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

A great 350 crate engine with noticible idle, but still maintains good vacuum for all your power accessories.

• Horsepower: 350 hp
• Torque: 400 lb/ft

Block Information:

• Seasoned OE 4 bolt main 1pc seal 1996-2000 
• Bore/Stroke: 4.040" x 3.480"
• Displacement: 350ci

Rotating Assembly:

• Crankshaft: OE Reground 1 piece seal crank
• Balance: External rear, internal front
• Rods: OE powder metal 5.7"
• Compression Ratio: 9.5:1
• Pistons: Hypereutectic
• Rings: Moly

Camshaft Specs:

• Camshaft: Hydraulic roller
• Cam Duration @ .050": Intake 220 / Exhaust 224
• Cam Lift: Intake .495" / Exhaust .502"
• Lobe Separation Angle: 110lsa
• Timing Chain: Double roller

Cylinder Head Information:

• Cylinder Heads: Vortec cast iron
• Combustion Chamber: 67cc
• Valve Size: 1.94" Intake / 1.50" Exhaust
• Rocker Arms: Stamped steel 1.5

Oil Pan Information:

• Oil Pan: Rear sump 5qt (not for Chevelles with steering behind crossmember, some Corvettes, and 1962-1967 Chevy II's
• Oil Pump: Melling standard volume

 Base Engines

• Short Block
• Camshaft
• Timing Set
• Cylinder Heads
• Valve Covers
• Timing Cover
• Oil Pan
• Oil Pump & Pickup Tube

Recommended Components

• Exhaust: 1-5/8" Headers
• Firing Order: 18436572
• Octane: 91+
• Oil: 10W30 (Conventional / Non Synthetic) 
• Oil Filter: Wix or K&N
• Spark Plug Gap: .035"
• Stall Converter: Stock
• Timing: 34-36 Degrees 

• Balancer: Internal balance
• Carburetor: Quick Fuel 680cfm vacuum secondary electric choke #793-HR-680-VS
• Distributor: HEI (iron gear)
• Flexplate/Flywheel: External balance 1987-Up
• Intake Manifold: Edelbrock Performer RPM #350-7116
• Fuel Pump: Holley Mechanical 110gph #510-12-327-11
• Spark Plugs: Autotile #417-605
• Spark Plug Wires: 8mm
• Water Pump: OE long pump

 Disclaimer: The parts listed are ATK's recommendations of parts to be used to obtain the power figures listed. Power figures can vary based on parts used by the end user. Some modifications to the vehicle may be required using these and or other aftermarket parts.

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's, with no-load on the engine for the first 30 minutes. Let the engine cool down completely and repeat process 2-3 more times. Do not idle the engine for any extended period at this time, this is critical to break 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, adjust valves (where applicable).  Drive the next 500 miles normally, without high RPM's (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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