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Thread: Cam Gear Tuning and Theory

  1. #21
    Community Manager GokuSSJ4's Avatar
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    Re: Cam Gear Tuning and Theory

    here is something Scot posted: for those that havent read it

    -Advancing the Intake cam, and Retarding the Exhaust cam will open up the overlap a bit. This allows the cylinder to fill sooner due to the intake valve opening sooner, which can sometimes be advantageous in a turbocharged engine. This also helps to improve the idle quality since the Intake cam has a larger impact on the idle than the Exhaust cam does. Or, the exhaust cam can be retarded more than the intake cam, as in a -1 -4 setup. Both cams are retarded in this situation, but the exhaust cam is moved more, increasing the overlap.
    Ultimately this is one of those cases where a dyno comes in real handy. You move the cams around until you find the right combination. Unfortunately theory only gets you so far, and practice makes perfect..
    ''Yo, a$$G@@! This motherfucka's dead! Ain't no Chris Angel Mind freak, David Blaine trapdoor horseshit jumpin' off here!''

  2. #22

    Re: Cam Gear Tuning and Theory

    Quote Originally Posted by GokuSSJ4
    Quote Originally Posted by leaveit2bevo
    what do people usually make with your setup?
    Ted B
    has even recommended for straight 280's cams +2 -2
    it will help your idle as well! I had great results but then again i'm running 272/280 HKS cams at the moment.
    With the Big turbo i will try 280's or something with big lift... cam gear settings will be a must in order to obtain a desirable power band..
    GinuwineEvo8
    you can always take your set up to TT and have Alfred play around with your cam gears to see where the best results is found..
    To be quiet honest, you should be at least in the 330whp range .. something most be absolutly wrong, besides cam gear settings...
    how can increasing overlap help your idle?

  3. #23

    Re: Cam Gear Tuning and Theory

    Quote Originally Posted by alan678
    Would it be safe to try the +2/0 cam gear setting on a set of 272i/264e setup? Also how is the idle with this setting??? i currently have mine set at -3/-3 from the [forum-restricted] site (what they recommend on the Stage 1+) and the cams lump pretty good...just wondering...dont get me wrong...i would perfer performance over sound anyday...
    no the +2+0 won't do the same thing on a staggered non 280 setup. you can do it... it'll give you low end punch but it won't get you the have your cake and eat it too effect that it gives you on the 280s. also you staggered your cams the wrong way and increasing the timing advance will help even less in this situation as your 272 on the intake is already "helping" out your bottom end.

  4. #24
    Community Manager GokuSSJ4's Avatar
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    Re: Cam Gear Tuning and Theory

    no the +2+0 won't do the same thing on a staggered non 280 setup. you can do it... it'll give you low end punch but it won't get you the have your cake and eat it too effect that it gives you on the 280s. also you staggered your cams the wrong way and increasing the timing advance will help even less in this situation as your 272 on the intake is already "helping" out your bottom end.
    i believe on the UK boards they seem to love running that certain stagger seet up.. I have never try it and havent heard the results of it..
    also by advancing the intake cam, doesnt that allow better idle ? even scot explain it, referrence is your TECH thread on CAMS.. due to the intake cam having a larger impact on the car idle ..
    ''Yo, a$$G@@! This motherfucka's dead! Ain't no Chris Angel Mind freak, David Blaine trapdoor horseshit jumpin' off here!''

  5. #25

    Re: Cam Gear Tuning and Theory

    it does... but it's relative tightening the LSA is always going to make your idle worse... advancing the intake will make it less worse. it's not gonna improve anything especially in relation to keeping everything at 0 0. just advancing the intake might make things better overall even at a 0 0 setup but advancing intake and retarding exhuast is just gonna make it bad.

  6. #26

    Re: Cam Gear Tuning and Theory

    0 0 setting on my cangears running Jun 272's and the iddle is lumpy but once I get moving, it feels so smooth. btw my rpms dont dip to 800revs like the HKS 272's did!

  7. #27
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    Re: Cam Gear Tuning and Theory

    cosworth cams were different +4 +2
    272/280 HKS cams +2 - 2 HKS cams has shown great results but some changes might be needed due to my new set up .. so i will re dyno again and check out what best set up is needed, since im aiming for a better midrange..
    ''Yo, a$$G@@! This motherfucka's dead! Ain't no Chris Angel Mind freak, David Blaine trapdoor horseshit jumpin' off here!''

  8. #28

    Re: Cam Gear Tuning and Theory

    Quote Originally Posted by Blak94GSX
    -Advancing the Intake cam, and Retarding the Exhaust cam will open up the overlap a bit. This allows the cylinder to fill sooner due to the intake valve opening sooner, which can sometimes be advantageous in a turbocharged engine. This also helps to improve the idle quality since the Intake cam has a larger impact on the idle than the Exhaust cam does.
    Although this is an excellent post, I would have to disagree on some of this statement. Increasing overlap, increses charge dilution at idle and 8-stroking which gives the charicteristic rough idle lope that bigger cams produce.

    Incresing overlap tends to increse the mid range area because when both valves are open, more scavanging of the burnt exhaust from the cylinders can take place at these rpms. Its not just the intake valve opining sooner.

    However this is tricky on turbocharged motors as they typicaly have much more backpressure than an NA motor, especialy with smallish stock turbos. With small turbos there is more backpressure than boost pressure most of the time. What can happen is that you get reversion during the overlap period where hot exhaust gasses backflow into the combustion chamber. The CC gets hotter and the exhaust valves get really hot. This can contribute towards detonation. With small turbo'ed motors, like a 2G running a T25, it is usualy better to retard the intake and advance the exhaust when running larger cams to reduce overlap and reduce reversion.

    The EVO motor has a couple of things going for it that will reduce some of the negatives with incresing overlap with a turboed motor. First EVO's have pretty larger turbos for stock 2 liter motors. The 16G was sold as an upgrade for the 1 and 2G DSM's for years. Bigger turbo, less backpressure and less reversion. Second the EVO has a pulse converter exhaust manifold where cylinders 1-4 and 2-3 are paired together entering a twing scroll exhaust turbine housing. This allows for maximum seperation between exhaust pulses and reduces the likelyhood of exhaust reversion contamnination.

    So the EVO can tolerate bigger cams and more overlap than most stock turbo motors.
    EVO IX with lots of parts

  9. #29

    Re: Cam Gear Tuning and Theory

    the problem with your caveat is that it is a caveat. the problem when talking about cam tuning in general is that they are all specific circumstances. you say that increasing overlap increases charge dilution, but this is only under the circumstance that you're not at high rpm and possibly that you have more back pressure than throughput pressure.

    of course your correction is correct, but also only to as much of a limited scope as the initial claim was wrong.

  10. #30

    Re: Cam Gear Tuning and Theory

    Quote Originally Posted by trinyDeX
    the problem with your caveat is that it is a caveat. the problem when talking about cam tuning in general is that they are all specific circumstances. you say that increasing overlap increases charge dilution, but this is only under the circumstance that you're not at high rpm and possibly that you have more back pressure than throughput pressure.

    of course your correction is correct, but also only to as much of a limited scope as the initial claim was wrong.
    I think I made it clear that 8-stroking caused by charge dilution with more overlap occurs at idle.Â* So my contention is that more overlap causes a rouger idle, not a smoother one.Â* This always happens on all 4 stroke engines, unless it is tuned out with some sort of variable cam timing device. I think you are confusing idle charge dilution with reversion which are two different phenomina.
    EVO IX with lots of parts

  11. #31

    Re: Cam Gear Tuning and Theory

    oh well the part about idle is wrong on blak's part. i was talkin' about the other parts in your claims. what i'm trying to communicate is that many times the overlap doesn't cause reversion in a certain rpm band or for a certain displacement etc. so you sort of have to be really specific as to which part of what you're claiming is affected.

    However this is tricky on turbocharged motors as they typicaly have much more backpressure than an NA motor, especialy with smallish stock turbos. With small turbos there is more backpressure than boost pressure most of the time. What can happen is that you get reversion during the overlap period where hot exhaust gasses backflow into the combustion chamber. The CC gets hotter and the exhaust valves get really hot. This can contribute towards detonation. With small turbo'ed motors, like a 2G running a T25, it is usualy better to retard the intake and advance the exhaust when running larger cams to reduce overlap and reduce reversion.
    this is the part i was specifically addressing

  12. #32

    Re: Cam Gear Tuning and Theory

    Quote Originally Posted by trinyDeX
    oh well the part about idle is wrong on blak's part. i was talkin' about the other parts in your claims. what i'm trying to communicate is that many times the overlap doesn't cause reversion in a certain rpm band or for a certain displacement etc. so you sort of have to be really specific as to which part of what you're claiming is affected.
    Yes I totaly agree with you on that.
    EVO IX with lots of parts

  13. #33

    Re: Cam Gear Tuning and Theory

    sorry my ninja edit was not too ninja.

    you did qualify your caveat very well by providing the reason why evo motors can overlap more and not suffer the potentially unidealization of horsepower due to hot valves creating a lower knockthreshold.

  14. #34

    Re: Cam Gear Tuning and Theory

    Not sure what part about decreasing overlap to improve idle you are disputing... I can only assume you misread my post, unless you are trying to claim that increasing the overlap at idle will somehow improve the idle smoothness.
    All da cars are Nekkid!Â*&nbsp; www.dsmporn.com<br /><br /><br />www.roadraceengineering.com

  15. #35

    Re: Cam Gear Tuning and Theory

    Quote Originally Posted by trinyDeX
    oh well the part about idle is wrong on blak's part. i was talkin' about the other parts in your claims. what i'm trying to communicate is that many times the overlap doesn't cause reversion in a certain rpm band or for a certain displacement etc. so you sort of have to be really specific as to which part of what you're claiming is affected.

    However this is tricky on turbocharged motors as they typicaly have much more backpressure than an NA motor, especialy with smallish stock turbos. With small turbos there is more backpressure than boost pressure most of the time. What can happen is that you get reversion during the overlap period where hot exhaust gasses backflow into the combustion chamber. The CC gets hotter and the exhaust valves get really hot. This can contribute towards detonation. With small turbo'ed motors, like a 2G running a T25, it is usualy better to retard the intake and advance the exhaust when running larger cams to reduce overlap and reduce reversion.
    this is the part i was specifically addressing
    haha now after rereading the initial post by blak i'm a bit confused by the possibly easy to misconstrue "opening" lsa. although i was under the impression that advancing intake and retarding exhaust brings the two evens closer to each other

  16. #36

    Re: Cam Gear Tuning and Theory

    Quote Originally Posted by trinyDeX
    Quote Originally Posted by trinyDeX
    oh well the part about idle is wrong on blak's part. i was talkin' about the other parts in your claims. what i'm trying to communicate is that many times the overlap doesn't cause reversion in a certain rpm band or for a certain displacement etc. so you sort of have to be really specific as to which part of what you're claiming is affected.

    However this is tricky on turbocharged motors as they typicaly have much more backpressure than an NA motor, especialy with smallish stock turbos. With small turbos there is more backpressure than boost pressure most of the time. What can happen is that you get reversion during the overlap period where hot exhaust gasses backflow into the combustion chamber. The CC gets hotter and the exhaust valves get really hot. This can contribute towards detonation. With small turbo'ed motors, like a 2G running a T25, it is usualy better to retard the intake and advance the exhaust when running larger cams to reduce overlap and reduce reversion.
    this is the part i was specifically addressing
    haha now after rereading the initial post by blak i'm a bit confused by the possibly easy to misconstrue "opening" lsa. although i was under the impression that advancing intake and retarding exhaust brings the two evens closer to each other
    Uh, you were the one that copied all that nonsense from some other forum here... I assure you I didn't use LSA anywhere in my posts.

    Glad to see somebody actually reads my posts that are over 2 years old here though...
    All da cars are Nekkid!Â*&nbsp; www.dsmporn.com<br /><br /><br />www.roadraceengineering.com

  17. #37

    Re: Cam Gear Tuning and Theory

    so when you advance the intake and retard the exhaust you're not increasing overlap?

  18. #38

    Re: Cam Gear Tuning and Theory

    Quote Originally Posted by trinyDeX
    so when you advance the intake and retard the exhaust you're not increasing overlap?
    Yeah I guess my wording is a bit confusing since I was talking about idle two sentences before. I will reword it slightly for clarity. Thanks for bringing it to my attention.
    All da cars are Nekkid!Â*&nbsp; www.dsmporn.com<br /><br /><br />www.roadraceengineering.com

  19. #39

    Re: Cam Gear Tuning and Theory

    Quote Originally Posted by Blak94GSX
    Not sure what part about decreasing overlap to improve idle you are disputing... I can only assume you misread my post, unless you are trying to claim that increasing the overlap at idle will somehow improve the idle smoothness.
    This seems to read as incresing overlap improves idle quality. Perhaps some minor editing can make this more clear. Its an excellent post though.


    -Advancing the Intake cam, and Retarding the Exhaust cam will open up the overlap a bit. This allows the cylinder to fill sooner due to the intake valve opening sooner, which can sometimes be advantageous in a turbocharged engine. This also helps to improve the idle quality since the Intake cam has a larger impact on the idle than the Exhaust cam does.
    EVO IX with lots of parts

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