degreeing a cam

[willy]

Can someone explain degreeing a cam? I thought you just lined up the marks and it was good to go. I have a 1968 charger r/t with a 440. The guy i bought it from said it had a mild cam put in when the engin was re-built. I only have about 15" of vacuum at idle and have been debating putting a different cam in it to get more vacuum to the power brakes. Now I wonder if the cam was degreed to get more low end power and that is also giving me less vacuum? Could my solution for more vacuum be as simple as re-degreeing the cam?
Thanks,
Willy

[Cooter]

15" vacuum should be more than enough to run power brakes. You have another problem....
You need more research into why your brakes aren't up to par, other than swapping the cam. You could swap it out, but I suspect you'll find after all that work, your brakes still feel the same...

[doctor4766]

...or he may have been supplied with the wrong cam like I was from Mancinis.
Wondered why I was lucky to get around 11" of vacuum and the brakes wouldn't work.
Turned out the part number on the box was for a stockish magnum camshaft but a 509 lift was supplied.
Mancinis told me to check the colour coded blob on the end of the cam and sure enough it wasn't what it was supposed to be.

[willy]

I would still like to know what degreeing a cam means. Is it just rotating it one tooth off of lined up? Or something else. I have a very good lope at idle for it to be a mild cam.
Thanks,
Willy

[John_Kunkel]

Degreeing a cam is just the process of checking the cam position in relation to the crankshaft position...IOW if a cam lobe is supposed to open the intake valve at XX degrees before top dead center this can be verified by placing a degree wheel on the crank and a dial indicator on the lifter to see where it actually opens.

The last dozen cams I degreed were 4° advanced when installed with the marks lined up, I always assumed this is to compensate for chain stretch.

[BSB67]

Degreeing a cam is just the process of checking the cam position in relation to the crankshaft position...IOW if a cam lobe is supposed to open the intake valve at XX degrees before top dead center this can be verified by placing a degree wheel on the crank and a dial indicator on the lifter to see where it actually opens.

The last dozen cams I degreed were 4° advanced when installed with the marks lined up, I always assumed this is to compensate for chain stretch.

All of the cams that I have seen in the last 10 years have all had 4 degrees of advance ground in as specified on the cam card.  It seems to be the standard, at least for BB Mopar cams.

To the OP, if the cam, cam sprocket, crank sprocket, and crank are all machined correctly, then the cam to crank orientation will be correct when installed dot to dot.  Changing the orientation is done with a multi keyway crank sprocket, offset cam sprocket dowel bushing, or adjustable timing set.  Measurements can be taken at the lifter. or the valve.

[Chryco Psycho]

the reason to degree a cam as said above is to verify the valve timing to the crank / piston position . Why do it because the chain sprocket keyway or dowel pin position can be off by a few degrees or the cam itself may have the dowel  or keyway machined off by a few degrees , the worse I have seen is 11* off lining up the dots , ever wonder why some engines didn't make much power even with all the "right" parts ?

[willy]

Thanks for the explaination. That makes sense that parts could be off a few degrees. Before changing my cam I will degree it to see if it is in the proper orientation. Could it be effecting my vacuum if it is not degreed properly?
Thanks,
Willy

[elacruze]

Yes Willy, the most important event in cam timing is when the intake valve closes-that single point is what controls your cylinder pressure, and your intake vacuum. A few degrees either way can have a significant to huge effect.

[willy]

Thanks for the explaination from everyone. Degreeing my cam may solve all of my problems.
Thanks again,
Willy

[firefighter3931]

Before you go tearing the engine apart have a look at some tuning. Where is your initial timing set ? Often the timing settings will be less than optimal and this can hurt performance and manifold vacuum 

Comp Cams has an excellent tutorial on their website : http://www.compcams.com/technical/instructions/files/145.pdf



Ron

[willy]

My initial timing is on 18 degrees but it doesn't seem to make any difference in the vacuum wherever i set it
Willy

[BSB67]

My initial timing is on 18 degrees but it doesn't seem to make any difference in the vacuum wherever i set it
Willy

Unless something is really really wrong with the cam timing, I doubt that it will change the engine idle vacuum. 

[firefighter3931]

My initial timing is on 18 degrees but it doesn't seem to make any difference in the vacuum wherever i set it
Willy

Willy,

Are you saying that your idle vacuum is the same at 18*BTDC as say... 10* BTDC ?

When you timed it was the vacuum advance hose connected or not ?



Ron

[willy]

Ron,
I had the vacuum advance plugged and there isn't much difference in vacuum from 10-18 degrees. The brakes are fine when the rpms are above idle. when I first start it up and back it out of the garage or if i am in traffic idling for a while is when the brakes are iffy. I had an intake leak between the back 2 cylinders on the passenger side so i put in a blocked valley pan with gaskets on both side and that got the vacuun up to 15". It was about 14 before that. It starts and runs a lot better with the blocked pan since the gas doesn't perculate out of the carb when hot. So basically i am just looking for more vacuum at idle so the brakes work better.
Thanks,
Willy

[Chryco Psycho]

I always degree them & it is worth checking to be sure

[firefighter3931]

Ron,
I had the vacuum advance plugged and there isn't much difference in vacuum from 10-18 degrees. The brakes are fine when the rpms are above idle. when I first start it up and back it out of the garage or if i am in traffic idling for a while is when the brakes are iffy. I had an intake leak between the back 2 cylinders on the passenger side so i put in a blocked valley pan with gaskets on both side and that got the vacuun up to 15". It was about 14 before that. It starts and runs a lot better with the blocked pan since the gas doesn't perculate out of the carb when hot. So basically i am just looking for more vacuum at idle so the brakes work better.
Thanks,
Willy

Sounds like the vacuum is as good as it's going to get based on your experimentation with different base timing adjustments. It would be nice to know the cam profile that's in your engine. You can try advancing the cam a couple of degree's to see if that helps. There are vacuum reservoirs that will assist power brakes by storing vacuum for use when manifold vacuum is low. The other option is to just replace the cam.

From my experience 15in of vacuum is usually sufficient to run a PB booster. It might be worth looking at the booster itself for vacuum leaks to rule that out. It's possible that the diaphram has a small tear.


Ron

[willy]

Ron, I wish i knew what cam was in my engine, but the person that re-built it for the previous owner just said it was a mild cam. It doesn't seem mild to me with the lope i have at idle. There is always the possibility that my old vacuum guage is off, so today I am going to get a new one so i can take some readings at different advanse settins and different rpm's. I will post the results later today and that should tell us if i have a enough vacuum or not. My booster was re-built by the Ram Man and holds vacuum great without leaking down so I don't think I have a booster problem.
Thanks.
Willy

[willy]

Ron, I took new readings with a new gauge and they are different. All of the readings were taken in park with the vacuum advance plugged and idle set at 750 RPM's since that is the setting when I put it in gear.
1. 10 degrees 750 RPM's 15" of vacuum
2. 16 degrees 750 RPM's 15.5" of vacuum
3. 18 degrees 750 RPM's 16" of vacuum
4. 20 degrees 750 RPM's 16.5" of vacuum

I had my wife press on the brakes and I wrapped my hands around the rubber hoses going to the wheel cylinders and could feel them flexing a little bit.
Thanks,
Willy

[elacruze]

Hey Willy,

You should check your vacuum at 750 *with the car in gear*. It matters whether the engine is loaded or not, because although the RPM is the same the throttle setting is not.

Of course, safety is a priority so you'll need two people and some wheel chocks as insurance.

[willy]

Elacruze,
I checked it with the idle set at 900 rpm"s in park and it was 17" of vacuum. When I put it in gear with my foot on the brake it drops to 12" of vacuum. Does that mean I don't have enough vacuum for the power brakes to work properly? Am I back to a cam problem or a brake problem? I only have a problem when I am at idle, when the car is going down the road I have good brakes.
Thanks,
Willy

[firefighter3931]

Ron, I took new readings with a new gauge and they are different. All of the readings were taken in park with the vacuum advance plugged and idle set at 750 RPM's since that is the setting when I put it in gear.
1. 10 degrees 750 RPM's 15" of vacuum
2. 16 degrees 750 RPM's 15.5" of vacuum
3. 18 degrees 750 RPM's 16" of vacuum
4. 20 degrees 750 RPM's 16.5" of vacuum

I had my wife press on the brakes and I wrapped my hands around the rubber hoses going to the wheel cylinders and could feel them flexing a little bit.
Thanks,
Willy

I figured something was up with your "old" vacuum guage ; normally an increase in base timing will increase manifold vacuum....to a certain point.  Even very mild/stock cams will respond to increased ignition advance @ idle.

Hey Willy,

You should check your vacuum at 750 *with the car in gear*. It matters whether the engine is loaded or not, because although the RPM is the same the throttle setting is not.

Of course, safety is a priority so you'll need two people and some wheel chocks as insurance.

Eric is spot on ; you need to maximize vacuum "in gear" to see if it helps. You can try increasing idle speed up to 850-900 and that may help. If the cam has lots of duration/overlap then sometimes the idle circuit in the carb will not supply the right mixture to achieve a clean idle.

What carb are you running ?


Ron

[willy]

Ron, I am running an edelbrock #1411 with a totally stock engine except the "mild" cam.
Willy,

[firefighter3931]

Ron, I am running an edelbrock #1411 with a totally stock engine except the "mild" cam.
Willy,

The 1411 (electric choke) tends to be leaner VS the 1407 (manual choke)so that may be causing some issues. The cam you have in there probably wants a more agressive fuel curve/idle circuit.  

I'd set the base timing at 18* and up the idle speed to 850 in gear and see how the brakes feel. Check to see how much vacuum you have and report back.  



Ron

[willy]

Ron, Thanks for the help. I will do this tonight and report my findings. Can I measure the lift of my cam by removing the valve cover and measuring from the top of the rocker? That may tell us how agressive my cam is. How much vacuum should I have at idle in gear?
Thanks,
Willy