Cam degreeing. I totally don't understand.

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RussDavis

RussDavis

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New mild build 340. I think I understand the degreeing process. but from these cam specs what am I looking for at centerline. Doing what I've read, heard, watched. Off the #1 intake lifter I end up with 110. From these specs what number am I looking for?

264-264, 214-214 @50 lift int./ex 440 lobe separation 110. Centerlines int. 106, ex 114
 
RussDavis said:
New mild build 340. I think I understand the degreeing process. but from these cam specs what am I looking for at centerline. Doing what I've read, heard, watched. Off the #1 intake lifter I end up with 110. From these specs what number am I looking for?

264-264, 214-214 @50 lift int./ex 440 lobe separation 110. Centerlines int. 106, ex 114
Click to expand...

110 is the centerline. That's how many degrees the intake and exhaust lobe peaks are apart. That's ground in and cannot be changed. NORMALLY, the cam manufacturer USUALLY dictates 4* advanced which would mean 4* FROM the lobe separation or 106*. SO when you wheel it with the degree wheel you want to see 106 intake centerline. All things perfect, when you install the timing chain dot to dot, that's where it will land. But all things are rarely perfect, so you may need to adjust accordingly. If you go on the Comp Cams site, they have a nice explanation of how it's done.
 
Rusty, why does a cam company give you any advance number anyway?
Install 4 deg advanced, for instance.
Why don't they just grind that in?
 
Hyper_pak said:
Rusty, why does a cam company give you any advance number anyway?
Install 4 deg advanced, for instance.
Why don't they just grind that in?
Click to expand...


They do that so the guys that insist on dot to dot installs might be half assed close.

Cam timing is really pretty basic. You are timing the cam to a piston position, determined y the cam grinder. Usually that is the Intake Center Line. The Lobe Separation Angle is ground onto the cam. It is the maximum lift point of the intake lobe compare to the exhaust lobe. You can’t change this. Usually the ICL is the intake lobe centerline, but the rage has been to install the ICL 4 degrees advanced.

If you want to see graphically what all these look like, go to mgispeedware.com and click on the cam timing link.

I would expect you cam, with a 110 intake centerline will install at 106 degrees. That means when the piston is 106 degree After Top Dead Center the intake lobe will be at maximum lift.

Any manipulation of the position of the piston relative to intake lobe max lift is manipulating the characteristics of the cam.

IMO, if you have to change the IVC more than 2 degrees either way, the cam isn’t right for the application.

You can also use .050 lifter rise, but IMO you can induce way too many errors into it to make it worthwhile. I always check the .050 number to see how close it is. Lifter bore issue can affect the .050 number, which is why I don’t get too excited about it, and if there is a discrepancy between the two I always use the ICL.
 
If the cam ends up being advanced or retarded when you degree it, to get what you need, Mr Gasket sells offset cam keys in 2° and 4° offset to fine tune it get it where you need it to be if its close.
 
How about if you have to change the timing chain and sprocket set and don't know what the cam specs are? Is there an easy way to degree the cam without having to pull it out and figuring out the specs? Dial indicators on push rods to check lift, duration, overlap? Any videos out there to recommend?
 
Said another way
moving the centerline, simultaneously moves the Ica, and Ica is what traps pressure in your cylinders. This is or can be , important at low rpm, depending on your Static Compression ratio.
If you close the intake earlier, the engine will trap more low-rpm pressure, and have a stouter bottom end.
If you close the intake later, the engine will trap less low-rpm pressure, and reduce your low-rpm power.
But Moving the LSA has another effect. Each 4 degrees is said to move the top end power about 100 rpm. Whereas the next bigger cam is said to move the power 200 rpm. However, moving more than 4* is never recommended because of two other things that happen simultaneously; namely, the overlap changes. and the power stroke also changes.
This why YR can say what he did, namely;
yellow rose said:
IMO, if you have to change the IVC more than 2 degrees either way, the cam isn’t right for the application.
Click to expand...
Sacrificing overlap if you have headers, is giving up power. That is why when you put headers on an old hi-compression 340, they picked up a ton of power, with the now functional overlap, even tho it was quite modest.
Sacrificing power stroke, at WOT is not too big a deal, but when the duration becomes too short, the gas-mileage takes a dump.
Your cam is modest enough that most of these things are just spitballing.
 
cudamark said:
How about if you have to change the timing chain and sprocket set and don't know what the cam specs are? Is there an easy way to degree the cam without having to pull it out and figuring out the specs? Dial indicators on push rods to check lift, duration, overlap? Any videos out there to recommend?
Click to expand...
Yes there is a way to get very close, and there is another way to shortcut it.

1) is just to slam it in there and degree it to see where it falls, then map it out on paper. But you have to degree BOTH the intake and the exhaust, so you can figure out the actual as ground, LSA. Then you can decide if it needs to be moved.
2) if you just want it to run with no eye to performance, slam it in dot to dot. Then drop two lifters into the #6 holes with #1 at TDC compression. Then lay a straightedge across those two lifters. Then rock the engine back and forth ever so slightly until the straightedge contacts the lifters at 4 points, two outboard edges AND two inboard edges.
Now read the timing mark. This assumes your damper is on and accurate. If the timing mark is within 4* of TDC, "send" it.
 
it's pretty much impossible to dial the cam in purely by the lifter to cam lobe events near beginning of lift (0.00"-0.050") because the lifter movement is relatively gradual. You should use the lift either side of peak lift(say, +or- 0.050" or 0.075", or whatever) to find the much more precise centerline of the lobe "nose", and relate that to the EXACT TDC for that particular cylinder. From that, one can calculate backwards(and forwards) to confirm the advertised cam events. When you find that TDC for #1, you need to confirm the timing marks on dampener and timing cover. If it is good, use a center punch or a carbide scribe to match mark the outer ring of the dampener and the inner hub, so you will be easily able to verify in the future that the outer ring has not slipped.
 
..........And never doubt how "bad" it can be. Some time back I helped a member about 30 mi from here. He had a 318LA in a short bed pickup that was a dog. "We" discussed where it should be and I've forgotten I think we moved it 6? degrees, to get it advanced far enough to be effective and also to "make up" for tolerances in the timing drive and so on.
 
I worked on a Pontiac engine years ago, when the cam was installed with the timing gears lined up, the cam was 10° retarded. The Pontiac can use the same key as a small block Mopar so I had some. Learned to always degree the cam.
 
Crane cams claimed that if you adv/ret the cam, it needs to move 4* [ that is crank degrees, not cam degrees ] before the butt-meter will feel it...
 
Hyper_pak said:
Rusty, why does a cam company give you any advance number anyway?
Install 4 deg advanced, for instance.
Why don't they just grind that in?
Click to expand...

They do. Normally. The car is telling you that. You degree to make SURE it ends up "there".
 
cudamark said:
How about if you have to change the timing chain and sprocket set and don't know what the cam specs are? Is there an easy way to degree the cam without having to pull it out and figuring out the specs? Dial indicators on push rods to check lift, duration, overlap? Any videos out there to recommend?
Click to expand...

READ the Comp Cams site on how to degree a camshaft. It explains it.
 
Bewy said:
Crane cams claimed that if you adv/ret the cam, it needs to move 4* [ that is crank degrees, not cam degrees ] before the butt-meter will feel it...
Click to expand...

Possibly true.....also true is if you have to move it that far, you have one of two things. Either the cam is a gross mismatch OR you have some piss poor quality parts. Or possibly both.
 
RussDavis said:
New mild build 340. I think I understand the degreeing process. but from these cam specs what am I looking for at centerline. Doing what I've read, heard, watched. Off the #1 intake lifter I end up with 110. From these specs what number am I looking for?

264-264, 214-214 @50 lift int./ex 440 lobe separation 110. Centerlines int. 106, ex 114
Click to expand...


If your intake center line is 110 for the intake, then the exhaust center line will be:

2*lobe sep - intake centerline = exhaust centerline
2*110 - 110 = 220 - 110 = 110 BTDC = exhaust centerline

For advertised duration:

intake centerline - intake duration/2 = intake open
110 - (264/2) = 110 - 132 = -22 = intake open
This means that your intake valve will open at 22 BTDC

Intake centerline + intake duration/2 = intake close
110 + (264/2) = 110 + 132 = 242 ATDC
now to get the relationship back to TDC, just subtract from 360
360 - 242 = 118° BTDC = intake close

exhaust centerline - duration/2 = exhaust close
110 - (264/2) = 110 - 132 = 22 ATDC = exhaust close

exhaust close - exhaust duration = exhaust open
22 - 264 = 242° from exhaust close
Now to get the relationship back to TDC, subtract it from 360
360 - 242 = 118° ATDC = exhaust open


for duration @.050"

intake centerline - intake duration/2 = intake open
110 - (214/2) = 110 - 107 = 3° = intake open
This means that your intake valve will open at 3° ATDC

Intake centerline + intake duration/2 = intake close
110 + (214/2) = 110 + 107 = 217 ATDC
now to get the relationship back to TDC, just subtract from 360
360 - 217 = 143° BTDC = intake close

exhaust centerline - duration/2 = exhaust close
110 - (214/2) = 110 - 107 = 3° BTDC = exhaust close

exhaust close + exhaust duration = exhaust open
214 - 3 = 211° from exhaust close
Now to get the relationship back to TDC, subtract it from 360
360 - 217 = 143° ATDC = exhaust open


* Info based on intake centerline of 110°
 
so what type of performance issues would arise going dot to dot vs degreeing? has anyone experienced a "revelation" when degreeing as in the car **** and git way better than dot to dot?
 
Dartswinger70 said:
so what type of performance issues would arise going dot to dot vs degreeing? has anyone experienced a "revelation" when degreeing as in the car **** and git way better than dot to dot?
Click to expand...

Plenty of folks have found 'dot to dot' to vary significantly. The point of degreeing is not 'better performance' but instead it's done in order to KNOW your cam is in correctly. Assuming it's done right is asking to be proven wrong. It's relatively quick and easy to do, and should not be skipped.

If it's not in correctly, and it wasn't degreed, finding out after the fact can be a real pain in the ***. A cam that's too far advanced from intended installed CL can cause detonation and kill the engine. One which is way retarded may crash the valves into the pistons and also destroy the engine. Even if the engine survives, performance may not match the intention of the chosen cam - advanced cams make more low end, retarded tend to have higher HP peaks but will be a dog down low.
 
Dartswinger70 said:
so what type of performance issues would arise going dot to dot vs degreeing? has anyone experienced a "revelation" when degreeing as in the car **** and git way better than dot to dot?
Click to expand...

Sadly, things can be more than a bit off. I've seen timing marks over 10 degrees off, but can't remember cams being that far off. If you find TDC and degree your cam at least you will know it is installed in the right relationship to the crank and you can check your timing correctly. If you set your timing to 10*BTDC and it is really @tdc that can make a noticeable difference. And I only worked in the good old days when stuff was made right...
 
Phreakish said:
Plenty of folks have found 'dot to dot' to vary significantly. The point of degreeing is not 'better performance' but instead it's done in order to KNOW your cam is in correctly. Assuming it's done right is asking to be proven wrong. It's relatively quick and easy to do, and should not be skipped.

If it's not in correctly, and it wasn't degreed, finding out after the fact can be a real pain in the ***. A cam that's too far advanced from intended installed CL can cause detonation and kill the engine. One which is way retarded may crash the valves into the pistons and also destroy the engine. Even if the engine survives, performance may not match the intention of the chosen cam - advanced cams make more low end, retarded tend to have higher HP peaks but will be a dog down low.
Click to expand...
An issue I am thinking of is these newer outsourced parts, what if the "dots " are marked wrong. i have always ran mine dot to dot, but have degreed cams in tech school I have done it before but it was many years ago, and I probably didn't truly understand what i was doing. The teacher was like "good work" I said " i still dont know what i did...:)
 
If your using something like a roll master billet gear and chain setup you would think something like that would be dead on dot to dot.
 
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