Chevrolet L34 Specifications
| Engine Model: Chevrolet L34 |
| Engine Type: 4-cycle 8-cylinder OHV 16-valve liquid-cooled gasoline |
| Total Displacement: 396/402 cu.in (6.5/6.6 L) |
| Rated Engine Power: 350-360 Hp (260-267 kW) at 5200 rpm |
| Fuel System Type: Carburetor |
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The Chevrolet L34 represented a strategic offering
within the Mark IV Big-Block engine family, manufactured from 1966 through 1970.
Engineered as a high-performance hydraulic-lifter option, it occupied the middle
ground in Chevrolet’s performance hierarchy. It was positioned above the base
L35 396 cu.in (6.5L) and below the race-oriented, solid-lifter L78.
The L34 was distinguished by its use of high-flow “Oval Port” cylinder heads, a
performance-oriented camshaft, and a 4-barrel carburetor, delivering a balance
of robust streetable torque and top-end power. This engine became a cornerstone
of the muscle car era, serving as the quintessential powerplant for Chevrolet’s
“SS” (Super Sport) models, prized for its durability and formidable acceleration
characteristics.
Engine Type: Mark IV 90-degree V8, overhead valve (OHV)
Displacement (1966-1969): 396 cu.in (6.5 L)
Displacement (1970): 402 cu.in (6.6 L)
Compression Ratio: 10.25:1
Bore x Stroke (1966-1969): 4.094 in x 3.76 in (104.0 mm x 95.5 mm)
Bore x Stroke (1970): 4.126 in x 3.76 in (104.8 mm x 95.5 mm)
Firing Order: 1-8-4-3-6-5-7-2
Horsepower (Gross): 350 hp @ 5,200 rpm (early 1966)
Horsepower (Gross): 360 hp @ 5,200 rpm (1967-1970)
Torque (Gross): 415 lb-ft (563 Nm) @ 3,400 rpm
The foundation of the L34 was a heavy-duty cast iron
block, part of the Mark IV design renowned for its rigidity and strength. The
cylinder case featured a deep-skirt design, where the block walls extended below
the crankshaft centerline, providing exceptional support for the rotating
assembly. The casting number for L34-specific blocks often fell within the
3855961 or 3935441 range for the 396 cu.in (6.5L) variants.
The coolant passages were designed to accommodate the increased thermal demands
of the high-output configuration. Most production L34 engines utilized 2-bolt
main bearing caps on the five main journals, a configuration deemed sufficient
for the engine’s intended power output and hydraulic valvetrain characteristics,
though some early 1966 examples were fitted with 4-bolt main caps.
The L34 utilized cast iron cylinder heads, specifically
the “Oval Port” design, which featured large, rectangular intake ports with a
distinctive oval shape. This design was optimized for high-velocity airflow to
generate substantial low-end and mid-range torque, distinguishing it from the
“Rectangular Port” heads reserved for higher-rpm solid-lifter engines like the
L78.
The combustion chambers were of a closed design, contributing to the 10.25:1
compression ratio. The valve arrangement consisted of two valves per cylinder,
actuated by a hydraulic valvetrain. Standard valve sizes for the L34 heads were
2.065 in (52.5 mm) for the intake valves and 1.720 in (43.7 mm) for the exhaust
valves. The valves were angled at 26 deg from the vertical, a geometry that
promoted efficient cylinder filling and exhaust scavenging.
The induction system for the L34 was a high-performance
4-barrel carburetor setup. For the 1966 to early 1968 model years, the engine
was equipped with a Holley carburetor, typically a 4150 series model, with a
flow rating of 600 to 750 cubic feet per minute (cfm), depending on the specific
application and vehicle line.
From 1968 through 1970, Chevrolet transitioned to the Rochester Quadrajet (model
4MV), a spread-bore carburetor featuring small primary venturis for fuel economy
and responsiveness, alongside large secondary venturis for maximum airflow under
wide-open throttle conditions. The intake manifold was a cast iron unit with a
dual-plane design, which improved low-speed torque characteristics and ensured
even air-fuel distribution to the oval-port cylinder heads.
The lubrication system was a full-pressure, wet-sump
design. A high-volume oil pump, driven by the distributor shaft, drew lubricant
from a stamped steel oil pan. The system maintained a controlled flow of oil to
the five main bearings, connecting rod bearings, camshaft bearings, and the
hydraulic lifters.
Standard oil pressure for the L34 was maintained between 30 to 45 psi at idle
and ranged from 45 to 60 psi at cruising speeds. A full-flow oil filter was
mounted externally to the block to ensure all oil circulated through the filter
before reaching the critical bearing surfaces. The oil pan capacity was
typically 5 quarts (4.7 L) with the filter.
To manage the significant thermal output of the
Big-Block V8, the L34 was equipped with a robust cooling system. This included a
high-capacity radiator, often a copper-brass unit with a 4-core design in
vehicles equipped with air conditioning or heavy-duty cooling packages. A
thermostatically controlled coolant flow utilized a reverse-rotation water pump,
which was standard for the Mark IV engine family.
The thermostat was a high-flow unit with an opening temperature of 180°F (82°C)
for standard applications, though a 195°F (91°C) unit was used for vehicles in
colder climates. The system’s capacity, including the engine block, radiator,
and heater core, was approximately 21 quarts (19.9 L).
A conventional breaker-point distributor provided
ignition timing. Initial timing was typically set at 8 to 10 deg before top dead
center (BTDC), with mechanical (centrifugal) advance providing additional timing
as engine speed increased. A vacuum advance mechanism improved fuel economy and
part-throttle response.
Exhaust System: The L34 was paired with a dual exhaust
system featuring 2.5 in (63.5 mm) pipes and high-flow mufflers, often branded as
“Chambered” or “Turbo” style depending on the vehicle application.
Camshaft: A hydraulic flat-tappet camshaft was used. The specifications for the
L34 camshaft featured a duration of approximately 300 deg (advertised) and a
valve lift of 0.460 in for both intake and exhaust, providing a noticeable
performance idle without sacrificing drivability.
Overall Height: 29.5 in (749 mm) from oil pan rail to
air cleaner base.
Overall Width: 32.5 in (826 mm) across the valve covers.
Overall Length: 35.2 in (894 mm) from the water pump pulley flange to the
bellhousing mounting surface.
Dry Weight: 620 lb (281 kg) - this weight includes the cast iron block, cylinder
heads, intake manifold, and standard external components, excluding the
transmission and starter motor.
Valve Lash: Hydraulic lifters require no periodic
adjustment; zero lash is set by torquing the rocker arm nut to 20 lb-ft (27 Nm)
after the lifter is positioned on the base circle of the camshaft. Spark Plugs:
The recommended plug was an AC Delco R44TS or equivalent, with a gap of 0.035 in
(0.89 mm).
Ignition Timing: 8° to 10° BTDC with the vacuum advance line disconnected,
engine at idle speed of 700-750 rpm (manual transmission) or 600-650 rpm
(automatic transmission in drive). Engine Oil: Recommended viscosity was 10W-30
or 20W-40 for most driving conditions; capacity was 5 quarts (4.7 L) with
filter.
Coolant: A 50/50 mixture of ethylene glycol antifreeze and water, with a total
system capacity of 21 quarts (19.9 L). Drive Belts: Belt tension was set to
allow 0.5 in (13 mm) of deflection at the longest span between pulleys when
moderate pressure was applied.
Connecting Rod Nuts: 45 lb-ft (61 Nm)
Main Bearing Caps (2-bolt): 70 lb-ft (95 Nm)
Cylinder Head Bolts: 80 lb-ft (108 Nm)
Rocker Arm Stud Nuts: 20 lb-ft (27 Nm)
Intake Manifold Bolts: 30 lb-ft (41 Nm)
Exhaust Manifold Bolts: 20 lb-ft (27 Nm)
Flywheel or Flexplate Bolts: 60 lb-ft (81 Nm)
Spark Plugs: 20 lb-ft (27 Nm)
Oil Pan Bolts: 12 lb-ft (16 Nm)
Valve Cover Bolts: 5 lb-ft (7 Nm)
The Chevrolet L34 engine was the premier power option
for several Chevrolet “SS” models during its production run, offering a blend of
high performance and hydraulic lifter reliability that appealed to a broad range
of enthusiasts.
Chevrolet Chevelle SS 396: 1966-1970 - The L34 was a highly popular option for
the A-body platform, frequently paired with the M21 close-ratio 4-speed manual
transmission or the Turbo-Hydramatic 400 automatic.
Chevrolet Camaro SS 396: 1967-1969 - For the F-body, the L34 represented the top
hydraulic-lifter engine option, distinguished by functional hood scoops and a
comprehensive SS equipment package.
Chevrolet El Camino SS 396: 1966-1970 - The L34 provided the pickup-based El
Camino with full-size muscle car performance, making it a highly desirable
variant.
Chevrolet Nova: 1968-1969 - As a late addition to the lineup, the L34 was
available in the compact Nova, creating one of the most potent lightweight
muscle cars of the era.
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