What is involved?

Tuning cam timing involves using adjustable camshaft sprockets to alter the relationship between the camshafts and the crankshaft. Adjusting the cam timing to increase overlap (advancing the intake camshaft or retarding the exhaust camshaft) will usually produce more peak power, often with little sacrifice elsewhere in the rev range.

Valve clearance warning

Advancing the intake camshaft or retarding the exhaust camshaft will decrease the piston to valve clearance. The standard piston to valve clearance is quite small. If the pistons hits the valves, however slightly, the valves will bend. Aftermarket camshafts may further decrease the piston/valve clearance if they have more duration or valve lift than standard. Make sure you either know what the limits of adjustability of the camshafts are, or measure the clearance. Note that this is not easy with the VTEC engine as the high speed cam lobes need to be locked for the piston/valve clearance to be measured.

Before you start

Before the cam timing is adjusted it is important to measure the ignition timing so that the ignition timing can be kept constant if the intake camshaft is altered. Otherwise the dyno runs will not reflect the differences from changing the cam timing. One trick that works with a dial back timing light is to aim the light at the marks on the inside of the cam sprockets, and change the timing light setting until the marks line up. If the intake cam is adjusted then the ignition timing can be adjusted until the marks on the cam sprockets line up, as long as the dial on the timing light is in the same position.

Tuning

Either cam may be adjusted first, but usually it is best the adjust the intake camshaft then the exhaust camshaft. Make a number of dyno runs with different cam timing, and compare the results. Usually altering the cam timing will move peaks in the torque curve around, so one setting may not be obviously better than another. Do not just look at peak figures, look at the area under the torque curve in the expected rev range of the engine (which is average power).