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 1967-2000 Small Block Chevy 350ci engine, except 1992-1997 LT1 style engines

Engine Specifications

Power Ratings:

• Horsepower: 380 hp
• Torque: 415 lbs.-ft

*Tested using a performance mid-rise dual-plane intake manifold, 680 cfm carburetor with vacuum secondaries, headers, and an HEI distributor.

Block Information:

• 1996-2000 seasoned OE block
• 4-bolt main
• 1-piece rear main seal
• Passenger side dipstick 
• Displacement: 355 cubic inch

Rotating Assembly:

• Crankshaft: OE Reground 3.480 in. Stroke
• Balance: External rear (requires 1987-Up style flexplate or flywheel), internal front
• Rods: OE powder metal 5.700 in. Length
• Compression Ratio: 10:1
• Pistons: Hyperuetectic
• Rings: Moly

Camshaft Specs:

• Camshaft: Hydraulic roller tappet 
• Cam Duration @ .050 in.: Intake 220 / Exhaust 224
• Cam Lift: Intake .528 in. / Exhaust .536 in.
• Lobe Separation Angle: 110
• Timing Chain: Double roller

Cylinder Head Information:

• Cylinder Heads: ATK Aluminum
• Combustion Chamber: 64 cc
• Valve Size: 2.020 in. Intake / 1.600 in. Exhaust
• Rocker Arms: Billet aluminum roller rockers 1.6 ratio

Oil Pan Information:

• Oil Pan: Black 5 quart
• Oil Pump: Melling standard volume

  Long Block Includes

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

Notes

• If replacing a pre-1987 (2-piece rear main seal) engine, a new external balance flexplate/flywheel for 1987-Up style engines will be required. This engine will also require a passenger side dipstick (1980-Up vehicles). A driver's side dipstick will not work (Pre-1979).  
• This engine has provisions for a mechanical fuel pump.
• Requires Premium Fuel with 91+ octane 

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 the process 2-3 more times. Do not idle the engine for an 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. The 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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