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Thread: OP cam angles and ignition timing interaction

  1. #1

    OP cam angles and ignition timing interaction

    Hello. I think it goes without saying that changing OP cam angles will -probably- require changing ignition timing as well right?

    I did some testing on my near stock 2014 GT. My pulls were pretty consistent and were 3rd gear only from roughly 3000 to 7000 each time. I made about 2 pulls with the stock cam angles and 2 with custom ones (not sure if they were better or not which is why I was testing). The stock angles gave me consistently less ignition timing ability than my custom ones which seemed to be screaming for more ignition timing lol...

    Theorists please chime in. Why does changing cam angles at WOT allow more or less timing before detonation?? I wasn't getting any detonation at any point ever, however the knock advance was only adding a little timing on stock angles and hitting the advance limits on my custom ones LOL

  2. #2
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    Cylinder pressure. Changing the cam timing changes cylinder pressure. More cylinder pressure less tolerated timing before preignition.

  3. #3
    Advanced Tuner CCS86's Avatar
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    That seems to suggest that the stock angles were filling the cylinders better.

    Spark advance knock threshold generally goes up, as cylinder pressure goes down (less filling).

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    If MAF is higher, I'd say unaccounted for, excessive blow threw, giving the ecu false info, putting it in a safer than necessary point in the calibration.

    Did you need to adjust MAF because fuel trims started going lean from your changes?
    Near stock 14 at peak you should be in the low 40lb/min range at best.

  5. #5
    Advanced Tuner CCS86's Avatar
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    I did a bunch of testing based on the assumption that blow-through (especially on my boosted application) would show up as a false lean condition. I did not validate that theory. Even at 10 psi of boost, I saw no STFT difference between 0* overlap and 50*. My best guess is that when you start with a well ratioed intake charge, a fraction of charge getting blown past the exhaust valve combusts inside the exhaust before reaching the O2 sensor.

    In this case, a false lean condition gets quickly corrected to rich, which is actually more knock prone.

    Blow-through would definitely reduce trapped charge, lowering dynamic cylinder pressure, and reducing the tendency to knock. It's most likely a net power loss any way you slice it.

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    It's the intake being to advanced that causes it. 11-14 are more prone due to their phaser not being mid lock.

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    Advanced Tuner CCS86's Avatar
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    Quote Originally Posted by murfie View Post
    It's the intake being to advanced that causes it. 11-14 are more prone due to their phaser not being mid lock.
    What is the "it" you are referring to?

  8. #8
    After reviewing the logs and plotting out a MAF comparison it would seem even though my angles were different I still made the same power. My custom angles from 4000-7000 in my test were BOTH more advanced on the intake and exhaust timing. The overlap was nearly identical with a little LESS overlap (than stock angles) at higher RPMs. One thing is sure... the VCT definitely affected ignition timing tolerance. IF my custom angles created less pressure, than the car saw this and added more timing to compensate resulting in the same power output..... What do you all think?

    This plot is a little excel program I created to treat MAF as HP, and calculate a torque line as well. I also have one that gets the engine brake torque from 2 logs and plots it out the same way. Blue is the stock cam angles and Red is the custom. HP and TQ lines. The conditions of these 2 runs despite totally different angles were near identical.. Every temp and also the fuel trims. For a few moments I thought I blundered and was looking at the same log lol.

    I've read on these forums from a guy who swears that STOCK cam angles are the best after a lot of testing. I have yet to see otherwise in truth... but maybe I need to get more radical to see a difference in power or is it pointless with axleback and a 4C as my only mods...


    OPTimingCompare3_4.JPG
    Last edited by blackbolt22; 2 Days Ago at 11:49 PM.

  9. #9
    Quote Originally Posted by murfie View Post
    If MAF is higher, I'd say unaccounted for, excessive blow threw, giving the ecu false info, putting it in a safer than necessary point in the calibration.

    Did you need to adjust MAF because fuel trims started going lean from your changes?
    Near stock 14 at peak you should be in the low 40lb/min range at best.
    Fuel trims looked near identical in all of my runs. Many times the % was exactly the same throughout the RPMs for each bank however my angles are far from stock! I went in the direction of a little less overlap in the 6000-7000 range.
    I flowed 43.35 lb/min on the MAF before I let off at 7000 exactly. Axle back mufflers is the only 'performance' mod other than my 4C

  10. #10
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    "It" was referring to blow through.
    Just to be clear, its only the peak cylinder pressure that determines the fuels knock threshold. BMEP can change and still have the same peak pressure.

    I would be shocked, but it would be amazing, if instead of DI injectors the new GT500 came with cylinder pressure sensors and no knock sensors.
    No evidence, but I don't think the PTWA lining stands up well to mild detonation. Also with DI and PD boost LSPI could be an issue.
    Last edited by murfie; 2 Days Ago at 02:25 AM.
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  11. #11
    Advanced Tuner veeefour's Avatar
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    Quote Originally Posted by blackbolt22 View Post
    After reviewing the logs and plotting out a MAF comparison it would seem even though my angles were different I still made the same power. My custom angles from 4000-7000 in my test were BOTH more advanced on the intake and exhaust timing. The overlap was nearly identical with a little LESS overlap (than stock angles) at higher RPMs. One thing is sure... the VCT definitely affected ignition timing tolerance. IF my custom angles created less pressure, than the car saw this and added more timing to compensate resulting in the same power output..... What do you all think?

    This plot is a little excel program I created to treat MAF as HP, and calculate a torque line as well. I also have one that gets the engine brake torque from 2 logs and plots it out the same way. Blue is the stock cam angles and Red is the custom. HP and TQ lines. The conditions of these 2 runs despite totally different angles were near identical.. Every temp and also the fuel trims. For a few moments I thought I blundered and was looking at the same log lol.

    I've read on these forums from a guy who swears that STOCK cam angles are the best after a lot of testing. I have yet to see otherwise in truth... but maybe I need to get more radical to see a difference in power or is it pointless with axleback and a 4C as my only mods...


    OPTimingCompare3_4.JPG
    Well they are the best - at least in Coyotes. I'm sure Ford does a great job in the lab.

    I see people swearing they have tweaked cams and gained 30-40 hp boosted - which might be the case but it doesn't mean you found a better set of cam angles.

    Keeping it simple - you have the best possibile cam angles for your stock N/A engine in your stock tune - period.
    Best possible cylinder pressure, just right before knock threshold. They might need a minor tweak for high RPM(intake manifold) in axis and that's all.

    Now while boosted things might get complicated and they need to be changed - again not that you will find the best possible angles but the angles in which engine is happy under boost.
    Take a look at the +2015 intake cam angles - 40 degree advance?!? This is crazy in the automotive world and it works only because IMRC is there. You remove IMRC, change cams or add
    boost and the engine can't swallow that crazy intake cam advance anymore. You literally have to make things worse - by putting an "ineffective" set of angles in your tune...
    Last edited by veeefour; 2 Days Ago at 03:01 AM.

  12. #12
    Quote Originally Posted by veeefour View Post
    Well they are the best - at least in Coyotes. I'm sure Ford does a great job in the lab.

    I see people swearing they have tweaked cams and gained 30-40 hp boosted - which might be the case but it doesn't mean you found a better set of cam angles.

    Keeping it simple - you have the best possibile cam angles for your stock N/A engine in your stock tune - period.
    Best possible cylinder pressure, just right before knock threshold. They might need a minor tweak for high RPM(intake manifold) in axis and that's all.

    Now while boosted things might get complicated and they need to be changed - again not that you will find the best possible angles but the angles in which engine is happy under boost.
    Take a look at the +2015 intake cam angles - 40 degree advance?!? This is crazy in the automotive world and it works only because IMRC is there. You remove IMRC, change cams or add
    boost and the engine can't swallow that crazy intake cam advance anymore. You literally have to make things worse - by putting an "ineffective" set of angles in your tune...
    I believe you about stock angles being the best for a stock engine however I do wonder why the exhaust op angle is 15 degrees retarded from mid to peak RPM, 3000-6500? I would expect something like 15 15 15 14 13.

    Also when I got my car I called some companies to ask if there were any gains to be had on a bone stock car like mine with a tune they all said not so much at peak RPM but definitely throughout the curve... as if Ford left a lot on the table as far as cam timing. Were they just trying to sell me something?

  13. #13
    Advanced Tuner veeefour's Avatar
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    Stock mani stock CAI there's almost nothing to gain with VCT tuning even throughout the curve. There's something but we are talking about 3-5 hp so it's not worth the hassle.

    The power comes from removing a buch of limiters in my experience and those tiny differences people trying to justify with MAF gains are simply environmental errors.

    Put a mani and CAI on it and yes you can gain a bit more throughout the curve - in a fact you should, you should work your way through the OP tables to make your new power-band happy.

    Then again don't expect 30hp form VCT tuning. Take a look at Ford's Power Pack 3 for S550 with GT350 mani and CAI - VCT is 100% the same.

  14. #14
    Advanced Tuner CCS86's Avatar
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    Quote Originally Posted by blackbolt22 View Post
    After reviewing the logs and plotting out a MAF comparison it would seem even though my angles were different I still made the same power. My custom angles from 4000-7000 in my test were BOTH more advanced on the intake and exhaust timing. The overlap was nearly identical with a little LESS overlap (than stock angles) at higher RPMs. One thing is sure... the VCT definitely affected ignition timing tolerance. IF my custom angles created less pressure, than the car saw this and added more timing to compensate resulting in the same power output..... What do you all think?

    This plot is a little excel program I created to treat MAF as HP, and calculate a torque line as well. I also have one that gets the engine brake torque from 2 logs and plots it out the same way. Blue is the stock cam angles and Red is the custom. HP and TQ lines. The conditions of these 2 runs despite totally different angles were near identical.. Every temp and also the fuel trims. For a few moments I thought I blundered and was looking at the same log lol.

    I've read on these forums from a guy who swears that STOCK cam angles are the best after a lot of testing. I have yet to see otherwise in truth... but maybe I need to get more radical to see a difference in power or is it pointless with axleback and a 4C as my only mods...


    OPTimingCompare3_4.JPG



    Here's the thing about equating MAF rate to HP: it doesn't take into account amount of trapped charge, cylinder pressure vs crank angle (which drives power extraction), etc.

    Even if you keep the same amount of overlap, but shift the cam timing, it's possible to change the amount of blow-through.

    I did a lot of test runs trying to use logged data to validate VCT changes under boost, and I did find some general trends. But, I decided some of my base assumptions were breaking down. I think the dyno is really our only way to validate these changes, but even the dyno has challenges of variability.