272/264 v 264/272
#16
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Originally Posted by Wangracing
You mention that in the chart comparing the two EVO VIII cam types the intake valve is delayed in closing by 2 degrees. On the std evo VIII it closes at 59 degrees and in the MR it closes at 63 degrees. I would have thought this would have been a 4 degree difference and would be regarded as retard, as in its opening 4 degrees later (from 21 degrees on the std VIII to 17 degrees on the MR) and closing 4 degrees later. So in effect would be represented by a -4 adjustment on the intake cam wheel.
The cams turn at half the crankshaft speed, so an adjustment of one cam degree = two crankshaft degrees. The valve events, lobe centerlines, and LSA are all reported in crankshaft degrees, but the cam wheels are indexed in cam degrees. Therefore, to retard the valve events by 4 degrees, one needs to use a setting of "-2" on the cam wheel. You need to be mindful of this, or you will find yourself very confused.
Originally Posted by Wangracing
Also on the centre line, I am not sure exactly how this is calculated, but I am guessing it is a representation in degrees of where the centre of the cam is. Using the MR intake cam, if its total duration is 260 degrees, then I am assuming the centre is 130 degrees after it opens. Given it opens 17 degrees (I am assuming BTDC) then its centreline would be 113 degrees ATDC as you mention. Am I on the right track??
Originally Posted by Wangracing
... Am I remotely on the right track???
Originally Posted by Wangracing
advancing the exhaust cam will get it open earlier and get more gas out and improve turbo spool.
Originally Posted by Wangracing
advancing the intake will get more charge in and improve top end . . .
Once one gets a solid mental picture of the cams in motion with respect to the crankshaft, he can predict the general characteristics of any given cam set just from effective lift/duration and lobe centerlines, without the need for a calculator, charts, etc.
#17
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Originally Posted by Ted B
Once one gets a solid mental picture of the cams in motion with respect to the crankshaft, he can predict the general characteristics of any given cam set just from effective lift/duration and lobe centerlines, without the need for a calculator, charts, etc.
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How bout another question....
I am installing a set of 272in and 264ex cams. I am trying to make a comparison to these and the stock cams and theorise on the cam timing. Do you know if the information on the centreline of the HKS cams is out there???
Would be interested in how the timing of there opening and closing compares to stock at a 0/0 setting and then compare how the well known cam timing changes out there move these events as compared to stock.
I am always a believer that the companies who build these motors do there R and D and have them setup in certain ways for good reason. Possible sometimes it is a compromised one setting to suit most applications, but at least it is a good starting point. Be nice to see how the aftermarket stuff comapares to stock.
ps. Oh and thanks for pointing out the difference between cam degrees and crank degrees. I am starting to get the picture now...
I am installing a set of 272in and 264ex cams. I am trying to make a comparison to these and the stock cams and theorise on the cam timing. Do you know if the information on the centreline of the HKS cams is out there???
Would be interested in how the timing of there opening and closing compares to stock at a 0/0 setting and then compare how the well known cam timing changes out there move these events as compared to stock.
I am always a believer that the companies who build these motors do there R and D and have them setup in certain ways for good reason. Possible sometimes it is a compromised one setting to suit most applications, but at least it is a good starting point. Be nice to see how the aftermarket stuff comapares to stock.
ps. Oh and thanks for pointing out the difference between cam degrees and crank degrees. I am starting to get the picture now...
#19
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You can find a good list of most available EVO cams and the specs thereof by going to the last post in this thread:
https://www.evolutionm.net/forums/sh...ad.php?t=86242
https://www.evolutionm.net/forums/sh...ad.php?t=86242
#21
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Ted,
just been doing some sketches to try to get my head around the opening and closing events of my intended cam install. (Note this is the HKS 272in 264ex)
Going by the numbers you have provided I have calculated the following. On the 272 the intake would open at 26 deg BTDC and close at 66deg ABDC. The exhaust valve driven by the 264 cam, the exhaust would open at 62deg BBDC and close at 22deg ATDC. Am I on the money here??
Just keen to know if I am gaining any understanding and manipulating the numbers correctly.
Thanks again for all your feedback.
just been doing some sketches to try to get my head around the opening and closing events of my intended cam install. (Note this is the HKS 272in 264ex)
Going by the numbers you have provided I have calculated the following. On the 272 the intake would open at 26 deg BTDC and close at 66deg ABDC. The exhaust valve driven by the 264 cam, the exhaust would open at 62deg BBDC and close at 22deg ATDC. Am I on the money here??
Just keen to know if I am gaining any understanding and manipulating the numbers correctly.
Thanks again for all your feedback.
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Have been doing some more thinking and sketches. Basically trying to get my head around the cam timing changes now. Please advise if you thing the following theorising is on track...
-2in +1 ex. Change is to open intake 24BTDC as opposed to 26BTDC and close 68ABDC as opposed to 66ABDC. Centre of this cam now at 112deg. Exhaust goes from open at 62BBDC to 63BBDC and closes at 21ATDC instead of 22ATDC. Centre of cam now at 111 deg. New LSA of setup is 111.5 deg. Sound right??
Compared to the -4in -1ex where the centre of the intake is now 114deg and the centre of the ex is 109 but the LSA remains at 111.5.
Any comments on the effect of these two settings?? Same LSA but different event timing of the opening and closing of valves.
Sorry if I am being painful, but really keen to get my head round this.
-2in +1 ex. Change is to open intake 24BTDC as opposed to 26BTDC and close 68ABDC as opposed to 66ABDC. Centre of this cam now at 112deg. Exhaust goes from open at 62BBDC to 63BBDC and closes at 21ATDC instead of 22ATDC. Centre of cam now at 111 deg. New LSA of setup is 111.5 deg. Sound right??
Compared to the -4in -1ex where the centre of the intake is now 114deg and the centre of the ex is 109 but the LSA remains at 111.5.
Any comments on the effect of these two settings?? Same LSA but different event timing of the opening and closing of valves.
Sorry if I am being painful, but really keen to get my head round this.
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Thanks again Ted.
Thanks for pointing out the cam degress v crank degrees isssue again. Seems I didn't quite have it. So if I was talking about using these settings at the cams, (eg -2/+1) the the effect at the crank is 2:1. eg. A 2 degree retard at the cam will give 4 degrees at the crank on the inlet and a +1 degree at the cam will give 2 at the crank.
Thanks again for all your help. Slowly getting there.
Would have taken this to PM but am hoping this discussion may also benefit others.
Thanks for pointing out the cam degress v crank degrees isssue again. Seems I didn't quite have it. So if I was talking about using these settings at the cams, (eg -2/+1) the the effect at the crank is 2:1. eg. A 2 degree retard at the cam will give 4 degrees at the crank on the inlet and a +1 degree at the cam will give 2 at the crank.
Thanks again for all your help. Slowly getting there.
Would have taken this to PM but am hoping this discussion may also benefit others.
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Just for my information. I'm not quite up on the advance / retard terminology.
The word "Advance" means adjusting the cam gears such that the valve will "Open sooner" than it normally would?
The word "Retard" means adjusting the cam gears such that the valve will "Open later" than it normally would?
Thanks,
~j.
The word "Advance" means adjusting the cam gears such that the valve will "Open sooner" than it normally would?
The word "Retard" means adjusting the cam gears such that the valve will "Open later" than it normally would?
Thanks,
~j.
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I am sure Ted will confirm this, but yes you are spot on. Advancing makes the opening and closing events happen sooner, retarding delays the event.
#28
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Originally Posted by Ted B
Your statement is generally correct or less correct, but there is some variation depending where in the crankshaft rotation the overlap occurs. For example, tighten the LSA by advancing your intake cam 2 degrees and note the changes in spool characteristics and midrange torque. Re-correct the LSA (but on different lobe centerlines) by advancing the exhaust cam 2 degrees and one can see the initial difference wasn't due strictly to a change in the intake lobe centerline.
In the case of the US vs. JDM cam settings, the JDM settings delay the closing of the intake valve by 2 cam degrees, which results in a lobe centerline of 113 degrees. This helps high rpm power a bit. As far as the difference in LSA, one would think by conventional thought that the tighter LSA in the US spec car would make for better high rpm breathing, but there is more to the picture. For example, time and again a car with a setting of -4/-1 will make more peak power than a -3/-3 (at the expense of some spool time), despite the tighter LSA in the latter setting.
In the case of the US vs. JDM cam settings, the JDM settings delay the closing of the intake valve by 2 cam degrees, which results in a lobe centerline of 113 degrees. This helps high rpm power a bit. As far as the difference in LSA, one would think by conventional thought that the tighter LSA in the US spec car would make for better high rpm breathing, but there is more to the picture. For example, time and again a car with a setting of -4/-1 will make more peak power than a -3/-3 (at the expense of some spool time), despite the tighter LSA in the latter setting.
#29
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Originally Posted by Wangracing
Thanks for pointing out the cam degress v crank degrees isssue again. Seems I didn't quite have it. So if I was talking about using these settings at the cams, (eg -2/+1) the the effect at the crank is 2:1. eg. A 2 degree retard at the cam will give 4 degrees at the crank on the inlet and a +1 degree at the cam will give 2 at the crank.
Originally Posted by trinydex
so is this a way of saying that a tight lsa produces power but a retarded light lsa might produce more (with some losses in the spool etc)? (at least for this example) because i want to know if i'm thinking along the same track.
Wide LSAs (110-116 deg) are best suited to street engines that require good idle vacuum and broad rpm power. A wide LSA tends to result in a broader, smoother curve.
A tighter LSA can create reversion problems if the exhaust backpressure is too high. Because of this, a turbo with an undersized hotside will be a limitation with a tight LSA. For example, the tight LSA (106 deg) in my setup that worked so well with a TME appears to have exacerbated a serious backpressure issue with the 20G9-6, which resulted in a substantial loss of midrange torque despite no change in boost pressure.
This is very basic, because just about every important design characteristic of an engine affects the behavior of any given LSA. Here's a decent article that I found with a quick search that gives a little more info:
http://www.hotrod.com/techarticles/18218/index.html