[LOWDOWN]

RE: 1969 Chev ZL1 Engine

How much real power?
Although rated at 430 horsepower by the old method, Chevrolet never released actual power figures for the as-installed production ZL-1 engine. Numbers were tossed around for years until Bill Porterfield decided to find out. Bill had acquired an original block from one of the cars and enough NOS parts to complete another engine. The engine was subjected to 5 levels of test. RPM was limited to 6750.

Engine Test
Configuration Result
---------------------------- --------
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
The ZL-1 was a legitimate 500+ horsepower engine.

Others have recently built ZL-1's with similiar or higher results. Several have dynoed in the 540-550 HP range. Modern components like piston rings may be the cause of the slightly higher performance.

Again, these are GROSS numbers, NOT SAE net.

Source: http://www.camaros.org/copo.shtml#engine (sidebar)

Typical Street Hemis (?!) on Mustang/DynoJet dynos generally put 325-350 hp to the rear wheels, net.