In my modification considering I keep finding myself remembering 1 question: Will (insert mod. here) affect my gas mileage?
One big thing that I think would help my 305 breathe quite a bit is a set of heads. Tax season is upon us and I am seriously considering heads, an intake manifold and nitrous. I like the idea of nitrous so much because it has such a small effect (I would think) on mileage, it's only on for a few seconds here and there.
Don't get me wrong here I'll sacrifice SOME mileage IF need be, but my Z is a daily driver during the summer.
So: will heads/intake manifold affect gas mileage?
Any reccommendations for an intake or heads?

 

I doubt just heads and intake will hurt your gas mileage, but I don't see those two mods being of much benefit either unless you have a cam to go in there as well.

 

Better heads moke more power. More power uses more gas. The more power it makes the more you will want to use that power.

You said 305. I'm assuming you have a 305TPI motor. Due to the smaller bore there aren't a lot of good 305 heads. Replacing the heads and intake and leaving the stock cam would be a total waste of your time. I'd build a mild 350 before I'd waste time on a 305.

Re'

 

It's a carb-ed 305. I thought the big problem with the 305's was that they were made to be emissions friendly, and couldn't breathe good. I assumed if you gave it bigger valves to suck air in and push exhaust out of- it would help greatly...
What kind of power would I get from a cam upgrade?

 

A bigger problem is you can't bolt 350 heads on them as the chambers are bigger than the bore and the valves will hit the block.

That I'm aware of World Products is about the only company to make performance heads for the 305, and they aren't that good at all. the 305 is also prone to detonation.

You could buy a good used 350 that would run better than the 305 (with heads) for less than the cost of the heads.

 

Heads will affec gas milage (I have no idea how much) but think of it this way, they must be a precise(sp) air to fuel mix, if your putting it tons and tons of air, and only 1 drop of gas, its not going to run. In other words, as air goes up, gas goes up.