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britishturbo
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« Reply #45 on: May 24, 2013, 10:14:21 AM »
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So timing a cam later in the cycle is advancing it? The opposite of ignition timing?
Here's a stock KFNW table from a 2.7 M Box:  Where you see 1 the cam is advanced - overlapped Where you see 0 the cam is normal (retarded) - no overlap Some suggest to advance the cam for longer int he rpm range to try and increase spool. One thing I want to warn about though... in my log I did yesterday even though I set it to advance the cam until 5500 the logs showed it stayed advanced all the way to 6800 |
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nyet
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« Reply #46 on: May 24, 2013, 10:37:29 AM »
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So timing a cam later in the cycle is advancing it? The opposite of ignition timing?
I'm confused about this as well. Retarding the exhaust valve increases overlap. Advancing the intake valve increases overlap. if "advance" means "increase overlap" i'd say something is wrong with using the word "advance", unless by "advance" you mean "advance the timing of the intake with respect to the exhaust by retarding the exhaust, assuming the intake timing remains the same" |
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britishturbo
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« Reply #47 on: May 24, 2013, 10:41:51 AM »
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I'm confused about this as well.
Retarding the exhaust valve increases overlap.
Advancing the intake valve increases overlap.
if "advance" means "increase overlap" i'd say something is wrong with using the word "advance", unless by "advance" you mean "advance the timing of the intake with respect to the exhaust by retarding the exhaust, assuming the intake timing remains the same"
The Exhaust cam does not move... the Intake cam gets Advanced. |
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britishturbo
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« Reply #48 on: May 24, 2013, 10:43:02 AM »
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IF you look at a 2.7 the timing belt drives the outside cams - the exhaust cams.
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nyet
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« Reply #49 on: May 24, 2013, 10:53:53 AM »
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Whoa. No wonder I was confused.
Thanks. Now everything is clear.
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julex
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« Reply #50 on: May 24, 2013, 12:21:12 PM »
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I have a question related to selective valvetrain upgrades.
Long story short I ended up with stock valvetrain with upgraded exhaust springs.
I understand the the first thing to catastrophically go are exhaust valves if you over-rev as they start floating at kiss piston or intake valves. If intake valve floats as well, it will only cause loss of power since some of the charge will escape back into manifold but the valve should close far before the ingnition takes place so "no big deal". The engine will just hit proverbial wall and driver will definitely feel that.
Considering the above upgrade, how much, do you recon, I extended my RPMs by doing just exhaust valves?
Thanks!
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s5fourdoor
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« Reply #51 on: May 24, 2013, 03:41:29 PM »
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Here's a stock KFNW table from a 2.7 M Box:
Where you see 1 the cam is advanced - overlapped
Where you see 0 the cam is normal (retarded) - no overlap
Some suggest to advance the cam for longer int he rpm range to try and increase spool.
One thing I want to warn about though... in my log I did yesterday even though I set it to advance the cam until 5500 the logs showed it stayed advanced all the way to 6800
Can you also please also post your KFNW with axis labels? KFNWWL, KFPBRK, KFPBRKNW, KFPRG, & KFURL too if you have time. |
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« Last Edit: May 24, 2013, 03:44:25 PM by nehalem »
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userpike
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« Reply #52 on: May 24, 2013, 07:41:17 PM »
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I have a question related to selective valvetrain upgrades.
Long story short I ended up with stock valvetrain with upgraded exhaust springs.
I understand the the first thing to catastrophically go are exhaust valves if you over-rev as they start floating at kiss piston or intake valves. If intake valve floats as well, it will only cause loss of power since some of the charge will escape back into manifold but the valve should close far before the ingnition takes place so "no big deal". The engine will just hit proverbial wall and driver will definitely feel that.
Considering the above upgrade, how much, do you recon, I extended my RPMs by doing just exhaust valves?
Thanks!
My recommendation here is to keep your "stock" max rev limit because even though you upgraded the exhaust valve springs you are limited by the stock intake springs, bottom line. Is a few extra hundred rpm (maybe that much) really worth being on the verge of catastrophic failure? If valves are floating, no matter which(intake/exhaust) it is bad news as there are no advantages to floating valves and we all know there are way high chances of collision. In my opinion you either should have saved some money and replaced the exhaust valve springs with OEM replacements or spent more and purchased a good set of both intake and exhaust springs. |
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Bische
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« Reply #53 on: May 25, 2013, 10:16:29 PM »
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So it is called advanced when inducing more overlap because it is the exhaust cam that is the driven?
Advancing in relation to cam drive and not engine cycle.
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userpike
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« Reply #54 on: May 25, 2013, 11:36:04 PM »
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So it is called advanced when inducing more overlap because it is the exhaust cam that is the driven?
Advancing in relation to cam drive and not engine cycle.
The timing relationship between the crankshaft and exhaust cam doesn't change because the timing belt is positively tensioned at all times (idealy) The "slack" in the chain between the exhaust cam and intake cam is tension controlled by the solenoid which is also "powered" hydraulically by engine oil pressure. It gets the signals from the ECU via pulse width modulation. When its powered, the cam advances as such that the valves open sooner because the solenoid tensions the chain which rolls the cam "forward" more so then if the chain has slack. |
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« Last Edit: May 26, 2013, 12:01:52 AM by userpike »
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Bische
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« Reply #55 on: May 26, 2013, 10:33:55 AM »
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The timing relationship between the crankshaft and exhaust cam doesn't change because the timing belt is positively tensioned at all times (idealy) The "slack" in the chain between the exhaust cam and intake cam is tension controlled by the solenoid which is also "powered" hydraulically by engine oil pressure. It gets the signals from the ECU via pulse width modulation. When its powered, the cam advances as such that the valves open sooner because the solenoid tensions the chain which rolls the cam "forward" more so then if the chain has slack.
I have a 100% understanding how the VVT works, I am just not comfortable with the terminology of the cam states. You like me also describe the cam as advanced when opening the valves sooner, but is this thread they describe the cam timing as retarded when opening earlier in the cycle. Hence my question if the cam state is concidered retarded in relation to the driven cam, the exhaust cam, and not in relation to the combustion cycle(opposite of ignition timing terminology). |
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Snow Trooper
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« Reply #56 on: May 26, 2013, 10:42:05 AM »
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I don't understand the disconnect happening here... The cam, when the actuator is active is advanced forward from its normal state. Normally the intake valves are still 100% shut when the exhaust valves are still opened. This advance we create makes the intake valves open sooner while the exhaust valves are still open, hence the term that they are advanced. This overlap makes it so that boost pushes through the cyl and gives the exhaust a little bump. Thus the reason why with tiny turbos where the exhaust side has way more pressure than the cold side the flow will actually go backwards in the upper rpms.
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cartoons?
6A 61 72 65 64 40 76 6C 6D 73 70 65 63
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userpike
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« Reply #57 on: May 26, 2013, 11:18:24 AM »
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I have a 100% understanding how the VVT works, I am just not comfortable with the terminology of the cam states.
You like me also describe the cam as advanced when opening the valves sooner, but is this thread they describe the cam timing as retarded when opening earlier in the cycle. Hence my question if the cam state is concidered retarded in relation to the driven cam, the exhaust cam, and not in relation to the combustion cycle(opposite of ignition timing terminology).
The VVT only changes from a "normal" state to an advanced state. So maybe what they are talking about is when the VVT reverts back to it's normal state which, is technically retarding the timing. But this makes it confusing. It's just either normal or advanced! With ignition timing, when using the term "advanced" means the spark/ignition/combustion/whatever is happening sooner(farther BTDC on the compression stroke). So if combustion is happening at -6 degrees BTDC, a more advanced ignition timing would be for example: -6.1 degrees BTDC or anything after -6 degrees on the compression stroke. |
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cerips
Full Member
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« Reply #58 on: May 26, 2013, 11:58:55 AM »
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The VVT only changes from a "normal" state to an advanced state. So maybe what they are talking about is when the VVT reverts back to it's normal state which, is technically retarding the timing. But this makes it confusing. It's just either normal or advanced!
With ignition timing, when using the term "advanced" means the spark/ignition/combustion/whatever is happening sooner(farther BTDC on the compression stroke). So if combustion is happening at -6 degrees BTDC, a more advanced ignition timing would be for example: -6.1 degrees BTDC or anything after -6 degrees on the compression stroke.
BTDC is Before Top Dead Centre so a negative value would be after top dead centre so -6.1 BTDC is retarded compared to -6 BTDC. |
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phila_dot
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« Reply #59 on: May 26, 2013, 12:40:15 PM »
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Normal state (retarded) the intake valves open ATDC.
Advanced state the intake valves open BTDC.
What's the confusion?
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