Cam Degreeing

Wbulk · #1 (**permalink**) 05-23-2009, 08:57 PM

I am building a 71 302 with some mild performance parts. I like to degree the cam on engines that are not just stock. I use the center line method that this cam company likes and it's just one degree off. Not bad. My roller timing set just has four degree adjustments so I figure it's not worth messing with.

I'm all set up so I figure I might as well check it further the old way, by checking the opening and closing degrees based on the cam card. I find the intake opening is fine but the intake closing is five degrees to long. The exhaust opening and closing are right on. So I end up with an intake duration that is 265 and exhaust is 260. I then set up everything on another cylinder and sure enough the same thing. It looks like the cam was ground wrong.

The specs are:
At .006 int open 24 BTDC close 56 ABDC

Actual Was open 24 BTDC close 61 ABDC (5 deg off)

I call the cam company and they say pay for shipping and send it to them. They will check it out, if it's bad they will send me another one. So, one week there, they have it a week, one week back, no motor work for three weeks.

The questions for cam experts, what is the down side to running this cam with five degrees more intake duration on the closing side than it is supposed to have, making it with a longer duration than the exhaust?

Rick Parker · #2 (**permalink**) 05-23-2009, 09:41 PM

Maybe pay the extra and get it there in much shorter time??? Depends on what the wait is worth to you??

Jerry Clayton · #3 (**permalink**) 05-24-2009, 10:38 AM

the .006 numers are hard to validate/check--thats why everybody uses .050 numbers
you said you liked the lobe c/l method and that it was just ONE degree off---does thay mean 1/2 +-??????
In the first or last .006 of lift you will find very little sognifinance??

I do assume that you are checking at the lifter, with correct type flat tappet or proper radius roller???

Wbulk · #4 (**permalink**) 05-24-2009, 11:01 AM

Comp Cams on my cam card only gave the opening and closing degrees at .006. The Center line degree method was one degree off on each side. You take the degrees at .050 on each side of the top of the lobe and divide by 2. I had 214, so that would be 107. Yes, I was checking at the lifter with a flat tappet.

Good point on the .006 checking is hard to get accurate. I was getting pretty consistent figures with each time I checked it and even when I checked another cylinder. Everything was really close except that closing on the intake side. Five degrees seems to be a lot.

Wayne

Wbulk · #5 (**permalink**) 06-05-2009, 09:06 AM

Sent the cam in to Comp cams. They confirmed it was ground wrong and sent me a new one. Their turn around time was pretty quick, just three days in and out. It's worth it to degree in a cam.