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Is degreeing REALLY necessary?

September 2 2013 at 11:23 AM
M.Rad.  (Login MRad)
Member
from IP address 70.195.196.9

Hi guys- my previous thread regarding cam selection highlighted my abysmal lack of understanding regarding cam timing.
I have read on this forum and in the mag.s that one should always degree a cam before running it.

I'm somewhat reluctant to mess with changing the advance or retard of my cam, simply because I may mess something up.( I was looking at my Summit-brand degree wheel while posting and still couldn't figure out my LSA)

So my question is this- is it really necessary to degree cams in these modern days? I mean, I'm sure the cam grinders are seldom, if ever, very far off on their grinds. Has anyone recently degreed a cam and found it to be badly off? How much?

And if a cam is off by, say, two degrees-how much power or driveability would I be leaving on the table? I get the impression it wouldn't be more than 5hp/tq. Am I right?

Besides, I'm sure I'll leave more than that on the table through limited tuning ability on my carb and dist. advance curves...

Regards,
M.R.

 
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tinman
(Login tinman351)
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108.83.220.115

Re: Is degreeing REALLY necessary?

September 2 2013, 12:17 PM 

maybe the cam isn't off more than 2*, but what about the timing set?

these are all set on '0', where's yours?

[linked image]

2* degrees I wouldn't sweat at all, but I would set the 2* to the Advance to compensate for inevitable chain stretch, rather than to the Retard where the 2* will grow to who knows what eventually

LSA is ground into the cam, that info is available on the cam card, it'll also say something like 'installed at 106* Intake Centerline' or ICL, that's what you're checking for while degreeing

do you have a link to the cam / card info?

there'll be phantoms, there'll be fires on the road... and the white man dancing


    
This message has been edited by tinman351 from IP address 108.83.220.115 on Sep 2, 2013 12:19 PM


 
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tinman
(Login tinman351)
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108.83.220.115

cam math by Randy GT350HR

September 2 2013, 12:22 PM 

original post here,
http://www.network54.com/Forum/119419/thread/1236232389/calculating+dynamic+comp+w-solid+lift+cam-

.050 lift figures are taken off of the proper style lifter for the cam or the end of the pushrod without the rocker installed to make it easier to setup the indicator. Seat to seat duration can be checked at the retainer and that's done with the correct lash and spring.

Opening and closing events can be calculated IF you know to things, 1 duration @.050 and 2 the actual lobe seperation ground into the cam.
Example, 240 @ .050 w/110 lsa would be I.O.=10*BTDC-I.C.=50* ABDC.

This is because the IO and IC + 180* has to = the total duration @ .050. A symetrical cam would flip flop the numbers and read EO @ 50*BBDC and EC @ 10*ATDC. So how the hell did I figure the 10 and 50? Ok here's a quick formula-------
IO=1/2 duration @ .050 minus lsa. 1/2 of 240=120-110=10
IC=duration @ .050 minus IO minus 180. 240-10-180=50 (10+180+50=240)
EC is the same as IO
EO is the same as IC

So now your a math scholar right? What about cam advance and retard and those damn dual pattern cams? Let's use the simple single pattern example with 4* advance. Advancing the cam changes the INSTALLED LSA to 106 this causes the exhaust to READ 114. WHY? Because the lobes are ground into the cam blank and will ALWAYS stay 110 on our theoretical cam, or whatever the grinder chooses on your blank. UNLESS you have dual overhead cams that's the fact.
So using the formula,
IO 240/2=120-106=14
IC=240-14-180=46
EC=240/2=120 114=6
EO=240-6-180=54
Now we're really getting somewhere!

Final exam is a dual pattern, advanced cam on a tight lsa (JOE'S favorite) 278-286 on 106 lsa +4* adv.
IO 278/2=139-102=37
IC=278-37-180=61
EC=286/2=143-110=33
EO=286-33-180=73
Again because the cam is advanced 4* the int is "in @ 102 s the exhaust has to be figured @ 110 since 102+110=212 divided by 2=106 the actual LSA ground on the cam...

Randy

there'll be phantoms, there'll be fires on the road... and the white man dancing

 
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M.Rad.
(Login MRad)
Member
70.195.196.9

Re: Is degreeing REALLY necessary?

September 2 2013, 12:35 PM 

Hi tinman- wow, that's quite a varriation. I guess what you're saying is that the inaccuracy may not be in the cam grinding so much as in the other components, or the stacking of several components? I can see how this could add up to more and more error. How noticeable is an error of say, 5-6 degrees?

As for my cam info, I have the card with me, but it didn't have overlap and LSA printed on it. Joe and George figured the LSA for this cam, but I'm still playing with the degree wheel to try and duplicate the results on my own. Little success, getting dizzy...

I read the cam timing tutorial on the Iskendarian website http://www.iskycams.com/techinfo.php) and was amazed how close my particular cam spec.s were to the theoretical example- within 2 to 4 degrees.

Anyway, between learning to read the wheel and set up the dial indicator, etc. it doesn't look like I'm going to master this in a weekend. Thanks for the illustration!
Regards,
M.R.

 
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tinman
(Login tinman351)
Member
108.83.220.115

you'll be an expert in no time

September 2 2013, 12:48 PM 

after I started posting to this thread I saw the other... just set up the timing set at '0' and find what the ICL (Intake Center Line) is and go from there. if the ICL comes up as 112*, you want to set the timing set in the + position. if it comes up @ 110*, still go to the + position and you'll be waiting for 2* chain stretch to get you to 108*

yes you need to consider the 'stacking' of component variation, sometimes they will cancel each other out, other times they'll stack enough to cause you to make an adjustment... no big deal it's just which key slot you use

some valve timing events aren't as critical as others as George points out, the exhaust close & intake determine overlap. you can't change the amount of overlap but you can control to some degree (no pun intended) where the overlap is centered. 6* to a certain valve event can be somewhat of a deal breaker, otherwise they would've ground the cam that way in the first place

give it a shot, set up the degree process & play with it until it starts making sense. there are several tutorials as you may have already found out in the 'net box

there'll be phantoms, there'll be fires on the road... and the white man dancing

 
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Falcon67
(Login Falcon67)
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209.165.224.67

I vote yes

September 2 2013, 3:31 PM 

Seen too many pieces of the puzzle off in various directions. I like to know what the number is and if it's right. That means dial indicator, lifter tool and a degree wheel. That sets the cam in place and gives you TDC which can then be used to verify the damper marks, or to create the correct marks. And that goes right to ignition timing where a couple of degrees here and there can make a difference.

1967 Falcon 4 door 351C-4V
1970 Mustang 351C-2V
http://raceabilene.com/kelly/hotrod
Owner built, owner abused.

 
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bigal
(Login xdgl358)
Member
121.91.19.60

Yes ...times three!

September 12 2013, 3:29 AM 

Yes.
It ensures you have the correct part/grind and that its fitted correctly.
Some cam makers grind advance into their cams like comp cams but others like crane dont.
I just fitted a crane H-288-2 last year and it was about 2-3deg retarded. So its worthwhile.

And also as falc67 stated its a good idea to verify TDC on front pulley for ign timing setting. I actually ground about 2mm from the edge of my timing pointer so when timing engine with light the angle im looking at timing marks on gives me a true reading!

 
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