i have a 350 bored 30 over its a motor out of a boat. what would i need to make this into a 383, i was told only a crank.

 

Welcome aboard.

It isn't quite that simple. The crank will change the stroke from 3.48" to 3.75". That means if all you change is the crank, the piston will be pushed up half the difference farther up in the cylinder, or 0.135" - which would cause the top of the pistons to hit the heads - not a good situation.

You either need to use shorter rods, 5.565" (which is what the factory did for 400 small block engines, from whence the 3.75" stroke cranks originally came), or pistons that put the rod pin 0.135" higher up toward the crown of the piston (which is what most 383 pistons are). The 400 cranks also had larger main bearing journals, so they need to be turned down to fit in a standard 350 block. The aftermarket makes new 383 cranks that have the right size journals, are new, and generally better quality than factory 400 cranks.

The other problems created by this longer stroke in a 350 block involve the rods swinger around in a wider arc and hitting things - like the block oil pan gasket rails, and maybe even the camshaft. The block needs to have the pan rails ground back to clear the rod bolts - a standard operation these days that any competent speed machine shop should be able to handle, or you can do it yourself. If you have a standard mild cam, you probably won't have problems with the rods hitting it.

 

thanks

 

In regards to cam clearance, most of the popular cam companies (like Crane Cams) make cams with a reduced base circle for these instances.