Thread: Camshaft advice (again...)

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Originally Posted by shawnlee28

Your on the right track now!!!
Just make sure the cam has a intake valve closing point that puts your dynamic compression close to 8.5 .This is where my exspertise ends.........I have no idea about lifts and lobe seperation and which what does when where.......but I know only certain lifts and lobe seperations are going to fall into the selection of cams that will give you the proper dynamic compression.

Shawnlee, I've watched you come along in your education and I'm very proud of you for making sense out of all the gobble-de-goop that I and others have posted on this forum. In my opinion, you have a better leg-up on cam selection than 90 percent of the rodders out there and I'm pretty sure that when you begin preaching the gospel of cam selection to newbies, they look at you like you have two heads.

As far as lift, the more the better within the confines of mechanical clearance. The things you have to check closely when getting into extreme lifts are:
1. piston to valve clearance. Ideally, 0.250". An absolute minimum would be 0.080" on the intake and 0.100" on the exhaust. Some builders say the absolute minimum is 0.100" on the intake and 0.120" on the exhaust. More is better. Less could be disastrous.
2. pushrod to head slot clearance. A miss is as good as a mile. Turn the motor through 720 degrees of rotation and observe closely.
3. rocker slot to rocker stud clearance. Use a piece of small diameter solder held between the slot and stud while turning the motor through 720 degrees of rotation. If the solder gets pinched, grind the rocker slot for clearance.
4. valve spring coil bind. At full lift, you must be able to slide a 0.010" feeler gauge between each and every coil. If insufficient clearance is observed, you may be able to remove some shims to correct the condition. If not, change to a different spring or different retainer.
5. retainer to valve guide boss interference. 0.0625" to 0.125" clearance at full lift. If insufficient, change to a different retainer or machine the top of the valve guide down slightly. This could be done at the same time as machining the guides for PC seals.

LSA, LDA. Lobe separation angle is the more commonly used term, but I grew up knowing it as lobe displacement angle. Either is correct. The short explanation is that a narrow angle (100 to 110) will give the motor more low end, building torque quickly and then laying down on the top. Manifold vacuum will be low. Idle will be choppy. A wide angle (111 to 118) will not make quite as much torque on the bottom, but more in the higher range. Manifold vacuum will be high. Idle will be smooth. Look at Compcams. They grind nearly all their cams on a 110 LDA, right in the middle of the range.