Ted B

iTrader: (6)

Be careful:

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.



Correct.


Just keep in mind that the single most important event is the point where the intake valve closes, which means the overall position (particularly lobe centerline) of the intake cam can be viewed as the centerpiece of the configuration. Once that is set, one can trim the position of the exhaust cam to set the LSA wherever desired. This is a very basic strategy, but it is a starting point.



Somewhat, but advancing it too far will begin venting combustion gases before their work is done.


Advancing the intake takes better advantage of the low speed sucking/pushing effect of the pistons, but can compromise efficiency on the top end, where the inertia effect is the driving force for air movement.


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.

Wangracing

Thanks Ted. This is what I am working towards. Just want to have an understanding of what the changes I am making I are doing rather than blindly following the pack.

Wangracing

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...

Ted B

iTrader: (6)

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

Wangracing

Thanks Ted. Had been following that thread but had missed your latest update with the centrelines etc added. Thanks again.

Wangracing

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.

Wangracing

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.

Ted B

iTrader: (6)

Post #21 is correct.

Post #22 is correct so long as you realize that your referrals to "-2in +1ex" and "-4in -1ex" are crank degrees. When those terms are typically used, they usually refer to cam gear settings, which are always expressed in cam degrees.

Wangracing

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.

jcnel_evo8

iTrader: (2)

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.

Wangracing

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.

trinydex

iTrader: (12)

i'm a little confused... don't people generally retard the exhaust and advance the intake?

trinydex

iTrader: (12)

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.

Ted B

iTrader: (6)

Correct. Remember that the only measurement expressed in cam degees are the actual cam gear settings. Everything else is expressed in crankshaft degrees.

A tight LSA (104-108 deg) tends to create a shorter, peakier power curve. Race engines that focus power into shorter, narrower powerbands typically use a tighter LSA.

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

Wangracing

Great article Ted. Will take a few reads of that one before that all sinks in....