cam timing

Hey all,

Just got a couple cams for our TAFC. Looked at the cam cards and they say to install at 35 deg with .8-something diameter rollers (don't have the card right infront of me). We run the 1" lifters. Wondering what difference the lifter roller diameter makes?

 

lifter dia

I've found it adds 4+ degrees duration to your cam profile. A .8 lifter sounds like something for chevy? You'll just have to roll it around with the degree wheel a few times and see where it is. Shouldn't effect lift.

 

You can find the cam centerline, and it doesn't matter what size roller.

 

Nathan, My 1" lifters have .920" dia rollers, Crane, most cams from Crane are ground for timming with a spacific dia. roller

 

Sorry, it does matter. Same reason cup cars that run SBC's use Ford diameter lifters. You know the dial indicator mount you use for dialing in a roller cam that has the roller on the end? We use one, but we make our own roller to match the one on the lifters.

 

Thats a good idea,( make the roller) and Nate size dose matter.

 

Dia?

I'm really intrested in finding out why roller dia makes a difference in finding lobe centerline.

 

Me too

 

I think what we'll do is set the cam timing with the 1 inch lifter, then make a bushing to fit the smaller lifter to see what the difference is.

 

Lifter size

Call Engle cams - Mark is who set me straight on the topic.

 

All,
You can find the cam lobe centerline with any roller diameter.
But, you can't degree the cam to the cam card numbers if the cam was ground for say a .920" roller and your are using an .800" roller. The roller diameter affects the duration (valve opening and closing time). Since most cam cards have you degree/index the cam in at .050" valve lift (open and close), the change in duration will affect the degree wheel numbers.
Trust me, I know the hard way. If you search my past posts, I was helping a guy with a standard Crane R296 cam with Crane .920" rollers. It would not degree in correctly. Of course I could get the intake open at .050" correct, but not the .050" from close number. (this is how I found the problem and suggest that everyone check the open and close on both intake and exhaust on #1 and #6)
The problem turned out that the cam was ground for a ~.7??" roller, and marked wrong.
Hope this helps.

 

I have watched this thread very closely because of my interest in getting the cam timing correct on my rig.
What I think I am seeing is that we are talking about two distinctly different things. Cam lift / lobe centerline degree and the duration of the lift.

The lobe center line shouldn't be affected whatsoever by the diameter of the roller. The diameter of the roller would certainly affect the "ramp speed" of the lifter or as we all know it, the duration of lift.

I think!

 

It doesn't make a difference in finding intake lobe centerline which is probalbly the way you degree the cam, me too! But for those that degree the cam on intake opening degrees it does.

Blessings...........Ron Clevenger.

 

Thanks for all the input on this thread. After thinking a bit I realized that I have gone to a .920 roller where before I had an .820. My question is, is there any way to compensate for the duration change in my tune-up? More fuel, less fuel..more timing less timing and why. Does the duration change my torque curve? Thanks in advance for any help.

 

You need to get a cam thats for the lifters you are using now, "Sig Earson" the best IMHO.

 

I would think the cam center line would effect the torque curve.and then the gearing you have may be wrong with the new curve. I would think it would change the amount of time the valve stays open and watch out for overlap. I would think you would loose compression. also. Maybe good maybe not. Call the manuf. on Monday. They are the people who know. Just a thought. Maybe someone who knows more could finish this reply. I sure would like to know. just for the knowledge. Don

 

I don't know a lot about blower cams so this is a question, are they (blower cams) usually smymetrical?

I have looked at several cam manufacturers website for the answer and been unable to find out.

If they are asymetrical then the size of the lifter will affect the ability to accuratly measure the cam timing with different size lifters.