All About Camshafts - Final Thoughts

A pump-gas engine with low cranking compression, roughly 165 psi or less will have poor bottom-end power, throttle response and fuel economy along with lazy acceleration. Note that cranking compression will vary, depending on whether the reading is taken at sea level or high in the mountains. Low cranking compression can be crutched by advancing the cam, which will increase low-speed cylinder pressure and power at the expense of top-end power. Correcting this problem may require a shorter cam with less duration and earlier closing intake valve along with a higher mechanical compression ratio.

Final Thoughts
Although dyno testing is a quick way for testing cams, remember that the best cam on the dyno may not be the fastest cam on the street or racetrack because gearing, traction, g-forces, weather conditions, and other factors have a major influence on performance. Clearly, there are many tradeoffs to make when juggling cam specifications. Simply put: Cam selection boils down to a fine balancing act.

Start out by matching duration, lift, overlap and IVC to the engine's application and parts combination. If you are building a serious performance engine and want to crank out the utmost in power, select a few cams that appear to match the engine's application, then dyno or trackside test each cam for best performance. Most engines perform best with a certain LSA. Try to identify that LSA. Then, experiment with various lifts and durations using the same LSA. In the end, it all boils down to: There is no such thing as a free lunch. With a bunch of money, gobs of time, and lots of dedication, your engine can have perfect timing and a winning personality.

SAMPLE TWIN CAM CAMSHAFTS
Company	Grind	Valve Timing	Duration at .053"	Duration at .020"	Valve Lift	Overlap at .053"	Lobe Center	Lobe Separation Angle	TDC Lift At Valve
H-D	1999	02/34	216	257	0.473	6	106	106	0.087
	EFI	36/04	220	260	0.473		106		0.11
Andrews	TW37s	10/46	236	272	0.51	18	108	110	0.131
		52/08	240	276	0.51		112		0.12
Andrews	TW37b	18/38	236	272	0.51	26	100	103	0.151
		46/14	240	276	0.51		106		0.14
Andrews	64G*	30/62	272	307	0.64	60	106	107	0.262
		66/30	276	312	0.64		108		0.232
S&S	585G*	20/45	245	281	0.585	40	102.5	106.25	0.186
		60/20	260	300	0.585		110		0.179
Screamin' Eagle	SE211	23/45	248	283	0.508	40	101	106	0.203
		59/17	256	291	0.508		111		0.17

Table 2 Valve lift with 1.625:1 rocker arm ratio. *Gear Drive, reverse rear cam rotation.Note the TW37s and TW37b cams have the same amount of duration and lift but the opening and closing valve timings are different, by changing the timing of the opening and closing events, Lobe Center, Lobe Separation Angle, and the amount of overlap change. Also note that duration values change when measured at different tappet lifts, such as .053" and .020". Accurate comparisons can only be made with measurements taken at the same tappet lift.