meyer30

iTrader: (2)

I have compcams XFI268HR13 cam and I called them to find out about installing it straight up and the guy said that was fine because the cam has 4 degrees advance already ground into it. What does that mean? Does that change how I need to set the timing? I've never heard of that before and was wondering if anyone else has.

matt_p

It means that when you install it straight up, it will installed be as if you advanced it 4 degrees since the advance is ground into the location of the lobes themselves. Advancing a cam lowers powerband, retarding raises it if you didn't already know.

Cam companies seem to do it to protect people from themselves (picking too large a cam).

Since you have you have a TPI intake, its best you just install the cam straight up and not retard the timing to counter the advance ground into the cam.

meyer30

iTrader: (2)

Ok thanks. So do I just set the timing like normal then?

Sonix

iTrader: (1)

Yep, exactly what matt said.
Just to add to that, it's referring to CAM timing, not IGNITION timing. So that's why you don't have to worry about it when it comes to "setting" timing (ignition timing, ie, turning the distributor).
Just don't even think about it, continue along as usual.

1989GTATransAm

iTrader: (3)

The cam has a 113 degree lobe seperation angle or LSA. Four degrees advanced means the intake lobe should be installed on a 109 degree intake centerline. By the way I have the same cam.

YOU NEED TO DEGREE THE CAM WHEN INSTALLING IT. When mine was installed "straight up" it was actually on a 106 degree intake centerline. So I used the four degree retard notch on my Cloyes timing chain. This brought the intake centerline to 110 degrees. That is actually right where I wanted it as Dyno Sim showed that to be the best power for my combination.

sofakingdom

iTrader: (1)

LSA is a different spec from intake centerline.

LSA = # of CAM degrees between intake lobe center and exhaust lobe center; refers to how far the exhaust lobe center is offset from the intake lobe center

ICL = # of CRANK degrees after TDC at which the intake reaches maximum opening; this is the event used as the base against which ALL OTHER cam timing events are measured

DO NOT get these confused!!!

You can have a cam with the intake centerline at 102° ATDC, and 117° of lobe sep; or 110° ICL and 106° LSA; or practically any 2 other numbers.

There is NO WAY to "calculate" the ICL when all you have is the lobe sep.

When people say the cam is "4° advanced", what does that mean? 4° advanced, with respect to what?

The answer of course could be any of several things; it could mean, 4° advanced with respect to a GM cam; or 4° advanced with respect to the cam grinder's intentions; or maybe something completely else. To quote a "spec" like that without saying what it's 4° advanced compared to, is about like walking up to somebody and saying "I have 10 more HP". OK... 10 more HP than what?

The cam grinder designed the cam to do a specific set of things, which it will most closely approximate doing if it's installed at the ICL it was designed to be iunstalled at. This is accomplished by using the timing set it was designed to be used with (NO they're not all the same), and installing it as it was intended to be installed.

meyer30

iTrader: (2)

Ok well I wasn't able to degree the cam when I installed it so is it possible for me to do this while the engine is in the car or do I have to remove the engine again?

sofakingdom

iTrader: (1)

Yes it can be done with the engine in the car; although it's MUCH easier to do it on the stand.

If you used the correct timing set, don't worry about it.

Think about it.... if you degreed it and discovered it was off, what would you do?

Just put it together like it's supposed to go; that is, if your timing set has multiple kewyays, use the "0" one.

People tend to get all spun up needlessly about this for some reason. Mostly when they don't understand what those specs actually mean. Fro the most part, any cam you buy from a quality mfr (Comp, Lunati, Crower, Crane, Isky, and the like) is going to be within a degree or 2 anyway.

And on top of that, depending on what timing set you used, it may change fairly dramatically in the first few hundred miles of operation anyway. You end up with "measure with micrometer, mark with chalk, cut with axe".

Z69

Straight up to the cam grinder will actually mean that the LSA & ICL will be equal. (don't believe me, go to Team Chevelle and do a search on UDHarold-he's a cam designer)
And by straight up the tech line snoozers mean the marks on the timing gears need to be set to the straight up marks. Not the +-4 marks.
So that a shelf 110 lsa cam for example will be installed at a 106 ICL.
That's why "they" say the cam is ground with 4* advance.

Which just to confuse you more isn't true either. The pin on the cam is actually drilled for the 4 deg advance. Cam cores are made in very few places so they are all pretty much the same.


And a cam should always be degreed in. Never know how far off the keys and pin locations are. Never mind the actual lobes. Even with quality parts.
-a lot guys with cam checking equipment won't buy shelf cams for anything more than a mild motor-

Some of the advance is built in to allow for chain stretch.
And some stock single keyway timing sets don't follow the straight up rule either. They will move the ICL.

sofakingdom

iTrader: (1)

No, they won't.

Yes I know Harold myself, have since the mid-late 70s sometime.

Imagine a cam made out of 3 parts: the nose, the intake lobes , and the exhaust lobes as an assembly. Imagine that you could rotate each of those 3 parts with respect to each other, and lock them down at any position.

ICL = the angle between the nose and the intake centerline, in CRANK degrees. Imagine that you locate the nose exactly at some specific CRANK displacement away from TDC, such as 106° ATDC; and then locate the intake lobes such that the valves are at exactly the lobe centerline. That's ICL.

LSA is then measured FROM THE ICL: = the angle between the ICL and the exh centerline, in CAM degrees. Imagine that you measure the CAM angle between the intake lobe and the exhaust lobe, which will be somewhere around 90° apart (actually usually a little more than 90° in the real world), since the exhaust stroke comes immediately before the intake stroke in an engine cycle, and each one lasts 90° of CAM rotation (180° of CRANK rotation), and the exh valve needs to reach max opening when the piston is about halfway up in the exh stroke and the intake needs to reach max opening when the piston has finished the exh stroke, passed through TDC, and has made it about halfway down on the int stroke.

Don't post wrong and misleading information, and then attempt to invoke someone as an authority to back up your misinformation that you don't know and are misquoting. And yes, I'm a member on the Chevelle board too.

"They" say that the cam is ground "with 4° advance" because GM started grinding their cams 4° reatrded from where they had previously been starting in about 1971.

Timing chain wear is not taken into account in the cam specs. However, some cam grinders design their cams such that after a reasonable amount of wear, the ICL will be where they REALLY want it. In other words, if you take such a cam and install it "retarded" from where it was DESIGNED to be installed, it will "measure" what you think it will at assembly, but then within a short time will be retarded from where the cam designer thought it should be.

Degreeing a cam is mostly just doing quality control for the cam mfr and timing set mfr. When PROPERLY INSTALLED ACCORDING TO THE INSTRUCTIONS USING THE RECOMMENDED PARTS, they're rarely off more than a couple of degrees.

meyer30

iTrader: (2)

Well the cam was installed straight up with a compcams timing chain setup that they recommended for that cam. So according to comp it's a matching set. Well I guess I'll just concentrate on getting it running correctly and go from there. I appreciate all the info I love learning. Besides they told me it should be installed straight up. Thanks again.

Z69

Ok, so I mislead by implying others do it as Harold does.
But what does this link below mean?
See the only post by Harold.
I couldn't find the one where he is specific about my statement above.
http://www.chevelles.com/forums/show...traight+ICL%22

To paraphase the king-
ICL is = to the angle between the nose??? technical term? and the ICL.
AFAIK you can't use the name of something in it's own definition.
I KNOW what you are talking about and I still had to read your explanation 3 times to get it straight.
I prefer the definition of ICL as the point of max lift in crank degrees.

And, ground advanced from what point? How is this point measured?

Here's a little more from Comps site

sofakingdom

iTrader: (1)

The ICL is the Intake Center Line. The spec commonly given for it is the number of degrees after TDC at which this physical event occurs, in CRANK degrees. There is no use of the term in its own definition.

ICL may or may not be the point of max lift. Cam lobes aren't always symmetrical; that is, they're not necessarily the same on the opening side as on the closing side. In fact most modern cams are not (they tend to have a steeper ramp on the opening side, and a longer "tail" on the closing side to set the valve down more gently than they open it). ICL is just that, the Intake Center Line; in other words, the "halfway" point between 2 other arbitrary events that are assumed to represent the "ends" of the lobe (usually the "advertised" lobe lift points of .006" or .004" or whatever else the particular mfr uses). Meaning, in addition to all the other confusion, that people who hallucinate that they're "degreeing" their cam by finding the point of max lift, are MOST LIKELY not finding the ICL at all; and that if they then "adjust" their timing set to make the peak lift point occur at the crank angle that is given on the cam card as the ICL, they will be installing their cam WRONG. About the only cams that doing it that way will work right on, are old Stone Age ones like the Summit/Edelbrock/Melling ones, REALLY old stock cams like the 151, etc., from back when lobes were super-simple and designed by trial and error, before ramps were steep enough to need to be asymmetrical.

Yes, you're exactly right as to what that angle represents, physically; ICL is the angle IN CRANK DEGREES between the bolt & dowel pattern on the nose of the cam, and the center line (NOT the peak lift point) of the #1 intake lobe. Then from there all the other intake lobes are assumed to be at the same angle with respect to their crank journals; which may or may not be strictly true in practice, given the amount of error in lifter bore machining that exists in production-line blocks.

I'm not sure what you're not sure about in Harold Brookshire's post in there. There's no mystery in it. He's saying that every 1° that the cam is advanced, moves all the intake events 1° earlier; and since the intake on that particular cam closes AFTER the piston has already reached BDC (end of the intake stroke) and is partway back up on the compression stroke, advancing the cam 1° DECREASES the angle that the intake valve is open during the compression stroke by 1° as well. Pretty straightforward, and doesn't have alot to do with the definition of ICL or LSA; but DOES have alot to do with DCR, which is what that post is generally talking about.

Z69

I didn't just come in here trolling.
I frequently use Harold as a reference because so many people list zero references to corroborate what they post. Especially things that aren't common knowledge.
I've spent more time than a lot amatuers have figuring out to a small degree how cams work. Sufficiently so that I've noticed that the mags have started using full race lobes in the "feature" engine articles.
I've had a few phone discussions with Harold and got to the point of having to stop at proprietary info with him.

You quoted me and said I was posting misinformation etc....
for clarity from Harolds' post-
And my question of ground advanced from what point.

Since it is so hard to stop at max lift, I use the +- .050 from max lift to approximate the ICL, compensate for asymmetry, and double check what I thought I got for max lift.
Which is also easier I think to see on the degree wheel and understand what's going on. And one of the method's Harold posts to use.

Here's another one of Harolds' jewels-
http://www.chevelles.com/forums/show...light=straight

an example on cam degreeing- a lot of CC's cams are done on a 110 lsa, 106 ICL. Suppose all you check are those two numbers. How do you know what came you have? -you don't-
This happened to me on my very 1st time degreeing a cam and I got the wrong cam. There's a 262 solid cam lobe in the catalog IIRC. Which is about what I got instead of the 294 solid I ordered. And yes it did say 294S on the end of the cam. -CC tech line reponse to "I've got 20" of vac at a 600 rpm idle on a 294S" was "that's great"......note 8-10" at 1000rpm is more common for that cam.

In hindsight, it was probably a HE268 or 270H cam instead.
I'll never know since I sent it to CC for warranty.
How did this happen? Well after asking around to a few engine builders.
Apparently some/all of the shelf cams are farmed out. So 500 or a 1000 or however many x cam profiles get ground and some poor guy gets to stand there and stamp all those cores or run them through a stamp machine or whatever.
I work in automotive parts manufacturing- the date stamp we use get's done wrong frequently.

Note- I had the machine shop degree my cam 1st and they just mumbled something about the numbers not looking right but it was on a 106.
That was money well spent......

sofakingdom

iTrader: (1)

That's correct about Comp and outsourcing. Their "high volume" cams, they have somebody else grind for them, to their specs. I used to know who that was, back when 2 of my brothers worked there, but I've forgotten. Doesn't seem to matter much now, but I do recall it was someone you would expect as having that sort of capability; comparable to GM's or Ford's sources for OE cams. Comp was doing that even as long ago as when Harold worked there, when I first met him, back in the 70s and early 80s. The machines they have in-house are used for lower-volume and "custom" production. For that matter, that's what Lunati does, or at least did when Joe still owned them; Holley may do differently now; but I don't think Ultradyne ever did that, before it imploded, because Harold's volume was never such that he required it.

But as far as cam specs and all that, it's pretty much a black art to most people. Yerbasic hotrodder thinks he knows alot more about cams than he actually does. Just like you see on the Chevelle board about all the goobs that bash Comp and glorify Lunati or Isky or whoever else, without having the VAGUEST idea how any of those companies actually produces their products or operates their business. The confusion between ICL and LSA is real typical of how little most people understand even the tip-of-the-iceberg part of cam designs that the mfrs publish; and what they publish, doesn't BEGIN to tell the whole story about what sets their product apart from the competition (or doesn't, as the case may be).

But again, max lift DOES NOT correspond to ICL. You CANNOT degree a modern cam off of max lift!! Even finding the 2 points .050" off of max lift and taking their midpoint, IS NOT guaranteed to be the ICL. Doing it that way DOES NOT "compensate" for lobe asymmetry, because most of the asymmetry in modern lobe designs is nearer the seat, NOT near peak lift.