ATK Core Return Process
JEGS and ATK appreciate your business and want to ensure that your core return is as smooth as possible.

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NOTE: Core return can be any Small Block Chevy 350ci engine, except 1992-1997 LT1 style engines

Engine Specifications:

• Horsepower: 345
• Torque: 400
• Block: 1987-2000 OE block 4-bolt main 1-piece seal
• Bore/Stroke: 4.040 x 3.480
• Displacement: 350
• Crankshaft: OE Reground external balance rear of crank/internal balance front of the crank
• Rods: OE powder metal 5.700 in.
• Pistons: Hypereutectic 9.1:1 compression
• Rings: Moly
• Camshaft: Hyd. roller
• Cam Specs: 220/224 @ 50 .495 in/.502 ex 110 LSA
• Timing Chain: Double roller
• Cylinder Heads: ATK cast iron 76cc/165cc 1.94/1.50
• Rocker Arms: Stamped steel 1.5 ratio
• Oil Pan: Rear sump 5qt (not for Chevelles with steering behind crossmember, some Corvettes and 1962-1967 Chevy II’s)
• Oil Pump: Melling high volume

Recommended Components:

• Balancer: PowerBond internal balance 8 in. #PB1046-N
• Flexplate/Flywheel: Pioneer #FRA-159 external balance 168 tooth
• Intake Manifold: Weiand stealth dual-plane #8150
• Distributor: HEI (Iron gear)
• Water Pump: OE long pump
• Carburetor: Quick Fuel 680 CFM vacuum secondary’s with electric choke #HR-680
• Fuel Pump: Holley mechanical 110 GPH #12-327-11
• Spark Plugs: Champion #RV12C
• Spark Plug Wires: 8 mm

Engine Info:

• Oil: Conventional / Non-synthetic 10W30 with Comp Cam zinc additive #159 for first 3000 miles
• Oil Filter: Wix or K&N per application
• Timing: 34-36 Degrees
• Spark Plug Gap: .035 in.
• Firing Order: 18436572
• Octane: 91+
• Stall Converter: 2200-2500
• Exhaust: 1 5/8 in. Headers

Disclaimer: The parts listed are ATK’s recommendations of parts to be used to obtain our power figures listed. Power figures can vary based on parts used by the end-user. It is the customer’s responsibility to verify components will work in their application. Some modifications to the vehicle may be required using these and or other aftermarket parts. . ATK reserves the right to substitute parts used in engines if necessary.

Engine Break-In Procedure

Use or break-in oil or conventional (non-synthetic) 10w30 oil with zinc additive for the first 500 miles of operation.  Do not drive for long periods at any single speed, always vary your speed. Do not tow a trailer or put other heavy loads on the vehicle. It is best to avoid long periods of idling during this period. Check the engine oil and coolant levels daily. 

Engines with flat tappet hydraulic cams only - Run the engine between 2,000 and 2,500 RPM, with no load on the engine for the first 30 minutes. Let the engine cool down completely and repeat processes 2-3 more times. Do not idle the engine for any extended length of time, this is critical for breaking in the camshaft.

At 500 Miles change the engine oil and filter using conventional (non-synthetic) oil with a zinc additive. Check fuel and ignition settings, and adjust valves (where applicable).  Drive the next 500 miles normally, without high RPMs (below 5000 RPM), hard use, or extended periods of high loading or long periods of idling.

Change the oil and oil filter again at 1,000 miles. Continue using conventional (non-synthetic) oils and zinc additive, until about 4,000 miles. At that point, you may run a quality 10w30 synthetic oil if you choose. Use of oil with zinc or a zinc additive for the life of your engine is recommended.

Emissions Note:

This part is only legal for sale and use on Uncontrolled (Non-Emissions Controlled) Vehicles or on vehicles used solely for the purposes of closed competition racing.

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