Hello everyone, new to the forums. I picked up a 87 iroc with a knocking 305. My plan is to drop a 350 4-bolt from a 75 blazer in it. What's a good reliable build to make 300-400 hp? I would like to throw nos at it on a later date. Is there anything I need off of the 305 to make the 350 fit? Any modifications to make it fit? Any help or pointers would be greatly appreciated.

 

1) look up! There's several stickies at the top of this section covering swaps of all kinds.

2) use and read through the threads already here - there's a ton of info that just doesn't need to be typed again.

 

I felt the exact same way last night when I first read this, but this morning I'm really bored, so here goes;
First, don't discard anything from the 305 until the 350 is running.
Second, you are going to need the mounts off the 305 block.
Third, you can't use the '87 flywheel or flexplate on the older crankshaft, and if the car has a stick, then you'll need the '84 flywheel. Then use the '87 starter. If both were automatic, then the '75 flexplate and starter will do.
fourth, you're not gonna get past 350 horses with '75 heads, and it'll take a really large cam to get close to 350 horses, because the '75 heads are junk.
If your 350 has dished pistons, you'd do better to use the 305 heads, assuming they're the ones with the casting number ending in 081, as they should be.
Otherwise, sell those 081 heads and buy some decent heads. If you get the '96-up Vortec 350 heads, then 400 horses is possible, but not with the stock '87 305 exhaust system. It won't even support 300 horses.
Plan on buying a 3" cat-back exhaust, then headers with Y-pipe. the 3" single will support 400 horses.