATDC
    Centreline = 70 ABDC
    Duration = 238 (0.006" lift)

    IVO = 14 ATDC (typo in the Cadillac forum)
    IVC = 71 ABDC
    Centreline = 48 BBDC
    Duration = 237 (0.006" lift)

    As mentioned I got the cam card for the Mace exhaust cam and it also shows a centreline of about 70 ABDC. Assuming the LFX intake has the same centreline that means for the Mace cams at 0.006" lift IVO = 1 ATDC and IVC = 83 ABDC (about 262 duration at 0.006"; Mace told me that the intake cam has the same profile as the exhaust). (post 34)

    Edit: adding the Mace cam cards since I hadn't before. As mentioned, the exhaust cam was provided by Mace via email, and the intake should be as this if it has the same centreline as the LY7 and LLT cams - if not, then since the Mace cams share the same profile, I guess whatever the centreline actually is the open/close values would just shift by that difference. Used the above 0.006" lift numbers as a reference so these numbers won't be exact.

    Mace cam cards.JPG
    Last edited by KillboyPowerhead; 05-31-2023 at 09:35 AM.

  3. #23
    Tried a few PE settings (0.885, 0.865, 0.85 lambda, or 13/12.7/12.5 AFR) and didn't notice a big difference between them, although if anything I think 0.85/12.5 performed a bit better, and this is also where my previous tuner (Overkill) set it so I'm going to leave it there. Read that a higher AFR can help reduce knock but didn't notice much difference - sometimes I got a couple degrees knock with 13.0 and sometimes none; other times I'd get about the same knock with 12.5 and sometimes none.

    For the SOI, as mentioned it seemed like an earlier SOI (higher number) performed a bit better. All said and done my numbers aren't too far from factory. Using the math below (think I posted this earlier) you can find where SOI needs to be to finish before 180 degrees BTDC. Knowing the Mace exhaust cam closes at ~334 BTDC (minus VVT settings), you can basically keep the factory SOI table except where the numbers are past EVC, in which case set to 334 - [VVT settings], and then if the math says your SOI needs to be even earlier than this you can add the 0.3 ms dwell time (0.36 degrees per 200 RPM). In my case, for 5000 RPM and up I'm only 1 - 5 degrees earlier than stock.


    Attaching my cam tables too. Haven't been to a dyno yet so can't say that these tables are ideal and I'm sure they're not perfect, but I seem to be getting the best airflows with these settings. As tunerpro mentioned, the profile of the tables is pretty similar to the stock tables at WOT. These tables are also fairly consistent with the trials I did as described in an earlier post (setting the whole table to 0, then 5, then 10, etc.).

    Intake cams current.jpgExhaust cams current.jpg

    Going to fill up with 93 now (been on 91 this whole time) and start adjusting spark. Currently using the factory table but going to slowly transition to what Overkill did and see what happens, and then schedule a dyno. Will update again if I see anything with changing spark. I suspect there are gains to be made since the recommended fuel is 87 and thus the factory spark tables will be tuned as such.

    Edit: just re-read a thread about how the VVT acts in these engines and immediately realized I hadn't been taking into account the fact that the cams are being adjusted in cam degrees while the SOI table is in crank degrees. So whatever the VVT table says you'll need to double that when adjusting the SOI when trying to inject right at/after EVC. D'oh.
    Last edited by KillboyPowerhead; 06-08-2023 at 10:36 AM.

  4. #24
    Just a quick update. Been adding spark back to where Overkill had it for 91. In the WOT areas, high RPMs I've added around 4 degrees or so compared to factory and am seeing a bit of improvement, engine revs from 4k to 7k in about 0.02 - 0.03 seconds faster based on a few WOT pulls, similar ambient temps. Will fill up with 93 next tank and add a couple more degrees to see what happens. Not significantly quicker but quicker nonetheless.

    Looking through the forum for anything I can find on Mace cams for the LFX or even LLT and there doesn't seem to be many positive things said. Unfortunately I didn't do much scanning before the cams, but I do have a scan from when I sent one to Overkill to do a recheck/retune (so had Overkill's original tune, full intake and exhaust) and was seeing up to 720 mg cylinder airmass; looking at a scan from a few months ago with similar intake/manifold temps but different tune (was still working on it, so different cams, SOI, spark, and I believe less optimal than now) and I was seeing over 800 mg airmass, up to 840, so over 10% gain from factory cams (also saw over 10% more on the MAF, and haven't made significant changes to the MAF in those high frequency areas). Not sure how that translates in terms of extra power/torque, but they're advertised as 40+ HP at 6800 RPM and they keep making power past that, so wondering if I'll see 50+. Will schedule a dyno soon, when I'm done with the 93 octane spark.

  5. #25
    Another update.

    Still haven't gone to a dyno yet but plan to soon - been busy enjoying the summer while it's here.

    Also decided not to bother with tuning 93 since some of the stations I frequent don't have 93, so 91 is good enough.

    When I first installed the cams I got the P0420 code and figured it was due to running rich (was 10 - 15% rich across the VVE table when I first started tuning), but now that the fueling is within 2% everywhere, the factory O2 sensor is back in and I haven't been downloading a tune every day (engine light/codes reset), the code eventually came back. Did some reading on how O2 sensors work and it looks like my post cat sensors are indicating that the cats are functioning properly as they show a mostly constant voltage, but the voltage is a bit high. While driving at steady state, bank 1 is averaging about 765 - 770 mV while bank 2 is averaging 690 - 695 mV. I'm not getting a P0430 code (bank 2) so I wonder if the code triggers when the average voltage is over 700 or 750 mV. Unfortunately I didn't do much logging before the cams so not sure what the voltage "should" be. I also have high-flow cats from Solo but have been running these for a few years with no codes, and it was only a few weeks after installing the cams that the code popped up.

    Noticed in one log that when the intake cams advanced (when from cruising to ~50% throttle) the post cat voltages dropped, so I added 4 degrees to both intake and exhaust in the cruising areas (extra 8 degrees overlap) and the voltages for both banks started averaging under 700 mV during the same cruising speed as before.

    Anyone know if adding extra overlap is a solution to the P0420 code? Is the higher voltage indicating that I should be adding more overlap? Or is a higher voltage just a result of the high-flow cats and cams (and/or VVT tuning), and there isn't necessarily anything wrong with having a higher voltage? I'm guessing the voltages raised a bit after installing the cats compared to factory but as mentioned I didn't do any scanning. I know I can just turn off the MIL/set to No Error Reported, but not sure if this would still prevent me from remote starting (code hasn't come back since I reset it yesterday so I can't confirm, but guess I'll find out in a few days). Will post this in the V8 forum as well since it'll get more attention.
    Last edited by KillboyPowerhead; 08-22-2023 at 07:22 AM.

  6. #26
    Tuner in Training
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    Apr 2023
    I've got a 2016 LFX in a canyon with the same aftermarket tune. I'm here with ya.
    Haven't started re-tuning mine yet, working on two other motors right now.
    I have the Performance Trends software and used it to simulate optimal cam timing for an L83, it has worked out very well.
    If you can re-iterate the OEM and Mace specs I can work on starting to building up the engine model and eventually tell you what the best settings will be.

    With the Gen 5 V8, the cam phasing was very convoluted, the cam has advance ground-in and you specify the amount of retard from "home position", how is the cam phasing represented in these ECMs?

    Have you been able to find any flowbench data on the heads, or geometric info on the intake (runner length / diameter)?
    I need all the engine specs like stroke, bore, valve size, CR etc to build the engine model.

    Using MAF will vary by air density, if corrected to VE you can actually use VE as a comparison, but honestly it's not worth much. Optimal cam timing has more to do with optimizing valve events and don't represent much of a CFM change. In reality your CFM is just a byproduct of displacement/intake duration/intake lift/head flow..... None of which vary with cam phasing.

  7. #27
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    Apr 2023
    Does this engine use the same VVE concepts as the Gen 5 V8?

  8. #28
    I've spent many hours looking for the LFX cam specs but never found them (they're not even in the GM manual), but did find LY7/LLT specs and then used them plus the exhaust cam card from Mace to figure out the intake cam specs, although there was some guess work involved. See post #22 for details.

    Never looked for flow bench data but in general there doesn't seem to be much info out there for the LFX. I guess you'd need geometric data for the whole intake system? I'm running the K&N Typhoon CAI, 80mm throttle body and the manifold spacer by Jacfab, and the TB, manifolds and spacer have all been modified/ported, so not sure how that would affect the measurements/air flow/dynamics.

    Not sure what VVE concepts you're referring to exactly but the E39A is a Gen V ECU so I imagine it's very similar to the V8 ECU's.

    I can get you whatever engine specs are in the manual if you'd like.

  9. #29
    Tuner in Training
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    Apr 2023
    If you could send me the shop manual that would be great.
    Otherwise I'd need: int/exh valve diameter, compression ratio, bore diameter, stroke, rod length, OEM HP/TQ (dyno plot even better).
    Geometric data like port diameter and length, and intake runner dimeter and length are useful in estimating the intake tuning, but I can make guesses if needed.
    If you are willing to take off the manifold then I would also want measurements of your modified components as well.

    From post #22, adding an additional 30-degrees of cam timing should make a substantial difference to the TQ/HP, have you noticed a substantial improvement?

  10. #30
    Unfortunately I didn't do much logging before the cams, but I did find one log that I sent to my original tuner (had same intake/exhaust as now but no cams) and under similar conditions (similar manifold air temps) I was seeing 10 - 15% more airflow from the MAF (~2300 lbs/hour vs. ~2100 lbs/hour at/near redline) by the time I found what seemed to be the best cam positions (post #23), so a pretty good increase I guess. You can adjust the cams up to 25 degrees.

    Haven't been to the dyno yet but will schedule eventually... been kind of waiting until later in the year when the air temps are cooler as that's when I did most of my cam tuning. meh. Once I have a dyno chart to reference I may go back to playing with the tune a bit, see if I can squeeze a bit more out of 'er.

    If you have an email (your user name?) I can send you a PDF.

  11. #31
    Tuner in Training
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    Apr 2023
    yea, for some reason my username is my email and I can't change it. thanks!

  12. #32
    Tuner in Training
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    Apr 2023
    Okay, I have my computer back up and running now. Reviewing the cam card I see 0.25669" cam lift, but what is the cam follower ratio?
    ie: what's the valve lift at 0.25669" cam lift

    From the maintenance spec sheet it seems like the OEM cam has a valve lift of 0.4252"

  13. #33
    Are you referring to rocker arm ratio? If so, I think it's listed as that in the manual; don't have it in front of me but I believe it's 1.65:1 which I guess also would make sense (0.4252"/0.25669" = ~1.65. Valve lift of the Mace cams and factory cams is the same).

  14. #34
    Tuner in Training
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    Apr 2023
    oh crap, the MACE cams only have 0.4252" lift?
    I assumed they must have increased the lift closer to 0.5" and back calculated a 1.9 ratio. I'll go back through the exercise with 1.65.
    With the lift just shy of 0.5" I was getting very different cam phasing than what's printed on the cam card and modelled +10 HP at 6750 and +35 ft-lb at 4250 RPM versus the cam card phasing.

    The piston to valve clearance will be tight on the exhaust valve so you'll want to compare the recommended exhaust phase angle versus what you've already ran.
    When I revise and post the recommendation keep in mind these are lobe centre line angles... Sometimes the computer is programmed by difference from "parked", so I'm not sure what you need to program to achieve the phasing.
    I've done this on an L83 already and the difference was immediately noticeable everywhere, I would expect a much greater improvement here.

  15. #35
    Sorry, just remembered that Mace advertises the lift as "standard" (which I take it to mean stock?), but via email they told me that the valve lift is 0.4400". I think I measured the Mace cam lobes with calipers but not sure if I still have that number written down...

  16. #36
    Tuner in Training
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    Apr 2023
    I'll work with 0.440", that's 1.7x so it makes sense...

  17. #37
    Tuner in Training
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    Apr 2023
    Here's what I found in my analysis. These are actual degrees, I'm not sure what you need to program.

    The low speed cam setting results in 17.8 in-hg of vacuum, GM usually specs 20 in-hg. If you don't like the idle quality you can add degrees to each cam setting evenly at low RPM if you like.
    You can transition in stages as I've detailed below, or make a smooth continuous blend.
    The ideal cam phasing is the same at a given RPM, the phasing changes GM makes at various MAP/MAF for a given RPM are just trying to perform EGR.

    Intake CL: 110 ATDC
    Exhaust CL: 120 BTDC

    transition from 2k -> 2.5k

    Intake CL: 100 ATDC
    Exhaust CL: 115 BTDC

    transition from 3k -> 4k

    Intake CL: 100 ATDC
    Exhaust CL: 110 BTDC

    transition from 6k -> 7k

    Intake CL: 115 ATDC
    Exhaust CL: 105 BTDC

  18. #38

    Does CL mean centerline? If so, the exhaust cam centerline at home position (VVT at 0 degrees) is ~72 degrees ABDC, or 108 BTDC. The exhaust cam can only retard so I wouldn't be able to advance past 108 BTDC, and could retard as late as 83 BTDC, or 97 ABDC (VVT can adjust up to 25 degrees). This would put the VVT settings as 0 degrees from 0 to 4 or 5k RPM, then toward 3 degrees at 7k (if I'm reading your chart correctly).

    Likewise with the intake cam, centerline at home ~48 BBDC or 132 ATDC and it can only advance, so I could move it from 107 ATDC to 132 (25 degrees max). VVT settings would be 22 degrees below 2k RPM, then 25 to 4k RPM, then toward 17 at 7k RPM.

    In my testing I found the intake cam needs to be fairly retarded at the higher RPM's, otherwise airflow was noticeably lower. Currently have 7 degrees at 7k RPM as opposed to 17. Otherwise I think my settings are similar to yours (kept at 22 but could advance more). The exhaust cam seemed to respond better being more advanced at higher RPM's, however, as opposed to retarded - my guess here is due to the integrated exhaust manifolds creating exhaust reversion (the adjacent cylinders suck in the exhaust because they're so close together). I wonder how the LLT cam settings differ with these cams... haven't spoken with anyone who's tuned these on an LLT.

    Perhaps I'll try dropping the exhaust cam to 0 at the lower/mid RPM's and see what happens. I believe I kept the lower/mid RPM's more retarded because that's what my previous tuner did, and I remember not noticing a significant difference between 0, 5 and 10 degrees here, so kept a similar profile to the stock/previous tuner's tune.

    Thanks for the input!

  19. #39
    Tuner in Training
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    Apr 2023
    You're right, CL is centerline.
    There's two basic concepts, Lobe Separation Angle and cam advance.
    In the DOHC world people tend to view the intake and exhaust cam as being independent, but they are very much interacting with each other.

    Lobe Separation Angle is the angle between both cam lobes, numerically you take the the CL's and average.
    Tighter LSA results in more overlap and generates more torque and power, up to a point.

    Then there's cam advance, advancing the cam below peak torque increases output, and retarding the cam above peak torque increases output.
    Volume flow isn't always highest at peak output because you can over-scavenge where fresh air passes right through the cylinder during overlap, expansion ratio can also be affected... Essentially, the dynamic compression ratio changes with cam phasing and it's possible a lesser volume flow can actually produce more power, this is why dynos are used and not just flow meters.

    My simulation made a number of assumptions, but it should be pretty close.
    You can see that I was finding 107 to be the ideal LSA below peak torque, 105 ideal in the mid power band and 110 at high RPM.
    The wide LSA of 115 was a recommendation to keep vacuum high.
    In a pushrod engine you would have to chose a single LSA, some LS and all Gen V allow you to advance/retard the cam to a very effective benefit.

    I'll take another look given the phase angle constraints you mention and see what comes out.
    The way things work the lobe phasing should be very close to optimal for the OEM and MACE cam, but the MACE increased overall torque slightly and moved peak torque up to a slightly higher RPM as a result of the longer duration.