A side effect of a tighter LSA camshaft is lower idle cylinder pressure and intake vacuum. While this isn't a huge issue, it does create driveability issues since the carburetor must be jetted up to compensate for a reduced signal in the intake manifold.
Lobe Separation Angle Test
In another dyno flog, we tested three cams in the same small-block Chevy with the only change being the lobe separation angle (LSA). This is defined as the spread in camshaft degrees between the intake and exhaust lobe centerlines and can be determined by adding the intake and exhaust lobe centerline figures together and dividing by 2. For example: 110 + 114 = 224/2 = 112 degrees LSA. This lobe spread is designed and ground into the camshaft and can only be changed by grinding another camshaft, unless you're working with a dual overhead cam (DOHC) motor, in which case you can move the intake cam or the exhaust cam or both to change the lobe spread all you want. Regardless of engine design, this spread determines overlap, which affects idle quality, midrange torque, as well as top-end power. What the testing showed us is that a tighter lobe separation angle (like 106 degrees) was worth more average power and more peak power than a wider lobe separation angle (like 114 degrees).
It's also important to remember that LSA is a mere angle. As you add duration to the intake and exhaust lobes while retaining the same LSA, the number of degrees of overlap will increase even with the same LSA. Of course, the opposite is also true when widening the LSA. This is why you will often see bigger cams with a wider LSA, which is an attempt to limit the amount of overlap.
Keep in mind that this particular test moved both the intake and exhaust lobes when increasing the lobe separation angle from 106 to 114 degrees. This also changed the opening and closing points for both the intake and exhaust. Since the intake closing is the most important, note that the 114-degree LSA also creates the latest intake closing point. This tends to improve top-end power. If we add the exhaust closing and intake opening point numbers at 0.050-inch tappet lift, this will deliver actual overlap at that checking height as shown in the chart. An interesting test would have been to retard and then advance the 110-degree LSA cam by four degrees. Retarding the cam would maintain the overlap yet put the intake closing point at the 45-degree ABDC that would duplicate the 114-degree test. Advancing the cam would have placed the intake closing at the 106-degree cam position. Those results would have allowed us to see the difference between overlap and the effect of intake closing. Basically, the wider (114-degree) lobe separation angle lost torque in the midrange compared to the tighter 106-degree LSA but made up ground with top-end power. Our contention is that the 114-degree LSA's better top-end power came as a result of the later-closing intake valve and not because of the reduced overlap. This tends to support the idea that a tighter LSA with a later-closing intake would be the best of both worlds. The price you pay for this would be greatly reduced bottom-end torque and a more erratic idle.
As you can see, there are a number of variables present in each and every camshaft that can be used to dial in the ultimate power in a street or race engine. Each engine will respond a little differently to these changes, but this test illustrates how overlap does have a positive affect on power.
Cam Specs Duration Duration LiftGrind (adv.)
(0.050)Lunati H230-235Intake 280 230 0.489 inExhaust 285
235 0.507 in
Valve Events @ 0.050-inch Tappet Lift
Exh. Open Exh. Close Int.
Open Int. Close Overlap106 LSA 47.5 BBDC 7.5 ATDC
13 BTDC 37 ABDC 20.5110 LSA 51.5 BBDC 3.5 ATDC 9 BTDC 41
ABDC 12.5114 LSA 55.5 BBDC 5 BTDC 5 BTDC 45 ABDC 10.0A
TDC--After Top Dead CenterBTDC--Before Top Dead CenterABDC--After Bottom Dead
CenterBBDC--Before Bottom Dead Center
Test 1 Test 2 Test 3 106 LSA 110 LSA 114 LSAPeak HP 434 @ 5,900
434 @ 5,500 428 @ 5,500Peak TQ 455 @ 4,500 449 @ 4,400 440 @
4,400Avg. TQ 416.8 lb-ft 414.4 lb-ft 405.6 lb-ftAvg. HP 347.0
345.7 339.5 Idle Vac. 8.5 in-Hg 9.6 in-Hg 11.4 in-HgC
rank Comp. 167 psi 160 psi 156 psi