[Geronimo]

I have a Comp 290b that I purchased in 1994. I printed a new cam card off Comp's web site and it states valve timing at 0.015". Duration is listed @ .050". I am degreeing this cam in and I get incorrect numbers @ .050" lift. Some I assume I am supposed to use 0.015" lift to get IO and IC measurements. However, when using 0.015" my degree wheel indicates I need more advance, and I can't see how that is unless the cam was not ground correctly originally. Did Comp cams alter the centerline back in those days? I want a 102 centerline which should equate to 4 degrees of cam advance, but I have advanced the cam 4 degrees and retarded the crank 4 degrees and am still have a 106 centerline? Please help this idiot understand cam degreeing!

Thanks Geronimo

[prostreet64]

Isn't the .015" the valve lash?

[prostreet64]

strike my last comment; lash won't have any bearing on degreeing-in the cam. But I do think the numbers for that cam are made at .050 lift.

[440GP69]

most cams are not ground correct and will be off a few degrees, some more than others, i personally have seen 4 degrees off

[screamingchief]

Full 290b6 cam specs: Part #51-659-5
Comp Cams 290b6 solid: (another popular catalog grind)
Spec = intake/exhaust
Adv.Dur. = 290°/304°
Dur. @ .050" = 255°/266°
Lobe lift = .360"/.356" Rec.lash = .026"/.028" w/1.5 rr
LSA = 106° ICL = 106° ECL = 106°

.050" events:
IO = 21.5° BTDC
IC = 53.5° ABDC
EO = 59° BBDC
EC = 27° ATDC
O/L @ .050" = 48.5°

Seat events:.020"
IO = 39° BTDC
IC = 71° ABDC
EO = 78° BBDC
EC = 46° ATDC
Total O/L = 85°

As for your degreeing issues,hard to say for sure,your description is kinda confusing.

You say you advanced it 4° at the cam,and retarded it 4° at the crank,are you saying you did both of those simultaneously???

If so conisder that some chainsets are marked by how much the move the deal in cam degrees and not crank degrees as that is easier for most folks to understand during degreeing,so if you did both (adv. 4° @ cam/ret. 4° @ crank) you would then have just canceled out each of those by doing the other.

Always make one change at a time.

I usually look for the IO @ .050" event first as a "quick & dirty" check of where I am,then I go ahead and do the "over the nose" centerline checking procedure to confirm that IO event,if those both agree with one another,likely the cam is where it's supposed to be.

Looking @ the "seat" IO event can be misleading at times,often it's just too close to the lash ramp to be reliable for this purpose.

And do note the 290b6 is usually not ground with any advance or retard,it is usually ground @ split overlap (or "straight up" if you prefer).

HTH.

[Geronimo]

I really appreciate all the information ( especially the specs). I started off dial indicating off the lifter. Since I now have the heads on I am using a HS rocker @ 0.00 lash. Food for thought, I believed if you retarded the crankshaft behind of rotation, that was the same as advancing the cam? Because once the crank reaches a given position the cam will have gotten there first, rotated further that is. Maybe I'm backwards on that, but that is how I see it. I am going to recheck everything and will post what I am getting. Currently I have placed the crank sprocket back at 0, and have a 4 degree advance key in the cam.

Thanks again
Geronimo

[TIN TIGR]

set io at 23 to 25 degrees btdc..run good exhaust and hold on..is this a 400 or 455?..what heads?..ask lucerne what he sets his at..

[Geronimo]

Okay Guys,
With a 2 degree advance key in the cam my IO was 32 and IC was 61 @ .020" This should make ICL 104.5. I then installed a 4 degree keyway from Butler and got IO 41 and IC 52 @ .020" This would make ICL 96. That seems a little tight?? I was hoping for 102 ICL. I will recheck IO and IC at .050", but I believe IO was 24.5 and IC was 35 giving me a ICL of 95.25. It is a 1967 firebird 406, ported d-ports, torker 2, 750 Holley DP, balanced, filled cross over, hussler 2" hedders, m20, 3:36 rear. I would love to run low 12 seconds??? So should I leave it with the 4 degree keyway in there? Or go back to the 2 degree?? The only issue I have is I want the car to flat get it.

Thanks
Geronimo

[screamingchief]

Ok,,,please explain to us how your coming up with these numbers???

They're all over the place and not even close to adding up here...

An IO of 32° BTDC @ .020" would indicate 7° retarded here,and your closing event number of 61° ABDC would be slightly off here as well.

And I have no idea how your getting a 104.5 ICL from those events???

The intake lobe @ 7° retarded based off the IO event would put the centerline around something like 113° ICL...

With an IO of 32°,do the math with an IC of 61°,and I cant get anywhere near that 104.5 ICL with your numbers???

Trying to figure out your math is making my head hurt!!!

With a 104° ICL the closing event should be @ appx. 69° ABDC.

And the IO event would be appx. 41° BTDC.

That would be 2° advanced...

Simple enough I would think.

Second set of numbers are'nt much better either,the centerline is wrong again,and the exhaust closing event is waaayyy off again???

See above,with a 96° ICL,the IO would be 49° BTDC and the IC 61° ABDC @ .020".

That would be 10° advanced to get a 96° ICL.

If your checking based on the valve events,your just looking to confirm the event numbers on the cam card,no complicated math is really needed to compute the ICL here.

What you need to grasp here,is the opening and closing events both move together in a fixed relationship,if the intake opens earlier,it's gonna close earlier too,and the relationship to the centerline is fixed as well,all you can change is the positon relative to the crankshaft via the installed centerline.

Generally speaking,I dont even mess with looking for the closing event numbers,if the opening events are right,the closing events will be,short of the cam being ground incorrectly or such.

Like I said,I start by looking for the intake opening event,then I check the "over the nose" centerline by checking .050 down from peak lift on the nose,adding those two numbers,and then dividing to get the centerline,if the IO event and the "over the nose" centerline are in agreement,the cam is where it is supposed to be.

So for the 290b6 @ 4° advanced,I would be looking for something around a 25.5° IO event @ .050" (or appx. 44° @ .020"),and the "over the nose" centerline measurement as 102° to confirm said 4° degrees advanced ICL.

Also,I never set-up the dial indicator to read off the rocker,it just adds to the list of possible candidates for adding error into the mix,get some longer dial indicator mandrels and get your readings directly off the lifter itself,less room for error that way,much more accurate IMHO.

HTH.

[79TA455STROKED]

Not to hijack but
I just degreed my solid roller.Cmae in at 112 so i adv it 2 deg to get the 110icl they wanted on the cam card.
How do you check the IO,IC and EO,EC points?

[screamingchief]

Originally Posted by 79TA455STROKED

How do you check the IO,IC and EO,EC points?

By closely watching the dial indicator and then checking the degree wheel when you hit the right point on the lobe.

The catch is you need an über-stable dial indicator set-up to get accurate & repeatable results,and you always gotta turn the engine over in the same direction to keep the slack in the chain from throwing the results off.

And as I said,I normally dont mess with checking the closing side,unless I'm getting funky readings on the opening side or something else is'nt as it should be.

Though I almost always end up triple checking mine before I'm convinced it's where it should be.

If I can get the IO event right,and the "over the nose" numbers where they should be,and get both of those to repeat within a half degree or so three times in a row,I'm pretty much done.

If this process is done "right",the numbers will repeat.

[79TA455STROKED]

I have the pro comp cam wheel setup.
Do you put lifter on base of cam,zero out the dial ind and then rotate till you get the .020 or .050 lift and then check degree wheel for io?
I had no problems degreeing cam,repeated 5 times to make sure it was rite and it was dead on!

[screamingchief]

Originally Posted by 79TA455STROKED

Do you put lifter on base of cam,zero out the dial ind and then rotate till you get the .020 or .050 lift and then check degree wheel for io?

Yessir,that is pretty much how I do it.

That's why I feel it's better to "quick check" that IO at the .050" point,at .020" your still fairly close to the lash ramp on a solid cam,and it can often be hard to tell just how far the valve is moving at that point,but by .050" it's a whole lot clearer IMO.

[issach428]

Are you sure you are on the intake and not the exhaust? I did that a while back and got so frustrated because everything was coming up wrong, then i realized i was on the exhaust lobe..... I wanted the icl at 104 and kept coming up with high 90's.

[Geronimo]

I most certainly am on an intake lobe. I am using an old cam dynamics degree wheel and it states on the wheel to find ICL (equals Duration divided by 2 minus IO). And duration is IO plus IC plus 180. I was degreeing off of the top of the rocker arm. My numbers would repeat time after time so WTF!!! I need to buy a real set-up, but the cam ran great with 2 degrees advance, it will run ok with 4 degrees advance. I would like to know where screamingchief came up with the 290b specs. Comps printable version of the cam card had few of those figures. Thanks for the specs. Is this not how we find ICL IO plus IC plus 180 divided by 2 minus IC

Anyway thanks to all who helped
Geronimo

[70 lucerne lemans]

I have mine advanced 4* .The specs Brett posted look correct from memory,I know the Comp website is wrong with the specs they have listed as being with 1.65 rockers.Your car should run well,your headers might be too big with the 400 ,unless your winding it up pretty good.Im not going to pretend to know everything about cam events and degreeing,that stuff gives me a headache,Chief has you covered there.

[Skip Fix]

I usually use the 0.050 down each side of max lift for getting the lobe centers.(add together divide/2-old UD way I think Comp has it in their book too). I use the other cam card numbers just as another double check.

[screamingchief]

Originally Posted by Geronimo

I am using an old cam dynamics degree wheel and it states on the wheel to find ICL (equals Duration divided by 2 minus IO). And duration is IO plus IC plus 180

Those formulas are right,but there is something wrong with their use here.

No offense intended,but you kinda suck @ math Geronimo.

Dont feel bad,I'm not a huge fan of math either,but this stuff I do in spite of my distaste for the stuff.

Your stated degreeing results:
IO ~ 32
IC ~ 61
ICL ~ 104.5

Now do the math using those formulas,seeing as were talking the intake lobe,take and divide the 290° of seat (.020") duration by 2,you get 145,this number will be the same for every problem looking for seat events using that formula as the intake duration is a "known quantity" and does not change for this computation.

Now subtract the IO events from that 145,so 145 - 32 = 113,so you indeed end up showing an ICL of 113°.

Just as I said above,using those numbers that cam was retarded 7° when showing an IO event @ 32° BTDC...

Do the duration math and it's obvious your numbers are incorrect somewhere.

32 + 64 = 96 ~ 96 + 180 = 276° duration,WRONG were looking for 290° intake duration,so for sure that IC event is off here,as is the 104.5° ICL you quoted.

See why I said it was making my head hurt...

The second set of numbers is only slightly better,in that you get close on the IO event,but all the rest is still a mess.

IO ~ 41
IC ~ 52
ICL ~ 96

290 ÷ 2 = 145 ~ 145 - 41 = 104,so with the IC event @ 41 you would have a 104° ICL.

Said that above as well...

But then you look at what you stated for an ICL,,,96° ICL???

Like I said,I dunno how the hell your getting those numbers,but something is wrong here.

Then go and do the duration deal again.

41 + 52 = 93 ~ 93 + 180 = 273,WRONG AGAIN,with this deal were still looking for the 290° duration figure,and again the IC event is suspect at best.

Lets try the .050" numbers:

IO ~ 24.5
IC ~ 35
ICL ~ 95.25

255 ÷ 2 = 127.5 ~ 127.5 - 24.5 = 103,so there you go,a 103° ICL based on the 24.5° IO event.

Your "computed" ICL,,,95.25???

Like I said,I have no idea how your getting those ICL numbers.

Lets see what happens when doing the duration math on those .050" events.

24.5 + 35 = 59.5 ~ 59.5 + 180 = 239.5,,,hmmmm,,,WRONG yet another time,,,remember,,,now were looking for 255° of duration @ .050".

I'll let ya'll in on a little secret,I've repeated it enough times already,so it's not like I've been holding out on ya'll,just ignore the closing side of the lobe when checking valve events,they'll just confuse and mislead you!!!

If the opening side is where it's supposed to be,the closing side should be as well,but you wont always be able to see that very well on a degree wheel,but the point is short of getting a misground cam,you often hafta take it on faith that the grinder got that part right.

Quick check with the IO event,then do the centerline check "over the nose" to confirm the installed centerline,adjust as needed,repeat checking process till you get it where you can live with,and then your done.

Pretty simple when all is said and done.

HTH.

[screamingchief]

Originally Posted by Geronimo

I would like to know where screamingchief came up with the 290b specs.

Are you sure???

It means more math...

Not a whole lot different from the math formulas on your degree wheel.

I've posted that info before,can "cut & paste" it here if you want me to.

The one thing it does'nt account for 100% is asymmetric lobes though,but even with those lobes it will still be within a degree or two in 90% of those cams.

But as it relates to that,do note that the 290b6 lobes are "old school" lobes,and IIRC they are'nt asymmetrical,I believe they are symmetric,so for that cam those formula computations should be spot on,and I know my numbers always matched the comp numbers on that cam dead on,have checked them more times than I care to mention.

But short of a cam-pro or cam-doctor computerized analysis and printout,an average fella would be hard pressed to beat the accuracy of a few simple mathematical formulas.

HTH.

[Geronimo]

You are indeed a wise one. I believe I need to throw that old (too small) cam dynamics degree wheel away, and I am going to get an indicator that mounts in the lifter bore. But I do now know why my numbers were so screwed up . I had a couple of ideas that were, well not worth a crap. Reading you explantion made sense! I would agree my ICL is 103 or damn close to it. For some idiotic reason I was computing math that wasn't needed and taking intake closing readings incorrectly Duh! I got over excited and a bit nervous being a virgin at degreeing a cam. Like a lot of things I overcomplicate procedures that should be simple. I will keep checking cams until I get the complete hang of it.

Thanks agin,
Geroniomo