Re: The 30-30 Camshaft vs. The LT 1
Sound has more to do with exhaust system configuration than the camshaft. For example the '62 and '63 FI engines sound very different even though they are essentially the same engine. The primary reason is the crossover on '62s that '63s don't have, but the piping size and shape and internal details of the mufflers have a lot to do with it, too.
Lobe center angles can be very misleading and don't mean anything unless you are comparing the same lobes. Also, the 30-30 and LT-1 cams have asymmetric lobes, so the point of maximum lift does not correspond to the center of the lobe, but the distance between the points of maximum lift is usually quoted as the "lobe center". For a given design of inlet and exhaust lobe the lobe center angle is a relative measure of overlap, but is meaningless when comparing two different sets of lobes. The following is the measured effective overlap is sq-in-degs (from the Engine Analyser simulation program) for the three SB mechanical lifter cams using 1.94"/1.50" valves and the timing points at .006" valve lift with rocker ratio adjusted lash to take up the clearance at the top of the ramp.
Dunt.: 0.9, 110.5 LCA, (110.5 deg between pts of max lift)
30-30: 3.7, 112.5 LCA, (114 deg between pts of max lift)
LT-1.: 1.2, 114.9 LCA (114 deg betwenn pts of max lift)
As you can see, the Duntov cam has the narrowest LCA, but the least effective overlap. The 30-30 has more effectice overlap than is beneficial for an engine with conventional exhaust manifolds, which is why it only makes marginally more peak power than the LT-1 cam, but takes a HUGE hit in low end torque.
Another factor that effects the sharpness of the exhaust note is the point at which the exhaust valve opens. The earlier the opening, the steeper the initial wave due to higher cylinder pressure. The LT-1 has the earliest opening exhaust valve of the three.
Duke
Sound has more to do with exhaust system configuration than the camshaft. For example the '62 and '63 FI engines sound very different even though they are essentially the same engine. The primary reason is the crossover on '62s that '63s don't have, but the piping size and shape and internal details of the mufflers have a lot to do with it, too.
Lobe center angles can be very misleading and don't mean anything unless you are comparing the same lobes. Also, the 30-30 and LT-1 cams have asymmetric lobes, so the point of maximum lift does not correspond to the center of the lobe, but the distance between the points of maximum lift is usually quoted as the "lobe center". For a given design of inlet and exhaust lobe the lobe center angle is a relative measure of overlap, but is meaningless when comparing two different sets of lobes. The following is the measured effective overlap is sq-in-degs (from the Engine Analyser simulation program) for the three SB mechanical lifter cams using 1.94"/1.50" valves and the timing points at .006" valve lift with rocker ratio adjusted lash to take up the clearance at the top of the ramp.
Dunt.: 0.9, 110.5 LCA, (110.5 deg between pts of max lift)
30-30: 3.7, 112.5 LCA, (114 deg between pts of max lift)
LT-1.: 1.2, 114.9 LCA (114 deg betwenn pts of max lift)
As you can see, the Duntov cam has the narrowest LCA, but the least effective overlap. The 30-30 has more effectice overlap than is beneficial for an engine with conventional exhaust manifolds, which is why it only makes marginally more peak power than the LT-1 cam, but takes a HUGE hit in low end torque.
Another factor that effects the sharpness of the exhaust note is the point at which the exhaust valve opens. The earlier the opening, the steeper the initial wave due to higher cylinder pressure. The LT-1 has the earliest opening exhaust valve of the three.
Duke
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