Camshaft intake centre line

[Chargerguy74]

Just finished degreeing my camshaft. My cam card states a 243 degree intake duration at 0.050 tappet lift. I got 244...cool. Onto my intake centre line. The cam card states 106 degree centre line will make this cam 4 degrees advanced. So, averaging my degrees at 0.050 before and after max lobe lift I get 103 degrees. Repeated and obtained the same results. Is my centre line 3 degrees out? Am I interpreting the results correctly in regards to my cam card? And should this be corrected? Thanks!

[Chargerguy74]

Also, my crank sprocket is positioned with the key in the "O" marked keyway, this puts a "0" at the 12 o'clock position on the sprocket.

[firefighter3931]

The intake centerline method is the preferred way to degree in a cam. 

http://www.compcams.com/technical/instructions/files/145.pdf

It sounds like that is the way you did it, correct ?

If so, based on your results of a 103* ICL the cam is 3* advanced from where the manufacturer recommends. Most cam companies build in 4* of advance so if you install the cam straight-up it will technically be advanced 4* 

If your timing set has multiple keyways you can try retarding it a few degrees and re-check. 


Ron

[Chargerguy74]

Thanks Ron!

Just read the comp instructions. Yup, that is the way I did it. I've checked it 4 times now (just redid it). 103 twice, refound and rezeroed for #1 TDC and started from scratch. This time I obtained 103.25 twice. So I am 7 degrees advanced right now, correct? There are 3 keyways on my crank sprocket. "O" (where it is now) "R" and "A" but as far as I can tell, there is no marking stating how many degrees retarded the "R" keyway is, or for the advanced position either. EDIT: it appears they're 4* by the numbers I obtained and it also seems as though 4* advanced or retarded is normal for the 3 keyway sprockets.

[Chargerguy74]

Alright, went to the "R" keyway, and got a repeated ICL of 107.25*.

[firefighter3931]

OK, it sounds like your timing set has the 4* advance/retard keyway based on your results. 

Now the decision becomes ; do I install it 1.25 degrees retarded or 2.75 degrees advanced (from the recommended installed centerline) 

Advancing the cam will bring the power curve in sooner....retarding the cam timing will bring it in later. 



Ron

[Chargerguy74]

Ron, based on your experience, do you think it would be better to run 2.75 degrees advanced from the recommended ICL, or buy a different sprocket with 2* increments and try to get closer? How much lower could the power band be brought in being this much advanced? Would 1.25* retarded really be noticeable? Thanks!!!

[firefighter3931]

Ron, based on your experience, do you think it would be better to run 2.75 degrees advanced from the recommended ICL, or buy a different sprocket with 2* increments and try to get closer? How much lower could the power band be brought in being this much advanced? Would 1.25* retarded really be noticeable? Thanks!!!

It really depends on the whole combination. 

What is the engine build ; compression, exhaust, intake manifold, carb etc...

-how much gear and tire diameter ?
-what stall speed or is it a stick ?

The reason cam manufacturers dial in some advance is to allow for chain stretch. Over time the timing chain will stretch and this will affect cam timing down the road. A little advanced is better than retarded. 

With a heavy street car it's important to have lots of low end grunt to get the heavy mass moving. That cam is fairly healthy with 243@.050 duration so I'd be more inclined to install it at 103 vs 107. For every 2* of advance you're altering the powerband roughly 200rpm.....so this change would result in approx. 300rpm lower powerband which migh be a good thing depending on the combination. 


Good job taking the time to time to degree the cam in...now you can make an informed decision with no guesswork 


Ron

[Chargerguy74]

74 Charger, so about 4000lbs. 4 speed. Gonna try an OD 833. 275/60 R15s and 3.55s out back. 10.5:1 compression, 950 Holley DP, M1 intake, ported 516s, TTI headers, 2.5" X pipe exhaust.

Thanks. Due  to the lack of proper tools, I almost said "screw it, it's probably good"...but then I couldn't sleep at night.

[firefighter3931]

74 Charger, so about 4000lbs. 4 speed. Gonna try an OD 833. 275/60 R15s and 3.55s out back. 10.5:1 compression, 950 Holley DP, M1 intake, ported 516s, TTI headers, 2.5" X pipe exhaust.

Thanks. Due  to the lack of proper tools, I almost said "screw it, it's probably good"...but then I couldn't sleep at night.

With the 3.55 gears, 4000 lbs and tallish 28in tires I would definitely install it at 103. The build is somewhat port limited even though the 516's have some work done to them. It'll be done making power at 5500-5800 rpm anyway so moving the power curve lower is the right choice, inmo. 

Make sure you check for piston to valve clearance ; .080 intake/.100 exhaust is safe on a street car. The proper valve springs are also important and the guides will need to be trimmed down for retainer clearance. Stock heads are only good for ~.510 valve lift until you trim the valve guides down and install positive style seals....just a heads-up 


Ron

[Chargerguy74]

I thought that might be the case (hindered by the heads). I was just saying yesterday I wish I bought aftermarket heads...which I will still do for next year. The guides were cut down for sure. Thanks for the pointers!