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350 Small Block Chevy Engine Guide - Square Body Trucks

AI
SquareBodyAI
• 9 min read • Updated 3 days, 15 hours ago

350 Small Block Chevy Engine Guide - Square Body Trucks

Overview

The Chevrolet 350 cubic inch (5.7L) small block V8 was the most popular and versatile engine option available in GM Square Body trucks from 1973-1987. This legendary powerplant served in C10, C20, K10, K20, K5 Blazer, and Suburban models, offering a perfect balance of power, reliability, and serviceability that made it the backbone of GM's truck lineup.

The 350 small block went through significant changes during the Square Body era, transitioning from pre-emissions carbureted engines to computer-controlled fuel injection systems. Understanding these variations is crucial for proper maintenance, restoration, and modification of your Square Body truck.

Key Applications:
- 1973-1980: Carbureted versions with various compression ratios
- 1981-1986: Computer Command Control (CCC) carbureted systems
- 1987: Throttle Body Injection (TBI) introduction
- Available in: All Square Body models except base C10 in certain years

Common Issues

Carburetor-Related Problems (1973-1986)

  • Rochester Quadrajet flooding: Caused by worn needle/seat assemblies or incorrect float adjustment
  • Vacuum leak issues: Deteriorated vacuum lines affecting idle quality and emissions
  • Choke problems: Malfunctioning electric or divorced choke systems causing hard starting

Computer Control Issues (1981-1987)

  • ECM failures: Engine Control Module problems causing poor performance and check engine lights
  • Oxygen sensor degradation: Affects fuel mixture and emissions compliance
  • Distributor problems: HEI distributor pickup coil and module failures

Mechanical Wear Issues

  • Intake manifold gasket leaks: Common on engines with 100,000+ miles
  • Timing chain stretch: Causes rattling on startup and poor performance
  • Oil pump wear: Leads to low oil pressure, especially in high-mileage engines
  • Valve guide wear: Results in oil consumption and blue smoke

Cooling System Problems

  • Radiator inadequacy: Original 2-core radiators often insufficient for modified engines
  • Water pump failures: Bearing wear and impeller corrosion
  • Thermostat housing corrosion: Causes coolant leaks and overheating

Parts & Materials Needed

Basic Maintenance Parts

Oil Filter: AC Delco PF52 or equivalent
Oil: 5W-30 or 10W-30 (5 quarts)
Spark Plugs: AC Delco R45TS (1973-1980), R43TS (1981-1987)
Air Filter: AC Delco A49C
Fuel Filter: AC Delco GF61 (carbureted), GF652 (TBI)

Common Replacement Parts

  • Intake Manifold Gaskets: Fel-Pro MS96018 or equivalent
  • Timing Chain Set: Cloyes 9-3100A (double roller recommended)
  • Water Pump: AC Delco 252-713
  • Thermostat: 180°F or 195°F (Stant 13478 or 13358)
  • Distributor Cap/Rotor: AC Delco D328A/D465A

Performance Upgrade Parts

  • Carburetor: Edelbrock 1406 (600 CFM) or Holley 0-80457S (600 CFM)
  • Intake Manifold: Edelbrock 2101 Performer or GM Performance 12496822
  • Exhaust Headers: Hooker 5204-1HKR or Hedman 78200
  • Camshaft: Comp Cams 268H or Edelbrock 2102 (mild upgrades)

Specialized Tools

  • Timing light with advance capability
  • Vacuum gauge set
  • Compression tester
  • Torque wrench (capable of 65 ft-lbs for intake manifold)

Step-by-Step Guide

Basic Tune-Up Procedure

1. Spark Plug Replacement

  1. Remove spark plug wires one at a time to avoid mixing firing order
  2. Clean around spark plug wells to prevent debris from falling into cylinders
  3. Remove old plugs with 5/8" spark plug socket
  4. Gap new plugs to 0.045" (1973-1980) or 0.060" (1981-1987)
  5. Install new plugs hand-tight plus 1/4 turn with wrench
  6. Reconnect plug wires ensuring proper routing

2. Points and Condenser (1973-1974 only)

  1. Remove distributor cap and rotor
  2. Disconnect point wire and condenser wire
  3. Remove point set retaining screw
  4. Install new points, gap to 0.019"
  5. Install new condenser
  6. Set timing to specification using timing light

3. Oil and Filter Change

  1. Warm engine to operating temperature
  2. Raise vehicle safely on jack stands
  3. Remove drain plug with 15mm wrench
  4. Remove oil filter (located on passenger side of block)
  5. Install new filter with thin coat of oil on gasket
  6. Reinstall drain plug with new gasket, torque to 25 ft-lbs
  7. Add 5 quarts of appropriate oil

Carburetor Adjustment (Rochester Quadrajet)

Idle Mixture Adjustment (1973-1980)

  1. Warm engine to operating temperature
  2. Connect tachometer and set parking brake
  3. Turn mixture screws clockwise until engine begins to stumble
  4. Back out screws 1/4 turn at a time until highest RPM is achieved
  5. Adjust idle speed screw to achieve 700 RPM (manual) or 600 RPM (automatic) in drive

Computer Controlled Systems (1981-1986)

  • Warning: Mixture screws are sealed and should not be adjusted without proper equipment
  • Idle speed adjustment only: Set to 500 RPM in drive with A/C off
  • Use propane enrichment method for mixture verification

Year/Model Differences

1973-1975: Pre-Catalytic Converter Era

  • Compression Ratio: 8.5:1
  • Horsepower: 145-160 HP
  • Ignition: Points (1973-1974), HEI (1975)
  • Carburetor: Rochester 4MV Quadrajet
  • Emissions: Basic PCV and EGR systems

1976-1980: Early Emissions Era

  • Compression Ratio: 8.5:1 (1976-1979), 8.2:1 (1980)
  • Horsepower: 165 HP (1976), declining to 130 HP (1980)
  • Ignition: HEI distributor standard
  • Carburetor: Rochester M4MC/M4ME Quadrajet
  • Emissions: Catalytic converter, AIR system, EGR

1981-1986: Computer Command Control

  • Compression Ratio: 8.2:1 (1981-1985), 9.0:1 (1986)
  • Horsepower: 130-155 HP
  • Ignition: HEI with EST (Electronic Spark Timing)
  • Carburetor: Computer-controlled Rochester E4MC/E4ME
  • Emissions: Closed-loop oxygen sensor feedback, extensive vacuum controls

1987: Throttle Body Injection Introduction

  • Compression Ratio: 9.0:1
  • Horsepower: 155 HP
  • Fuel System: TBI (Throttle Body Injection)
  • Ignition: HEI distributor with EST
  • Emissions: Refined computer control, improved driveability

Model-Specific Applications

C10/C20 (1/2-ton and 3/4-ton)

  • Standard 350 availability varied by year
  • 1973-1979: Optional on C10, standard on many C20s
  • 1980-1987: More widely available across trim levels

K10/K20 (4WD Models)

  • 350 more commonly standard due to 4WD power requirements
  • NP205 or NP208 transfer case depending on year
  • Different oil pan configuration for ground clearance

K5 Blazer

  • 350 standard in most years
  • Removable top models may have different exhaust routing
  • 1973-1975: Full convertible top
  • 1976-1987: Fixed rear window with removable rear section

Suburban

  • 350 standard due to vehicle weight and towing requirements
  • Longer exhaust system with different routing
  • Heavy-duty cooling system standard

Tips & Best Practices

Maintenance Best Practices

  • Change oil every 3,000 miles with conventional oil, 5,000 with synthetic
  • Replace air filter annually or every 12,000 miles
  • Inspect vacuum lines regularly - replace cracked or hardened lines immediately
  • Use quality gasoline - minimum 87 octane, consider ethanol-free fuel for storage

Performance Modifications

  • Start with basics: Ensure engine is in good mechanical condition before modifications
  • Upgrade cooling: Install 3 or 4-core radiator for any performance modifications
  • Consider cam timing: Stock camshafts are designed for low-end torque, perfect for truck duty
  • Headers vs. manifolds: Headers provide better performance but may cause heat and clearance issues

Carburetor Tips

  • Quadrajet advantages: Excellent fuel economy, good power potential when properly tuned
  • Common mistakes: Over-adjusting mixture screws, ignoring vacuum leaks
  • Rebuild intervals: Every 100,000 miles or when performance degrades
  • Aftermarket options: Edelbrock and Holley carburetors offer simpler tuning

Computer System Maintenance (1981-1987)

  • Keep connections clean: Use dielectric grease on electrical connections
  • Replace oxygen sensor: Every 60,000 miles or when codes appear
  • Scan for codes: Use paperclip method or OBD-I scanner for diagnostics
  • Don't ignore check engine light: Address codes promptly to prevent catalytic converter damage

Troubleshooting

Poor Idle Quality

Symptoms: Rough idle, stalling, inconsistent RPM
Diagnosis Steps:
1. Check for vacuum leaks using carburetor cleaner spray method
2. Verify base timing setting (varies by year, typically 6-8° BTDC)
3. Test fuel pressure (5-7 PSI for carbureted engines)
4. Inspect PCV system operation

Common Solutions:
- Replace cracked vacuum lines
- Adjust or rebuild carburetor
- Replace PCV valve
- Clean or replace IAC valve (TBI engines)

Hard Starting

Cold Starting Issues:
1. Check choke operation - Should close when cold, open when warm
2. Verify fuel delivery - Listen for fuel pump operation
3. Test starter draw - Should be under 200 amps
4. Inspect spark quality - Blue spark indicates good ignition

Hot Starting Issues:
1. Check for vapor lock - Install heat shield or reroute fuel lines
2. Test fuel pump pressure - Should maintain pressure when hot
3. Verify ignition timing - Retarded timing helps hot starting
4. Check engine temperature - Overheating causes hard starting

Low Power/Poor Performance

Systematic Diagnosis:
1. Compression test - Should be 140-170 PSI with less than 10% variation
2. Timing verification - Use timing light to check base and total advance
3. Fuel system pressure - Test at idle and under load
4. Exhaust restriction - Check for clogged catalytic converter

Performance Solutions:
- Timing chain replacement - If stretched beyond 4° retard
- Carburetor rebuild - If fuel delivery is inadequate
- Exhaust system upgrade - Remove restrictions while maintaining emissions compliance
- Air filter replacement - Ensure adequate airflow

Overheating Issues

Cooling System Diagnosis:
1. Pressure test system - Should hold 15 PSI for 15 minutes
2. Check thermostat operation - Should open at rated temperature
3. Verify water pump function - Look for coolant circulation
4. Inspect radiator efficiency - May need cleaning or replacement

Cooling Upgrades:
- Install 180°F thermostat - Improves cooling margin
- Upgrade to 3 or 4-core radiator - Increases heat dissipation
- Add electric cooling fans - Improves low-speed cooling
- Use 50/50 coolant mixture - Optimal heat transfer and protection

Computer System Codes (1981-1987)

Code Retrieval Method:
1. Locate ALDL connector under dash (usually near steering column)
2. Jump terminals A and B with paperclip
3. Turn ignition to ON position (don't start)
4. Count check engine light flashes

Common Codes:
- Code 13: Oxygen sensor circuit
- Code 21: Throttle position sensor
- Code 32: EGR system malfunction
- Code 42: Electronic spark timing circuit
- Code 45: Oxygen sensor rich indication

Code Resolution:
- Always verify basic engine condition before replacing sensors
- Check wiring and connections before replacing components
- Clear codes after repairs and test drive to verify fix
- Some codes require specific driving cycles to reset

Fuel System Problems

Carburetor Float Issues:
- Symptoms: Flooding, hard starting, black smoke
- Test: Remove air cleaner, observe fuel level in bowl
- Solution: Adjust float level per service manual specifications

Fuel Pump Diagnosis:
- Mechanical pumps (1973-1986): Test pressure at carburetor (5-7 PSI)
- Electric pumps (1987 TBI): Test pressure at TBI unit (9-13 PSI)
- Volume test: Should pump 1 pint in 30 seconds

TBI System Issues (1987):
- Injector cleaning: Use quality fuel injector cleaner every 15,000 miles
- Pressure regulator: Should maintain 12 PSI at idle
- IAC valve: Clean with carburetor cleaner if idle problems occur

This comprehensive guide covers the essential aspects of the 350 small block Chevy in Square Body trucks. Regular maintenance following these procedures will ensure reliable operation and longevity of this proven powerplant.