I just acquired a crate engine 10066036 which came with 33417369 heads. I also have a 86 iroc z28 lb9 parts car and I intend to use the tpi setup on the 350. Which heads would perform better for probably short term until I can afford a decent set of aftermarket aluminum heads. The heads that are already on the 350 which I believe to have the 76cc combustion chambers, or the lb9 305 heads with the 58cc chambers?

 

The heads on that motor are basically the same as the old 882 or 993 smogger castings. The LB9 heads might be worth a bit of power, but mostly because they will raise compression on the motor from it's pathetic 8.5:1 spec (it's actually lower than that in reality, but let's not quibble) to a more reasonable ~9.5:1.

More to the point, your LB9 heads have the proper intake bolt pattern to work with your TPI lower intake, which is going to make the swap go a lot smoother.

I say swap the heads before you put it in.

 

Ok. Suppose it ends up being less of a temporary option and I end up just keeping them on. I suppose the 350 heads are going to flow better. If I had them milled to bump the compression up, would they then perform better than the lb9 heads?

 

Also, suppose I just go with the 305 heads, what all will need to be done to them to accept a mild cam and perform well on a 350?

 

Well, if you plan on keeping them on there for a while, I'd make sure they are in good shape- guides, seats, crack-free, etc. The 350 heads probably flow a LITTLE bit more, but not enough to write home about, in my opinion. Valve sizes are 1.84/1.50 vs. 1.94/1.50 between them.

The LB9 heads, like most SBC heads, will run into clearance issues when lift gets up around .470". Either choose a cam with less lift than that or plan on having some machine work done to mill the tops of the guides down for more clearance. Upgrade valve springs per cam manufacturer's recommendations.

You'd have to do this to the -369 heads, too. They have roughly the same limitations with respect to the valvetrain up top.

I wouldn't toss a bunch of money at those heads- it won't add any real value to them. You're only doing this for yourself.

 

Have a machine shop open up the intake valve seats on the LB9 heads to 1.94" and put the 350 valves in. Like Damon said, use valve springs that will handle the cam you're using.

A little do-it-yourself porting after the seats are cut would help them flow a little better as well.