I bought a custom set of cams from a buddy. Is there a way to measure them to tell the size or lift so I will know if my stock valve-tran will handle them? I measured a lobe at 2.25 inch or 57 mm
Odd Question trying to learn
- Thread starter Brian5934
- Start date
-
Sponsors (?)
trinity_gt
10 Year Member
Can you measure the base circle of the lobe? If so then you can derive lobe lift and, when multiplied by the rocker ratio, valve lift.
You should note that you're only going to derive valve lift from this measurement: Without knowing the duration, intake center and lobe separation you're not really going to know if the cam is suitable for your application.
You should note that you're only going to derive valve lift from this measurement: Without knowing the duration, intake center and lobe separation you're not really going to know if the cam is suitable for your application.
If I only knew what that stuff was I would be in better shape haha, sorry for my lack of knowledge base circle would be takin from the lobe or where the lobe meets the shaft? Rocker Ratio?
trinity_gt
10 Year Member
The base circle is the diameter of the circle upon which the lobe is ground. When the valve is closed, the follower is riding on the "base circle". However high above this the lobe rises represents the "lobe lift." It sounds like you measured the cam from the lobe tip to the base circle and you got a value of ~2.25". But without knowing the diameter of the base circle itself you don't know how high the lobe rises. So turn the measuring tool 90-degrees so you measure the diameter of the lobe at right angles to the tip of the lobe. For most cams this will give you the base circle diameter. It will be a value smaller than the first measurement you made. The difference between these two is the lobe lift.
For example, if you measure 2.25" in one dimension and 1.950" at 90-degrees then the lobe lift is 2.250 - 1.950 or 0.300".
The rocker ratio is a measure of distances between the point of load application, the fulcrum (pivot) and the valve tip. As a simple example, think of a see-saw. If the pivot is in the middle the "rocker ratio" is 1:1 because for every unit of movement on one side, the other side moves the same amount (opposite direction.) Now move the pivot to a point 1/3 of the distance from where the movement is applied. If the see-saw was 12" long you would then have the pivot 4" from one side and 8" from the other. The ratio for this will be 2:1, meaning that the tip at the long end will move 2 units for every one unit of movement at the short end. It's like a gear ratio. In the SOHC (and DOHC for that matter...) modular engines, the rocker geometry is different than a see-saw but the principle is the same.
Rocker arms typically have ratios in the 1.5 - 1.7:1 range. The total valve lift will be lobe lift * rocker ratio. So if you had a 1.6:1 rocker ratio and a 0.300" lobe lift you'd nominally see 0.3*1.6 or 0.480" valve lift.
Are there any marks on these cams? Any casting numbers or other identification marks?
Ok I believe the lobe lift is 0.250 if I measured it correctly. Cast number on the left cam is 660 262724 and thankyou for taking the time to explain this to me
Not sure if all mustangs would have the same ratios from the factory but the internals of the motor are stock if that help with rocker ratio I do not have time right now to tear it apart for measurements or the correct tools to measure
trombonedemon
Well-Known Member
That explaination needs to be a Cam-explaination sticky, any mods agree? I'm sure that hasn't been explained before, I've looked.
Similar threads
