Cam Sheet does not match Can Specs

Hi,

I’ve recently degreed two camshafts Skunk2 Pro 2 and Skunk2 Pro 1 with VTEC locked and 0 lash. I used the opening and closing points at .040” to degree the cams which is where Skunk2 lists the opening and closing events. I also used the Centerline method.

The issues is that the Cam Spec sheet and the actual measurements do not match. For instance, if I dial in the opening and closing then the centerline doesn’t match. Then if I dial in the centerline, the opening and closing points do not match. There is a discrepancy of about 3-5 degrees no matter which method I used. I ended up using the centerline method for both cams even though the open and closing points didn’t match. Ended up with about 5 degrees advance from stock after all said an done.

Obviously my question is why does this happen?

Thank You!

I did the same thing with GSC power division camshafts and also found that actual figures don't match the advertised timing. I was explained that it is due to not 100 accuracy of cam degreeing and measurement process which to me is hard to believe...

I too have heard that, and I agree. The specs should be 100% accurate or there is no point in degreeing in the first place.

The problem with any valve train that has a rocker being operated directly is that the effective valve lift ratio can vary depending on which flank it is being measured on. Take a look at the camshaft lobe, rocker pivot and valve positions - now look at where the rocker contacts the camshaft lobe on the leading and trailing flanks - see how the distance between the pivot and the contact patch is different? That's why using the 'split' method for establishing the centre-line doesn't work, as you would expect with a 'bucket' type cam' follower, it's because the relative position for the same lift is different.

If one of you is dead keen, measure and plot the lift-degrees for a range of test lifts, and you should see it more clearly.

This can be rather pronounced with symmetrical lobe grinds and some cam' manufacturers 'may' supply asymmetric profiles, but not something I'm familiar with. There can actually be benefits of this asymmetry.

Pretty much all my setting up has been with 'bucket' followers, and Andre pointed out this very flaw in setup to me a year or two back, as I had also been confused by this too.

YAY, found something that should help the understanding - https://www.pattakon.com/pattakonVtec.htm

If you look at the animations, you can see the lift/lowering is clearly different for the leading and trailing flanks, so it should be obvious that when checking by lift the 'centre-line' will be continuously changing.

I’ve never heard of pattakon until now and thats absolutely fascinating. I’m going to have to sit with that for a while. But I do believe I understand now what you’re saying. It seems now that there has to be a compromise in order to degree these honda cams and you have to use one method. So my next question is, which method should I use?

Neither had I, I was just looking for something to illustrate what I was trying to convey and I think that did it beautifully. Good read, too.

Use the opening and closing points as they're what have most affect on the camshaft characteristics, from what you said, it also seems to be their official method?

I'm not sure which method Skunk2 recommends but they have an instruction on how to degree cams and they use the centerline method.

Ah, I mis-read what you'd said - looks like you'll need to contact them directly - nothing on their interweb site about this, maybe in a FAQ section?

I'm just going to email them directly

Hi John did you get a reply from your email i would be interested to know what the out come is

Regards ross