Cylinder Head Milling

[brokecanadianstudent]

Hello there, new member here with a question
I drive a '94 4.0L Supercab RWD M5OD w/3.08 rear end. I recently came across of free 4.0L heads that I'd like to install, and I'd like to know what, if anything, I could do to make a little more power. I was thinking of having them milled for compression, how much can be milled off safely?

 

[adsm08]

What year are they from?

Postin' from teh Galaxy

 

[RonD]

Higher compression means higher octane fuel is required, power increase won't be much compared with cost each time you get gas.

Porting the 4.0l heads, intake and upper intake can increase power.
Porting means the intake valve holes on the heads line up perfectly with the holes on the intake, this allows less turbulent air flow, more air = more power.
Stock 4.0l ports do not line up

polishing means removing the casting bumps inside the intake valve area of the head and intake manifold, again it allows less resistant/turbulent airflow.

Yes, year of the head is important, you need to find that out

 

[brokecanadianstudent]

The heads are from a '94 Explorer