So I have a 91 Si with a SOHC ZC swap with I/H/E. From my understanding the ZC is basically a D16A6 but with a bit more aggressive cam. I currently get 30mpg with mixed driving and terrible tires. Is it worth going to premium gas? Would I notice more power/better fuel economy?

 

no

 

you might notice a lil more power but i doubt it

 

There are no benefits by running your engine on premium gas. The only difference will be the higher cost.

 

If you plan on getting a tune it would benefit you...thats about the only way it will benefit you.

 

Why would you benefit running higher octane gas because you get a tune?
From my understanding, the tune itself will be the benefit only for the bolt-ons the OP has added. This has nothing to do with octane on an internally stock motor.

Octane determines how the fuel reacts under compression. You need higher octane in a higher compression engine.
If you use too low of octane, the fuel can self ignite and then you risk "pre-ignition" / engine knock and bad things to come.
Since the OP hasn't increased compression in any way, it is fine running with the octane the manufacturer recommends.
The most they will see out of running higher octane fuel is the pride of upholding the overpriced wallet gouging gas market.

 

If you don't get knocking with regular then using premium is a waste of money.

 

with a tune and premium gasoline you will need to advance timing for optimum power.

 

A slight correction; what you described is "Detonation", i.e. small pockets of end gas combusting and causing "knocking" or "pinging". Pre-ignition is when the fuel ignites prior to the spark event (hence the term "pre-ignition"), something which happens typically from engine damage or severe deposits inside the combustion chamber. If an engine is prone to pre-ignition, no amount of octane is going to help, the engine will simply self destruct in a few revolutions.

 

^^this