Actual ZL-1 Horsepower.

[William]

Bill Porterfield did just this about 15 years ago with a carefully rebuilt engine from ZL1 #26.

All accessories, production 375.7 HP
exhaust manifolds, Camaro
chambered exhaust system,
36 degrees timing

As above with 2-1/8" headers 418.9 HP
replacing the manifolds

Air cleaner, alternator, AIR 447.2 HP
pump removed

Carb re-jetted, timing set 444.2 HP
to 39 degrees

Chambered exhaust system 523.6 HP
removed

Note the chambered exhaust system everybody craves cost almost 80 hp.

http://www.camaros.org/copo.shtml