Since most of the 305 builds land here in the TBI section, figured I'd post here.

Getting ready to mod my '91 305 TBI. Will use LT1 cam, Vortec heads (305 not milled 350) and 4bbl dual plane intake with adapter plate, 350 injectors and G92 exhaust manifolds / 3" exhaust will round out the package.

Am I about to make a huge mistake in any form? I know I'll need a chip made. I know headers are a help, but I can't use them at this point in the build.

 

Not all Vortec heads have bolt holes for thirdgen exhaust manifolds.

 

No exhaust crossover in Vortec heads; it'll likely be a cold-blooded engine. Also no EGR, so emissions checks could be problematic.

Depending on intake height + adapter plate, hood clearance could be an issue.

Seems like a lot of effort to go through to still have a 305.

 

Uh-oh. Thanks for pointing that out. I'll double check.

 

Emissions aren't a worry, I did wonder about the crossover though. Runs rough when it's cold now so I guess that won't change!

 

Checked them out, yep, they won't fit. Thanks for mentioning this, you saved me a ton of work!

 

Man, I just learned something too.

 

What holes are missing? Photos?

The only thing that I can think of without seeing the parts or gaskets, is that the Vortec heads may not have the extra pair of bolt holes that some older heads have, where the rear exhaust manifold bolt is farther to the rear, rather than alongside the rear port.

 

That's exactly it. The right manifold's rear most bolt is further back than a 'regular' manifold. The is not an extra hole on the vortec head or a boss to drill and tap one. I guess standard small block headrers would work, but again check carefully first!