Alright, so humour me please b/c I'm a bit of a nerd when it comes to wanting to know how all that theory actually translates to differences in real world.

We've all heard that "area under the curve" is a good metric as far as cam's ability to make power. Idea being: per given crank degrees rotation the further the lobe profile is lifting the valve off it's seat the greater that area, the better the flow potential, etc. There is of course far more to the whole picture as far as the actual ramp profiles, valve opening and closing events and all that jazz go, but I'm a simple guy and so with the equipment available to me I wanted to visualize the differences between a fairly closely spec'd two camshafts:

Allow me to present:

Exhibit A
Hughes Engines HE3844AL - hydraulic flat tappet
286/290 advertised duration
237/244 duration @ 0.050"
INTAKE - opens 13 BTC, closes 44 ABC, max lobe lift 0.357
EXHAUST - opens 53 BBC, closes 11 ATC, max lobe lift 0.360
108LSA

Exhibit B
CompCams XR292HR based custom grind (13084B and 3039B lobe profiles but on 112 LSA and ICL of 108)
290/300 advertised duration
240/248 duration @ 0.050"
INTAKE - opens 12 BTC, closes 48 ABC, max lobe lift 0.365
EXHAUST - opens 60 BBC, closes 8ATC, max lobe lift 0.363
112 LSA

Alright, so small differences to an amateur like myself, but the big deal here was the chance for me to measure the lobe profile (lift) for both of these cams and compare them (the HE3844 was in my 360 motor, that came out, and the XR292 is going into the W2 stroker that's finally on the engine stand and currently being worked on).

Without further ado, here is what I came up with:



Bottom line: the area between the solid and the dotted lines is the EXTRA area under the curve that the roller cam brings. It is interesting that while the opening ramp adds a good amount of extra lift for a given crank deg. rotation, that same is not true on the closing side. In fact it is the flat tappet cam that is a bit more aggresive here having just a little more lift until the valve is back on the seat.

I measured this by capturing the lobe lift with a 0.0005" precision indicator directly against the lobe (using CompCams #4926 cam lobe follower / lift checking tool) every 5 crank degrees.

Kind of neat to finally see that difference, and so I thought I'd share!

EDIT: I attached the chart image if the on-line posted stuff is not coming up...side-effect, it looks like for everyone else who sees the on-line version there are now two images showing up (they are the same).

Your linked image isn't coming up

Its coming up for me.

Where the area change is located is important.
The only way to get the 2 curves congruent is to design one of them badly (disregard thrust, acceleration and velocity limitations).

I've mentioned this before here and elsewhere, with absolutely no interest.
It was discovered long before engines had roller tappets that the entire lift curve could be significantly tweaked by moving the tappet centerline (body, axle, 6:00 o'clock roller position) laterally away from the center of the lobe base circle, Generally it's advanced (a lobe rotating CW will have its tappet moved to the left).
Why doesn't anyone use it?
Harley-Davidson did on every engine they built for 60 years.

Is the flat tappet foot for that tool .904” diameter?
If it’s smaller, there’s a good chance the edge of the foot was making contact with the flank of the lobe.

Nope, it is not. It's the Chevy 0.840-2 size...which you can easily spot since there is plenty of room in the lifter bore as you set the tool up. To double check I did actually setup my timing rig and used the matching lifter, the numbers came out the same. So it must be just the nature of this cam that it worked out fine on the lobes I measured (basically did all the ones on the Driver side bank since it was visually easy to see the lobe lift as I turned the crank).

You know, if there is one remark I will make it is the following: there were several lobes on that flat tappet cam that absolutely were NOT up to spec, and/or perhaps actually wore down?

Several of them had up to 0.020" miss in the lift, and that matched up when I mic'd the lobes aftwerwards. No obvious wear otherwise, but to my eye it seemed like the nose of the lobe was starting to wear away...the otherwise shiny (on other lobes) spot was gone and instead it appeared dull gray.

Anyways, this engine was in my weekend driver, all of about 6K miles over about 8 yrs of summer cruising, always using Valvoline VR Race Oil (10w40), so good ZDDP content with great oil pressure. I will post some pics in another thread since I'm not quite sure how to interpret the bearings wear (normal vs abnormal) not having done much of this kind detailed engine tear-down before.

Do you have more details about this? a diagram for comparison maybe?
Thanks

The cam is going away.

Change it now before the failing cam lobe debris kills the bearings

Oh you guys, that motor is all done now. I already pulled it from the car, stripped it down to just the single piston (#1), the cam and the timing chain and thought it was the perfect time to do this little "science experiment".

Like I said, I was always curious what the difference of a hydraulic roller vs flat tappet lobe profile would be on two cams that are very similar in specs, which I think these two are.

Just a theory: but with no other data available, I’ve always looked at the relationship between the advertised number and the .050 number, and figured that was a fair indicator of how aggressive the ramp of a given cam is. IE: the less less variance between the two numbers, the more aggressive that lobe must be. This assumes a LOT, I know. But if it takes one lobe less rotation to get from seat to .050 than another lobe, the former would be more aggressive and offer more area under the curve than the ladder example. My assumption is that that same ramp speed continues up the curve, so to speak.

??? Thoughts?

The comparison between the cam specs and the graphs is puzzling.

It is hard to pull exact numbers from your graph, but based on your measurements the @0.050 specs on the CompCam are not correct. By the graph it appears the 0.050 intake for the Comp starts at 171* and the close at 294* or 2 x (294-171) = 246, What are your actual measurements? The 0.050 intake duration numbers for the Hughes cam looks accurate, at least based on the graph. I understand the roller should get to 0.050 faster.

Also, in the specs for both cams the intake opening point is almost the same (are those 0.020 numbers?), but the graph shows otherwise. The graph has the intake closing point almost the same but the specs say otherwise.

Advertised duration for the Comp also may be off by a fair margin, again based on your measurements, but it is hard to judge the opening point.

In order to compare the area under the curve, I presume these cams are considered similar. By my reckoning, the Comp cam is 8-10* bigger than the Hughes. Am I missing something?

Dave