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Thread: Turbo Camshafts

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    Turbo Camshafts

    Interesting link that explains turbo camshaft considerations http://horsepowercalculators.net/sup...and-cam-timing

    Click here to enlarge

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    Funny you bring this up now. Over the last few days I started obsessing with cam tuning and learning what it is all about specifically when it comes to FI and turbo setups. Here's a link that helped me get full clarity on the topic of what it means to retard vs. advance a cam on either the exhaust or the intake side (talking about the graph).

    http://www.max-boost.co.uk/max-boost...%20Ma%27am.htm

    The image I'm referring to:

    Click here to enlarge

    I now understand how Cobb is able to make more power towards redline than the piggybacks, and it is through VANOS changes on both the intake and exhaust cams when moving and the engine is warm. There are also different settings for spool and idle warm/cold cam operation individually for intake and exhaust. Its really amazing how adjustable the cams are from the DME calibration point of view.

    Cobb basically retards both the intake and exhaust cams making for a fatter area under the power curve while also stretching it a bit further the right (more top end), while also reducing overlap. I've learned that overlap in general is to be reduced on turbo setups although in some cases some overlap is actually wanted as the additional air coming off the turbo that skims the top of the pistons serves a cooling purpose (so called turbo "chill" Click here to enlarge)

    Key thing I found, that helps understand and get clarity here, is getting a grasp on what retard vs. advance of a cam really is and to understand that moving the lobes in that chart towards one side (say left) will advance BOTH cams, and moving the lobes to the other side will retard both cams, thereby shifting the power curve around. The other thing to understand is what "overlap" is and why you may want it reduced on a turbo/FI setup and not so much on an NA car.

    Great topic, would love to discuss it so anyone with comments fire away..

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    You want to avoid overlap on FI cars to prevent blowing your boost out the exhaust, true?

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    Click here to enlarge Originally Posted by ATP Click here to enlarge
    You want to avoid overlap on FI cars to prevent blowing your boost out the exhaust, true?
    You got it, especially on highly backpressured setups like stock turbos when they're run outside their efficiency range and/or especially with restrictive exhaust setups on top of that...in situations where backpressure isn't as high as on stock turbo setups you'd be ok with a bit of overlap to get the turbo chill...its all a numbers game really and requires dyno time to see any true benefits...

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    Great thread! Hope to see some development for the N54 valve train in the future.

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    I've compared Cobb 2+ versus map0 and the benefits with Cobb are decreased overlap in the mid-range retarding intake primarily... but they seem to be similar toward 5.5k rpms where it's most crucial.
    http://www.e90post.com/forums/showthread.php?t=617176

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    Click here to enlarge Originally Posted by JoshBoody Click here to enlarge
    I've compared Cobb 2+ versus map0 and the benefits with Cobb are decreased overlap in the mid-range retarding intake primarily... but they seem to be similar toward 5.5k rpms where it's most crucial.
    http://www.e90post.com/forums/showthread.php?t=617176
    you're interpreting the angles the same way I did initially, which was wrong...both intake and exhaust are retarded and on top of that the overlap has been decreased...i've confirmed it with Rob as well...take a look at the graph I posted above and try to understand why adding degrees on the intake cam doesn't advance but retard...going lower on the cam degrees on the exhaust side also retards that cam..

    Its because the exhaust sits on the side left of TDC and intake sits on the right from TDC in that graph...mull it over and it'll make sense

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    I don't think I am... lower degree value is an advance (open sooner) and higher degree is a retard (open later). I could have mis-stated somewhere though. So to reduce overlap you advance exhaust and retard intake. i'm not sure how else you could interpret it.

    I just graphed both in positive, so its easier for viewing, but you add (-) to exhaust for actual crank degrees.

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    Click here to enlarge Originally Posted by JoshBoody Click here to enlarge
    I don't think I am... lower degree value is an advance (open sooner) and higher degree is a retard (open later). I could have mis-stated somewhere though. So to reduce overlap you advance exhaust and retard intake. i'm not sure how else you could interpret it.

    I just graphed both in positive, so its easier for viewing, but you add (-) to exhaust for actual crank degrees.
    You are wrong. Lower degree on the exhaust cam is a retard. Higher degree value on the intake cam is also a retard. Fact

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    Click here to enlarge Originally Posted by dzenno Click here to enlarge
    You are wrong. Lower degree on the exhaust cam is a retard. Higher degree value on the intake cam is also a retard. Fact
    well this is just how you define the 2 terms... seems strange to me. But your graph seems to labels adv and retard as I was saying.

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    Click here to enlarge Originally Posted by JoshBoody Click here to enlarge
    well this is just how you define the 2 terms... seems strange to me. But your graph seems to labels adv and retard as I was saying.
    hehe look closer and read your post above again...intake cam isn't being advanced, its being retarded in the cobb maps, as well as the exhaust...

    intake cam:
    say its at 90deg for certain load/rpm cell. If you change that to 100deg now (added degrees) you're moving the center lobe to the right, meaning "retard" not advance...This is what the VANOS change on the intake cam looks like in the latest Cobb maps (just different degree values, above is just an example)

    exhaust cam:
    say its at 100deg for certain load/rpm cell. If you change that to 90deg (less degrees), now you're moving the center lobe to the right, meaning retarding it...This is what the VANOS change on the exhaust cam looks like in the lastest Cobb maps (just different degree values, above is just an example)

    exhaust cam you're right, intake cam you're mixing it up...took me a while to understand as well and the chart i posted above was a light bulb...i thought just like you that the intake was being advanced which is wrong

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    DZ, I don't know where you are getting confused. BUT advance is sooner and retard is later... period! Crank degrees should be expressed in as -360 to 360 instead of 2 360 cycles... maybe this is the confusion.

    Your statement above about Cobb retarding exhaust means they are increasing overlap on the exhaust side... this is true in relation to stock setpoints. Upon high load it is initially advanced though from about -85 to -110 and then kept steady. Stock hits -115ish in the mid-range, retarded to -110ish up top.

    For intake Cobb keeps a fairly steady 110ish degrees. Stock is 85ish ramping to 110deg around 5500rpm. So Cobb has less overlap in the mid-range, but similar to stock starting around 5500rpm.

    The +/- of different cam timing is interesting. If maxing boost generally less overlap the better, but if you have a more efficient system this isn't so critical and increasing compression and avg cylinder pressures can be beneficial.

    ps. my first post I did say intake advanced, but I edited it very shortly noticing my mistake.

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    I always said both are retarded in relation to stock...ok good on the same page now or so it seems

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    My former subie tuner via Cobb AP was a guru of cam tuning (called AVCS there). Huge impact on spool and finding more torque at higher RPM. Even made the exhaust note a bit different at idle for you if you so chose.

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    Yep overlap reduction makes for a nice quiet exhaust too Click here to enlarge

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    How about a protune with some vanos and spark timing work such that I spit flames between shifts. It's the ricer in me.

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    Very good topic! I used to do a lot of work with camshafts in 8V VW engines, some turbo, some not.

    Here is what I can contribute to this topic:

    1. The N54 ECU can adjust BOTH the intake and exhaust camshafts from -72 to +72 degrees via VANOS.
    2. When the engine is cold, the adjustment range is from -10 to +10 degrees. This is one of the reasons why you don't make as much power when engine is cold.

    Say our cams are ground to 270 degrees which is a rather aggressive cam for FI. I think they are in the 250 range but that's just a guess here. There are 360 degrees in a full circle. So, as the camshaft completes a full revolution, the valves will be open at some extent or another for 270 degrees of that rotation.

    When the ECU adjusts VANOS angles, effectively, all it is doing is changing the grind of the camshaft. Simple math will tell you that it is impossible for our cars to have camshafts with anything bigger than 288, which would mean the valves are open all the time when Vanos is at +72 degrees.

    Contrary to popular belief, some (little) overlap is actually beneficial for FI engines. It is designed to cool off the exhaust valves and also for improving emissions by dumping fresh air into the exhaust. I doubt that N54 has overlap though.
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    Somewhat related: Camshaft lobe design affects torque output. A more egg-shaped lobe will produce more torque but for a narrower rpm band. A more flatter cam lobe will produce less torque, but that would be available over a longer rpm range. With VANOS you can essentially tune the car for max torque very easily!

    EDIT: The size of the cam lobes is greatly limited by the valve springs. A valve spring with thick coils will not allow for the valves to travel further down when pushed by a more egg-shaped cam. The coils on the valve springs end up hitting each other in the extreme case. If that happens you end up shearing lifters and in the worst case, cam bearings.

    Also, each valve spring has a specific operating range. If you compress the valve spring too much, it may need more time to extend itself. At high-rpms, you end up with "floating valves": a situation where the valve spring does not have enough time to expand and close the valve. This is bad on many levels.

    Those are the primary reasons why one upgrades the valve springs: ability to run camshafts with increased valve lift and ability to run higher RPMS
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    Click here to enlarge Originally Posted by dzenno Click here to enlarge
    You are wrong. Lower degree on the exhaust cam is a retard. Higher degree value on the intake cam is also a retard. Fact
    +1

    Example: It the cylinder head is raised by a thicker gasket both cams will move a bit in the engines rotation direction (advanced), let's say 5 degrees on the crank. In case the lobe centers were 105/105 from the beginning it will now be LC 100 for intake and 110 exhaust even though they have physically been moved in the same direction.

    The terms advance (be earlier) and retard (be late) are well defined.
    Last edited by R1000K3; 04-05-2012 at 11:49 PM.

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    Moving to General and considering Advanced Tech.
    Stage 2 or 2.5 E9X M3 S65 V8 supercharger kit for sale: http://www.boostaddict.com/showthrea...r-kit-for-sale

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