1966 big block camshaft spec

[David C.]

Can anyone tell me where I can find published values for 1966 L36 and L72 camshaft specifications for duration, lift lobe center and separation, both intake and exhaust?

Thanks,

Dave

[Cecil L.]

Re: 1966 big block camshaft spec

Try the back of the 66 Service Manual in the Specifications section.

[Joe L.]

Re: 1966 big block camshaft spec

Can anyone tell me where I can find published values for 1966 L36 and L72 camshaft specifications for duration, lift lobe center and separation, both intake and exhaust?

Thanks,

Dave

Dave-----


L-36----duration @ 0.050"= 214 degrees intake; 218 degrees exhaust
max lift w 1.7:1 rockers= 0.461" intake; 0.480" exhaust
lobe centerline= 115 degrees

L-72----duration @0.050"= 242 degrees intake; 242 degrees exhaust
max lift w 1.7:1 rockers= 0.496" intake; 0.492" exhaust
lobe centerline=114 degrees

[David C.]

Re: 1966 big block camshaft spec

Thank you much gentlemen.

[Jerry M.]

Re: 1966 big block camshaft spec

Dave-----


L-36----duration @ 0.050"= 214 degrees intake; 218 degrees exhaust
max lift w 1.7:1 rockers= 0.461" intake; 0.480" exhaust
lobe centerline= 115 degrees

L-72----duration @0.050"= 242 degrees intake; 242 degrees exhaust
max lift w 1.7:1 rockers= 0.496" intake; 0.492" exhaust
lobe centerline=114 degrees

Joe I thought lift on L 36 is .490 Int AND L 72 is .520 Int and Exh

[Joe L.]

Re: 1966 big block camshaft spec

Joe I thought lift on L 36 is .490 Int AND L 72 is .520 Int and Exh

Jerry-----

As far as I can tell, cross-referencing various sources, the lift specs I provided for the L-36 cam are correct.

I was incorrect on the L-72 lift specs, though. They should be 0.520" on both the intake and exhaust. I don't know where I came up with the numbers I did. In fact, even as I was typing them they just "didn't feel right", but I didn't cross-check them. Maybe I was tired.

[Duke W.]

Re: 1966 big block camshaft spec

One thing to consider is that mechanical lifter cam specs cannot be directly compared to hydraulic lifter camshaft specs.

The reason is that part of the first .050" lobe lift of a mechanical lifter camshaft is clearance ramp, and the valve does not move. By comparison, at least theoretically, all of the lobe lift above the base circle of a hydraulic lifter camshaft is turned into lift at the valve.

The constant velocity clearance ramp height of the L-72 camshaft (The same lobe is used on both sides.) is .012", so if valve clearance is set to take up all lash at the very top of the clearance ramp, it takes .062" lobe lift to create the equivalent valve lift as .050" of hydraulic lifter camshaft lobe lift.

The same argument applies to total lift since lift figures are "gross" including the clearance ramps, and the issue with both hydraulic and mechanical lifter camshafts is further complicated by actual rocker ratio behavior. It is not constant, but varys with lift, usually increasing with increasing lift, but may not actually achieve the "specified" ratio.

The.062" lobe lift of the L-72 cam is 231 degrees, which is the value that should be compared to hydraulic lifter camshafts, so it's not nearly as much "bigger" than the L-46/68 camshaft as the published specs might lead you to believe if you don't understand the above issues.

Duke

[Bill M.]

Re: 1966 big block camshaft spec

Jerry-----

I was incorrect on the L-72 lift specs, though. They should be 0.520" on both the intake and exhaust. I don't know where I came up with the numbers I did. In fact, even as I was typing them they just "didn't feel right", but I didn't cross-check them. Maybe I was tired.

Joe:

I just ran across this in the archives. Here's how you got the numbers:

Intake: 0.520 - 0.024 lash = 0.496
Exhaust: 0.520 - 0.028 lash = 0.492

You're both right if you "feel" the gage right when you're lashing them!