Comp Cams catalog, see attachment, specifically the RED square.

What are the two columns in that red square telling me: is this a tappet lift @TDC for a 106 and 110 LSA cams, or is this for an INTAKE (intake lobes shown in the example) centerline of 106, or...?

If either one, how does that work given the number of different combinations we can all put together?

Seems like I am missing something blatantly obvious here...possibly because I have NEVER had to do this before!!!

I am asking because I think the custom ground Comp Cams hydraulic roller cam I have here (bought 2nd hand from a national retailer's sale of "returned items", still brand new, so was never used) actually has the WRONG exhaust lobe on it. I just installed the cam in the block, went to degree it in, the INTAKE was pretty good (although a couple of degrees advanced actually) but the EXHAUST is completely out of whack. The durations do NOT match what the cam card says they should be, and so I'm in the process of reverse-engineering it to figure out of the 3 possible lobes that are closest catalog match to my numbers, which one is actually on the cam.

Thanks!

With the cam installed at 106 ILC it should have that lifter lift, lobe lift, at TDC, same on the other number, I think.
Have you tried calling them?
If not maybe you should, especially since it is a custom grind the exhaust lobes may be ground on way different lobe centers than the intakes are

I would also do a check at .050 lobe lift and again at .050 lift before closing to get the duration at .050 for the exhaust lobes as well as plot the lobe center on the same exhaust lobes. I would check both the #1 and # 6 lobes on the intakes and exhaust to make sure if it is ground goofy or just a custom grind
Sometimes it takes work to make sure you got the deal you wanted and hope for, especially on camshafts
Please let us know what you find on this rascal

That indicates tappet lift for that particular lobe number installed at 106 degrees centerline and 110 degrees centerline. It can apply to an exhaust lobe @106 btdc and @110btdc, or an intake lobe installed @106 atdc and 110 atdc. These specifications are just for a lobe placement in relation to the piston @tdc and makes no referrence to another lobe such as LSA.

yep!

Find a shop that has a cam doctor. In 5 minutes you will know what you have. I got a cam from Edelbrock one time, started to degree it and nothing would jive, local machine shop has a cam doctor, not only was it the wrong cam, it was not even a cam Edelbrock had in their catalog. Other nice thing was when I said I checked it with a cam doctor, there was no argument, just an apology and a new cam in the mail.

http://www.powermechanics.com/camdoctor.html

OK, thanks you guys. Looks like my 2nd guess, which is that these were lobe centerline references was the correct one.

Here is what I have found so far:

1) INTAKE - lobe ID 13084B
- found the centerline, that being 108, so spot on
- found the duration at: 0.006, 0.050 and 0.200, all these being spot on
- found the valve OPEN & CLOSE events to be actually 2 deg advanced: cam is a 112LSA but with 4 deg advance already built in, meanwhile my numbers imply that the valve timing itself is actually 6 deg advanced, that could be a good thing to bring the torque curve a bit lower I think?

2) EXHAUST (the ugly child) - lobe ID 3039B
- found the duration at: 0.006, 0.050 and 0.200, none of these match
- found the valve OPEN & CLOSE events to be off by about 4 deg per each side, so: OPEN is actually 63 BBDC (as oposed to 60 per cam card) and CLOSE is actually 13 ATDC (as opposed to 8 per cam card)

Take a look at the attached images. I've included the Comp Cams cam card (which is where the lobe IDs come from), the cam etching markings match what the cam card shows. I've also included the marked up XR292HR-10 cam card (off the shelf - which is the closest matching spec) which I marked up with the 'per design' specs and 'ACTUAL' specs I'm measuring.

In short, it looks like the INTAKE stuff is pretty good (for an amateur like myself LOL), but the EXHUAST is about a step bigger, so 256@0.050" as opposed to 248@0.050".

I will go back and re-measure all this again.

So far in my research to better interpret the above results, and piece it all together, I found the following handy site which calculates some of the cam specs based on the cam timing events => Cam Specs Calculator

The results are as follows:



If my measurements are correct I am not sure how to interpret the impact the bigger EXHAUST lobe has on this cam. Keep in mind, this is going into a W2 408 stroker with 4K stall 727, 4.10 gearing out back and 3600 lbs total vehicle weight, this being a 95% street car.

My suspicion is that the longer exhaust duration may actually allow for better higher RPM breathing, which may be complementary to the stroker's ability to compensate at the lower RPM level for the over-scavenging that longer exhaust duration will bring. Again, with far too much reading and too little hands on experience of my own, this is all pure speculation! lol

I'm heading out to the garage right now to MEASURE the actual EXHUAST centerline because that calculation of 115 seems awefully ugly looking?

If I came up with those measurements for that cam card, I’d send it back.

I'm BACK!

You guys...so a bit of self-made problem here (wrong number pulled from the degree wheel), but at least having re-worked the numbers (double and triple checked now against two cylinders as per Cab's advice) the results clarify why the cam specs are what they are.

Sooo...without further ado, here is what the actual specs are:

1) INTAKE
- 296 advertised (0.006) duration
- 248 @0.050"
- .364 lobe lift

2) EXHAUST
- 300 advertised (0.006) duration
- 256 @0.050"
- .363 lobe lift

3) LSA
- confirmed we are on 112

4) Installed INTAKE lobe centerline
- 110

5) Lobe Centerline
- 108

Which all means that this cam is a bit bigger than what I had originally thought it was: 248 vs 240.

I have now spent about 4 hrs trying to get through to Comp Cams (multiple occasions, stuck in queue, finally gave up), and maybe it's just the season, or maybe it's the whole COVID thing, but I'm giving up and just want to move on with my build!

Therefore, my question to you all is somewhat changed: given the ACTUAL cams specs, will my static CR of 10.3 be a problem?

Keep in mind this has to run on 91 octane pump gas. Installed straight up this gives me a DCR of 8 (with 163 projected psi) and advanced 4 deg bumps me to 8.25 (with 170 projected psi). Take a look at the attached screenshot, I ran a few "what if" scenarios there. The top table shows the NEW roller, the bottom one has the pertinent figures for the old Hughes HE3844AL cam, which was installed straight-up (highlighted in GREEN) and the calculated DCR numbers matched very closely to what the actual cranking compression psi reading was (185-190).

Seems like this would be within the safety marigin, but given the duration of the intake it just feels like I should be at 11:1 static at least.

What do you think?

What does #5 mean?

Oh man...I am freaking out here, not another "ooppsie..." I hope!

Alright, so here are the verbatim instructions I am following while calculating for #4 and #5. These are literally a copy/paste from either the Comp Cams "Cam Degreeing Instructions" PDF, or the WebCamshafts Calculator page I have been referencing.

#4 - Installed Intake Centerline @0.050" (WebCamshafts)

Take the open number plus the closing number plus 180°, which will be the duration at .050. Next divide the duration into 2. Subtract the open from that number, which will equal the centerline of the intake cam.

+14° Opening Before Top Dead Center (BTDC)

+54° Closing After Bottom Dead Center (ABDC)

+180° Distance from Top Dead Center (TDC) to Bottom Dead Center (BDC)

=248° Total Duration @ .050 inches of lift

248°/2 = 124°

124° - 14° = 110° Lobe Center

#5 - Lobe Centerline (CompCams Instructions)

It simply involves positioning the center, or point of maximum lift, of the #1 intake lobe with Top Dead Center (TDC) of the #1 piston. In other words: get a measure 0.050" before, get to the top of the lobe and down another 0.050", capture the numbers, divide by 2 and you have the answer.

61 ATDC + 158 ATDC = 219

...now dive by 2 = 109.5

So actually, Thank You because I goofed in my spreadsheet and in fact that should be a 110 instead of 108 that I had in my previous post. Now I have the correct match between #4 and #5.

That number points out one more incorrect spec on the cam card, because the cam is supposed to have 4 deg advance ground in and it appears it only has 2 degrees.

Make sense?

"That number points out one more incorrect spec on the cam card, because the cam is supposed to have 4 deg advance ground in and it appears it only has 2 degrees."

Well, the cam gear, crank gear, crankshaft key, crank throw......any of these can account for the 2 degrees of mismatch. I've got four or five sets of b-block timing gears/chain. Single bolt, 3-bolt, Mopar Performance, RollMaster, TRW, El-cheapo gear drive and something else. All sets are off a little. The MP was the worst with the timing dot on the wrong side of the gear...No joke.

I don’t see that it was asked........

What are you using for a cam follower for degreeing purposes?

Valid point...in my case, I am using the direct cam lobe follower, and since this a roller I am using the 'rounded/ball' follower as well.

Take a look at the attached photos.

Both the piston TDC and the cam lobe lift dial indicators are is 0.001" with a full sweep avalable (so no binding or hanging anywhere).

So a different diameter ball would also give different readings, have you used the roller lifter & checked the #'s ?

I would use the lifters your going to run in the motor to check the valve timing, not something that will never be in a running motor
Make sure the stem of the dial indicator is aligned with the travel of the lifter also, side to side and front to back
Have you heard the old adage that Murphy hates hot rodders and drag racers HE DOES

csk,


Hmm, well, I always thought the reason for different diameter wheels was to handle the faster cam lobes. Meaning, the larger the wheel, the steeper the lobe I can build, otherwise the lobe lift rate/curve may overcome the roller's ability to "climb it" safely. To put it in other words: if you were to size down the diameter of the wheel to an ever smaller value, eventually you would get to such a small diameter (that it's effectively a point) which would simply dig into the lobe regardless of how small of a lift rate that lobe actually has, and basically anything but circular lobe would cause that point to dig-in.

Otherwise, the movement (lift) the lobe imparts on the wheel/follower is linear, is it not?

Anyways, both you and Cab_Burge suggest a good alternative approach, one which I would have to do next anyways as I needed to check the valve to piston clearance. So I might as well toss the lifters in there and set things up to read the degrees right off of these.

You know, I picked up that cam checking tool specifically to rule out any possible geometry distortions one might get into if the measuring jig isn't quite set up perfectly, and the angles introduce some lost lifter motion.

Alrigth you guys...I have just about beat this thing to death multiple times now!

Here is what I have concluded: the bigger duration @0.050" metrics only appear to show when checking with the CompCams direct lobe follower checking tool.

Not exactly sure why, I would have expected that if the checking tool's lobe follower had a larger diameter ball tip (as compared to the diameter of the roller lifter wheel itself) that may have added a couple of degrees, but overall I saw a +4 on the front and +4 on the tail end longer duration, that seems like a LOT.

The actual follower tip diameter is 0.750", and while I'm not sure what the CompCams roller lifter wheel diameter is (8920-16), it honestly does NOT look like they are all that much smaller...soooo what gives?

The thing that's got me scratching my head is the following: initially I checked the INTAKE lobe first, and I was using the direct lobe follower right from the start. The numbers I got matched what the cam card showed, it is only once I checked the EXHAUST lobe that things started to look weird - by all accounts I was looking at 240 on the intake and 256 on exhaust. Per the feedback I got from you guys I went back to re-checking all the numbers and at this point in time it looks like I introduced something else to my process that picked up those +4 and +4 extra degrees of duration.

So what happened here? I cannot believe that the follower is causing this, it must be something else that I'm doing (or how I'm doing this), but I have absolutely nothing to point to...ughhhh???

I always use the lifter I am going to run, this is why !!!!

At this point, I’d say enough man hours have already been spent checking that cam over.

Pick an intake c/l and button it up.

I think CSK means THAT is why, the motor knows what the valves are doing when running, that is the main reason to use what you will have in the motor to do your cam degreing
As far as the lifter wheel diameter affecting the valve opening and closing you need to do that test on the lifters on both the .750 and a the .820-wheel diameter and write the results down and then check it at the valve retainers You will learn some more on what affects valve timing and lift at the retainers up:
BTW, did you know Murphy loves messing with us hot rodders and racers