[Gearhead999]

Not to get into a flame war here.
You are right that the intake valve is opened when the piston is on its downstroke [intake stroke] and there interferance isn't a problem.

But, the intake valve, many times, on performance cams opens before top dead center [BTDC] and closes after bottom dead center [AFDC]. I pasted part of a cam spec card for a Crane Hyd Roller HR-216-325-2S-12.

You can see that the Intake valve opens at 28.0 degrees BTDC and closes at 70.0 degrees ABDC. That is why I would be concerned about valve to piston clearance at TDC. And the Exhaust valve opens 76.0 before bottome dead center [BBDC] and closes at 30.0 degrees after top dead center [ATDC]. So the valves are open at TDC, where clearance becomes an issue.


Lift: Intake @Cam 325 @Valve 520 All Lifts are based
on zero lash and theoretical rocker arm ratios.
Exhaust @ Cam 339 @Valve 542
Rocker Arm Ratio 1.60

Cam Timing: TAPPET @.004
Lift: Opens Closes ADV Duration
Intake 28.0 BTDC 70.0 ABDC 278.0 °
Exhaust 76.0 BBDC 30.0 ATDC 286.0 °


Take care, Go STEELERS !!!!