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degreeing a cam

Started by willy, November 16, 2011, 07:28:01 PM

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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...
" I have spent thousands of dollars and countless hours researching what works and what doesn't and I'm willing to share"

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.
Gotta love a '69

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.
Pardon me but my karma just ran over your dogma.

BSB67

Quote from: John_Kunkel on November 17, 2011, 04:53:38 PM

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.


500" NA, Eddy head, pump gas, exhaust manifold with 2 1/2 exhaust with tailpipes
4150 lbs with driver, 3.23 gear, stock converter
11.68 @ 120.2 mph

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.
1968 505" EFI 4-speed
1968 D200 Camper Special, 318/2bbl/4spd/4.10
---
Torque converters are for construction equipment.

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  :yesnod:

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



Ron
68 Charger R/T "Black Pig" Street/Strip bruiser, 70 Charger R/T 440-6bbl Cruiser. Firecore ignition  authorized dealer ; contact me with your needs

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

Quote from: willy on November 18, 2011, 03:36:14 PM
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. 

500" NA, Eddy head, pump gas, exhaust manifold with 2 1/2 exhaust with tailpipes
4150 lbs with driver, 3.23 gear, stock converter
11.68 @ 120.2 mph

firefighter3931

Quote from: willy on November 18, 2011, 03:36:14 PM
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
68 Charger R/T "Black Pig" Street/Strip bruiser, 70 Charger R/T 440-6bbl Cruiser. Firecore ignition  authorized dealer ; contact me with your needs

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

Quote from: willy on November 19, 2011, 09:33:29 AM
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
68 Charger R/T "Black Pig" Street/Strip bruiser, 70 Charger R/T 440-6bbl Cruiser. Firecore ignition  authorized dealer ; contact me with your needs

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.
1968 505" EFI 4-speed
1968 D200 Camper Special, 318/2bbl/4spd/4.10
---
Torque converters are for construction equipment.

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

Quote from: willy on November 20, 2011, 11:51:46 AM
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.  :yesnod: Even very mild/stock cams will respond to increased ignition advance @ idle.

Quote from: elacruze on November 20, 2011, 12:36:50 PM
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
68 Charger R/T "Black Pig" Street/Strip bruiser, 70 Charger R/T 440-6bbl Cruiser. Firecore ignition  authorized dealer ; contact me with your needs

willy

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

firefighter3931

Quote from: willy on November 20, 2011, 06:26:40 PM
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.  :yesnod:

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


68 Charger R/T "Black Pig" Street/Strip bruiser, 70 Charger R/T 440-6bbl Cruiser. Firecore ignition  authorized dealer ; contact me with your needs

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