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Converting a 305ci to 350ci

What parts do i need to change in my 92 GMC Sierra when changing a 305ci to a 350ci?

What exactly are you replacing? Do you have a complete engine, long block, short block, what? If it is complete engine, you shouldn’t have an issue if both are SBC configurations.

Yes i have complete engine long block what is SBC?

My issue is a popping like missfire would my exaust cause that?

but its missfiring threw the throtle body

Small Block Chevrolet (V8). i.e. the engine block used by both the 305 and the 350 so assuming the two engines are from similar years the interchange should actually be quite easy. You’ll probably need the computer from the donor vehicle, but as far as I know that might be it.

I believe the only difference is the heads.

Do you know how i could find out for sure that i need a new computer to run my new 350ci motor?

It would take more than just the computer. The computer will deliver signals to various componants but will not change any physical dimensions. The diff between a 305 cid & a 350 cid is 45cid and a computer will not change that.

Your 305 ECM (computer) is the same one used with the 350, but the PROM (chip) is different. The 350 also uses larger injectors.
Google “305 350 chevy swap TBI” and you’ll find all the info you need:

I think meaneyedcatz has it right about needing to replace the computer. The reasoning is the air volume going into the engine is measured by Manifold Absolute Pressure which has to be a calculated measurement based on engine air volume, and other variables such as throttle position. That calculation is now wrong based on the engine size. I am guessing the engine is running lean.

You need the 350 vibration dampener (not sure about the dampener because the 305 crankshaft may be key slotted differently) and timing chain cover because the timing marks are different or used to be. The 350 is off to the side and the 305 is straight up. You can buy a chrome timing mark for the 350 and probably use the 305 timing chain cover, or buy a chrome one of those too.

Firing order, ignition timing, not correct or sometimes if the heads have been off, valves adjusted too tight.