* Crankshaft Differences: The main difference is the stroke. A 400 crank has a longer stroke than a 350 crank, meaning the pistons travel further up and down in the cylinder. This necessitates several changes to accommodate the longer stroke.
* Connecting Rods: The 400's longer stroke requires longer connecting rods to maintain proper piston-to-wall clearance. You can't use the 350 rods.
* Pistons: You'll need pistons designed for a 400's stroke and the corresponding connecting rods. The piston's compression height (distance from the pin center to the top of the piston) must be correct to achieve the desired compression ratio and avoid piston-to-head interference.
* Block Modifications: The 350 block's main bearing journals (where the crankshaft sits) are likely smaller in diameter than the 400 crank's journals. This means you'll either need to find a 350 block with the larger journals or have the 350 block's journals machined to accept the 400 crank. This is a precision machining job requiring expertise and specialized equipment.
* Oil Clearance: The crankshaft's oil clearances must be checked and adjusted precisely. Incorrect clearance can lead to catastrophic engine failure.
* Cam: The camshaft's timing might need adjustment to account for the changes in stroke and piston travel.
* Clearances: With the longer stroke, you'll need to carefully check for piston-to-valve clearance. The longer stroke increases the chances of the piston hitting the valves during operation, requiring potentially extensive head work or specialized pistons.
* Balancing: After all the components are installed, the rotating assembly (crankshaft, pistons, connecting rods) must be dynamically balanced to prevent vibrations and ensure smooth operation. This is crucial to avoid engine damage.
In summary: It's not a simple swap. It requires significant machining, specialized parts, and expert engine building skills. The cost and effort involved are often comparable to or greater than simply building a 400 engine from the ground up. Unless you have extensive engine building experience or access to a professional engine shop, this project is highly discouraged.
