Roadster71

What are the differences?

PatsLs1vette

the zz3 was 345 hp and the zz4 was 355 hp,

specs on zz3
High Output 350 (ZZ3)

PN: 10185072
Cost: about $3000 (includes many accessories, intake, distributer and water pump)
Displacement: 350 cubic inches (5.7L)
Horsepower: 345 at 5200 rpm
Torque: 387 lb-ft at 3250 rpm
Max RPM: 5800
Compression ratio: 9.8:1
Bore & Stroke: 4.00" x 3.48"
Pistons: Cast hypereutectic aluminum
Rods: 1053 forged steel "pink"
Heads: Cast aluminum, angled plugs, 58cc
Head specs: 1.94"/1.50"
Camshaft: Hydraulic roller tappet
Cam specs: 208/221 .474"/.510" 308/316 (advertised)
Idle: 750 rpm

Part Number: 24502609 (ZZ4)
Displacement: 5.7-liter (350 c.i.d.)
Bore/Stroke: 4.00”x3.48”
Engine Block: 10105123 Four Bolt Main, Cast Iron
Compression Ratio: 10:1
Pistons: High silicon aluminum piston with offset pins, 10159436.
Crankshaft: 12556307 Forged Steel
Connecting Rods: 10108688 PM rods
Camshaft: Hydraulic roller tappet (#10185071)
Valve Lift (Intake/Exhaust): .474”/.510”
Duration (Intake/Exhaust): 208°/221° @ .050” tappet lift
Valve Lash (Intake/Exhaust): Zero/Zero
Cylinder Heads: Aluminum, 58cc chambers, 12556463.
Valve Diameter (Intake/Exhaust): 1.94”/1.50”
Valve Springs: LT4 chrome silicon, 12551483.
Rocker Arm Ratio: 1.5:1, 10089648
Distributor: HEI with centrifugal and vacuum advance, 01104067.
Spark Plugs: MR43LTS Gap .045, AC FR5LS Gap .035, Rapid Fire #5 Gap .045.
Fuel Requirement: Unleaded Premium 92 Octane
¹Ignition Timing: 12° BTDC @ 800 RPM, 36° total @ 3,200 RPM with vacuum advance disconnected.
Max. Rec. RPM: 5800 rpm

Roadster71

Thanks for the information.