Lobe Indexing

If you had to actually make a camshaft, would you know where to put and index each lobe. Not something that is necessary to know unless you are in the camshaft manufacturing business. It does come in handy when you are wanting to know the firing order of a camshaft. The most common situations are a Small Block Chevrolet with a different firing order like a 7-4 or a 7-4, 3-2 swap. Ford Windsor and standard Ford camshafts are also common. Do you know how to tell the difference?

On a V8 pushrod engine with a cylinder bore bank angle of 90-degrees and a crankshaft with 90-degree throws, one cylinder fires every 90-degrees of crankshaft rotation (0-90-180-270-360-450-540-630). It takes two crankshaft rotations to complete the 4-strokes of the engine.  Since the crankshaft rotates 90-degrees for each cylinder to fire, the camshaft will rotate 45-degrees (0-45-90-135-180-225-270-315). The camshaft turns one-half the speed of the crankshaft so it only takes one revolution for all eight cylinders to fire. This will apply to any common V8 even-fire pushrod engine.

The lifter bore bank angle is either added or subtracted to the 45-degree lobe index on the camshaft. This will only apply to the four lobes on the opposite bank from the number one cylinder. On the Chevy engine the lifter bore bank angle is 82-degrees. The Ford is 83-degrees. Engines with splayed or offset lifter bores take a little more thought but are just as easy to figure out.

The standard firing order on a Small Block Chevy is 1-8-4-3-6-5-7-2. The left cylinder bank is 1-3-5-7. The right bank is 2-4-6-8. The lifter bore bank angle is 82-degrees. Lobes 1-3-5-7 will be in 45-degree increments. Lobes 2-4-6-8 will be in 45+82-degree increments. Here are the results:
1 - 0
8 - 45+82=127ccw
4 - 90+82=172ccw
3 - 135ccw
6 - 180+82=262ccw
5 - 225ccw
7 - 270ccw
2 - 315+82=397ccw (37ccw)
These are the lobe positions on the camshaft when looking from the front end. The lobe positions are in degrees and are ccw (counter clockwise) from the 12 o'clock position. The same approach applies to any firing order. Looking down the camshaft will tell you if the intake or the exhaust lobes are in the correct position for a particular firing order.

Try doing the standard Ford Small Block (1-5-4-2-6-3-7-8) and Ford Windsor (1-3-7-2-6-5-4-8) firing order on you own. The right cylinder bank is 1-2-3-4. The left bank is 5-6-7-8. The lifter bore bank angle is 83-degrees. Pay close attention to whether it's added or subtracted from forty-five. Post your results in the comments.