you need to work out exactly how much comp you will have ("more" is not always better)

more comp on a tired bottom end wil kill it in no time
a12 head has small ports even nissan thought a14 needed bigger ports

Some reading for ya

A12 onto A14 with some photos

Questions about A12 head onto A14 block

It's possible that you may in fact get more compression, but if the compression goes much higher than the 9.5 to 1 which I believe is stock, then you will need the more expensive premium fuel, or to retard the spark a little which will negate the reason for the compression increase.

On the upside the smaller ports & valves in a stock A12 head will help ensure better bottom end performance & will probably give you quite good mileage but just move the red libe on your tach back a bit as it won't rev as well as a stock A14 would.

But hey, it's a Ute, a workhorse that's slow anyway so the A12 head, which will fit right on, will help you to avoid any nasty old speeding tickets.

i was told that it would create more compression???? um the a12 is out of my 1200 ute and im replacing it with an a14

Depends on what A12 head it is. What car did the A12 engine come from?

Why?

I want to no if u can put an a12 head on an a14 and if so what should i be aware of??