Rent a chassis dyno for a few hours, and do a lash cycle.
Start by testing as-is. Make two pulls to make sure everything is consistent. Make all pulls with the coolant temp the same.
Then start with the intake valves, tighten them all a thousandth or two. If power goes up, tighten some more. If power drops, go a thou or two bigger than you started with.
Once you find the best last for the intake, do the same with the exhaust lash.
Starting at 0.026" / 0.026" (per the cam card) and ending up at 0.021" / 0.024" was worth 15rwhp at peak and 25rwhp at about 1500rpm below peak on one of my old motors.
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'73 T/A (sold). Low budget stock headed 8.3:1 455, 222/242 116lsa .443/.435 cam. FAST Sportsman EFI, 317rwhp/385rwtq on 87 octane. 13.12 @103.2, 1.91 60'.
'67 Firebird [sold], ; 11.27 @ 119.61, 7.167 @ 96.07, with UD 280/280 (108LSA/ 109 ICL)solid cam. [1.537, 7.233 @93.61, 11.46 @ 115.4 w/ old UD 288/296 108 hydraulic cam] Feb '05 HPP, home-ported "16" D-ports, dished pistons (pump gas only), 3.42 gears, 275/60 DR's, 750DP, T2, full exhaust
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