Heat is good, but too mutch heat is bad. With the iron heads, you can keep too mutch heat in the cc, causing detonation (pre-ignition) Witch will cause power loss, as well as destroy the engine.

Beau PM me, daddy will teach you young grasshoppa.

 

AH young grasshoppa sees the floating leaf.

As for the daddy business...... :

 

The deal w/ iron and aluminum heads is that the Al will pull more heat out of the combustion chamber...during combustion particularly, which actually does take more energy out of the combustion charge's expansion than with iron heads. That's why typically iron headed engines will run lower compression and make comparable power to Al heads. The head never reaches combustion temp and is pulling heat (energy) from the chamber at varying rates that change with the temperature and pressure changes. I think the main reason Al is growing more common is the weight advantage...maybe less wear and tear on manufacturing equipment as well.

For IAT's, the colder intake temps mean denser air, denser air = more oxygen = more fuel burned = more power produced. Also lower intake temps will reduce knock and allow the computer to run more timing advance to a point.

 

so there are advantages and drawbackes to each material. i suppose its on personal preference and what kind of things you are planning to do to your motor in the future

 

As far as I know the Al heads flow better also. There was a test in a Mag a few months ago about Al vs. Iron. It was pretty interesting, and teh difference in power alone was surprising (not nearly as mutch as I had figgured) but the Al did make a little more, the other advantages though made the big difference.

 

Cast iron heads deliver more power than aluminum heads because cast iron retains heat better than aluminum, which dissipates the heat faster. The bottom line is, more heat in a combustion chamber means greater potential for power. You'll have to run a higher compression ratio AND burn premium fuel to match the cast iron heads with regard to the heat issue. Of course aluminum heads offer a substantial weight savings. That's a no brainer!

 

a follow up post...

Here is another Article that might help you out.

http://www.chevyhiperformance.com/t...538/index3.html
The same article copy and pasted.

One of the most frequently asked cylinder-head questions is, “Is aluminum that much better than iron?” CHP performed a test using a 383ci small-block with a Crane PowerMax roller cam (232/240 at 0.050 with 0.525/0.543-inch lift) fitted with a pair of almost-identical World Products Sportsman II iron and Sportsman II Lite aluminum heads. The heads offered almost identical port configurations and intake port volumes (200 cc), valve sizes, and chamber sizes. In fact, the only difference was that the aluminum heads used CNC-machined combustion chambers while the iron heads were as cast.

Accepted cylinder-head theory contends that iron heads do not conduct as much heat away from the cylinder as aluminum does, so the iron heads should make more power—everything else being equal. Surprisingly, in our test the aluminum heads made more power than the iron heads by an average of 4.6 hp throughout the entire curve. The iron heads made a peak of 407 hp and 449 lb-ft of torque, while the aluminum heads made 408 hp and 454 lb-ft of torque. We attributed the difference to the aluminum’s CNC-machined chamber, which improved combustion efficiency. We still believe that given true identical iron and aluminum heads, the difference would have been 1 or 2 percent in favor of the iron heads.

The more important question is not really iron versus aluminum, but rather the airflow potential of the heads in question relative to their price. Given this criterion, the best head would be the one with the most intake and exhaust airflow for the least amount of money. Aluminum weighs less and is generally much easier to repair. Iron is less expensive but weighs more. The choice is up to you.

 

so based on that test, no offence to scojo, but the experimentors had their preconceived notions that iron is better, performed a reputable test and then, with the results yielded that were not in favor of their original line of thought, decided to say well this happened BUT we thinks its because of this so we still think we are right even though the test said we're not....it just doesnt make sense, IMO the difference could have been due to the CNC or "almost-identical" attributes but that should be left for personal decision instead of the tester disregarding the results. honestly, the only way to truely know is get a pair of the EXACT same speced heads, aluminum/iron, on the exact same block, aluminum/iron with the exact same components and if one is cast and one is cnc, then just cnc mill out both or bore both out using the same machine to give both heads and same size, and finish quality. who am i to be the professional though, im just the consumer