My friend has a set of 128 casting 86 Vette alum heads he is selling me for $200, planning on changing the valve seals on them tomorrow and put the heads on next week.

I want to know if I am going to lose any performance (I know I'll shed about 50lbs from the front end), and if there is anything that I should look out for when doing the swap?

What head gaskets should I use as well?

 

It's mostly the weight savings that will provide benefits. You'll actually reduce your effective compression, since the aluminum heads have smaller chambers than iron heads for the same displacement engines to make up for the greater heat flow through the aluminum material.

Potential wise, the heads are very similar. Both need porting, and the LB9's need larger valves.

 

Aren't my heads and the vette heads 58cc? I know that the Iron L98 heads were 64cc or something and putting alum vette heads raised the cc ratio a lot.

 

You're putting them on a 305, right?

Think about it:
350 iron head, 64cc
350 aluminum head, 58cc
305 iron head, 58cc

The 350 static CR went from around 9.3:1 with iron heads to around 10:1 with the aluminum heads. But, due to heat loss with aluminum, the 350's both put out (basically) the same power on the same fuel.

Therefore, putting 58cc aluminum 350 heads on a 305 will lower your effective CR and therefore power. Same as putting 64cc iron 350 heads on a 305 lowers power (although that's because it lowers the static CR).

 

Ok, now you have me really confused.

 

He's trying to tell you that going from cast to aluminum you have to raise CR to stay at the same power level. So even though both have same combustion chamber cc's, and same compression ratio, the aluminum heads will cost you some hp due to heat loss.

 

oh, ok I understand now. So, I should run a thinner head gasket to raise the CC ratio to compensate?

 

Probably cant. Stock, they came with .020 gaskets (or close) so between that and the piston depth at TDC, there's little space to be had. Much shorter and you'll start having issues with piston-head contact.
I'm not sure the power loss is going to be all that bad to tell you the truth. The only thing I would do is search on those heads, they are 'early' design and I forget what the difference is between those and the later and if thats of any importance.