Crane Cam F-288/4134-6

[reknapp52]

So after I blew my motor up in Phoenix, I bought a motor from a friend, and used the short block with cam installed, and replaced heads, etc. with my parts. Didn't tear down the short block to inspect it, did a quick check on the cam and found the intake centerline to be 108, which is, in my experience a pretty normal number to see for a big block Mopar. Went to Great Bend for Div. 5 event, during T-N-T found that the car was just a TURD! I withdrew from the event and brought the car back home.

I researched the cam specs online, and an intake centerline number is not given, just opening and closing numbers @ .050. When checking those numbers it appears that my cam is 12 degrees retarded, meaning that the center point of the very top of my intake lobe will be at 96 degrees. That seems crazy, I've never run a cam with the intake centerline that far advanced. Any thoughts??

[pmrphil]

Just by the part number that cam has a 106 lobe separation. Not quite sure when you say 108 centerline what you mean? Also, what is 12 degrees retarded? If the cam is in at 96 intake centerline, it would be advanced too far. I would probably install that cam around 103, depending on how loose the converter is, where you plan to shift, etc. Good luck.

[reknapp52]

In the past I have always measured .050 on both sides of max lift of the intake lobe to degree my cam. Using that method this cam is in the motor at 108 ATDC. The Crane specs on the cam call for an intake opening number of 42 degrees BTDC and closing 66 degrees ABDC (measured .050 off the base circle). Using this method I get a reading of 114 ATDC for the center of the intake profile. My gut tells me to use my old method and install it at 102.

[reknapp52]

My mistake-- after doing a little more work with the dial indicator, I've found that this cam is NOT the one in this "new" short block. That's why the numbers I was seeing didn't add up.

[Tom Broome]

Originally Posted by reknapp52

In the past I have always measured .050 on both sides of max lift of the intake lobe to degree my cam. Using that method this cam is in the motor at 108 ATDC. The Crane specs on the cam call for an intake opening number of 42 degrees BTDC and closing 66 degrees ABDC (measured .050 off the base circle). Using this method I get a reading of 114 ATDC for the center of the intake profile. My gut tells me to use my old method and install it at 102.

First lets decipher the cam, Crane "logic" says F-288/4134-6 means that at least the intake lobe is 288 degrees duration at .050. 4134 references the lobe lift (multiply that by rocker ratio for gross lift) and that little -6 at the end means the cam was ground with a lobe separation of 106 degrees.

I agree with your Gut, but lets go through your math.
Intake opening 42 BTDC, Intake closing 66 ABDC. There's 180 degrees between TCD and BDC. So...42+66=108...plus180=288. that matches the cam card number for .050 duration. The center of a lobe of 288 degrees is at 144 degrees from .050 opening. BUT we need the intake centerline in reference to TDC. SO....144-42=102 ATDC. That would be the intake centerline the cam card called for.
Most of the time it's perfectly acceptable to degree a cam "over the nose", that is .050 on both sides of max lift. But there are some instances where the opening and closing sides of a camshaft are not symmetrical. In those cases the nose of the cam lobe may not be perfectly centered between the opening and closing events. Since cylinder pressure is affected by the opening and closing timing (not the point of maximum lift), it's always good practice (to me) to start with the .050 numbers. AND...if you know the .050 numbers, and your balancer happens to show all 360 degrees, and you happen to run a belt drive timing setup. You can then simply pop the intake rocker off number one cylinder, qualify the .050 opening location, and verify if (and how much) belt stretch is affecting your original work.